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Petitioned Public Health Assessment
Soil Pathway Evaluation,
Isla de Vieques Bombing Range,
Vieques, Puerto Rico

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February 7, 2003
Prepared by:

Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry

IV. Evaluation of the Soil Exposure Pathway

A. Introduction

What is meant by exposure?

ATSDR's PHAs are driven by exposure or contact. Chemicals released into the environment have the potential to cause harmful health effects. Nevertheless, a release does not always result in exposure. People can only be exposed to a chemical if they come in contact with that chemical. If no one comes into contact with a chemical, then no exposure occurs, thus no health effects could occur. Often the general public does not have access to the source area of the environmental release; this lack of access becomes important in determining whether the chemicals are moving through the environment to locations where people could come into contact with them.

The five elements of an exposure pathway are: (1) source of contamination, (2) environmental media, (3) point of exposure, (4) route of human exposure, and (5) receptor population. The source of contamination is where the chemical was released. The environmental media (i.e., groundwater, soil, surface water, air, etc.) transport the chemical. The point of exposure is where humans come in contact with the contaminated media. The route of exposure (i.e., ingestion, inhalation, dermal contact, etc.) is how the chemical enters the body. The persons actually exposed are the receptor population.
The route of a chemical's movement is the pathway. ATSDR identifies and evaluates exposure pathways by considering how people might come into contact with a chemical. An exposure pathway could involve air, surface water, groundwater, soil, dust, or even plants and animals. Exposure can occur by breathing, eating, drinking, or by skin contact with a substance containing the chemical.

Exposure does not always result in harmful health effects. The sections below describe the conditions under which harmful effects might be expected to occur.

How does ATSDR determine which exposure situations to evaluate?

ATSDR scientists evaluate site-specific conditions to determine whether people are being exposed to site-related contaminants. When evaluating exposure pathways, ATSDR identifies whether exposure to contaminated media (soil, water, air, waste, or biota) is occurring through ingestion, dermal (skin) contact, or inhalation. Figure 9 describes ATSDR's exposure evaluation process.

If exposure is possible, ATSDR scientists then consider whether contamination is present at levels that might affect public health. ATSDR scientists select chemicals for further evaluation by comparing them against health-based comparison values. Comparison values are developed by ATSDR from available scientific literature concerning exposure and health effects. Comparison values are derived for each of the media and reflect an estimated chemical concentration that is not expected to cause harmful health effects for a given chemical, assuming a standard daily contact rate (e.g., amount of water or soil consumed or amount of air breathed) and body weight.

Comparison values are not thresholds for harmful health effects. ATSDR comparison values represent chemical concentrations many times lower than levels at which no effects were observed in experimental animal or human epidemiologic studies. If chemical concentrations are above comparison values, ATSDR further analyzes exposure variables (e.g., duration and frequency) for health effects, including the toxicology of the chemical, other epidemiology studies, and the weight of evidence.

Some comparison values used by ATSDR scientists include ATSDR's environmental media evaluation guides (EMEG), reference dose media evaluation guides (RMEG), and cancer risk evaluation guides (CREG). EMEGs, RMEGs, and CREGs are non-enforceable, health-based comparison values developed by ATSDR for screening environmental contamination for further evaluation. Risk-based concentrations (RBCs) and soil screening levels (SSLs) are health-based comparison values developed by EPA Region III to screen sites not yet on the National Priorities List (NPL), respond rapidly to citizens inquiries, and spot-check formal baseline risk assessments. Appendix A describes the comparison values used in this PHA.

More information about the ATSDR evaluation process can be found in ATSDR's Public Health Assessment Guidance Manual at http://www.atsdr.cdc.gov/HAC/HAGM or by contacting ATSDR at 1-888-42-ATSDR. Appendix B defines some of the technical terms used in this health assessment.

If someone is exposed, will they get sick?

Exposure does not always result in harmful health effects. The type and severity of health effects that occur in an individual as the result of contact with a chemical depend on the exposure concentration (how much), the frequency and duration of exposure (how long), the route or pathway of exposure (breathing, eating, drinking, or skin contact), and the multiplicity of exposure (combination of chemicals). Once exposure occurs, characteristics such as age, sex, nutritional status, genetics, lifestyle, and health status of the exposed individual influence how that individual absorbs, distributes, metabolizes, and excretes the chemical. Taken together, these factors and characteristics determine the health effects that can occur as a result of exposure to a chemical in the environment.

Considerable uncertainty exists regarding the true level of exposure to environmental contamination. To account for that uncertainty and to protect public health, ATSDR scientists typically use high-end, worst-case exposure level estimates to determine whether harmful health effects are possible. ATSDR used the following conservative approaches throughout this public health evaluation:

  • As noted in Section II.H Summary of the Available Soil Sampling on Vieques, the soil samples collected by USGS and PRDNR in 1972 (Learned et al. 1973) may be as much as 4-fold higher than the true values (possibly due to differences in analytic procedures). However, regardless of the reason(s) for this apparent high-bias, these higher values were used by ATSDR to evaluate potential health effects.
  • Bioavailability is the extent to which a substance can be absorbed by a living organism and can cause an adverse physiological or toxicological response.
    ATSDR did not adjust the exposure doses to account for the low bioavailability (see text box for definition) of some of the metals in soil (e.g, arsenic, chromium, iron, lead, manganese, mercury, vanadium, and cadmium under certain circumstances), which leads to overly conservative estimated exposure doses. For example, laboratory studies have demonstrated that when arsenic-contaminated soil is ingested, only one-half to one-tenth of the arsenic in the soil is actually absorbed (Freeman et al. 1993; Freeman et al. 1995; Groen et al. 1994; Casteel et al. 1997b; and Rodriguez et al. 1999 as cited in Battelle and Exponent 2000). If one were to adjust for the low bioavailability of arsenic, for example, the exposure dose would be reduced by 0.1 to 0.5.
  • Averages were calculated using detected concentrations only and do not take into account nondetected values. Even though this tends to overestimate the true average values, ATSDR chose to base our health evaluations on the more conservative averages to be more protective of public health.

Therefore, the estimated exposure levels are usually much higher than the levels to which people are really exposed. If the exposure levels indicate harmful health effects are possible, a more detailed review of exposure, combined with scientific information from the toxicological and epidemiologic literature about the health effects from exposure to hazardous substances, is performed.

What exposure situations were evaluated in this PHA?

ATSDR evaluated two scenarios that describe the potential pathways of human exposure to the soil of Vieques (see Table 8). Those potential pathways are:

  1. The residents and visitors of Vieques (the receptor population) can come in contact with the constituent chemicals of the soil (environmental media) in the residential portion of the island. Chemicals from the LIA (the source) could potentially be carried to the residential area of Vieques (point of exposure) through the air since the prevailing winds are from east to west. Human exposure to the soil in the residential area could result in exposure not only to the natural constituents of the soil, but also to any additional chemicals that may have been carried by the wind from the LIA.
  2. Individuals (the receptor population) can come into contact with the chemicals of the soil (environmental media) when they enter the LIA (the source). The longest exposure to this potential source of contamination occurred when protestors occupied the LIA from April 1999 to May 2000.

During typical behavior patterns, people incidentally (i.e., accidentally) ingest soil (route of exposure) when they eat food with their hands, smoke a cigarette, or put their fingers in their mouths because soil or dust particles can adhere to food, cigarettes, and hands. As a result of a normal phase of childhood in which they display hand-to-mouth behavior, children are particularly sensitive because they are more likely to ingest more soil than adults. Dermal exposure (route of exposure) to the soil can also occur through a variety of activities such as gardening, outdoor recreation, or construction. Because of this likely exposure to the soil, ATSDR evaluated potential health effects resulting from incidental ingestion and dermal contact.

This PHA, the Soil Pathway Evaluation, evaluates only those pathways related to exposure via incidental ingestion and dermal contact with potentially contaminated soil on Vieques, both in the residential area and on the LIA. Other pathways, such as exposure to the groundwater, air, and fish are not assessed in this PHA. They are being addressed by ATSDR in separate pathway evaluations (see Sections I and VIII for more details).

B. Methods Used to Evaluate Public Health

Overview

An exposure dose is the amount of chemical a person is exposed to over time.
To evaluate exposures to soil at Vieques, ATSDR examined available data to determine whether chemicals were above ATSDR's comparison values. For those that did exceed comparison values, ATSDR derived exposure doses (see text box for definition) and compared them against health-based guidelines. ATSDR also reviewed relevant toxicological data to obtain information about the toxicity of chemicals of interest. As stated previously, exposure to a certain chemical does not always result in harmful health effects. The type and severity of health effects expected to occur depend on the exposure concentration, the frequency and duration of exposure, the route or pathway of exposure, and the multiplicity of exposure.

Comparing Data to ATSDR's Comparison Values

Comparison values are derived using conservative exposure assumptions, reflecting concentrations much lower than those observed to cause harmful health effects. Thus, comparison values are protective of public health in essentially all exposure situations. As a result, concentrations detected at or below ATSDR's comparison values do not warrant health concern. While a concentration at or below the relevant comparison value could reasonably be considered safe, it does not necessarily follow that any environmental concentration exceeding a comparison value would produce harmful health effects. It cannot be emphasized too strongly that comparison values are not thresholds of toxicity. The likelihood that harmful health outcomes will actually occur depends on site-specific conditions and individual lifestyle, as well as genetic factors affecting the route, magnitude, and duration of actual exposure--not an environmental concentration alone.

The majority of chemicals detected in the soil on Vieques were at or below comparison values and not further evaluated (see Table 9). Chemicals above comparison values were considered for further evaluation, prompting ATSDR to estimate exposure doses using site-specific exposure assumptions.

Deriving Exposure Doses

ATSDR derived exposure doses for those chemicals detected above ATSDR's comparison values. Exposure doses are expressed in milligrams per kilogram per day (mg/kg/day). When estimating exposure doses, health assessors evaluate chemical concentrations to which people could have been exposed, together with the length of time and the frequency of exposure. Collectively, these factors influence an individual's physiological response to chemical exposure and potential outcomes. Where possible, ATSDR used site-specific information regarding the frequency and duration of exposures. When site-specific information was not available, ATSDR employed several conservative exposure assumptions to estimate exposures.

The following equation estimates incidental ingestion of chemicals in soil:

Estimated exposure dose equals Conc. times IR times EF times ED divided by BW times AT

Where:

Conc.: Concentration of chemical in parts per million (ppm, which is also mg/kg)
IR: Ingestion rate: adult = 100 milligrams (mg) of soil per day; child = 200 mg of soil per day*
EF: Exposure frequency, or number of exposure events per year of exposure: 365 days/year
ED: Exposure duration: adult = 70 years; child = 6 years
BW: Body weight: adult = 70 kilograms (kg); child = 10 kg
AT: Averaging time, or the period over which cumulative exposures are averaged (6 years or 70 years x 365 days/year)

* According to EPA's Exposure Factors Handbook (1997) the recommended mean values for soil ingestion are 100 mg of soil per day for children and 50 mg of soil per day for adults, but "200 mg/day for children may be used as a conservative estimate of the mean." ATSDR used more conservative ingestion rates to account for situations where people may incidentally consume more soil than under typical conditions (Calabrese et al. 1990 and Van Wijnen et al. 1990 as cited in EPA 1997).

Using Exposure Doses to Evaluate Potential Health Hazards

ATSDR analyzes weight of evidence to determine whether exposures might be associated with harmful health effects (noncancer and cancer). As part of this process, ATSDR examines relevant toxicologic, medical, and epidemiologic data to determine whether estimated doses are likely to result in harmful health effects. As a first step in evaluating noncancer effects, ATSDR compares estimated exposure doses (calculated using maximum concentrations) to conservative health guideline values, including ATSDR's minimal risk levels (MRLs) and EPA's reference doses (RfDs). The MRLs and RfDs are estimates of daily human exposure to a substance that are unlikely to result in noncancer effects over a specified duration. Estimated exposure doses that are less than these values are not considered to be of health concern. To maximize human health protection, MRLs and RfDs have built in uncertainty or safety factors, making these values considerably lower than levels at which health effects have been observed. The result is that even if an exposure dose is higher than the MRL or RfD, it does not necessarily follow that harmful health effects will occur.

But if health guideline values are exceeded, ATSDR examines the health effects levels discussed in the scientific literature and more fully reviews exposure potential. ATSDR reviews available human studies as well as experimental animal studies. This information is used to describe the disease-causing potential of a particular chemical and to compare site-specific dose estimates with doses shown in applicable studies to result in illness (known as the margin of exposure). For cancer effects, ATSDR compares an estimated lifetime exposure dose to available cancer effects levels (CELs), which are doses that produce significant increases in the incidence of cancer or tumors, and reviews genotoxicity studies to understand further the extent to which a chemical might be associated with cancer outcomes. This process enables ATSDR to weigh the available evidence in light of uncertainties and offer perspective on the plausibility of harmful health outcomes under site-specific conditions.

When comparing to actual health effects levels in the scientific literature, ATSDR tries to estimate more realistic exposure scenarios to use for comparison. In this level of the evaluation, an average concentration (5) is used to calculate exposure doses to estimate a more probable exposure. It is highly unlikely that anyone would incidentally ingest the maximum concentration on a daily basis and for an extended period of time because not all the soil contains the maximum concentration of any given chemical. Therefore, it is more likely that soil containing a range of concentrations would be ingested over time.

Using Other Methods to Evaluate Potential Health Hazards

When dealing with exposure to lead ATSDR uses, in addition to the traditional methodologies described above, a second approach. A substantial part of human health effects data are expressed in terms of blood lead level rather than exposure dose. Thus, ATSDR developed this secondary approach to utilize regression analysis with media-specific uptake parameters to estimate what cumulative blood lead level might result from exposure to a given level of contamination. This is accomplished by multiplying the detected concentration by a media-specific slope factor, which is 0.0068 ± 3*(0.00097) micrograms per deciliter (µg/dl) per ppm in soil (ATSDR 1999c). The Centers for Disease Control and Prevention (CDC) have determined that health effects are more likely to be observed if actual exposures are at or above 10 µg/dl. This second approach is a screening tool for evaluating expected blood lead levels--it is not used in lieu of a toxicological exposure dose evaluation.

Sources for Health-based Guidelines

By Congressional mandate, ATSDR prepares toxicological profiles for hazardous substances found at contaminated sites. These toxicological profiles were used to evaluate potential health effects from exposure to soil on Vieques. ATSDR's toxicological profiles are available on the Internet at http://www.atsdr.cdc.gov/toxpro2.html or by contacting the National Technical Information Service (NTIS) at 1-800-553-6847. For more information about the toxicological profiles, please call ATSDR at 1-888-42-ATSDR. EPA also develops health effects guidelines, and in some cases, ATSDR relied on EPA's guidelines to evaluate potential health effects from exposure to soil. These guidelines are found in EPA's Integrated Risk Information System (IRIS)--a database of human health effects that could result from exposure to various substances found in the environment. IRIS is available on the Internet at http://www.epa.gov/iris. For more information about IRIS, please call EPA's IRIS hotline at1-301-345-2870 or e-mail at Hotline.IRIS@epamail.epa.gov.

Chemicals Without Health-based Guidelines

Essential nutrients (e.g., calcium, magnesium, phosphorous, potassium, and sodium) are important minerals that maintain basic life functions; therefore, certain doses are recommended on a daily basis. Because these chemicals are necessary for life, MRLs and RfDs do not exist for them. They are found in many foods, such as milk, bananas, and table salt. Exposure to these essential nutrients in the soil will not result in harmful health effects.

Health-based comparison values also do not exist for a few other chemicals detected in soil on Vieques. For these chemicals, ATSDR looks more closely at the chemicals' prevalence, at other scientific literature, and at natural levels found in the soil. Bismuth, gold, lanthanum, tungsten, and ammonium perchlorate were detected in less than 3% of the samples. These chemicals are not prevalent on the island; thus the potential for people to come in contact with them is limited. Scandium, yttrium, and zirconium were detected much more frequently. But these elements are present at concentrations within the ranges in which they naturally occur in United States soil (see Table 2). The fact that no scientific literature exists on the health effects of these elements could suggest no one has determined that exposure to these chemicals is harmful. Therefore, given the limited exposure to some of the chemicals and the apparent lack of a health-exposure relationship with the others, these chemicals are not evaluated further within this PHA.

C. Public Health Evaluation

Question 1: Are the residents of Vieques being exposed to harmful levels of chemicals in the soil on Vieques?

No. The levels of metals and other chemicals detected on Vieques are too low to be of health concern for both adults and children through incidental ingestion or dermal contact with the soil. Of the metals detected in the soil across Vieques, only seven (arsenic, cadmium, chromium, iron, manganese, lead, and vanadium) were detected above comparison values (see Table 9). After detailed evaluations of these seven metals, as well as mercury, ATSDR concluded that all the chemicals detected in the soil on Vieques were at concentrations too low to be of health concern for anyone incidentally ingesting or touching the soil.

Exposure from Incidental Ingestion of Soil on Vieques

For exposure through incidental ingestion, ATSDR derived conservative exposure doses for the metals detected above comparison values by using the maximum concentrations in the equation listed in the Methods Used to Evaluated Public Health section (IV.B) and by comparing the estimated exposure doses to standard health guideline values (MRLs and RfDs). See Figure 10 for the locations of the maximum detections of these metals. The following exhibit contains the expected doses for six of the seven metals detected above comparison values (see Table 9). Lead was not included in the exhibit because an oral health guideline is not available for lead.

Exhibit 3.

Estimated Exposure Doses Compared to Health Guidelines
Metal Maximum Detected Concentration(ppm) Estimated Exposure Dose (mg/kg/day) Oral Health Guideline(mg/kg/day) Basis for Health Guideline
Adult Child
Arsenic 36 0.000051 0.00072* 0.0003 chronic MRL/RfD
Cadmium 31.3 0.000045 0.00063* 0.0002 chronic MRL
Chromium 700 0.001 0.014* 0.003 chronic RfD(Chromium VI)
Iron 150,000 0.21 3.0* 0.3 chronic RfD
Manganese 5,000 0.0071 0.10* 0.02 chronic RfD
Vanadium 500 0.00071 0.01* 0.003 intermediate MRL

* Estimated exposure exceeds health guideline; however, an exposure dose that is higher than the MRL or RfD does not necessarily result in harmful health effects. These metals are further evaluated in this section of the PHA.

Using the maximum detected concentration, the resulting exposure doses for all of the metals were below the conservative health guidelines for oral exposure for adults--indicating that all of the chemicals detected on Vieques are at concentrations too low to be of health concern for adults. The exposure doses for children were above health guidelines for all of the metals. However, calculated exposure doses higher than the health guidelines do not automatically mean harmful health effects will occur. Rather, they are an indication that ATSDR should further examine the harmful effect levels reported in the scientific literature and more fully review exposure potential.

The following discussions detail ATSDR's evaluations of exposure from incidental ingestion of arsenic, cadmium, chromium, iron, lead, manganese, and vanadium--all found in the soil on Vieques. Even though mercury does not have a comparison value or health guideline, toxicological and epidemiological information is available. Therefore, mercury was also evaluated in further detail using information from its toxicological profile.

Are residents being exposed to harmful levels of arsenic in the soil?

No. Adult exposure from incidentally ingesting arsenic in soil on Vieques is not expected to result in harmful health effects; the estimated exposure dose is below the conservative health guideline. Similarly, because the estimated exposure dose is below levels of health effects documented in the toxicological literature, childhood exposure is not expected to result in harmful health effects. Childhood exposure is evaluated further in this section following a brief description of the different forms of arsenic, their uses, fate and transport in the body, and potential health effects.

Arsenic occurs naturally in soil and in many kinds of rocks; it is widely distributed in the Earth's crust. Most arsenic compounds have no smell or distinctive taste. In the environment arsenic is usually combined with other elements such as oxygen, chlorine, and sulfur. When combined with these elements arsenic is called inorganic arsenic. When combined with carbon and hydrogen it is called organic arsenic. The organic forms of arsenic are usually less harmful than the inorganic forms (ATSDR 2000a). To be protective of public health during the evaluation, all of the arsenic detected on Vieques was assumed to be in the more harmful inorganic form. Therefore, all of the effects levels reported from the literature are for exposure to inorganic arsenic.

Currently, about 90% of all commercially produced arsenic is used to pressure-treat wood. Arsenic is also a component of some munitions. In the past, arsenic was widely used as a pesticide; in fact, some organic arsenic compounds are still used in pesticides. Other important arsenic uses are in lead-acid car batteries, semiconductors, and light-emitting diodes.

Incidental ingestion of arsenic-contaminated soil is one way arsenic can enter the body. Once in the body, the liver changes some of the arsenic into a less harmful organic form. Both inorganic and organic forms of arsenic leave the body in urine. Studies have shown that 45-85% of the arsenic is eliminated within one to three days (Buchet et al. 1981a; Crecelius 1977; Mappes 1977; Tam et al. 1979b as cited in ATSDR 2000a); however, some will remain for several months or longer.

None of these health effects are expected to result from exposure to arsenic in soil on Vieques. As explained below, the arsenic concentrations present on Vieques are too low to cause an exposure dose that would result in harmful health effects, including an increase in cancer.
Inorganic arsenic is a poison that can cause death if ingested in large doses (e.g., 2 to 121 mg/kg/day). Ingesting lower levels can cause stomach and intestine irritation or decreased production of red and white blood cells. Long-term oral exposure to (i.e., ingestion of) inorganic arsenic can result in darkening of the skin and appearance of small corns or warts on the palms, soles of the feet, and torso. The health effects expected to result from exposure to high concentrations of organic arsenic are uncertain, but could include nerve injury or stomach irritation. The U.S. Department of Health and Human Services (DHHS), the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), and EPA have all independently determined that arsenic is carcinogenic to humans.

Daily exposure to the maximum concentration of arsenic for 70 years is not expected to cause any harmful health effects for adults living on Vieques because the resulting exposure dose is too low to be of health concern (i.e., below conservative health guidelines, see Exhibit 3). Lifetime exposure to the maximum concentration of arsenic in soil on Vieques would also not result in an increase in cancer because the expected lifetime dose (0.000051 mg/kg/day) from exposure to the maximum concentration of arsenic is lower than the most conservative cancer effects level (CEL; that is, lung cancer resulting from exposure to 0.0011 mg/kg/day of arsenic in water).

Childhood exposure to arsenic was further evaluated using a more realistic exposure scenario--an average concentration to calculate an exposure dose. By using an average concentration, ATSDR can estimate a more probable exposure. Using the same equation and assumptions used above in the health guideline comparison, but substituting the average arsenic concentration (8.91 ppm) for the maximum concentration, the calculated exposure dose for children is 0.00018 mg/kg/day. ATSDR then compared this potential exposure to actual health effects levels in the toxicological and epidemiological literature (ATSDR 2000a).

Even though it is highly unlikely that a child would contact soil with the maximum concentration of arsenic on a daily basis for an extended period of time—because lower concentrations were detected in the residential area and the maximum detection is located in the conservation zone east of the LIA (see Figure 10)—ATSDR did calculate exposure doses for this hypothetical scenario. The dose expected to result from children incidentally ingesting the maximum concentration of arsenic on a daily basis is 0.00072 mg/kg/day, which is still below all health effects levels, including the NOAEL, reported in the toxicological and epidemiological literature.
The oral health guideline is based on a study in which humans were exposed to arsenic at a dose of 0.0008 mg/kg/day for more than 45 years. No adverse health effects were noted. Some of the other studies describe less serious health effects (e.g., fatigue, headache, dizziness, insomnia, nightmare, and numbness) resulting from exposure to 0.005 mg/kg/day of arsenic, and serious health effects (e.g., increased prevalence of cerebrovascular disease and cerebral infarction) resulting from long-term exposure to 0.002 mg/kg/day of arsenic. All of these exposure levels, including the no observed adverse effects level (NOAEL) of 0.0008 mg/kg/day, are higher than the levels expected to result from childhood exposure to concentrations of arsenic detected in soil on Vieques.

A majority of available data focuses on exposure to arsenic in adults, but children are sometimes more susceptible than adults to health effects. Some information suggests that arsenic metabolism in children is less efficient than in adults; so children might not convert as much inorganic arsenic into the less harmful organic form (Concha et al. 1998b as cited in ATSDR 2000a). See the Child Health Initiative section of this PHA for a brief discussion concerning the greater susceptibility children could have from exposure to arsenic.

Note that exposure to arsenic is based on levels detected in the soil at the LIA and near the Vieques Municipal Airport. Sampling conducted in the residential area was not sufficiently sensitive to detect the low levels of arsenic possibly existing on Vieques. The maximum and average soil concentrations used to calculate exposure doses are based on sampling conducted in areas where residents and visitors are restricted and are, therefore, not exposed to such arsenic levels on a daily basis. The majority of the data (39 of 41 detections) are from the LIA, and as noted in Section III.C, the soils of the LIA have been influenced by Navy training activities and contain elevated levels of arsenic. Therefore, by incorporating these conservative assumptions, the exposure doses that were calculated were based on a possible worst-case scenario.

In addition, most of the available information on arsenic comes from epidemiologic studies in which humans drank contaminated water. When present in water, arsenic is readily absorbed by the body and is assumed to have a 100% bioavailability; but the bioavailability of arsenic in soil is much lower (estimated 3% to 50%; Rodriguez et al. 1999; Ruby et al. 1996, 1999 as cited in ATSDR 2000a). Therefore, only a portion of the arsenic in soil is expected to be readily absorbed into the human body. That said, however, all of ATSDR's evaluations assumed 100% bioavailability of arsenic from soil.

Based on the foregoing, ATSDR concludes that arsenic levels found in the soil would not result in harmful health effects for any adults or children who might incidentally ingest soil while living on Vieques.

Are residents being exposed to harmful levels of cadmium in the soil?

No. Because the estimated exposure dose is below the conservative health guideline, adult exposure from incidentally ingesting cadmium in soil on Vieques is not expected to result in harmful health effects. Similarly, because the estimated exposure dose for children is below levels of health effects documented in the toxicological literature, childhood exposure is also not expected to result in harmful health effects. Childhood exposure is evaluated further in this section following a brief description of cadmium and its uses, its fate and transport in the body, and potential health effects.

Cadmium is an element found naturally in soil and rocks throughout the earth's crust. It has no recognizable odor or taste. Although in its pure form it is a soft, silver-white metal, it is usually found as a mineral combined with other elements such as oxygen, chlorine, or sulfur. Cadmium is widely used in industrial and consumer products, including batteries, pigments, metal coatings, plastics, and some metal alloys. Munitions, fertilizers, and cigarettes also contain cadmium.

Generally, the main sources of cadmium exposure are through smoking cigarettes and, to a lesser extent, eating foods contaminated with cadmium. Incidental ingestion of soil containing cadmium can also lead to cadmium entering the body. But only about 5 to 10% of ingested cadmium is actually absorbed by the body; the majority is passed out of the body in feces (McLellan et al. 1978; Rahola et al. 1973 as cited in ATSDR 1999b). Cadmium that is absorbed goes to the kidneys and liver. Because only small portions of cadmium slowly leave the body, once it is absorbed, it tends to remain in the body for years. The body changes most of the cadmium into a form that is not harmful, but if too much cadmium is absorbed, the liver and kidneys cannot convert all of it into the harmless form (Goyer et al. 1989; Kotsonis and Klaassen 1978; Sendelbach and Klaassen 1988 as cited in ATSDR 1999b).

Note that none of these health effects are expected to result from exposure to cadmium in soil on Vieques. As explained below, the cadmium concentrations present on Vieques are too low to cause an exposure dose that would result in harmful health effects, including an increase in cancer.
Most of the available research on the health effects from exposure to cadmium are from animal studies. Very few people are actually exposed to high levels of cadmium, and long-term exposure to low levels is difficult to determine given the many other factors that come into play in human exposure. The available research has shown that ingesting high levels of cadmium severely irritates the stomach. Ingesting lower levels of cadmium over a long time can lead to cadmium buildup in the kidneys, thus damaging the kidneys and possibly causing bones to become fragile.

Studies of cadmium in humans and animals have not found an increase in cancer, however, more research is needed before a definitive conclusion can be reached regarding whether cadmium does or does not cause cancer. As a conservative approach, IARC has determined that cadmium is carcinogenic to humans. DHHS reasonably anticipates that cadmium is a carcinogen. EPA has determined that when inhaled, cadmium is a probable human carcinogen.

As shown in Exhibit 3, because the resulting exposure dose is below conservative health guidelines, daily exposure to the maximum concentration of cadmium for 70 years is not expected to cause any harmful health effects for adults living on Vieques. Lifetime exposure to the maximum concentration of cadmium on Vieques is also not expected to result in an increase in cancer because the expected lifetime dose (0.000045 mg/kg/day) is lower than the CEL (increased rates of prostatic adenomas resulted in rats from exposure to 3.5 mg/kg/day of cadmium in food).

Childhood exposure to cadmium was further evaluated using an average concentration, which better represents actual exposures, to calculate an exposure dose. Using the same equation and assumptions described previously, with the average cadmium concentration (1.6 ppm) in place of the maximum concentration, the calculated exposure dose for children is 0.000032 mg/kg/day. ATSDR then compared this potential exposure to actual health effects levels in the toxicological and epidemiological literature (ATSDR 1999b).

Though it is highly unlikely that a child would contact soil with the maximum concentration of cadmium on a daily basis for an extended period of time—because lower concentrations were detected in the residential area and the maximum detection is located on the LIA (see Figure 10)—ATSDR did calculate exposure doses for this hypothetical scenario. The dose expected to result from children incidentally ingesting the maximum concentration of cadmium on a daily basis is 0.00063 mg/kg/day, also below all levels of exposure reported in the literature.
The oral health guideline is based on a study in which no adverse health effects were reported for people who were exposed to 0.0021 mg/kg/day of cadmium in their food over their lifetime. Another study involving humans describes serious health effects (renal tubule interstitial lesions) occurring from exposure to 0.0078 mg/kg/day of environmental cadmium for more than 25 years. The reported levels of exposure, including the NOAEL of 0.0021 mg/kg/day, are two orders of magnitude higher than levels expected to result from childhood exposure to concentrations of cadmium detected in the soil on Vieques.

Little good information is available to document human health effects from exposure to cadmium, and virtually none focuses on exposures in children. Children are sometimes more susceptible than adults to health effects. The available animal research indicates that younger animals absorb more cadmium than adults and are more susceptible to a loss of bone and decreased bone strength than adults. See the Child Health Initiative section of this PHA for a brief discussion concerning the greater susceptibility that children may have from exposure to cadmium.

Note that exposure to cadmium is based on levels detected in the soil on the LIA. Sampling conducted in the residential area was not sensitive enough to detect the low levels of cadmium that might be present on Vieques. The maximum and average soil concentrations used to calculate exposure doses are based on sampling conducted in an area where residents and visitors are restricted and are, therefore, not exposed to these cadmium levels on a daily basis. Also as noted in Section III.C, the soils of the LIA have been influenced by Navy training activities and contain elevated levels of cadmium. Therefore, by incorporating these conservative assumptions, the exposure doses that were calculated were based on a possible worst-case scenario. In addition, it should also be noted that only two out of 28 cadmium detections were above ATSDR's comparison value (see Table 9). This indicates that the majority of the concentrations were detected at levels not warranting health concern.

Therefore, ATSDR does not expect that exposure to cadmium levels found in soil would result in harmful health effects for either adults or children who could incidentally ingest soil while living on Vieques.

Are residents being exposed to harmful levels of chromium in the soil?

No. Adult exposure resulting from incidental ingestion of chromium in soil on Vieques is not expected to result in harmful health effects; the estimated exposure dose is below the conservative health guideline. Childhood exposure is also not expected to result in harmful health effects because the estimated exposure dose is below levels of health effects documented in the toxicological literature. Childhood exposure is evaluated further in this section following a brief description of the different forms of chromium, their uses, fate and transport in the body, and potential health effects.

Chromium occurs naturally in rocks, soil, volcanic dust, animals, and plants. It is present in three main forms: chromium 0, chromium III (trivalent chromium), and chromium VI (hexavalent chromium). Chromium III occurs naturally in the environment and is an essential nutrient required by the body to promote sugar, protein, and fat usage. It is also used in the brick lining for high-temperature industrial furnaces, for making metals and alloys, and for chemical compounds. Chromium VI and chromium 0 are the result of industrial processes. Chromium 0 is a steel-gray solid used mainly to make steel and other alloys. Mixtures of chromium III and VI are used for chrome plating, dye and pigment manufacturing, leather tanning, wood preserving, drilling muds, rust and corrosion inhibitors, textiles, and toner for copiers. Chromium is also a component of some munitions. Chromium compounds have no detectable taste or odor.

Incidental ingestion of soil containing chromium can lead to chromium entering the body. Chromium VI is more easily absorbed than chromium III, but once inside the body, chromium VI is converted into chromium III. Most of the chromium ingested will exit the body in feces within a few days and never enter the bloodstream. Only a very small amount (0.4 to 2.1%) can pass through the walls of the intestine and enter the bloodstream (Anderson et al. 1983; Anderson 1986; Donaldson and Barreras 1966 as cited in ATSDR 2000b).

None of these health effects are expected to result from exposure to chromium in soil on Vieques. As explained below, the chromium concentrations present on Vieques are too low to cause an exposure dose that would result in harmful health effects, including an increase in cancer.
Chromium VI is more harmful than chromium III, an essential nutrient required by the body. The National Research Council recommends that adults ingest 50-200 µg of chromium III every day and has established safe and adequate daily dietary intakes of 10-80 µg for children (NRC 1989 as cited in ATSDR 2000b). Ingesting small amounts of chromium III and VI is not expected to cause harmful health effects; ingesting large amounts, however, has been shown to cause upset stomachs, ulcers, convulsions, liver and kidney damage, or even death (resulting from a one-time ingestion of 7.5 or 29 mg/kg/day of chromium VI).

When inhaled, Chromium VI is a known human carcinogen; exposure to chromium VI in the air has been linked to an increase in lung cancer. DHHS has determined that certain chromium VI compounds are known human carcinogens. IARC has determined that chromium VI is carcinogenic to humans and chromium 0 and chromium III are not classifiable as to their carcinogenicity. EPA has determined that chromium VI in air is a human carcinogen but insufficient evidence exists to determine whether chromium VI and chromium III in food and water are human carcinogens.

Although some or all of the chromium detected on Vieques could be chromium III, an essential nutrient; as a conservative approach to the health evaluation, ATSDR assumed that all of the chromium was the more harmful chromium VI. Therefore, all of the health effects levels reported from the literature are for exposure to chromium VI.

As shown in Exhibit 3, because the resulting exposure dose is below conservative health guidelines, daily exposure to the maximum concentration of chromium for 70 years is not expected to cause harmful health effects for adults living on Vieques. Exposure from incidental ingestion of soil contaminated with chromium is also not expected to result in an increase in cancer; the scientific evidence available suggests that oral exposure to chromium would not result in cancer. Animal studies involving chromium ingestion have found no evidence of carcinogenicity.

Childhood exposure to chromium was further evaluated using an average concentration, which better represents actual exposures, to calculate an exposure dose. Using the same equation and assumptions described previously, with the average chromium concentration (58.2 ppm) in place of the maximum concentration, the calculated exposure dose for children is 0.0012 mg/kg/day. ATSDR then compared this potential exposure to actual health effects levels in the toxicological and epidemiological literature (ATSDR 2000b).

Although it is highly unlikely that a child would contact soil with the maximum concentration of chromium on a daily basis for an extended period of time—because lower concentrations were detected in the residential area and the maximum detections are located in the EMA (see Figure 10)—ATSDR did calculate exposure doses for this hypothetical scenario. The dose expected to result from children incidentally ingesting the maximum concentration of chromium on a daily basis is 0.014 mg/kg/day. This is also below the effects levels reported in the literature for long-term exposure.
The oral health guideline is based on a study in which no adverse health effects were reported in animals exposed to 2.5 mg/kg/day of chromium VI in their drinking water. The only long-term human study documented in the literature reported less serious health effects (oral ulcer, diarrhea, abdominal pain, indigestion, vomiting, leukocytosis, and immature neutrophils) from exposure to chromium VI in the environment at an exposure dose of 0.57 mg/kg/day. These levels of exposure are two and three orders of magnitude higher than doses expected to result from childhood exposure to concentrations of chromium detected in the soil on Vieques.

A limited amount of information is available on the toxicity of chromium in children, and most of these data involve cases in which children ingested lethal doses of chromium VI. Children are sometimes more susceptible to health effects than adults, but whether this is true for chromium is unknown. One animal study reported that more chromium III entered the bodies of newborns than adults (Sullivan et al. 1984 as cited in ATSDR 2000b). While children need small amounts of chromium III for normal growth and development, whether this is true for chromium VI is unknown.

Note that only 10 times out of 463 detections was chromium detected above ATSDR's comparison value (see Table 9). This indicates that the vast majority of the concentrations were detected at levels not warranting health concern.

ATSDR concludes that exposure to chromium levels found in residential soil would not result in harmful health effects for either adults or children who might incidentally ingest soil while living on Vieques.

Are residents being exposed to harmful levels of iron in the soil?

No. Adult exposure resulting from incidental ingestion of iron in soil on Vieques is not expected to result in harmful health effects; the estimated exposure dose is below the conservative health guideline. Similarly, childhood exposure is also not expected to result in harmful health effects because the estimated daily consumption is below levels known to result in childhood poisoning. Childhood exposure is evaluated further in this section following a brief description of iron, its uses by the body, and recommended intakes.

Iron is a naturally occurring element in the environment. In fact, by weight it is the fourth most abundant element in the earth's crust (LANL 2001). The most common iron ore is hematite, which frequently can be seen as black sand along beaches and stream banks. As a pure metal, iron is very reactive chemically and will rapidly corrode, especially in moist air or at high temperatures. It is hard and brittle, and is usually combined with other metals to form alloys, including steel. Iron is a component of some munitions.

Iron is also an important mineral, assisting in the maintenance of basic life functions. It combines with protein and copper to make hemoglobin, which transports oxygen in the blood from the lungs to other parts of the body, including the heart. It also aids in the formation of myoglobin, which supplies oxygen to muscle tissues (ANR 2000). Without sufficient iron, the body cannot produce enough hemoglobin or myoglobin to sustain life. Iron deficiency anemia is a condition occurring when the body does not receive enough iron. The National Academy of Sciences' Recommended Dietary Allowance is 10 mg/day for children, adult men, and adults over the age of 50; 15 mg/day for women under the age of 50; and 30 mg/day for pregnant women (FDA 1997). The U.S. Food and Drug Administration's (FDA) Reference Daily Intake for iron is 18 mg/day (Kurtzweil 1993).

As shown in Exhibit 3, because the resulting exposure dose is below conservative health guidelines, daily exposure to the maximum concentration of iron for 70 years is not expected to cause harmful health effects for adults living on Vieques.

Acute iron poisoning has been reported in children under 6 years of age who have accidentally overdosed on iron-containing supplements for adults. According to the FDA, doses greater than 200 mg per event could poison or kill a child (FDA 1997). Doses of this magnitude are generally the result of children ingesting iron pills and not from incidentally ingesting iron in soil.

Even though it is highly unlikely that on a daily basis for an extended period of time a child would contact soil with the maximum concentration of iron—because the soil contains a range of concentrations, it is more likely that a range of soil concentrations would be ingested over time—ATSDR did calculate a daily consumption for this hypothetical scenario. The amount expected to result from children incidentally ingesting the maximum concentration of iron is 30 mg/day, which would also not lead to an exposure above the levels known to be harmful to children.
Generally, iron is not considered to cause harmful health effects except when swallowed in extremely large doses, such as in the case of accidental drug ingestion. Therefore, toxicological and epidemiological literature is limited. For comparison, ATSDR calculated a daily consumption from exposure to the average concentration of iron in soil (45,600 ppm) using a modification of the dose equation described in the Methods Used to Evaluate Public Health section (IV.B) (Dose = Conc. x IR). Exposure to iron in the soil would increase a child's daily consumption of iron by 4.56 mg/day. The median daily intake of dietary iron is roughly 11-13 mg/day for children 1 to 8 years old and 13-20 mg/day for adolescents 9 to 18 years (NAS 2001). Therefore, the daily increases in consumption (from incidentally ingesting soil from Vieques) are not likely to cause a person's daily dose to exceed levels known to induce poisoning (e.g., >200 mg/event). Further, the body uses a homeostatic mechanism to keep iron burdens at a constant level despite variations in the diet (Eisenstein and Blemings 1998).

Therefore, based on the foregoing, ATSDR concludes that exposure to iron levels found in the residential soil would not result in harmful health effects for either adults or children who might incidentally ingest soil while living on Vieques.

Are residents being exposed to harmful levels of lead in the soil?

No. Adult and child exposures from incidentally ingesting lead are not expected to result in harmful health effects; the estimated exposure doses are below levels of health effects documented in the toxicological literature, and the calculated blood lead level is below CDC's health guideline. These exposures are evaluated further in this section following a brief description of lead and its uses, its fate and transport in the body, and potential health effects.

Lead is a bluish-gray metal naturally found in small amounts in the Earth's crust. Detection of large amounts is usually the result of human activities. Lead has no distinguishable taste or smell. It can exist in a metallic form or combine with other chemicals to form lead compounds or salts. Lead is used in the production of batteries, ammunition, metal products, and in ceramic glazes and paints. It is also used in a variety of medical (e.g., radiation shields to protect against X-rays and in fetal monitors), scientific (e.g., electronic circuitry), and military (e.g., jet turbine engine blades and military tracking systems) equipment. In the past, some lead compounds were used in gasoline to increase the octane rating. Their use was phased out in the 1980s and leaded gasoline was banned in 1996.

Incidental ingestion of lead will cause some lead to enter the body and bloodstream. The amount of lead that enters the body depends on how old you are and when your last meal was eaten. More lead will enter the blood in children than in adults (Alexander et al. 1974; Blake et al. 1983; James et al. 1985; Rabinowitz et al. 1980; Ziegler et al. 1978 as cited in ATSDR 1999c). When soil was incidentally ingested by people who had recently eaten, 2.5% of the lead was absorbed. On the other hand, about 26% of the lead entered the bloodstream in people with empty stomachs (Maddaloni et al. 1998 as cited in ATSDR 1999c). Within a few weeks, 99% of the amount of lead absorbed by adults will exit in urine and feces (Rabinowitz et al. 1977 as cited in ATSDR 1999c), whereas only about 68% of the lead taken into children will leave their bodies (Ziegler et al. 1978 as cited in ATSDR 1999c). Once in the body, lead will travel to soft tissues, such as the liver, kidneys, lungs, brain, spleen, muscles, and heart. After several weeks of continual exposure, most of the lead moves from the soft tissue into bones and teeth. In adults, about 94% of the total amount of lead in their bodies can be found in bones. In children, about 73% of lead in their bodies is stored in their bones (Barry 1975 as cited in ATSDR 1999c).

None of these health effects are expected to result from exposure to lead in soil on Vieques because, as explained below, the lead concentrations present on Vieques are too low to cause an exposure dose that would result in harmful health effects.
In both adults and children, lead primarily affects the nervous system, resulting in decreased performance or weakness in fingers, wrists, and ankles. Exposure to high levels of lead can severely damage the brain and kidneys and can cause miscarriages in pregnant women. No evidence exists that lead causes cancer in humans. Still, some animal testing has shown kidney tumors to develop if the animals are given large doses of lead (27-371 mg/kg/day). DHHS has determined that lead acetate and lead phosphate reasonably can be expected to cause cancer. EPA classifies lead as a probably human carcinogen.

Although it is highly unlikely that an adult or child would contact soil with the maximum concentration of lead on a daily basis for an extended period of time—because lower concentrations were detected in the residential area and the maximum detection is located in AFWTF (see Figure 10)—ATSDR did calculate exposure doses for this hypothetical scenario. The doses expected to result from incidentally ingesting the maximum concentration (1,000 ppm) of lead on a daily basis are 0.02 mg/kg/day for children and 0.0014 mg/kg/day for adults. The exposure dose for adults is well below the effects level reported in the literature. The exposure for children is within the reported range of less serious health effects from acute and intermediate exposure to capsules containing lead. But because none of the concentrations in the residential area were above 100 ppm, it is extremely improbable that children would contact concentrations of 1,000 ppm of lead in the soil on a daily basis. In addition, the vast majority of the lead samples on Vieques had much lower concentrations—all but 8 of the 463 detections were below 100 ppm.
Although a health guideline is not available for lead, toxicological and epidemiological information is available. Therefore, exposure to lead was evaluated in detail for both adults and children. The average lead concentration (17.1 ppm) together with the listed assumptions, were used in the equation described in the Methods Used to Evaluate Public Health section (IV.B). The calculated exposure doses are 0.000024 mg/kg/day for adults and 0.00034 mg/kg/day for children. ATSDR then compared these potential exposures to actual health effects levels reported in the toxicological and epidemiological literature (ATSDR 1999c).

In the few acute and intermediate studies in people, less serious health effects (decreased aminolevulinic acid dehydratase activity and increased red blood cell porphyrin) resulted from exposure to 0.01 to 0.03 mg/kg/day of lead in capsules. Health effects from chronic exposure to lead have not been documented in humans. No adverse effects were observed in animals chronically exposed to 0.57-27 mg/kg/day of lead. These reported health effects levels are several orders of magnitude higher than would be expected to result from exposure to concentrations of lead detected in soil on Vieques.

It should be noted that lead was only detected above EPA's soil screening level for play areas in 2 out of 463 detections (see Table 9). This indicates that the vast majority of the concentrations were detected at levels below those of health concern.

Also, to evaluate potential increases in cancer from exposure to lead, ATSDR compared the lifetime exposure dose for adults to the CELs reported in the literature. Three long-term studies in animals described renal tubular adenomas and carcinomas when animals consumed food or water with 27 to 371 mg/kg/day of lead. But because of the high doses of lead used, ATSDR cautions against using these animal studies to predict whether cancer will actually occur in humans. Still, these doses are much higher than the doses expected to result from lifetime exposure to the maximum concentration of lead in the soil on Vieques.

Although extremely unlikely for the reasons described earlier, exposure to the maximum concentration on a daily basis could result in blood lead levels ranging from 3.89 to 9.71 mg/dl. These levels are still below the level considered safe by CDC.
Children are more susceptible to lead poisoning than are adults. Because their bodies tend to absorb more lead than adults' bodies, children experience more severe health effects at lower doses than adults. To add an additional perspective about whether harmful health effects are expected to occur, ATSDR also determined the blood lead level expected to result from exposure to lead in soil on Vieques using the formula described in the Methods Used to Evaluate Public Health section (IV.B). Exposure to the average soil concentration is estimated to result in blood lead levels ranging from 0.067 to 0.17 µg/dl--well below CDC's level of concern (10 µg/dl).

For these reasons, ATSDR does not expect that exposure to lead levels found in the residential soil would result in harmful health effects for either adults or children who might incidentally ingest soil while living on Vieques.

Are residents being exposed to harmful levels of manganese in the soil?

No. Adult exposure resulting from incidental ingestion of manganese in soil on Vieques is not expected to result in harmful health effects; the estimated exposure dose is below the conservative health guideline. Childhood exposure is also not expected to result in harmful health effects because the estimated exposure dose is below levels of health effects documented in the toxicological literature. Childhood exposure is evaluated further in this section following a brief description of manganese and its uses, its fate and transport in the body, and potential health effects.

Manganese is naturally found in many types of rocks and comprises about 0.1% of the earth's crust (ATSDR 2000c). Pure manganese is a silver-colored metal; it does not, however, occur in the environment as a pure metal. It is usually combined with other elements (e.g., oxygen, sulfur, and chlorine) to form compounds and does not have a distinctive taste or smell. Manganese compounds are mined and used to produce manganese metal, which is combined with iron to make various types of steel. Some manganese compounds are used in the production of batteries, in dietary supplements, and as ingredients in ceramics, pesticides, and fertilizers. Manganese is also a component of some munitions. Additionally, manganese is present in many foods, including grains and cereals, and is found in high concentrations in tea.

Manganese is an essential trace element and is required by the body to break down amino acids and produce energy. Incidental ingestion of soil containing manganese can result in manganese entering the body. Most manganese, however, is excreted in feces. About 3 to 5% of manganese is absorbed by the body when ingested (Davidsson et al. 1988, 1989; Mena et al. 1969 as cited in ATSDR 2000c). Typically, people have small amounts of manganese in their bodies. Under normal circumstances, the amount is regulated so the body has neither too much nor too little (EPA 1984a as cited in ATSDR 2000c). For example, if large amounts of manganese are consumed, large amounts will be excreted. The total amount of manganese in the body tends to stay the same even when exposed to higher levels than usual. Still, if too much manganese is ingested, the body might not be able to adjust and eliminate the additional amount.

None of these health effects are expected to result from exposure to manganese in soil on Vieques because, as explained below, the manganese concentrations present on Vieques are too low to cause an exposure dose that would result in harmful health effects.
Consuming too much manganese can cause weakness, stiff muscles, trembling hands, or nerve disease. One study reported that people who drank water with high concentrations of manganese and other chemicals experienced symptoms similar to those associated with the condition referred to as manganism (mental and emotional disturbances, and body movements that are slow and clumsy). Manganism, however, is typically the result of inhaling high levels of manganese dust in the air. It is not certain whether eating or drinking too much manganese can cause symptoms of manganism.

As shown in Exhibit 3, because the resulting exposure dose is below conservative health guidelines, daily exposure to the maximum concentration of manganese for 70 years is not expected to cause any harmful health effects for adults living on Vieques.

Children have typically not been studied for health effects from exposure to manganese. The existing data indicate that children experience similar toxicity effects as adults. Yet no studies were identified that determined whether children are more or less susceptible to manganese than adults. Although animal studies indicate that infant animals take in and retain more manganese than adults, the level of manganese children need to stay healthy is unknown (ATSDR 2000c).

Childhood exposure to manganese was further evaluated using an average concentration--which better represents actual exposures--to calculate an exposure dose. Using the same equation and assumptions described previously, with the average manganese concentration (1,220 ppm) in place of the maximum concentration, the calculated exposure dose for children is 0.024 mg/kg/day.

The Food and Nutrition Board of the National Research Council determined that 2-5 mg of manganese/day for adults is an "estimated safe and adequate daily dietary intake" (NRC 1989 as cited in EPA 1998). The World Health Organization (WHO) concluded that 2-3 mg/day is adequate for adults and 8-9 mg/day is "perfectly safe" (WHO 1973 as cited in EPA 1998). Based on these studies, EPA has determined that an appropriate reference dose for manganese in food is 10 mg/day, which EPA calculated to a NOAEL of 0.14 mg/kg/day. Therefore, the NOAEL is higher than the levels expected to result from childhood exposure to concentrations of manganese detected in the soil on Vieques.

In addition, the daily consumption from exposure to the average concentration of manganese in soil was calculated using a modification of the dose equation described in the Methods Used to Evaluate Public Health section (IV.B) (Dose = Conc. x IR). Exposure to manganese in the soil would increase a child's normal daily consumption of manganese through food by 0.24 mg/day. This relatively small daily increase in manganese consumption is not likely to increase a child's daily dose above the levels considered safe by WHO and the Food and Nutrition Board of the National Research Council. But this depends entirely on each child's normal dietary intake of manganese.

Note also that manganese was only detected once out of 463 detections above the comparison value (see Table 9). This indicates that the vast majority of the concentrations were detected at levels not warranting health concern.

Based on the foregoing, ATSDR concludes that exposure to manganese levels found in the residential soil would not result in harmful health effects for either adults or children who might incidentally ingest soil while living on Vieques.

Are residents being exposed to harmful levels of mercury in the soil?

No. Adult and child exposures from incidental ingestion of mercury are not expected to result in harmful health effects; the estimated exposure doses are below levels of health effects documented in the toxicological literature. These exposures are evaluated further in this section following a brief description of the forms of mercury, their uses, fate and transport in the body, and potential health effects.

Mercury exists naturally in the environment in several different forms: metallic mercury (also known as elemental mercury), inorganic mercury, and organic mercury. Metallic mercury is the pure form of mercury; it is a shiny, silver-white metal, liquid at room temperature. Inorganic mercury is formed when metallic mercury combines with elements such as chlorine, sulfur, or oxygen. Most inorganic mercury compounds are white powders or crystals, with the exception of mercuric sulfide, which is red (but turns black after exposure to light). When mercury combines with carbon, organic mercury compounds are formed. The most common organic mercury is methylmercury, which when pure is a white crystalline solid. Microorganisms (bacteria and fungi) and natural processes can change mercury from one form to another. The most common organic mercury compound generated through these processes is methylmercury.

Metallic mercury is used in thermometers, fluorescent bulbs, barometers, batteries, and some electrical switches. Silver-colored (amalgam) dental fillings typically contain about 50% metallic mercury. Some people who practice Espiritismo, Voodoo, Palo Mayombe, or Santeria, use metallic mercury (sold as azogue in botanicas) in their religious or ethnic rituals. Various fungicides, topical antiseptics, antibacterials, and red-colored dyes contain inorganic mercury compounds. Some organic mercury compounds have been used as antifungal agents in paints and on seed grains. Mercury is also a component of some munitions.

The different forms of mercury are absorbed and distributed differently in the body.

  • When small amounts of metallic mercury are incidentally ingested, only about 0.01% of the mercury will enter the body through the stomach or intestines (Sue 1994; Wright et al. 1980 as cited in ATSDR 1999a). More can be absorbed if one suffers from a gastrointestinal tract disease. The small amount of metallic mercury that enters the body will accumulate in the kidneys and the brain, where it is readily turned into inorganic mercury. It can stay in the body for weeks or months, but most is eventually excreted through urine, feces, and exhaled breath.
  • Typically, less than 10% of inorganic mercury is absorbed through the stomach and intestines. But it has been reported that up to 40% can be absorbed in the intestinal tract (Clarkson 1971; Morcillo and Santamaria 1995; Nielson and Anderson 1990, 1992; Piotrowski et al. 1992 as cited in ATSDR 1999a). Once in the body, a small amount of the inorganic mercury can be converted into metallic mercury, which will be excreted or stored as described above. Inorganic mercury enters the bloodstream and moves to many different tissues, but will mostly accumulate in the kidneys. Inorganic mercury does not easily enter the brain. It can remain in the body for several weeks or months and is excreted through urine, feces, and exhaled breath.
  • Methylmercury is the most studied organic mercury compound. It is readily absorbed in the gastrointestinal tract (about 95% absorbed) and can easily enter the bloodstream (Aberg et al 1969; Al-Shahristani et al. 1976; Miettinen 1973 as cited in ATSDR 1999a). It moves rapidly to various tissues and the brain, where methylmercury can be turned into inorganic mercury, which can remain in the brain for long periods. Slowly, over months, methylmercury will leave the body, mostly as inorganic mercury in the feces.

None of these health effects are expected to result from exposure to mercury in soil on Vieques because, as explained below, the mercury concentrations present on Vieques are too low to cause an exposure dose resulting in harmful health effects, including an increase in cancer.
Permanent damage to the nervous system, brain, or kidneys can result from exposure to mercury. The different forms of mercury, however, have different effects in the body. Ingesting organic mercury, such as methylmercury, will affect areas of the brain and can result in personality changes, tremors, changes in vision, deafness, muscle incoordination, loss of sensation, and difficulties with memory. On the other hand, inorganic mercury does not readily enter the brain and is not expected to cause neurological damage. Still, swallowing large amounts of inorganic mercury will damage the stomach and intestines and result in nausea, diarrhea, or ulcers. The kidneys are sensitive to damage from all forms of mercury, but if damage is minimal, the kidneys tend to recover once the mercury is expelled from the body. Because it is not readily absorbed in the gastrointestinal tract, ingesting metallic mercury is not likely to result in any severe harmful health effects.

Only limited animal studies and no human data are available to determine whether mercury is a carcinogen. IARC and DHHS have not classified mercury as to its human carcinogenicity. EPA has determined that mercury chloride (an inorganic mercury compound) and methylmercury (an organic mercury compound) are possible human carcinogens.

Neither a comparison value or a health guideline is available for mercury. Still, toxicological and epidemiological information are available. Accordingly, exposure to mercury was evaluated in detail for both adults and children. The average mercury concentration (0.028 ppm) together with the listed assumptions were used in the equation described in the Methods Used to Evaluate Public Health section (IV.B). The calculated exposure doses are 0.00000004 mg/kg/day for adults and 0.00000055 mg/kg/day for children. ATSDR then compared these potential exposures to actual health effects levels in the toxicological and epidemiological literature (ATSDR 1999a). Because organic mercury compounds are more readily absorbed when ingested than metallic or inorganic mercury, health effects would occur at a lower exposure dose to organic mercury than to metallic or inorganic mercury. Therefore, as a conservative approach, ATSDR assumed that all of the mercury detected on Vieques was organic mercury and based this review on exposure to organic mercury compounds.

Although it is highly unlikely that an adult or child would contact soil with the maximum concentration of mercury on a daily basis for an extended period of time—because lower concentrations were detected in the residential area and the maximum detection is located on the LIA (see Figure 10)—ATSDR did calculate exposure doses for this hypothetical scenario. The doses expected to result from incidentally ingesting the maximum concentration (4.21 ppm) of mercury on a daily basis are 0.000006 mg/kg/day for adults and 0.000084 mg/kg/day for children—also well below the effects levels reported in the literature.
In three studies, people had been chronically exposed to 0.0005 to 0.0013 mg/kg/day of methylmercury in their food and experienced no adverse health effects. When they were exposed to 0.0012 mg/kg/day of methylmercuric chloride in their food, they experienced less serious health effects (delaying walking and abnormal motor scores in children). These effects levels reported in the literature, including the NOAELs of 0.0005-0.0013 mg/kg/day, are several orders of magnitude higher than the exposure expected to result from adults and children incidentally ingesting soil on Vieques.

Despite the fact that the carcinogenicity of mercury is still uncertain, ATSDR compared the lifetime exposure dose for adults to the CELs reported in the literature. Four long-term studies described increases in renal adenomas and carcinomas when animals consumed food or water containing 0.69 to 4.2 mg/kg/day of mercury. These doses are several orders of magnitude higher than the doses expected to result from lifetime exposure to the maximum concentration of mercury in the soil on Vieques.

Information concerning systemic health effects in children from exposure to various forms of mercury have been well documented in the literature. Children tend to experience similar toxicological health effects as seen in adults. During critical periods of development, however, children are more susceptible to effects from exposure to metallic mercury and methylmercury. See the Child Health Initiative section of this PHA for a brief discussion concerning the greater susceptibility that children could have from mercury exposure.

Note that exposure to mercury is based on levels detected in soil at the LIA. Mercury analyses have not been conducted in the residential area of Vieques. The maximum and average soil concentrations used to calculate adult and child exposure doses are based on sampling conducted in an area to which residents and visitors are restricted. Therefore, people are not being exposed to these mercury levels on a daily basis. Also, as noted in Section III.C, the soils of the LIA have been influenced by Navy training activities and contain elevated levels of mercury. Therefore, by incorporating these conservative assumptions, the exposure doses that were calculated were based on a possible worst-case scenario.

In conclusion, ATSDR does not expect that exposure to mercury levels found in the soil would result in harmful health effects for either adults or children who could incidentally ingest soil while living on Vieques.

Are residents being exposed to harmful levels of vanadium in the soil?

No. Because the estimated exposure dose is below the conservative health guideline, adult exposure from incidentally ingesting vanadium in soil on Vieques is not expected to result in harmful health effects. Childhood exposure is also not expected to result in harmful health effects because the estimated exposure dose is below levels of health effects documented in the toxicological literature. Childhood exposure is evaluated further in this section following a brief description of vanadium together with its uses, its fate and transport in the body, and potential health effects.

Vanadium is a white to gray metal that is often found as crystals. It occurs naturally in fuel oils and coal and is usually combined with other elements such as oxygen, sodium, sulfur, or chloride. Vanadium compounds are used to make steel, rubber, plastics, and ceramics. Vanadium is also a component of some munitions.

Most of the vanadium that is ingested by humans is not absorbed (only 0.1% to 2.6% is absorbed, Conklin et al. 1982; Roshchin et al. 1980 as cited in ATSDR 1992b), rather most passes through the body unchanged and is excreted in feces. Small amounts, however, can enter the bloodstream after being swallowed. Once in the body, vanadium is quickly excreted in urine.

None of these health effects are expected to result from exposure to vanadium in soil on Vieques because, as explained below, the vanadium concentrations present on Vieques are too low to cause an exposure dose that would result in harmful health effects.
Very few studies have investigated any adverse health effects from exposure to vanadium. Most of the available information is the result of animal testing. Although animal testing is a useful way for scientists to learn how a chemical is absorbed, used, and released, some uncertainty remains concerning the application of these test results to humans. That said, less serious developmental and systemic health effects were reported from oral exposure to vanadium. When female rats drank water contaminated with vanadium, some minor birth defects occurred. Information is not available on the carcinogenicity of vanadium. In studies that investigated health effects other than cancer, however, no increase in tumors was observed in animals exposed to vanadium in their drinking water.

As shown in Exhibit 3, daily exposure to the maximum concentration of vanadium for 70 years is not expected to cause any harmful health effects for adults living on Vieques because the resulting exposure dose is below conservative health guidelines.

Childhood exposure to vanadium was further evaluated, using an average concentration, which better represents actual exposures, to calculate an exposure dose. Using the same equation and assumptions described previously, with the average vanadium concentration (162 ppm) in place of the maximum concentration, the calculated exposure dose for children is 0.0032 mg/kg/day. Note that the calculated exposure for children is only slightly above the health guideline (0.003 mg/kg/day). Because health guidelines have built-in uncertainty factors, exposure doses slightly above the health guideline are not expected to result in harmful health effects. Regardless, however, of this generality, ATSDR compared the potential childhood exposure to the available health effects levels in the toxicological and epidemiological literature (ATSDR 1992b).

Although it is highly unlikely a child would contact soil with the maximum concentration of vanadium on a daily basis for an extended period of time—because the soil contains a range of concentrations, it is more likely that a range of soil concentrations would be ingested over time—ATSDR did calculate exposure doses for this hypothetical scenario. The dose expected to result from children incidentally ingesting the maximum concentration of vanadium on a daily basis is 0.01 mg/kg/day, which is also below the health effects level reported in the literature.
The oral health guideline is based on a study in which no adverse health effects were observed when animals were given 0.3 mg/kg/day of vanadium in their water. Several other animal studies reported no adverse health effects from oral exposure to vanadium in doses ranging from 0.54 to 17 mg/kg/day. The only study conducted on humans reported exposures to vanadium in capsules containing a dose of 1.3 mg/kg/day did not result in any adverse health effects. The lowest dose shown to cause less serious health effects (hemorrhagic foci and vascular infiltration) in animals is 0.57 mg/kg/day. Long-term exposure to vanadium in water resulted in less serious health effects (altered lung collagen) from exposure to 2.8 mg/kg/day. Serious health effects (hemorrhagic foci effects increased) resulted from animals exposed to 2.87 mg/kg/day of vanadium in their drinking water. The reported health effects levels, including the NOAELs of 0.3 to 17 mg/kg/day, are higher than the levels expected to result from childhood exposure to concentrations of vanadium detected in soil on Vieques.

Therefore, ATSDR concludes that exposure to vanadium levels found in the residential soil would result in harmful health effects for either adults or children who might incidentally ingest soil while living on Vieques.

Exposure from Dermal Contact with Soil on Vieques

Dermal exposure to chemicals detected below comparison values should not cause harmful health effects. In essentially all exposure situations, including dermal contact, comparison values are derived using conservative exposure assumptions that are protective of public health. Therefore, only those metals detected above comparison values (arsenic, cadmium, chromium, iron, manganese, lead, and vanadium) were evaluated for exposure through dermal contact (see Table 9). Mercury does not have a comparison value; because, however, toxicologic information is available, this metal was also further evaluated.

Unlike the evaluation for incidental ingestion, dermal contact is not evaluated quantitatively through deriving exposure doses. Rather, this evaluation is a qualitative discussion of the metal's potential to be absorbed into the body through the skin. Considerable uncertainty exists for quantitatively estimating dermal exposure, especially for contact with soil because there is very little chemical-specific data available and the predictive techniques have not been well validated (EPA 1992a).

In general, metals are not readily absorbed through the skin. Exposure to metals through dermal contact results in a much lower dose than the previously discussed incidental ingestion pathway. The following paragraphs outline the absorption potential for each of the seven metals detected above comparison values, as well as mercury.

  • Dermal exposure to arsenic is usually not of concern because only a small amount will pass through skin and into the body (4.5% of inorganic arsenic in soil, Wester et al. 1993 as cited in ATSDR 2000a). Direct skin contact with inorganic arsenic could cause some irritation or swelling, but skin contact is not likely to result in any serious internal effects.
  • Dermal exposure to cadmium is not known to affect human health because under normal conditions, virtually no cadmium can enter the body through the skin (less than 0.2% from soil, Wester et al. 1992 as cited in ATSDR 1999b).
  • Unless the skin is damaged, very little chromium will enter the body through contact with the skin. Nevertheless, some people are allergic to chromium and will develop rashes, redness, or swelling when in contact with chromium (ATSDR 2000b).
  • No specific studies regarding dermal exposure to iron are available; but metals such as iron are not readily absorbed through the skin. EPA uses an absorption factor of 1% for metals when chemical-specific data are lacking (EPA 1995). This absorption factor would result in a minimal amount of iron entering the body.
  • Only a small amount of lead is absorbed by the body through the skin (0.3%, Moore et al. 1980 as cited in ATSDR 1999c). What is absorbed represents a much smaller amount than that absorbed via ingestion (EPA 1986a as cited in ATSDR 1999c). Leaded gasoline does contain a lead compound that can be quickly absorbed. Leaded gasoline, however, is no longer sold; thus it is unlikely that people will contact the form of lead that can enter the body through skin.
  • Very little inorganic manganese will enter the skin if one contacts contaminated soil. Still, animal research has shown that organic manganese compounds can be absorbed through dermal contact. One compound, potassium permanganate, has been reported to damage the skin. Two pesticides that contain manganese (maneb and mancozeb) can cause skin reactions in people who have allergies to these pesticides or work with large quantities of them (ATSDR 2000c). Dermal exposure to organic manganese compounds in the soil on Vieques can lead to an increase in overall dose. If it is conservatively assumed that the dose expected to result from dermal exposure is equal to the dose from incidental ingestion of manganese, one arrives at a cumulative exposure dose below EPA's NOAEL.
  • Small amounts of inorganic mercury and an organic form of mercury, methylmercury, can enter the body through skin contact. But this represents a much smaller amount than that absorbed via ingestion. Other organic mercury compounds, such as dimethylmercury, are readily absorbed through the skin (ATSDR 1999a). Dermal exposure to mercury in the soil on Vieques could lead to an increase in overall dose if organic mercury compounds are present. Even if we conservatively assume that the dermal dose is equal to the ingested dose, it would still result in an exposure at least an order of magnitude lower than the reported NOAELs.
  • No specific studies regarding dermal exposure to vanadium are available. However, because of its low solubility, it is not considered to be readily absorbed through the skin (ATSDR 1992b). In addition, EPA uses a conservative absorption factor of 1% when chemical-specific information is not available. This would also indicate only a very small amount of vanadium entering the body.

In conclusion, ATSDR does not expect that dermal contact with soil on Vieques will result in harmful health effects. In the rare instance when a person is allergic to a specific metal (e.g., chromium and manganese), skin irritation could develop. The overall internal dose, however, is not likely to be large enough to add substantially to the expected exposure resulting from incidental ingestion of the soil.

Exposure to Multiple Chemicals

Several studies, including those conducted by the National Toxicology Program in the United States and the TNO Nutrition and Food Research Institute in the Netherlands, among others, generally support the conclusion that if each individual chemical is at a concentration not likely to produce harmful health effects (as is the case on Vieques), exposures to multiple chemicals are also not expected to be of health concern (for reviews, see Seed et al. 1995; Feron et al. 1993).

Question 2: Were the protestors who occupied portions of the LIA from April 1999 to May 2000 exposed to harmful levels of chemicals in the soil?

No. Both adult and child protestors were not exposed to harmful levels of chemicals present in the soil on the LIA. Of the chemicals detected in the soil on the LIA, only two (arsenic and iron) were detected above comparison values. These two metals are evaluated in greater detail below. All other chemicals were at concentrations too low to be of health concern for anyone incidentally ingesting or touching the soil.

In June 2000, a Navy contractor collected and analyzed five surface soil samples from sites specifically representing areas where protestors lived from April 1999 to May 2000 (see Figure 5) (CH2MHILL 2000a). The samples were analyzed for metals and explosive compounds. In addition, from May 1999 to April 2000, personnel from Servicios Científicos y Téchnicos, Inc. collected and analyzed soil and sediment samples for metals and other inorganic compounds (Garcia et al. 2000). Some of the highest and next highest detections were in areas of the LIA occupied by protestors. Table 10 summarizes the chemicals detected in these areas.

Of the chemicals detected in the areas on the LIA occupied by protestors, only concentrations of arsenic and iron were detected at levels above comparison values (see Table 10). All other chemicals were detected at concentrations too low to be of health concern. A comparison value is not available for mercury. As with the previous evaluation for residents of Vieques, ATSDR derived conservative exposure doses for arsenic, iron, and mercury and compared the estimated doses to standard health guideline values (MRLs and RfDs). The maximum concentrations and an exposure duration of 1 year were used in the equation referenced in the Methods Used to Evaluate Public Health section (IV.B) to determine the exposure dose for those who lived at the LIA for a year.

Were the protestors exposed to harmful levels of arsenic?

No. The estimated exposure doses for both adults and children are below the conservative health guideline for arsenic; therefore, exposure is not expected to result in harmful health effects.

ATSDR calculated exposure doses for those who could have incidentally ingested arsenic while living on the LIA for a year to be 0.0000096 mg/kg/day for adults and 0.00013 mg/kg/day for children. Both doses are below the health guideline ATSDR and EPA have determined is unlikely to result in noncancer effects (0.0003 mg/kg/day). This exposure is also not expected to result in an increase in cancer; the dose expected to result from exposure to the maximum concentration (0.00000013 mg/kg/day) is orders of magnitude lower than the most conservative CEL (0.0011 mg/kg/day). In addition, as stated above, only a small amount of arsenic can pass through the skin and be absorbed.Therefore, protestors who incidentally ingested or dermally contacted arsenic in the soil at the LIA were not exposed to harmful levels--the concentrations detected were too low to be of health concern for both adults and children.

Were the protestors exposed to harmful levels of iron?

No. Adult exposure to iron is not expected to result in harmful health effects because the estimated exposure dose is below the conservative health guideline. Similarly, childhood exposure is not expected to result in harmful health effects because the estimated daily consumption is below levels known to result in childhood poisoning.

For the protestors who lived on the LIA for a year, ATSDR calculated exposure doses from incidentally ingesting iron to be 0.097 mg/kg/day for adults and 1.3 mg/kg/day for children. The adult exposure to iron was below ATSDR's oral health guideline (0.3 mg/kg/day)--indicating that iron was detected at concentrations too low to be of health concern for adults. Childhood exposure was further evaluated by calculating a daily consumption from exposure to iron in soil using a modification of the dose equation (Dose = Conc. x IR). Exposure to the maximum concentration of iron in the soil would increase a child's daily consumption of iron by 6.79 mg/day. Since the median daily intake of dietary iron is roughly 11-13 mg/day for children 1 to 8 years old and 13-20 mg/day for adolescents 9 to 18 years (NAS 2001), this relatively small daily increase in consumption is not likely to cause a child's daily dose to be above the levels known to induce poisoning (>200 mg/event). In addition, the National Academy of Sciences and FDA recommend that people ingest a certain amount of iron (10 to 30 mg/day depending on age and gender) because iron is an important mineral essential for basic life functions. Further, the body uses a homeostatic mechanism to keep iron burdens at a constant level despite variations in the diet (Eisenstein and Blemings 1998). Finally, as stated above, only a minimal amount of iron could potentially enter the body through dermal absorption. Therefore, the protestors who lived on the LIA for a year and who might have incidentally ingested or contacted the soil were not exposed to harmful levels of iron.

Were the protestors exposed to harmful levels of mercury?

No. The estimated exposure doses for both adults and children are below the conservative health guideline for mercury; therefore, exposure is not expected to result in harmful health effects.

ATSDR calculated exposure doses from incidental ingestion of mercury in soil on the LIA to be 0.000000024 mg/kg/day for adults and 0.00000034 mg/kg/day for children. Both doses are orders of magnitude below the NOAELs of 0.0005-0.0013 mg/kg/day. This exposure is also not expected to result in an increase in cancer; the dose expected to result from exposure to the maximum concentration (0.0000000003 mg/kg/day) is several orders of magnitude lower than the reported CELs (0.69-4.2 mg/kg/day). In addition, if we assume that some mercury is dermally absorbed, the combined exposure is still orders of magnitude lower than the reported health effects levels. Therefore, both adults and children who might have incidentally ingested or dermally contacted mercury in the soil while living on the LIA for a year were not exposed to harmful levels--the concentrations detected were too low to be of health concern.

In conclusion, ATSDR does not expect that the protestors who occupied portions of the LIA from April 1999 to May 2000 were exposed to harmful levels of chemicals.


5. Averages were calculated using detected concentrations only and do not take into account nondetected values. Even though this tends to overestimate the true average values, we chose to base our health evaluations on the more conservative averages to be more protective of public health.


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