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PETITIONED PUBLIC HEALTH ASSESSMENT

EGLIN AIR FORCE BASE
(a/k/a USAF EGLIN AIR FORCE BASE ARMAMENT DIVISION)
EGLIN AIR FORCE BASE, OKALOOSA COUNTY, FLORIDA


APPENDIX B: AIR MODELING ASSUMPTIONS AND RESULTS

  1. Herbicide Air Modeling

Because Eglin Air Force Base (AFB) does not have comprehensive records that document exactly when, where, and the quantity of chemicals sprayed throughout the base, ATSDR modeled potential air exposures resulting from spraying activities at the Herbicide Exposure Unit–the area on Eglin AFB believed to be sprayed with the greatest quantities of potentially toxic chemicals. From 1962 to 1970, varying mixtures of chemicals were sprayed at the Herbicide Exposure Unit to test the effectiveness of defoliants for use in the Vietnam Conflict (Engineering-Science 1993). Modeling was conducted for the six chemicals sprayed at the Herbicide Exposure Unit (see Table B-1).

Modeling Approach

Rather than simulating the many complex factors that affect how toxic chemicals disperse in air, ATSDR evaluated a simple and overestimated exposure situation: What would have happened if the entire amount of chemicals used at the Herbicide Exposure Unit remained airborne and blew toward off-base locations, rather than mostly depositing on the ground and vegetation at the Herbicide Exposure Unit? Though obviously unrealistic, this scenario provides an extreme upper bound estimate of what the actual ambient air concentrations might have been during relatively intense spraying activities. ATSDR used the SCREEN3 air dispersion model (EPA 1995) and Eglin AFB chemical use data to estimate air concentrations at the nearest base property line–roughly 3,000 meters (or nearly 2 miles) from the center of the Herbicide Exposure Unit. The SCREEN3 air dispersion model is one of many Gaussian air dispersion models that has been designed to evaluate atmospheric dispersion for stationary sources.

Several assumptions need to be made when modeling atmospheric dispersion of contaminants from any source. Examples of assumptions ATSDR made to model dispersion of herbicides sprayed at Eglin AFB are listed here. Table B-2 outlines the model inputs used during this analysis.

  • First, ATSDR focused on the time frame 1962 to 1970, or the period when the greatest quantities of herbicides were sprayed.


  • Second, ATSDR simulated the release of contaminants as a continuous emissions source. Although aerial spraying at Eglin AFB did not occur continuously, this assumption is not expected to bias predictions of annual average concentrations, because spraying reportedly occurred during all seasons of the year, during various times of day, and during a wide range of meteorological conditions.


  • Finally, and perhaps most notably, ATSDR assumed in its initial evaluations that the entire amount of herbicides sprayed remained airborne, rather than depositing on the target. This assumption was made to assess the worst-case scenario. ATSDR notes, however, that recent studies involving US Environmental Protection Agency (EPA) researchers on aerial spraying of many different pesticides and herbicide formulations in agricultural settings has found that less than 1% of the active ingredients sprayed remain aloft just 300 meters from the source (Teske et al. 2001)(11). This low rate of chemicals remaining airborne reflects the intent of spray application of pesticides and herbicides–spray application technologies are designed to transfer as much chemicals as possible to the intended target because chemicals that remain airborne and drift downwind are essentially wasted.

When running the model, ATSDR simulated emissions from a ground-level volume source. The source was considered to be square at the base (with lateral dimensions of 610 meters). The height of the source was 100 meters, based on data provided by the base indicating that herbicides were typically released at heights ranging from 45 to 150 meters (personal communication with Eglin AFB personnel, May 1999). By using a volume source, ATSDR essentially assumed that herbicides were continuously released from a "box" of air above the Herbicide Exposure Unit. Additionally, ATSDR considered rural atmospheric dispersion coefficients and simple terrain in this assessment. Finally, to estimate annual-average ambient air concentrations from the maximum hourly concentrations calculated by SCREEN3, ATSDR multiplied the output concentrations by 0.1–a factor commonly used to estimate annual average levels from SCREEN3 outputs (EPA 1992).

Modeling Results

Table B-1 lists the upper-bound ambient air concentrations that ATSDR estimated for the chemicals considered in this analysis. ATSDR emphasizes that these are upper-bound estimates because the initial modeling application assumed that the entire amount of material sprayed at the site remained airborne.

While concentrations at or below comparison values are considered safe, it does not automatically follow that any environmental concentration that exceeds a comparison value would be expected to produce adverse health effects. It cannot be emphasized strongly enough that comparison values are not thresholds of toxicity.Even when considering the extremely conservative assumptions in this analysis, the estimated average off-base concentrations for four of the chemicals– 2,4-dichlorophenoxyacetic acid (2,4-D); 2,4,5-trichlorophenoxyacetic acid (2,4,5-T); cacodylic acid; and picloram–were at least two times lower than current or previously published health-based comparison values (see Table B-1). In other words, the chemical usage data indicate that spraying activities at the Herbicide Exposure Unit did not cause concentrations of these four chemicals to reach "unsafe" or "unhealthy" levels at off-base locations. ATSDR notes again that actual ambient air concentrations of these chemicals were probably considerably lower than the upper-bound estimates shown in Table B-1, because a large portion of the chemicals undoubtedly deposited on the ground surface before reaching locations beyond the Eglin AFB property line.

Potential arsenic exposures. As Table B-1 shows, the upper-bound estimate of the annual average concentration of arsenic (0.009 micrograms per cubic meter, or µg/m3) was higher than the lowest health-based comparison value (cancer risk evaluation guide: 0.0002 µg/m3). As a result, a more detailed review of the environmental and toxicologic data for arsenic was necessary. Following are key observations from ATSDR's review:

  • The upper-bound estimate average concentration of arsenic (0.009 µg/m3) falls within the range of arsenic concentrations that have been documented for rural and urban areas (ATSDR 2000a).


  • The actual exposure concentrations at Eglin AFB were likely considerably lower than the upper-bound estimate. If 99% of the herbicides applied landed either on the intended target or on areas adjacent to the Herbicide Exposure Unit (as is consistent with data published in the "cropdusting" literature [Teske et al. 2001]), then the estimated annual average concentration of arsenic would be 0.0001 µg/m3–lower than ATSDR's health-based comparison value.


  • The literature on occupational and animal studies involving arsenic exposure indicates that even the upper-bound estimated concentration (0.009 µg/m3) is considerably lower than the range of exposure concentrations that have caused harmful effects in humans (0.7-613 µg/m3; ATSDR 2000a).

For the reasons listed above, ATSDR concludes that ambient air concentrations of arsenic at the facility boundary of Eglin AFB did not reach unhealthy levels as a result of the herbicide spraying applications.

Potential 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposures. Table B-1 indicates that the upper-bound estimate of annual average TCDD concentrations (2.8 x 10-5 µg/m3) is higher than the most conservative health-based comparison value that ATSDR located (4.2 x 10-8 µg/m3). Because both the modeling analysis and the health-based comparison value include several layers of conservatism, or "margins of safety," ATSDR conducted a more detailed review of TCDD releases and exposures to determine whether unhealthy inhalation exposures could have occurred. Key observations follow:

  • The estimated intake rate is based on the unrealistic assumption that community members breathed air at Eglin AFB's boundary continuously 24 hours a day, 365 days a year and that the winds blew directly toward the community members. Because of this, ATSDR expects that actual exposures were lower.


  • As stated before, the upper-bound estimates of ambient air concentrations in Table B-1 assume that all of the herbicides applied at Eglin AFB remained airborne and transported downwind. If ATSDR assumes that 99% of these formulations landed on the target or in its immediate vicinity (a reasonable assumption based on current literature [Teske et al. 2001]), then a more reasonable estimate of annual average ambient air concentrations of TCDD is 2.8 x 10-7 µg/m3. ATSDR notes that the detections of TCDD in soils at the Herbicide Exposure Unit is consistent with our assertion that the majority of the chemicals did not remain aloft.


  • Based on the average concentration assuming 99% deposition (or 2.8 x 10-7 µg/m3), the average daily intake of TCDD for an individual continuously exposed at the property boundary of Eglin AFB would be 5.6 x 10-6 µg/day. Although this intake is higher than the estimated average daily inhalation intake for the general United States population (1 x 10-6 µg/day), it is substantially lower than the overall average daily intake from all media (4.7 x 10-5 µg/day), which is dominated by TCDD in food products (Travis and Hattemer-Frey 1989 as cited in ATSDR 1998).


  • No human or animal toxicity data have been identified that specifically study adverse health effects associated with TCDD inhalation exposures (ATSDR 1998). Studies that have examined potential inhalation exposures examine populations known to reside or work in environments with above-background concentrations of chlorinated dibenzo-p-dioxins. Analyzing these studies is complicated by incomplete exposure data, exposure to other chemicals, and a small number of people in some of the studies. Therefore, the extent to which estimated doses can be compared to the toxicologic literature is limited, and any comparisons must be done with caution.
  • Some perspective can be gained by reviewing toxicity data from studies where animals were exposed to TCDD orally(12). Limited data in rats suggest that inhalation absorption of TCDD may be at least as efficient as oral absorption. Among the studies reviewed by ATSDR, a reproductive study in Rhesus monkeys was the study at which an effect (altered social behavior) was seen at the lowest dose–1.2 x 10-4 micrograms per kilogram per day (µg/kg/day) (Schantz et al. 1992 as cited in ATSDR 1998). Using this as the most protective comparative dose, the estimated inhalation doses at Eglin AFB (6.6 x 10-9 µg/kg/day for adults and 1.4 x 10-8 µg/kg/day for children) are several orders of magnitude lower(13). Cancer effects have been observed in animal studies at oral doses ranging from approximately 0.007-0.4 µg/kg/day (ATSDR 1998), these doses are also much higher, more than a million times higher, than those believed to have been encountered from herbicide testing at Eglin AFB.

Based on these observations, ATSDR concludes that people who lived along the perimeter of Eglin AFB in the 1960s might have been exposed to trace amounts of TCDD. However, to put this exposure into perspective–the inhalation exposures that might have occurred are far lower than estimates of dietary exposures that residents likely experienced at the same time. Thus, inhalation exposures to TCDD from past aerial application of herbicides did not substantially increase exposure to TCDD above normal background levels. In addition, when doses are estimated and compared, with caution, to the limited toxicologic data, the exposures at Eglin AFB are much lower. Therefore, potential exposure to TCDD from herbicide testing did not appear to be a public health hazard.

Summary of ATSDR's Findings

ATSDR analyzed available herbicide and pesticide spraying data for the Herbicide Exposure Unit–the area on Eglin AFB believed to be sprayed with the greatest quantities of potentially toxic chemicals. This analysis found that the toxic chemicals sprayed in this area probably never reached concentrations at off-base locations at levels thought to be associated with adverse health effects, even when considering extremely conservative exposure assumptions. Because the period of most intense spraying activity does not appear to pose a public health hazard, ongoing spraying activities, which use notably lower amounts and less toxic mixtures, also are not expected to pose past, present, or future public health hazards to off-base residents.

II. Modeling of Soil Contaminants Released During Fires

The text in the PHA presents ATSDR's analyses of exposures to smoke during fires. In these analyses, ATSDR not only considered the general components of smoke from such fires (e.g., particulate matter, carbon monoxide, and other chemical by-products of combustion), but also considered the possibility that additional contaminants could be released. Specifically, if fires reach sufficiently high temperatures, they could also cause contaminants in soils, like metals and herbicides, to become airborne. Therefore, depending on the location of a fire, smoke from the fires could also contain metals and other pollutants.

To evaluate this exposure scenario, ATSDR considered whether wildfires near the Herbicide Exposure Unit could release trace amounts of soil contaminants to the air(14). ATSDR selected the Herbicide Exposure Unit for several reasons: (1) community members have expressed concern about past herbicide applications, (2) the Herbicide Exposure Unit is relatively close to the base property line, and (3) it is more reasonable to assume that wildfires might affect this part of the base, as compared to waste sites adjacent to buildings.

Modeling Approach

Because no air sampling has been conducted during fires at Eglin AFB, ATSDR developed a scenario to model and evaluate the public health implications of soil contaminants that might be released to the air. To estimate emissions, ATSDR assumed that a 5-acre section of the Herbicide Exposure Unit was contaminated at the maximum soil concentrations found in this area. ATSDR further assumed that the temperatures would cause the entire amount of soil contaminants in the top inch of soil in this 5-acre section to become airborne. This is an extremely conservative assumption. ATSDR already knows that contaminants remain in the surface soil at Eglin AFB, even in areas where fires have occurred in the past. ATSDR also assumed that the emissions from the soil would occur during a 24-hour period. The analyses, therefore, provide an upper-bound estimate of actual emissions from soils during fires. Modeling was conducted for eight chemicals identified as contaminants of concern in the Herbicide Exposure Unit (see Table B-3).

ATSDR again used the SCREEN3 air dispersion model (EPA 1995) to estimate the potential air quality impacts for the scenario being evaluated. This modeling assumes that winds continuously blow from the source (the fire) directly to the receptor (the nearest off base property). ATSDR modeled the emissions from fires as ground-level area sources, with dimensions of 142 meters (a 5-acre square), and rural dispersion coefficients. This model can also be a useful tool for assessing atmospheric dispersion for sources that move small distances, especially when the distances that the source moves is small when compared to the distance from the source to the receptor (as is the case for the Herbicide Exposure Unit at Eglin AFB). Table B-4 outlines the model inputs used during this analysis.

Modeling Results

Table B-3 lists the modeling results for the eight contaminants considered. Specifically, the table indicates: the maximum soil concentration used as an input to the modeling analysis, the estimated highest 24-hour average ambient air concentration that would result at the nearest offsite location, and the lowest ambient air concentration found to be associated with adverse health effects following acute exposures. More detail on each of these data fields follows:

  • The maximum soil concentration in the Herbicide Exposure Unit was taken directly from values reported in site documents and reviewed elsewhere in this PHA. As stated previously, for purposes of the modeling ATSDR assumed that the top inch of surface soil in an entire 5-acre area of the Herbicide Exposure Unit was contaminated at this maximum level. ATSDR also assumed that the entire amount of contamination in this area was released to the air in a 24-hour period.


  • The highest 24-hour average ambient air concentration is an output from the dispersion model. The model generated this value by assuming that winds consistently blew from the source toward the receptor for the entire 24-hour period, and during the least favorable meteorological conditions (e.g., very light winds, highly stable atmospheric conditions). The modeling results should be viewed as a worst-case scenario. Finally, ATSDR notes that the concentrations listed in Table B-3 would only occur for a 24-hour period.


  • The final column in Table B-3 lists, for the eight chemicals considered, the lowest ambient air concentration found to be associated with adverse health effects following acute exposures. These data points are based entirely on compilations of toxicologic and epidemiologic studies reviewed in ATSDR's corresponding toxicological profiles. It should be noted that adverse health effects following acute exposures to lower air concentrations can occur, because the available toxicologic studies have not considered the entire range of exposure concentrations. Nonetheless, the data currently available show that the highest estimated 24-hour average ambient air concentration (even with the conservative assumptions) are all at least 40 times lower than the exposure concentrations found to cause adverse health effects.

Summary of ATSDR's Findings

ATSDR used a modeling analysis to assess the likelihood of fires causing unhealthy amounts of soil contaminants to be released to the air. Even when evaluating one of the most contaminated areas at Eglin AFB and assuming that all contaminants in the top inch of surface soil are released to the air in a fire, ATSDR found that exposures that could result are not at levels of health concern. In other words, previously existing soil contamination in areas that are burned do not cause harmful health effects because these contaminants would not reach off-base areas at levels associated with adverse health effects. As noted in the main part of this PHA, smoke that is released from burning vegetation can cause health problems for people who are exposed to it.

Table B-1.

Upper-Bound Estimates of Annual Average Air Concentrations for Chemicals Applied at the Eglin AFB Herbicide Exposure Unit Between 1962 and 1970(assumes all herbicides sprayed remained airborne)
Chemical Upper-Bound Estimate of Annual Average Air Concentration at Base Boundary
(µg/m3)
Health-Based Comparison Value
(µg/m3)
Type of Comparison Value
2,4-D 0.78 37 RBC
2,4,5-T 0.76 37 RBC
Picloram 0.01 (See notes) (See notes)
Arsenic 0.009 0.0002 CREG
Cacodylic Acid 0.06 (See notes) (See notes)
TCDD 2.8 x 10-5 4.2 x 10-8 RBC

Notes:

The upper-bound concentration estimates of 2,4-D and 2,4,5-T are both considerably lower than the listed health-based comparison values, which are EPA Region 3's risk-based concentrations for non-carcinogenic health effects. Thus, exposures to these levels of chemicals are not believed to result in adverse health effects.

The upper-bound concentration estimates for picloram and cacodylic acid are 0.01 µg/m3 and 0.06 µg/m3, respectively. These are both considerably lower than the RBCs EPA Region 3 had previously published for these chemicals, which were 260 µg/m3 for picloram and 11 µg/m3 for cacodylic acid. Both chemicals, however, no longer appear on EPA's list of RBCs.

Refer to the Herbicide Air Modeling section for further interpretation of exposures to arsenic and TCDD.

Abbreviations:

CREG - cancer risk evaluation guide
RBC - risk-based concentration
µg/m3 - micrograms per cubic meter


Table B-2:

Inputs for the Herbicide Air Modeling Evaluation
Parameter Selected Value Rationale
Source to consider Aerial spraying of chemicals at the Herbicide Exposure Unit Because no air sampling was ever conducted to characterize drift from the aerial spraying, modeling was the only tool available to evaluate past exposures.
Type of source Volume No source type in the SCREEN3 model has been developed to specifically represent emissions from aerial application of chemicals. Using a volume source assumes that chemicals throughout a volume (i.e., the air space beneath the aircraft and the ground) can potentially blow downwind.
Vertical dimension of volume source 46 meters The initial vertical dimension of a volume source is calculated by dividing the actual dimension by 2.15. This value was selected by taking the midpoint of the range of spray heights identified by base personnel (45 to 150 meters) and dividing by 2.15.
Horizontal dimension of volume source 142 meters ATSDR assumed the spray targets for individual applications spanned an area of 610 meters by 610 meters. No detailed information was provided by the base to help select this input parameter.
Urban vs. Rural Rural Based on the absence of significant terrain features and urban development, rural dispersion coefficients were used in this evaluation. Ambient air concentrations predicted with rural dispersion coefficients are higher than those predicted with urban dispersion coefficients.
Terrain Simple Topographic maps indicate that no significant terrain features are in the area that would warrant complex terrain modeling.
Emission Rates Vary by chemical ATSDR calculated chemical emission rates by assuming that the amount of chemicals that were reportedly used between 1962 and 1970 were released continuously. This is essentially an exercise of division (total mass used by the time frame) and unit conversions. Specific data for these chemicals follows:
Chemical

2,4-D
2,4,5-T
Picloram
Arsenic
Cacodylic acid
TCDD

Total Usage (1962-1970)(15)

169,200 pounds
166,300 pounds
2,250 pounds
2,050 pounds
13,600 pounds
6.1 pounds

Emission Rate (g/s)

0.270
0.266
0.00359
0.00328
0.0218
0.00000987


Table B-3.

Upper-Bound Estimates of 24-Hour Average Ambient Air Concentrations at Offsite Locations That Might Result from Soil Contaminants Being Emitted During a Fire
Chemical Maximum Soil Concentration at Herbicide Exposure Unit (ppm) Estimated 24-Hour Average Ambient Air Concentration at Offsite Locations (µg/m3) Lowest Ambient Air Concentration Found to be Associated with Adverse Health Effects Following Acute Exposures (µg/m3)
Arsenic 10 10.4 627,000
Cadmium 1 1.2 170
Chromium 13 13.6 900
Nickel 5 4.79 220
Dioxins 2.15 x 10-4 2.24 x 10-4 NA
DDT 0.46 0.48 NA
alpha-Chlordane 0.021 0.022 154,000
Benzo(a)pyrene 0.66 0.69 NA

Notes:

"Dioxins" refers to the sum of all dioxin compounds. The soil and air concentrations for dioxins are expressed on a toxic equivalent (TEQ) basis.

The final column lists the lowest ambient air concentration found to be associated with adverse health effects following acute exposure. This number is based on the lowest air concentration documented in ATSDR's toxicological profiles found to cause adverse health effects, regardless of the severity, and regardless of whether in laboratory animals or humans. Some additional notes on these values follow: the entry for nickel is based on an exposure study involving nickel subsulfide; ATSDR's toxicological profiles have not identified levels of significant exposure for acute inhalation to dioxins, DDT, and benzo(a)pyrene.

Refer to the Modeling of Soil Contaminants Released during Prescribed Burns and Wildfires section for more information on ATSDR's modeling analysis of this exposure scenario and interpretations of the data in this table.

Abbreviations:

µg/m3 - micrograms per cubic meter
ppm -parts per million


Table B-4.

Model Inputs for the Analysis of Soil Contaminants Released During Fires
Parameter Selected Value Rationale
Source to consider Prescribed burns occurring at the Herbicide Exposure Unit This site was considered due to its proximity to the petitioner and the documented presence of soil contamination.
Type of source Area No source type in the SCREEN3 model has been developed to specifically represent emissions from a high-temperature source that covers an area. The area source option enables predictions of air quality impacts from chemicals released over a broad planar surface, like the soils of the Herbicide Exposure Unit, but buoyancy cannot be considered. A point source allows for representation of buoyancy effects, which may be important in fires, but does not consider the lateral movement of the fire. Simulations comparing point to area source predictions found that concentrations predicted by the area source model were 2.5 times greater than those predicted by the point source model.
Area considered 5 acres Assumed dimension over which maximum soil concentrations occur.
Urban vs. Rural Rural Based on the absence of significant terrain features and urban development, rural dispersion coefficients were used in this evaluation. Ambient air concentrations predicted with rural dispersion coefficients are higher than those predicted with urban dispersion coefficients.
Terrain Simple Topographic maps indicate that no significant terrain features are in the area that would warrant complex terrain modeling.
Emission rates Vary by chemical No information was available on the amount of soil contaminants that might be released to the air during a fire. To evaluate this scenario, ATSDR first calculated an upper-bound estimate of the amounts of chemicals found in the top inch of soil, by assuming that the highest concentration detected existed over the entire 5 acre area of concern. ATSDR then assumed that the emissions of soil contaminants during a fire would likely not be greater than this amount of chemical in the surface soil. Based on this approach, the emission rates were computed as follows.

Contaminant

Arsenic
Cadmium
Chromium
Nickel
Dioxin (sum of TEQs)
DDT
alpha-Chlordane
Benzo(a)pyrene

Emission Rate (g/s/m2)

4.41E-06
5.29E-07
5.78E-06
2.03E-06
9.49E-11
2.03E-07
9.26E-09
2.91E-07



APPENDIX C: INFORMATION ON HOW ATSDR ASSESSES EXPOSURE

I. Estimates of Human Exposure Doses and Determination of Health Effects

What is meant by exposure?

ATSDR's public health assessments 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 people 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 people 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.

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.

If exposure is possible, ATSDR scientists then consider whether contamination is present at levels that might affect public health. ATSDR selects 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 standard 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 animals 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.

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.

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. These 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 medical, toxicologic, and epidemiologic literature about the health effects from exposure to harmful substances, is performed.

II. Overview of ATSDR's Methodology for Evaluating Potential Public Health Hazards

An exposure dose is the amount of chemical a person is exposed to over time.To evaluate exposures on Eglin Air Force Base (AFB), ATSDR evaluated available data to determine whether contaminants were above ATSDR's comparison values. For those that were, ATSDR derived exposure doses (see text box for definition) and compared them against health-based guidelines. ATSDR also reviewed relevant toxicologic and epidemiologic data to obtain information about the toxicity of contaminants of interest. It is important to remember that 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 toxicity of the chemical, the frequency and duration of exposure, and the multiplicity of exposures.

Comparing Data to ATSDR's Comparison Values

Comparison values are derived using conservative exposure assumptions. Comparison values reflect concentrations much lower than those that have been observed to cause adverse 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 are not considered to warrant health concern. While concentrations at or below the relevant comparison value can reasonably be considered safe, it does not automatically follow that any environmental concentration exceeding a comparison value would be expected to produce adverse health effects. It cannot be emphasized strongly enough that comparison values are not thresholds of toxicity. The likelihood that adverse health outcomes will actually occur depends on site-specific conditions and individual lifestyle and genetic factors that affect the route, magnitude, and duration of actual exposure, and not an environmental concentration alone.

For this public health assessment, ATSDR evaluated data collected from sites within the Tom's Bayou drainage basin (surface water and sediment samples); from Weekly Pond (fish samples); and from Mullet, Trout, and Basin Creeks (surface water, sediment, and fish samples) to determine whether people were exposed to contaminant concentrations that exceeded ATSDR's comparison values. The majority of detected contaminants fell at or below comparison values and were not evaluated further. Contaminants that were above comparison values were deemed worthy of further evaluation, prompting ATSDR to estimate exposure doses using site-specific exposure assumptions.

Deriving exposure doses

ATSDR derived exposure doses for those contaminants that were detected above ATSDR's comparison values or did not have 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 be 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 about the frequency and duration of exposures. In cases where site-specific information was not available, ATSDR applied several conservative exposure assumptions to estimate exposures for on-base and off-base residents, and those who use the area for recreational purposes.

The following equation was used to estimate recreational exposure to contaminants in surface water:

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

where:

C: Maximum concentration in parts per million (ppm)
IR: Ingestion rate: 0.15 liters per day§
EF: Exposure frequency, or number of exposure events per year of exposure: 365 days/year
ED: Exposure duration, or the duration over which exposure occurs: adult = 30 years; child = 6 years
BW: Body weight: adult = 70 kg; child = 16 kg*
AT: Averaging time, or the period over which cumulative exposures are averaged (6 years or 30 years x 365 days/year for noncancer effects; 70 years x 365 days/year for cancer effects)

§ The ingestion rate is based on swimming for 3 hours per event (EPA 1997).
* ATSDR assumes that older children (i.e., toddlers) would be more likely to play in the creeks and Tom's Bayou.

The following equation was used to estimate recreational exposure to contaminants in sediments:

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

where:

C: Maximum concentration (ppm)
IR: Ingestion rate: adult = 100 mg per day (0.0001 kg/day)§; child = 200 mg per day (0.0002 kg/day)§
EF: Exposure frequency, or number of exposure events per year of exposure: 365 days/year
ED: Exposure duration, or the duration over which exposure occurs: adult = 30 years; child = 6 years
BW: Body weight: adult = 70 kg; child = 16 kg*
AT: Averaging time, or the period over which cumulative exposures are averaged (6 years or 30 years x 365 days/year for noncancer effects; 70 years x 365 days/year for cancer effects)

§ The ingestion rate is a standard assumption for soil (ATSDR 2002b).
* ATSDR assumes that older children (i.e., toddlers) would be more likely to play in the creeks and Tom's Bayou.

The following equation was used to estimate exposure to contaminants in fish:

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

where:

C: Maximum concentration (ppm)
IR: Ingestion rate: adult = 54 grams per day (0.054 kg/day)§; child = 27 grams per day (0.027 kg/day)§
EF: Exposure frequency, or number of exposure events per year of exposure: 365 days/year
ED: Exposure duration, or the duration over which exposure occurs: adult = 30 years; child = 6 years
BW: Body weight: adult = 70 kg; child = 16 kg*
AT: Averaging time, or the period over which cumulative exposures are averaged (6 years or 30 years x 365 days/year for noncancer effects; 70 years x 365 days/year for cancer effects)

§ The ingestion rate represents daily intake averaged over a year for a person eating seven meals of fish a month (EPA 1991b).
* ATSDR assumes that older children (i.e., toddlers) are eating fish.

Using exposure doses to evaluate potential health hazards

ATSDR analyzes the weight of evidence of available toxicologic, medical, and epidemiologic data to determine whether exposures might be associated with harmful health effects (noncancer and cancer). As part of this process, ATSDR examines relevant health effects 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 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.

For carcinogens, ATSDR also calculates a theoretical increase of cancer cases in a population (for example, 1 in 1,000,000 or 10-6) using EPA's cancer slope factors (CSFs), which represent the relative potency of carcinogens. This is accomplished by multiplying the calculated exposure dose by a chemical-specific CSF. Because they are derived using mathematical models which apply a number of uncertainties and conservative assumptions, risk estimates generated by using CSFs tend to be overestimated.

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.

Using other methods to evaluate potential health hazards

When dealing with exposure to lead, ATSDR uses a second approach in addition to the traditional methodologies described above. A substantial part of human health effects data for lead are expressed in terms of blood lead level rather than exposure dose. Thus, ATSDR developed a 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 micrograms per deciliter (µg/dl) per ppm of lead ingested; ATSDR 1999b). The Centers for Disease Control and Prevention (CDC) has determined that health effects are more likely to be observed if blood lead levels are at or above 10 µg/dl.

Essential nutrients (e.g., calcium, magnesium, 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. Ingestion of these essential nutrients at the concentrations found at Eglin AFB will not result in harmful health effects.

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 contamination at Eglin AFB. 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 at 1-800-553-6847. EPA also develops health effects guidelines, and in some cases, ATSDR relied on EPA's guidelines to evaluate potential health effects. 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 at 1-301-345-2870 or e-mail at Hotline.IRIS@epamail.epa.gov.

III. Evaluation of Health Hazards Associated with Contamination at Eglin AFB

ATSDR evaluated data that were collected from sites within the Tom's Bayou drainage basin (surface water and sediment samples); from Weekly Pond (fish samples); and from Mullet, Trout, and Basin Creeks (surface water, sediment, and fish samples). For each of these areas, contaminant concentrations were compared to comparison values. Many of the contaminants were detected below their corresponding comparison values. For each pathway in which chemicals were detected above comparison values or did not have comparison values, exposure doses were calculated. For most of the chemicals, the calculated exposure doses were less than their respective health guidelines (i.e., MRLs and RfDs) and were not expected to cause an increase in cancer outcomes. After evaluating the available toxicologic data for those chemicals where the exposure doses exceeded health guidelines, ATSDR concludes that none of the chemicals were detected at levels of health concern in any of the evaluated areas. More details about each of the exposure pathways follow.

Tom's Bayou

Tom's Bayou is located in Valparaiso, Florida, and is used for various recreational activities by those people who reside around the bayou. Several small ponds and streams are located on Eglin Main Base, which drain into the bayou. Several Installation Restoration Program (IRP) sites are located at the headwaters or along these surface water bodies, potentially contributing to contamination in Tom's Bayou. The US Fish and Wildlife Service (FWS) and Florida Department of Environmental Protection (FDEP) sampled Tom's Bayou for overall system quality during environmental surveys. In addition, Eglin AFB has conducted several investigations at many of the IRP sites within the Tom's Bayou drainage basin. Surface water and sediment samples from the surface water bodies that drain into the bayou have been analyzed for metals, volatile organic compounds, pesticides, herbicides, dioxins, and PCBs (CH2MHILL 1996; EA Engineering, Science, and Technology 1997; Earth Tech 2001a, 2001c, 2001e; Eglin AFB 1994, 2000c; Harrison et al. 1979; Harrison and Crews 1981; O'Brien & Gere Engineers 1996). The majority of the chemicals were either not detected or were detected below comparison values. Table C-1 lists the chemicals that were detected above comparison values. Arsenic, antimony, thallium, trichloroethene, dichlorodiphenyldichloroethane (DDD), dichlorodiphenyldichloroethylene (DDE), dichlorodiphenyltrichloroethane (DDT), dieldrin, heptachlor, and aroclor-1254 were detected above comparison values in the surface water; and arsenic, benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluoranthene, dibenz(a,h)anthracene, indeno(1,2,3-cd)pyrene, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), DDD, DDE, DDT, dieldrin, and aroclor-1260 were detected above comparison values in the sediment.

Exposure doses were calculated for each of the chemicals listed in Table C-1 using the formulas and assumptions described previously. Most of the exposure doses were below their respective MRLs and RfDs and; therefore, were not at a level of health concern (see Table C-2). These calculated exposures overstate the actual exposures occurring in Tom's Bayou because (1) people are not expected to consistently be exposed to the maximum concentration on a daily basis and for an extended period of time, more realistically people would encounter a range of concentrations, including none, since not every chemical was detected in every sample, (2) adults and children are not expected to be recreating in the bayou as often as 365 days of the year, and (3) the majority of the data are from sites that are located on Eglin Main Base and it is expected that the concentrations would be lower in the bayou than at the source areas. Only arsenic, TCDD, and DDT in the sediment were above health guidelines and are evaluated further:

  • Arsenic. Although elemental arsenic sometimes occurs naturally, arsenic is usually found in the environment in two forms–inorganic (arsenic combined with oxygen, chlorine, and sulfur) and organic (arsenic combined with carbon and hydrogen). The inorganic forms of arsenic are usually more toxic than the organic forms (ATSDR 2000a). Once in the body, the liver changes some of the inorganic arsenic into the less harmful organic form (i.e., by methylation). This process is effective as long as the dose of inorganic arsenic remains below 0.05 mg/kg/day (ATSDR 2000a).
  • Being exposed to the maximum concentration of arsenic found in the sediment at any of the IRP sites within the Tom's Bayou drainage basin would result in exposure doses of 0.000081 mg/kg/day for adults and 0.00071 mg/kg/day for children (see Table C-2). As noted above, the metabolism (i.e., how it is broken down in the body) of inorganic arsenic has been extensively studied in humans and animals. ATSDR's estimated doses are well below those that inhibit the body's ability to detoxify or change it to non-harmful forms (doses greater than 0.05 mg/kg/day inhibit detoxification). Therefore, the amount of arsenic that a person might be exposed to in the sediment of Tom's Bayou should be controlled by normal metabolic processes in the body. In addition, several studies reported CELs ranging from 0.01-0.05 mg/kg/day, which are also much higher than the estimated doses (ATSDR 2000a). Considering the use of the conservative assumptions noted previously, ATSDR concludes that the arsenic levels are too low to be of health concern for both children and adults who might use Tom's Bayou for recreational activities.

  • TCDD is one of 75 different compounds commonly referred to as polychlorinated dioxins. A lot of research has been conducted evaluating exposures to TCDD, which is one of the most toxic dioxins to mammals (ATSDR 1998). The oral health guideline (ATSDR's MRL) is based on a study in which adverse health effects were reported in animals exposed to 1.2 x 10-7 mg/kg/day of TCDD in their food (Schantz et al. 1992 as cited in ATSDR 1998). The estimated exposure doses resulting from exposure to the sediment (adult: 1.2 x 10-9 mg/kg/day and child: 1.0 x 10-8 mg/kg/day) are lower than this level (see Table C-2). In addition, several studies reported CELs ranging from 7.1 x 10-6 -3.6 x 10-4 mg/kg/day, which are also higher than the estimated doses (ATSDR 1998). Considering the use of the conservative assumptions noted previously, ATSDR concludes that the TCDD levels are too low to be of health concern for both children and adults who might use Tom's Bayou for recreational activities.


  • DDT is a pesticide that was commonly used in the past to control insects on agricultural crops. In 1972, the use of DDT was banned in the United States, however, it continues to be used in other countries (ATSDR 2000). The oral health guideline (EPA's RfD) is based on a study in which no adverse health effects were reported in animals exposed to 0.05 mg/kg/day of DDT in their food (Laug et al. 1950 as cited in EPA 1991a). The calculated doses resulting from exposure to the sediment (adult: 0.0001 mg/kg/day and child: 0.00088 mg/kg/day) are much lower than this level. In addition, several studies reported cancer effects (i.e., CELs) at doses ranging from 0.33-116 mg/kg/day, which are also much higher than the estimated doses (ATSDR 2000). Considering the use of the conservative assumptions noted previously, ATSDR concludes that the DDT levels are too low to be of health concern for both children and adults who can use Tom's Bayou for recreational activities.

Weekly Pond

Weekly Pond is a small, catch-and -release pond that the Air Force had opened to fishing for base personnel and their guests (Water and Air Research 1984). In the mid-1980s, Eglin AFB sampled fish tissue (catfish, bluegill, and bass) and detected pesticides (DDD, DDE, and DDT) (Eglin AFB 1989). Other contaminants have not been identified in Weekly Pond. The results were reported as a sum of DDD, DDE, and DDT concentrations (i.e., no individual concentrations were provided). The maximum concentration was 2.53 ppm, higher than each individual pesticide's comparison value (EPA's RBCs are DDD: 0.013 ppm, DDE: 0.0093 ppm, DDT: 0.0093 ppm). Therefore, exposure doses were calculated using the formulas described previously. Because concentrations were not reported for each pesticide, ATSDR conservatively assumed that each pesticide was detected at the maximum sum concentration (2.53 ppm). The resulting doses were above EPA's chronic RfD of 0.0005 mg/kg/day (adult: 0.002 mg/kg/day and child: 0.004 mg/kg/day). Therefore, ATSDR further examined the effects levels seen in the literature and more fully reviewed exposure potential to help predict the likelihood of adverse health outcomes.

  • DDD, DDE, and DDT are pesticides that were commonly used in the past to control insects on agricultural crops. Both DDD and DDE are breakdown products of DDT, which was used to a great extent. The oral health guideline (EPA's RfD of 0.0005 mg/kg/day) is based on a study in which no adverse health effects were reported in animals exposed to 0.05 mg/kg/day of DDT in their food (Laug et al. 1950 as cited in EPA 1991a). The calculated doses resulting from eating fish from Weekly Pond (adult: 0.002 mg/kg/day and child: 0.004 mg/kg/day) are lower than this level. In addition, several studies reported cancer effects (i.e., CELs) at doses ranging from 0.33-116 mg/kg/day, also much higher than the estimated doses (ATSDR 2000). Considering that the maximum concentration used in the exposure equation was a sum of all three pesticides, ATSDR concludes that the pesticide levels are too low to be of health concern for either children or adults who in the past might have eaten fish from Weekly Pond.

Mullet, Trout, and Basin Creeks

Mullet, Trout, and Basin Creeks receive surface water runoff from the Herbicide Exposure Unit. The headwaters of all three creeks are located in areas closed to all forms of public access. Still, they flow into areas that are open to seasonal recreational activities (with appropriate Eglin AFB permits). According to the Baseline Risk Assessment, none of the creeks are visited very often (EA Engineering, Science, and Technology 1997). In 1995, the Air Force sampled surface water, sediment, and fish from Mullet, Trout, and Basin Creeks for organic compounds, pesticides and herbicides, dioxins and furans, PCBs, and inorganics (EA Engineering, Science, and Technology 1997). The majority of the chemicals were either not detected or were detected below comparison values. Table C-3 lists the chemicals that were detected above comparison values in Mullet, Trout, and Basin Creeks. Only arsenic, aldrin, heptachlor, and delta-hexachlorocyclohexane (delta-HCH) were detected above comparison values in the surface water. Arsenic and benzo(a)pyrene were detected above comparison values in the sediment, and arsenic, benzo(a)pyrene, aldrin, heptachlor, and delta-HCH were above comparison values in fish.

Using the formulas and assumptions described previously, exposure doses were calculated for each of the chemicals listed in Table C-3. All but one (arsenic in fish) of the exposure doses were below their respective MRLs and RfDs and, therefore, were not at a level of health concern (see Table C-4). These calculated exposures overstate the actual exposures occurring at Mullet, Trout, and Basin Creeks because people are not expected to be exposed consistently to the maximum concentration on a daily basis and for an extended period of time. More realistically, people would encounter a range of concentrations, including none, because not every chemical was detected in every sample and adults and children are not expected to be visiting the creeks as often as 365 days of the year. And further evaluation of arsenic in fish from the creeks showed the following:

  • Arsenic. As noted previously, arsenic is usually found in the environment in two forms–inorganic and organic, with the inorganic forms of arsenic being more toxic than the organic forms (ATSDR 2000a). In fish and shellfish, generally only about 1-20% of the total arsenic is in the more harmful inorganic form (ATSDR 2000a; Francesconi and Edmonds 1997; NAS 2001; FDA 1993). Arsenic can be found in most foods, but seafood, particularly shellfish, contains the highest concentrations (FDA 1993). Once in the body, the liver changes some of the inorganic arsenic into the less harmful organic form (i.e., by methylation). This process is effective as long as the dose of inorganic arsenic remains below 0.05 mg/kg/day (ATSDR 2000a).
  • Consuming the maximum concentration of arsenic from Mullet, Trout, or Basin Creek up to 7 times a month would result in exposure doses of 0.0004 mg/kg/day for adults and 0.0008 mg/kg/day for children (see Table C-4). As noted above, the metabolism of inorganic arsenic has been extensively studied in humans and animals. ATSDR's estimated doses are well below those that inhibit the body's ability to detoxify or change it to non-harmful forms (doses greater than 0.05 mg/kg/day inhibit detoxification). Therefore, the amount of arsenic that a person might consume in fish from the creeks should be controlled by normal metabolic processes in the body. In addition, several studies reported CELs ranging from 0.01-0.05 mg/kg/day, which are also much higher than the estimated doses (ATSDR 2000a). Considering the use of the conservative assumptions noted previously and that ATSDR did not account for only 1-20% of the total arsenic was the more harmful inorganic form, ATSDR concludes that the arsenic levels are too low to be of health concern for either children or adults who could have eaten fish from Mullet, Trout, and Basin Creeks.

Table C-1.

Chemicals Detected Above Comparison Values at IRP Sites within the Tom's Bayou Drainage Basin
Chemical Maximum Concentration Comparison Value Type
Surface Water (ppb)
Arsenic 1.6 0.02 CREG
Antimony 5.3 4 child RMEG
Thallium 2.5 0.5 MCLG/LTHA
Trichloroethene 1.6 0.09 CREG
Dichlorodiphenyldichloroethane (DDD) 0.3 0.1 CREG
Dichlorodiphenyldichloroethylene (DDE) 0.29 0.1 CREG
Dichlorodiphenyltrichloroethane (DDT) 2.9 0.1 CREG
Dieldrin 0.019 0.002 CREG
Heptachlor 0.049 0.008 CREG
Aroclor-1254 0.5 0.2 child RMEG
Sediment (ppm)
Arsenic 57 0.5 CREG
Benzo(a)pyrene 4.9 0.1 CREG
Benzo(a)anthracene 6.8 0.87 RBC
Benzo(b)fluoranthene 5.6 0.87 RBC
Dibenz(a,h)anthracene 1.2 0.087 RBC
Indeno(1,2,3-cd)pyrene 3 0.87 RBC
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) 0.00082 0.00005 chronic child EMEG
DDD 4 3 CREG
DDE 2.2 2 CREG
DDT 70 2

CREG

Dieldrin 0.21 0.04 CREG
Aroclor-1260 4 0.32 RBC

Notes:

The concentrations listed are the maximums from the available data for all sites within the drainage basin.

Lead was evaluated by calculating a cumulative blood lead level. The resulting blood lead level from the maximum concentration (1,100 ppm) was below CDC's effects level of 10 µg/dl (7.5 µg/dl).

Abbreviations:

CREG - cancer risk evaluation guide
EMEG - environmental media evaluation guide
LTHA - lifetime health advisory for drinking water
MCLG - maximum contaminant level goal
RBC - risk-based concentration
ppb - parts per billion
ppm - parts per million


Table C-2.

Exposure Doses for Chemicals Above Comparison Values at IRP Sites within the Tom's Bayou Drainage Basin
Chemical Maximum Detected Concentration (ppm) Estimated Exposure Dose (mg/kg/day) Oral Health Guideline
(mg/kg/day)
Basis for Health Guideline
Adult Child
Surface Water
Arsenic 0.0016 8.1 x 10-6 3.6 x 10-5 0.0003 chronic MRL
Antimony 0.0053 1.1 x 10-5 5.0 x 10-5 0.0004 chronic RfD
Thallium 0.0025 5.4 x 10-6 2.3 x 10-5 0.00007 chronic RfD
Trichloroethene 0.0016 3.4 x 10-6 1.5 x 10-5 0.006 chronic RfD
DDT 0.0029 6.2 x 10-6 2.7 x 10-5 0.0005 chronic RfD
Dieldrin 0.000019 4.1 x 10-8 1.8 x 10-7 0.00005 chronic MRL
Heptachlor 0.000049 1.1 x 10-7 4.6 x 10-7 0.0005 chronic RfD
Aroclor-1254 0.0005 1.1 x 10-6 4.7 x 10-6 0.00002 chronic RFD
Sediment
Arsenic 57 8.1 x 10-5 7.1 x 10-4 0.0003 chronic MRL
TCDD 0.00082 1.2 x 10-9 1.0 x 10-8 1.0 x 10-9 chronic MRL
DDT 70 1.0 x 10-4 8.8 x 10-4 0.0005 chronic RfD
Dieldrin 0.21 3.0 x 10-7 2.6 x 10-6 0.00005 chronic MRL

Notes:

Bolded text indicates that the calculated exposure dose is above the health guideline.

DDD and DDE in surface water were evaluated for cancer health effects using an EPA cancer slope factor only because a noncancer health guideline is not available. The resulting risks were within acceptable ranges (DDD: 6.6 x 10-8 and DDE: 9.1 x 10-8).

Benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluoranthene, dibenz(a,h)anthracene, indeno(1,2,3-cd)pyrene, DDD, DDE, and aroclor-1260 in sediment were evaluated for cancer health effects using an EPA cancer slope factor only because a noncancer health guideline is not available. The resulting risks were within acceptable ranges (benzo(a)pyrene: 2.2 x 10-5, benzo(a)anthracene: 3.0 x 10-6, benzo(b)fluoranthene: 2.5 x 10-6, dibenz(a,h)anthracene: 5.4 x 10-6, indeno(1,2,3-cd)pyrene: 1.3 x 10-6, DDD: 5.9 x 10-7, DDE: 4.5 x 10-7, and aroclor-1260: 4.9 x 10-6).

Abbreviations:

MRL - minimal risk level
RfD - reference dose
mg/kg/day - milligrams per kilogram per day
ppm - parts per million



Table C-3.

Chemicals Detected Above Comparison Values in Mullet, Trout, and Basin Creeks
Chemical Maximum Concentration Comparison Value Type
Surface Water (ppb)
Arsenic 3.0 0.02 CREG
Aldrin 0.013 0.002 CREG
Heptachlor 0.01 0.008 CREG
delta-Hexachlorocyclohexane- (HCH) 0.007 0.006 CREG

Sediment (ppm)

Arsenic 4 0.5 CREG
Benzo(a)pyrene 0.34 0.1 CREG
Fish (ppm)
Arsenic 0.48 0.0021 RBC
Benzo(a)pyrene 0.0025 0.00043 RBC
Aldrin 0.00085 0.00019 RBC
Heptachlor 0.00085 0.0007 RBC
delta-HCH 0.00085 0.0005 RBC

Abbreviations:

CREG - cancer risk evaluation guide
RBC - risk-based concentration
ppb - parts per billion
ppm - parts per million


Table C-4.

Exposure Doses for Chemicals Above Comparison Values in Mullet, Trout, and Basin Creeks
Chemical Maximum Detected Concentration
(ppm)
Estimated Exposure Dose (mg/kg/day) Oral Health Guideline
(mg/kg/day)
Basis for Health Guideline
Adult Child
Surface Water
Arsenic 0.003 6.4 x 10-6 2.8 x 10-5 0.0003 chronic MRL
Aldrin 0.000013 2.8 x 10-8 1.2 x 10-7 0.00003 chronic MRL
Heptachlor 0.00001 2.1 x 10-8 9.4 x 10-8 0.0005 chronic RfD
delta-HCH 0.000039 8.4 x 10-8 3.7 x 10-7 0.0003 chronic RfD (gamma-HCH)
Sediment
Arsenic 4 5.7 x 10-6 5.0 x 10-5 0.0003 chronic MRL
Fish
Arsenic 0.48 3.7 x 10-4 8.1 x 10-4 0.0003 chronic MRL
Aldrin 0.00085 6.6 x 10-7 1.4 x 10-6 0.00003 chronic MRL
Heptachlor 0.00085 6.6 x 10-7 1.4 x 10-6 0.0005 chronic RfD
delta-HCH 0.00085 6.6 x 10-7 1.4 x 10-6 0.0003 chronic RfD (gamma-HCH)

Notes:

Only arsenic in fish was detected above the health guideline (bolded).

Benzo(a)pyrene was evaluated for cancer health effects using an EPA cancer slope factor only because a noncancer health guideline is not available. The resulting risks were within acceptable ranges (sediment: 1.5 x 10-6 and fish: 6.0 x 10-6).

Abbreviations:

MRL - minimal risk level
RfD - reference dose
mg/kg/day - milligrams per kilogram per day
ppm - parts per million


11 It should be noted that release heights for cropdusting applications (<3 meters) are considerably lower than those for aerial application of chemicals at Eglin AFB (45 to 150 meters). However, the amount of chemical that deposits on the ground is a function of several factors–tree height, the chemical, and efficiency of the spray equipment–in addition to the release height. Therefore, it is unclear whether a higher release height would significantly affect the amount of chemical deposited on the ground at Eglin AFB.
12 In the absence of human data, animal data can be used to study possible human effects as long as the inherent uncertainties of doing so are kept in mind.
13 The following equation was used to estimate inhalation doses: D = [C x IR x EF]/[BW] where
D = average daily inhalation dose (µg/kg/day)
C = contaminant concentration in inhaled air: maximum concentration = 2.8 x 10-7 µg/m3
IR = inhalation rate: adult = 15 m3/day; child = 4.5 m3/day (EPA 1997)
EF = exposure factor (unitless): 0.11
BW = body weight: adult = 70 kg; child = 10 kg
14 Eglin AFB does not conduct prescribed burning at the Herbicide Exposure Unit.
15 Source: EA Engineering, Science, and Technology 1997

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