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How a chemical enters a person's blood after the chemical has been swallowed, has come into contact with the skin, or has been breathed in.

Acute Exposure:
Contact with a chemical that happens once or only for a limited period of time. ATSDR defines acute exposures as those that might last up to 14 days.

Additive Effect:
A response to a chemical mixture, or combination of substances, that might be expected if the known effects of individual chemicals, seen at specific doses, were added together.

Adverse Health Effect:
A change in body function or the structures of cells that can lead to disease or health problems.

The Agency for Toxic Substances and Disease Registry. ATSDR is a federal health agency in Atlanta, Georgia that deals with hazardous substance and waste site issues. ATSDR gives people information about harmful chemicals in their environment and tells people how to protect themselves from coming into contact with chemicals.

Background Level:
An average or expected amount of a chemical in a specific environment. Or, amounts of chemicals that occur naturally in a specific environment.

Used in public health, things that humans would eat - including animals, fish and plants.

A group of diseases which occur when cells in the body become abnormal and grow, or multiply, out of control

Any substance shown to cause tumors or cancer in experimental studies.

See Comprehensive Environmental Response, Compensation, and Liability Act.

Chronic Exposure:
A contact with a substance or chemical that happens over a long period of time. ATSDR considers exposures of more than one year to be chronic.

Completed Exposure Pathway:
See Exposure Pathway.

Comparison Value (CVs):
Concentrations or the amount of substances in air, water, food, and soil that are unlikely, upon exposure, to cause adverse health effects. Comparison values are used by health assessors to select which substances and environmental media (air, water, food and soil) need additional evaluation while health concerns or effects are investigated.

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA):
CERCLA was put into place in 1980. It is also known as Superfund. This act concerns releases of hazardous substances into the environment, and the cleanup of these substances and hazardous waste sites. ATSDR was created by this act and is responsible for looking into the health issues related to hazardous waste sites.

A belief or worry that chemicals in the environment might cause harm to people.

How much or the amount of a substance present in a certain amount of soil, water, air, or food.

See Environmental Contaminant.

Dermal Contact:
A chemical getting onto your skin. (see Route of Exposure).

The amount of a substance to which a person may be exposed, usually on a daily basis. Dose is often explained as "amount of substance(s) per body weight per day".

Dose / Response:
The relationship between the amount of exposure (dose) and the change in body function or health that result.

The amount of time (days, months, years) that a person is exposed to a chemical.

Environmental Contaminant:
A substance (chemical) that gets into a system (person, animal, or the environment) in amounts higher than that found in Background Level, or what would be expected.

Environmental Media:
Usually refers to the air, water, and soil in which chemical of interest are found. Sometimes refers to the plants and animals that are eaten by humans. Environmental Media is the second part of an Exposure Pathway.

U.S. Environmental Protection Agency (EPA):
The federal agency that develops and enforces environmental laws to protect the environment and the public's health.

The study of the different factors that determine how often, in how many people, and in which people will disease occur.

Coming into contact with a chemical substance.(For the three ways people can come in contact with substances, see Route of Exposure.)

Exposure Assessment:
The process of finding the ways people come in contact with chemicals, how often and how long they come in contact with chemicals, and the amounts of chemicals with which they come in contact.

Exposure Pathway:
A description of the way that a chemical moves from its source (where it began) to where and how people can come into contact with (or get exposed to) the chemical.

ATSDR defines an exposure pathway as having 5 parts:
  1. Source of Contamination,

  2. Environmental Media and Transport Mechanism,

  3. Point of Exposure,

  4. Route of Exposure; and,

  5. Receptor Population.

When all 5 parts of an exposure pathway are present, it is called a Completed Exposure Pathway. Each of these 5 terms is defined in this Glossary.

How often a person is exposed to a chemical over time; for example, every day, once a week, twice a month.

Hazardous Waste:
Substances that have been released or thrown away into the environment and, under certain conditions, could be harmful to people who come into contact with them.

Health Effect:
ATSDR deals only with Adverse Health Effects (see definition in this Glossary).

Indeterminate Public Health Hazard:
The category is used in Public Health Assessment documents for sites where important information is lacking (missing or has not yet been gathered) about site-related chemical exposures.

Swallowing something, as in eating or drinking. It is a way a chemical can enter your body (See Route of Exposure).

Breathing. It is a way a chemical can enter your body (See Route of Exposure).

Lowest Observed Adverse Effect Level. The lowest dose of a chemical in a study, or group of studies, that has caused harmful health effects in people or animals.

See Cancer.

Minimal Risk Level. An estimate of daily human exposure - by a specified route and length of time -- to a dose of chemical that is likely to be without a measurable risk of adverse, noncancerous effects. An MRL should not be used as a predictor of adverse health effects.

The National Priorities List. (Which is part of Superfund.) A list kept by the U.S. Environmental Protection Agency (EPA) of the most serious, uncontrolled or abandoned hazardous waste sites in the country. An NPL site needs to be cleaned up or is being looked at to see if people can be exposed to chemicals from the site.

No Observed Adverse Effect Level. The highest dose of a chemical in a study, or group of studies, that did not cause harmful health effects in people or animals.

No Apparent Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where exposure to site-related chemicals may have occurred in the past or is still occurring but the exposures are not at levels expected to cause adverse health effects.

No Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where there is evidence of an absence of exposure to site-related chemicals.

Public Health Assessment. A report or document that looks at chemicals at a hazardous waste site and tells if people could be harmed from coming into contact with those chemicals. The PHA also tells if possible further public health actions are needed.

A line or column of air or water containing chemicals moving from the source to areas further away. A plume can be a column or clouds of smoke from a chimney or contaminated underground water sources or contaminated surface water (such as lakes, ponds and streams).

Point of Exposure:
The place where someone can come into contact with a contaminated environmental medium (air, water, food or soil). For examples:
the area of a playground that has contaminated dirt, a contaminated spring used for drinking water, the location where fruits or vegetables are grown in contaminated soil, or the backyard area where someone might breathe contaminated air.
A group of people living in a certain area; or the number of people in a certain area.

Potentially Responsible Party. A company, government or person that is responsible for causing the pollution at a hazardous waste site. PRP's are expected to help pay for the clean up of a site.

Public Health Assessment(s):
See PHA.

Public Health Hazard:
The category is used in PHAs for sites that have certain physical features or evidence of chronic, site-related chemical exposure that could result in adverse health effects.

Public Health Hazard Criteria:
PHA categories given to a site which tell whether people could be harmed by conditions present at the site. Each are defined in the Glossary. The categories are:
  1. Urgent Public Health Hazard

  2. Public Health Hazard

  3. Indeterminate Public Health Hazard

  4. No Apparent Public Health Hazard

  5. No Public Health Hazard

Receptor Population:
People who live or work in the path of one or more chemicals, and who could come into contact with them (See Exposure Pathway).

Reference Dose (RfD):
An estimate, with safety factors (see safety factor) built in, of the daily, life-time exposure of human populations to a possible hazard that is not likely to cause harm to the person.

Route of Exposure:
The way a chemical can get into a person's body. There are three exposure routes:
- breathing (also called inhalation),
- eating or drinking (also called ingestion), and
- or getting something on the skin (also called dermal contact).

Safety Factor:
Also called Uncertainty Factor. When scientists don't have enough information to decide if an exposure will cause harm to people, they use "safety factors" and formulas in place of the information that is not known. These factors and formulas can help determine the amount of a chemical that is not likely to cause harm to people.

The Superfund Amendments and Reauthorization Act in 1986 amended CERCLA and expanded the health-related responsibilities of ATSDR. CERCLA and SARA direct ATSDR to look into the health effects from chemical exposures at hazardous waste sites.

Sample Size:
The number of people that are needed for a health study.

A small number of people chosen from a larger population (See Population).

Source (of Contamination):
The place where a chemical comes from, such as a landfill, pond, creek, incinerator, tank, or drum. Contaminant source is the first part of an Exposure Pathway.

Special Populations:
People who may be more sensitive to chemical exposures because of certain factors such as age, a disease they already have, occupation, sex, or certain behaviors (like cigarette smoking). Children, pregnant women, and older people are often considered special populations.

A branch of the math process of collecting, looking at, and summarizing data or information.

Superfund Site:
See NPL.

A way to collect information or data from a group of people (population). Surveys can be done by phone, mail, or in person. ATSDR cannot do surveys of more than nine people without approval from the U.S. Department of Health and Human Services.

Synergistic effect:
A health effect from an exposure to more than one chemical, where one of the chemicals worsens the effect of another chemical. The combined effect of the chemicals acting together are greater than the effects of the chemicals acting by themselves.

Harmful. Any substance or chemical can be toxic at a certain dose (amount). The dose is what determines the potential harm of a chemical and whether it would cause someone to get sick.

The study of the harmful effects of chemicals on humans or animals.

Abnormal growth of tissue or cells that have formed a lump or mass.

Uncertainty Factor:
See Safety Factor.

Urgent Public Health Hazard:
This category is used in ATSDR's Public Health Assessment documents for sites that have certain physical features or evidence of short-term (less than 1 year), site-related chemical exposure that could result in adverse health effects and require quick intervention to stop people from being exposed.


Human Exposure Pathway Evaluation and the Use of ATSDR Comparison Values

The Agency for Toxic Substances and Disease Registry (ATSDR) assesses a site by evaluating thelevel of exposure in potential or completed exposure pathways. An exposure pathway is the waychemicals may enter a person's body to cause a health effect. It includes all the steps between therelease of a chemical and the population exposed, including: (1) a chemical release source, (2)chemical movement, (3) a place where people can come into contact with the chemical, (4) a routeof human exposure, and (5) a population that could be exposed. In this assessment, ATSDRevaluates chemicals in environmental media that people residing near a site may consume, inhale,or contact.

Health assessors use comparison values (CVs) as screening tools to evaluate environmental datathat is relevant to the exposure pathways. CVs represent media-specific contaminantconcentrations that are used to select contaminants for further evaluation to determine thepossibility of adverse health effects. CVs used in this document include ATSDR's environmentalmedia evaluation guide (EMEG) and cancer risk evaluation guide (CREG). CVs are derived fromavailable health guidelines, such as ATSDR's minimal risk levels and EPA's cancer slope factor.

Category of CVs used in this public health assessment are described below and the specific CVsare listed in Table B-1.

Cancer Slope Factor (CSF)
Usually derived from dose-response models and expressed in mg/kg/day, CSFs describe the inherent potency of carcinogens and estimate an upper limit on the likelihood that lifetime exposure to a particular chemical could lead to excess cancer deaths.

Cancer Risk Evaluation Guide (CREG)
Estimated contaminant concentrations that would be expected to cause no more than one excess cancer in a million (10-6) persons exposed over a 70-year life span. ATSDR's CREGs are calculated from EPA's cancer potency factors.

EPA Region III Risk-Based Concentration
EPA combines reference doses and carcinogenic potency slopes with "standard" exposure scenarios to calculate risk-based concentrations, which are chemical concentrations corresponding to fixed levels of risk (i.e., a hazard quotient of 1, or lifetime cancer risk of 10-6, whichever occurs at a lower concentration) in water, air, fish tissue, and soil.

Lowest Observed Adverse Effect Level (LOAEL)
The lowest dose of a chemical that produced an adverse-effect when it was administered to animals in a toxicity study.

Maximum Contaminant Level (MCL)
The MCL is the drinking water stand established by EPA. It is the maximum permissible level of a contaminant in water that is delivered to a free-flowing outlet. MCLs are considered protective of human health over a lifetime (70 years) for individuals consuming 2 liters of water per day.

Minimal Risk Levels (MRL)
MRLs are estimates of daily human exposure to a chemical (i.e., doses expressed in mg/kg/day) that are unlikely to be associated with any appreciable risk of deleterious noncancer effects over a specified duration of exposure. MRLs are calculated using data from human and animal studies and are reported for acute (< 14 days), intermediate (15-364 days), and chronic (> 365 days) exposures. MRLs are published in ATSDR Toxicological Profiles for specific chemicals.

The derivation of a CV uses conservative exposure assumptions, resulting in values that are muchlower than exposure concentrations observed to cause adverse health effects; thus, insuring theCVs are protective of public health in essentially all exposure situations. That is, if theconcentrations in the exposure medium are less than the CV, the exposures are not of healthconcern and no further analysis of the pathway is required. However, while concentrations belowthe CV are not expected to lead to any observable health effect, it should not be inferred that aconcentration greater than the CV will necessarily lead to adverse effects. Depending on site-specific environmental exposure factors (for example, duration of exposure) and activities ofpeople that result in exposure (time spent in area of contamination), exposure to levels above theCV may or may not lead to a health effect. Therefore, ATSDR's CVs are not used to predict theoccurrence of adverse health effects.

The CVs used in this evaluation are defined as follows: The CREG is a concentration at whichexcess cancer risk is not likely to exceed one case of cancer in a million persons exposed over alifetime. The CREG is a very conservative CV that is used to estimate cancer risk. Exposure to aconcentration equal to or less than the CREG is defined as an insignificant risk and is anacceptable level of exposure over a lifetime. The risk from exposure is not considered as asignificant risk unless the exposure concentration is approximately 10 times the CREG andexposure occurs over several years. The EMEG is a concentration at which daily exposure for alifetime is unlikely to result in adverse noncancerous effects.

Elements of a Completed Exposure Pathway

In evaluating public health hazards, ATSDR first tries to determine exposure in the past, present,and future. ATSDR does this by carefully evaluating the elements of an exposure pathway thatmight lead to human exposure. These elements include: (1) a source of site-related contamination,such as drums or waste pits; (2) an environmental medium in which the contaminants might bepresent or from which they might migrate, such as groundwater or soil; (3) points of humanexposure, such as drinking water wells or gardens; (4) routes of exposure, such as breathing,eating, drinking, or touching a substance containing the contaminant; and (5) a receptorpopulation. (Figure 3 explains the exposure pathway evaluation in more detail.) ATSDR thenidentifies an exposure pathway as completed or potential, or eliminates that pathway from furtherevaluation. A completed exposure pathway exists in the past, present, or future if all elements ofhuman exposure link the contaminant source to a receptor population. A potential pathway is onethat ATSDR cannot rule out, even though we cannot find one of the necessary elements.

If a completed or potential exposure pathway exists, ATSDR then considers whether anychemicals were present, are present, or are expected to become present.

Selecting Chemicals for Further Evaluation

Identifying chemicals for further evaluation is a process that requires ATSDR to examinecontaminant concentrations at the site, the quality of environmental sampling data, and thepotential for human exposure. A thorough review of each of these issues is required to accuratelyselect chemicals in the site-specific human exposure pathway. The following text describes theselection process.

In the first step of the chemical selection process, the maximum contaminant concentrations arecompared directly to health-based CVs. ATSDR considers site-specific exposure factors to ensureselection of appropriate health CVs. If the maximum concentration reported for a chemical is lessthan the health CV, ATSDR concludes that exposure to that chemical is not of public healthconcern; therefore, no further data review is required for that chemical. However, if the maximumconcentration is greater than the health CV, the chemical is selected for additional data review. Inaddition, any chemicals detected that do not have relevant health CVs are also selected foradditional data review.

CVs have not been developed for some contaminants, and, based on new scientific informationother CVs may be determined to be inappropriate for the specific type of exposure. In those cases,the contaminants are included for further review if current scientific information indicatesexposure to those contaminants may be of public health concern.

The next step of the process requires a more in-depth review of data for each of the contaminantsselected. Factors used in the selection of the chemicals includes the number of samples withdetections above the minimum detection limit, the number of samples with detections above anacute or chronic health CV, and the potential for exposure at the monitoring location.

Table B-1. Comparison Values by Chemical and Environmental Medium

Contaminant Groundwater/
Surface Water
Comparison Values
Comparison Values
Value (ppb) Source Value (ppm) Source
Volatile Organic Compounds
Benzene 0.6
Chlorobenzene 100
child I-EMEG
20,000child C-EMEG
Chloroform 6
500child C-EMEG
child I-EMEG
10,000child I-EMEG
Methylene chloride 5
child RMEG
3,000child C-EMEG
Tetrachloroethylene5 MCL500child C-EMEG
Trichloroethylene5MCL0.087RBC, residential
Vinyl chloride2MCL0.1CREG
Semi-volatile Organic Compounds
Benzo(a)pyrene 0.005
0.087RBC, residential
1,4-Dichlorobenzene 75
child I-EMEG
bis(2-Ethylhexyl)phthalate 3
0.32RBC, residential
Pesticides/Polychlorinated Biphenyls
Aroclor 1260 0.2 child C-EMEG for Aroclor 1254 0.2 child C-EMEG for Aroclor 1254
Metals (total)    
Antimony 4
20child RMEG
Arsenic 0.02
Barium 700
child RMEG
50child C-EMEG
Beryllium 4
child C-EMEG
4,000child RMEG
Cadmium 2
child C-EMEG
10child C-EMEG
Chromium30 child RMEG
(chromium VI)
200child RMEG(VI)
Lead15EPA action level400EPA SSL
Mercuryno value  3,000child RMEG
Manganese500child RMEG1,000child RMEG
Nickel200child RMEG5.5RBC, residential
Thallium2MCL 200child I-EMEG
Vanadium30child I-EMEG30child I-EMEG

C-EMEG - chronic environmental Media Evaluation Guide
CREG - Cancer risk Evaluation Guide
I-EMEG - intermediate environmental media evaluation guide
MCL - EPA's maximum contaminant level
ppb - parts per billion
ppm - parts per million
RBC - EPA Region III risk-based concentration
RMEG - reference dose media evaluation guide


Estimates of Human Exposure Doses and Determination of Health Effects

After identifying contaminants in site media above comparison values, ATSDR further evaluatesexposures to these contaminants considering information about exposures combined with scientificinformation from the toxicological and epidemiological literature. If necessary, ATSDR estimatesexposure doses, which are estimates of how much contaminant a person is exposed to on a dailybasis. Variables considered when estimating exposure doses include the contaminant concentration,the exposure amount (how much), the exposure frequency (how often), and the exposure duration(how long).

The estimated exposure doses can be used to evaluate potential noncancer and cancer effectsassociated with contaminants detected in site media. When evaluating noncancer effects, ATSDRcompares the estimated exposure dose to standard toxicity values, including ATSDR's minimal risklevels (MRLs) and the U.S. Environmental Protection Agency's reference doses (RfDs), to evaluatewhether adverse effects may occur. The chronic MRLs and RfDs are estimates of daily humanexposure to a substance that is likely to be without appreciable risk of adverse noncancer effectsover a specified duration. The chronic MRLs and RfDs are conservative values, based on the levelsof exposure reported in the literature that represent no-observed-adverse-effects levels (NOAEL) orlowest-observed-adverse-effects-levels (LOAEL) for the most sensitive outcome for a given route ofexposure (e.g., dermal contact, ingestion). Uncertainty (safety) factors are applied to NOAELs orLOAELs to account for variation in the human population and uncertainty involved in extrapolatinghuman health effects from animal studies. ATSDR also reviews the toxicological literature andepidemiology studies to evaluate the weight of evidence for adverse effects.

When evaluating the potential for cancer to occur, ATSDR uses cancer slope factors (CSF) thatdefine the relationship between exposure doses and the likelihood of an increased risk of developingcancer over a lifetime. The CSFs are developed using data from animal or human studies and oftenrequire extrapolation from high exposure doses administered in animal studies to lower exposurelevels typical of human exposure to environmental contaminants. The CSF represents the upper-bound estimate of the probability of developing cancer at a defined level of exposure; therefore, theytend to be very conservative (i.e., overestimate the actual risk) in order to account for a number ofuncertainties in the data used in extrapolation. ATSDR also considers the cancer effect levels(CELs) reported in the literature. The CEL is the lowest dose of a chemical in a study, or group ofstudies, that was found to produce increased incidences of cancer (or tumors).

Exposure from Inadvertent Ingestion of Surface Soil at Site 14: Water Towers 16-A, O-C2,and 504-A

Elevated levels of arsenic and lead were detected in surface soil in the past at Site 14. ATSDRidentified dermal contact and incidental ingestion of contaminated soil for further evaluation.Determining whether health effects might develop from exposure to environmental contaminantsrequires evaluating the concentrations of the contaminants to which people may have beenexposed and how often and how long exposure to those contaminants occurred. Health effects arealso related to individual characteristics such as age, gender, and nutritional status that influencehow a chemical might be absorbed, metabolized, and eliminated by the body. Together, thesefactors help influence the individual's physiological response to chemical contaminant exposureand potential noncancer (noncarcinogenic) or cancer (carcinogenic) outcomes.


Noncancer Effects

The estimated concentrations of arsenic in Site 14 soils (up to 101 J ppm) were below ATSDR'sadult EMEG of 200 ppm, but exceeded the child EMEG of 20 ppm. These screening values haveuncertainty, or "safety", factors built in. Both EMEG values, however, are based on the assumptionof chronic, daily exposure, and, because the soil samples came from around the water towers ratherthan from highly frequented, popular play areas, the derived exposure doses will likely overestimateactual exposures, perhaps significantly. Furthermore, the EMEG is based on a drinking water study.The drinking water study assumed 100% bioavailability of arsenic in water; however, bioavailabilityof arsenic in soil is much lower (estimated at 3% to 50%). Only a portion of arsenic in soils,therefore, is expected to be readily absorbed into the human body. In addition, the frequency ofexposure to these particular soils will be much less than the daily exposure to drinking water. Thepopulation in the drinking water study may have also been more sensitive to arsenic's toxicitybecause of its poor nutritional status (ATSDR 1998).

ATSDR also reviewed available toxicological literature on arsenic. Most available information onthis metal comes from laboratory animal studies and epidemiologic studies in humans drinkingcontaminated water, which limits the studies' usefulness in assessing health effects for individualsexposed to contaminated NSA soil. Actual doses at the water towers might have been lower, andabsorption of arsenic from soil would be lower than that from drinking water. (The ATSDR oralMRL is based on drinking water studies.) Several epidemiologic studies of moderate-sizedpopulations (20 to 200 people) exposed to arsenic through drinking water have detected no dermalor other effects at average chronic doses of 0.0004 to 0.01 mg/kg/day (ATSDR 1998). Using thedefault assumption that a 10 kilogram (kg) (or 22 pound) child ingests 200 milligrams (mg) of Site14 soil per day, the corresponding dose of soil-derived arsenic would be much less than doses thatresult in adverse health effects as reported in the literature. Therefore, ATSDR does not expect thatthe levels of arsenic detected in soil at the water towers would result in any noncancer adverse healtheffects.

Cancer Effects

The concentrations of arsenic in Site 14 soil (estimated up to 101 J ppm) exceeded ATSDR'sconservative CREG of 0.5 ppm, but the levels are not sufficient to pose a carcinogenic hazard undersite-specific conditions of exposure. The Department of Health and Human Services, theInternational Agency for Research on Cancer, the National Toxicology Program, and EPA have allindependently determined that arsenic is carcinogenic to humans. When exposure occurs by the oralroute, the main carcinogenic effect appears to be an increased risk of skin cancer. This conclusion isbased on a number of studies of populations exposed to elevated levels of arsenic in drinking water(ATSDR 1998). However, there are no studies that specifically address the carcinogenic potential ofarsenic in contaminated soil. It should be noted that only about 300 cases of arsenical skin cancerhave been reported in the United States, and virtually all of them were related to occupationalexposures. Because arsenic may not be as bioavailable in soil as in water, and because the humanbody has the ability to detoxify low doses of the metal, it is unlikely that the level of arsenic detectedin NSA soils would increase the risk of cancer (ATSDR 1998).


Small children might be particularly sensitive to the effects of long-term exposure to lead. Healthofficials assess lead exposure by determining blood lead levels. Correlations between blood leadlevels and adverse effects are fairly well understood and are studied to evaluate the potential for leadexposure to cause adverse health effects (e.g., nervous system effects, slowed child growth, anddevelopmental brain damage). The relationship between environmental concentrations of lead andblood lead levels can be estimated by multiplying the detected concentration by a media-specificslope factor of 0.0068 for soil (ATSDR 1999a). Because blood lead levels begin to taper off athigher soil concentrations (the relationship is not linear at high concentrations), this formula isuseful when evaluating exposures occurring to relatively low levels. The formula considers theextent to which lead from various routes of exposure (ingestion, inhalation) may cause blood leadlevels to rise.

ATSDR estimated the possible contribution of lead in soil using the above equation and the maximum concentration of lead (5,030 ppm) present at Site 14. For comparison, ATSDR uses the Centers for Disease Control and Prevention (CDC) recommended guideline for lead. CDC recommends follow-up and/or treatment for children with blood lead levels equal to or greater than 10 micrograms per deciliter (µg/dL). Scientific studies have shown blood lead levels above 10 µg/dL may be associated with neurological or behavioral problems (ATSDR 1999a).

Our estimates suggest that the blood lead level would have risen to 34 µg/dL for a child who incidentally ingested the most highly lead-contaminated soil at Site 14. This level is three times greater than the CDC's screening level of 10 µg/dL. This estimate is based on the maximum detected concentration, however, it likely over estimates actual past exposures of a child to lead in soil. Our estimate was derived from the maximum soil concentration and assumed that a child would be in the area and would always contact the area of greatest contamination. In all likelihood, the greatest part of a child's visit to the area would not be spent on soil containing the highest detected concentrations of lead. First, the area was covered with grass. Second, a majority of the samples contained lead levels below 400 ppm. ATSDR therefore further analyzed exposure to lead using the geometric mean of 290 ppm. (The geometric mean is used when the data show a wide range of concentrations.) The blood lead level using the geometric mean is 2 µg/dL, a level well within the CDC screening level of 10 µg/dL.

Exposure to PCBs from Consumption of Fish from Trindle Spring Run

PCBs were the contaminants detected at the highest concentrations and posing the greatest potentialhealth hazard to individuals eating fish caught in Trindle Spring Run. Although concentrations inTrindle Spring Run rainbow trout (0.6 to 1.2 ppm) and slimy sculpin (0.2 to 1.2 ppm) were belowFDA's tolerance levels of 2 ppm, the levels exceeded levels found in fish taken from a controlstream (0.2 ppm). The highest PCB levels reported for rainbow trout were measured in thecomposite sample of fish from the upstream portion, suggesting that other sources of PCBs may befound upstream of the storm water drainage ditch's (SWDD's) confluence with the creek. For slimysculpins, the highest concentrations were noted in fish samples collected from the downstreamextent of the creek. Over months or years eating contaminated fish, PCBs can accumulate to levelsthat would affect your health. Therefore, people who eat fish regularly can be particularly susceptibleto PCBs that build up over time. Today, a limited fish consumption advisory issued by thePennsylvania Department of Environmental Protection (PADEP) urges people to limit consumptionof rainbow trout caught from Trindle Spring Run to one meal a month. Nonetheless, ATSDRevaluated the fish sampling data to assess potential public health hazards.

Noncancer Effects

Some of the ways in which PCBs cause noncancer effects in adults include changes in the blood,liver, and immune functions. Children appear to be even more sensitive to the effects of PCBs thanadults. Developmental problems have been reported in children whose mothers were exposed toPCBs even before becoming pregnant. PCBs can also pass through a mother's milk to her baby.Babies exposed to PCBs while in the uterus can have lower birth weights and delayed physicaldevelopment.

ATSDR estimated exposure doses using the maximum detected concentration of PCBs in rainbow trout collected downstream of the SWDD and different consumption rates. (Even though slightly higher levels were reported for slimy sculpins than were reported for rainbow trout, ATSDR used the rainbow trout data in exposure estimates because rainbow trout is the more widely sought after and consumed species at Trindle Spring Run.) A person who eats one meal per month might incur an exposure dose that is slightly higher but within the same order of magnitude as the MRL for PCBs (Aroclor 1254) of 0.00002 mg/kg/day. For more frequent consumption of Trindle Spring Run (two or more meals per month), estimated exposure doses exceed the MRL by more than one order of magnitude.

Table C-1. Estimated Exposure Doses from Consumption of Trindle Spring Run Fish

Number of Trindle Spring Fish Meals per Month Estimated Dose of PCBs
1 8 -ounce0.000090.00002
2 8-ounce0.000180.00002
4 8-ounce0.000450.00002
7 8-ounce0.000760.00002

Even though one fish meal per month slightly exceeds the MRL, no harmful effects are expected atthis level. The estimated exposure dose for consuming fish is in fact about one order of magnitudelower than the most conservative NOAEL found in other chronic oral animal studies (ATSDR1999b). Therefore, ATSDR does not expect any adverse non-cancer effects for people who continueobserving the PADEP fish consumption advisory warning for Trindle Spring Run.

Cancer Effects

A number of animal studies have examined the possibility of PCBs causing cancer, butepidemiological studies in humans do not provide enough information to determine if PCBs arecarcinogenic. Several reviews of epidemiological studies (primarily, worker exposures to PCBs)have been inconclusive or have not shown an association between PCBs and cancer (ATSDR1999b). Compared to the cancer effect level found in animal studies, ATSDR's estimated humanexposure dose (based on one fish meal per month) of 3.9 x 10-5 mg/kg/day for adults isapproximately five orders of magnitude lower than the administered doses that induced cancereffects in rats. Rats that ingested certain PCB mixtures over their lifetimes developed liver cancer.Based on these animal studies, EPA classifies PCBs as a Category B2 carcinogen, indicating that itis a probable human carcinogen. The EPA's National Center for Environmental Assessmentrecommended that a cancer slope factor of 2.0 (mg/kg/day)-1 be used for PCBs in biota. Therefore,the cancer risk from eating rainbow trout from Trindle Spring Run under the assumed exposurescenario would be 8 x 10-6 .This risk level is lower than the range typically acceptable for the generalpopulation.

Again, it should be emphasized that the risk level calculation is extremely conservative and likelyoverestimates exposures. Moreover, given the inconclusive link between oral PCB exposure andhuman cancer, it is highly unlikely that the consumption of Trindle Spring Run fish is going to resultin adverse cancer effects for the local fishing population. Still, as a prudent public health measure,ATSDR recommends that people continue to observe the limited fish consumption advisory forTrindle Spring Run.


Agency for Toxic Substances and Disease Registry (ATSDR). 1996. Toxicological Profile forArsenic (Update). August 1998.

Agency for Toxic Substances and Disease Registry. 1999a. Toxicological Profile for Lead (Update).Agency for Toxic Substances and Disease Registry, U.S. Department of Health and HumanServices. Research Triangle Institute. July 1999.

Agency for Toxic Substance and Disease Registry. 1999b. Toxicological Profile for PolychlorinatedBiphenyls (PCBs) (Draft). Agency for Toxic Substances and Disease Registry, U.S. Department ofHealth and Human Services. Research Triangle Institute. April 1999.


The Agency for Toxic Substances and Disease Registry (ATSDR) released the Naval Air Station,Mechanicsburg (NSA) Public Health Assessment (PHA) on February 28, 2002, for public reviewand comment. That public comment period ended April 15, 2002. During that period, ATSDR received the following comments/questions from two restoration advisory members (RAB) and twoagency representatives.

For comments that questioned the validity of statements made in the PHA, ATSDR verified orcorrected the statements. ATSDR has not addressed requests for information to be included in thePHA, unless the party who filed the request provided the supporting documentation. The list ofcomments does not include editorial comments concerning such things as word spelling or sentencesyntax.

  1. Comment: Describe the Navy and the U.S. Department of Health and Human Services plans for monitoring and /or testing groundwater underlying NSA for contaminants proven to be harmful to human health.
  2. Response: The Navy will continue to monitor on-site groundwater wells on a periodic basis,including new wells that are being added to better characterize groundwater contaminationbeneath Sites 3 and 9. Off-site monitoring wells are currently in place to determine the outerlimits of NSA-related contaminant migration in the groundwater. Using this system, theNavy will monitor groundwater movement from the NSA and off-site groundwater quality toidentify and diminish the threat of potential health hazards to off-site communities. Eventhough contaminants exist in the groundwater beneath the NSA, it is very important to notethat there is no public exposure to the groundwater contaminants. Groundwater underlyingNSA has never been used as a source of drinking water, nor will it be used for potable waterin the future. NSA and the surrounding community receive drinking water from municipalwater sources that safely meet federal and state drinking water standards.

    As a reminder, ATSDR scientists generally do not collect environmental sampling data.Instead, they review information provided by the Navy or from other groups, such as the U.S.Environmental Protection Agency (EPA), other government agencies, businesses, and thepublic.

  3. Comment: There is no conclusive evidence that the groundwater beneath NSA, andemerging into the Conodoquinet Creek, has not contaminated either private wells ormunicipal water supplied by two water companies.
  4. Response: Contamination from NSA has not affected the drinking water delivered toresidential taps. Most area residents receive their drinking water from either the PAWC orUnited Water Pennsylvania. EPA's Safe Drinking Water Act requires municipal watersuppliers to test their water regularly for the presence of contaminants, includingtrichloroethylene (TCE). Each of the Mechanicsburg public water suppliers tests for TCE intheir system or production wells either on a quarterly or annual basis. In recent sampling ofthe public water supplies, no TCE was detected at concentrations above ATSDR'scomparison values (CVs) or EPA's maximum contaminant levels (MCLs). Should acontaminant be detected above its MCL, the supplier is required to switch to an alternativedrinking water source or to purify the contaminated water.

    Some Mechanicsburg residents receive their drinking water from private wells. The Navyidentified two off-base wells as possibly being impacted by NSA contamination based ongroundwater flow from NSA and the well's proximity to the site. These private wells arelocated about 3,000 feet west of the property and are reportedly used for drinking water.Results of the well water sampling indicate that contaminants were either not detected orwere detected at levels below ATSDR's CVs and EPA's MCLs, levels that are notconsidered harmful. (CVs and MCLs are developed from scientific literature available onexposure and health effects. These values reflect an estimated contaminant concentration thatis not expected to cause harmful health effects.) To date, the regulators and Navy are notaware of any other downgradient wells from the site that have been or are expected to beimpacted by NSA contaminants.

  5. Comment: Some evidence indicates that polychlorinated biphenyls (PCBs) were detected insoil, sediment, and groundwater at NSA. However, the PHA does not provide evidence toprove that the contaminant PCB is at the acceptable level of 0.50 parts per billion (ppb) indrinking water.
  6. Response: PCBs are not present in municipal drinking water supplies at unacceptable levels.As stated in the PHA, and reiterated above, local municipal water suppliers must conductscheduled testing of the finished water quality to ensure it meets EPA drinking waterstandards. These tests include testing the drinking water for PCBs. Tests to date have notdetected PCBs in drinking water at levels above the EPA's MCL of 0.5 ppb. Even thoughPCBs have been detected in soil, PCBs bind strongly to soil, thus limiting their movementdown through the deeper soil layers to the underlying groundwater. This is particularly truefor Aroclors of PCBs with higher chlorine content, such as Aroclor 1260 that was detected inNSA soil.

  7. Comment: The PHA did not mention that the sediment at Site 9 contained high levels ofcontaminants and that contaminants entering sinkholes could be affecting the aquifer fromwhich the public and private drinking water is drawn.
  8. Response: ATSDR discusses PCBs at Site 9 in the Evaluation of Surface Water andSediment Pathway section of this PHA. As noted in that section, PCBs have been detected atlevels greater than 100 parts per million (ppm) in Segment 1 of Site 9, the storm water ditch.NSA has implemented several measures to prevent downstream migration of sediment,including construction of a gabion dam and removal of contaminated sediment. Post cleanuptests confirmed that the PCB levels in sediment were lower (0.08 ppm) and below EPA'srisk-based concentration of 0.32 ppm.

  9. Comment: The Mechanicsburg RAB requested that Pennsylvania's Department ofEnvironmental Protection (PADEP) post warnings against using the Trindle Springs Runand/or Conodoquinet Creek for swimming, wading, and/or tubing. The PADER has refusedthis request and NSA Mechanicsburg has done nothing to encourage the postings. Childrenand adults alike are known to use these waters for recreation.
  10. Response: The data reviewed by ATSDR do not indicate that contaminants haveaccumulated in Trindle Spring Run at levels that would be harmful to its recreational users.Sediment samples collected from the Trindle Spring Run downstream of its confluence withNSA storm water drainage ditch (SWDD) had PCB concentrations ranging from 0.07 ppm to0.104 ppm. These concentrations are many times lower than ATSDR's CVs for soil of 10ppm for an adult and 1 ppm for a child, and below levels of known health effects. Inaddition, only low levels of PCBs were detected in surface water and sediment samplescollected from both upstream and downstream of Trundle Spring Run's confluence with theSWDD. Furthermore, descriptions provided to ATSDR suggest that these surface waterbodies are not desirable for swimming or wading. Contact with or incidental ingestion ofsurface water or sediment containing the detected levels of PCBs is therefore not expected toharm people who might occasionally use Trindle Spring Run for limited recreational activity.Since only low concentrations were detected in Trindle Spring Run, surface water orsediment entering the Condoquinet River is not expected to be affected by harmful levels ofNSA-related contaminants.

  11. Comment: The commenter noted that dioxin was not mentioned in the PHA, even thoughdioxin was found in high levels in soil tested from Site 3.
  12. Response: Dioxins were detected in soil at Site 3, but generally at low levels. Only 1 of the32 samples collected from this site had a toxic equivalent (TEQ) dioxin soil concentrationabove ATSDR's acceptable screening value for dioxin TEQs of 1 ppb. (Dioxin results werecalculated in terms of TEQs to convert the concentration of individual dioxin congeners to anequivalent concentration of 2,3,7,8-tetrachlorinated dibenzo-p-dioxins, the most toxic of thedioxin congeners.) The only sample exceeding ATSDR's screening value had a TEQ of 3.4ppb. This sample was collected 4 feet below grade from the subsurface soil beneath the 5,000Cubic Yard Pile, where the general public is unlikely to have access. Based on thisinformation, ATSDR finds no evidence to suggest that dioxins at Site 3 pose a threat topublic health. ATSDR added this information to the PHA.

  13. Comment: There is no mention of Borough of Camp Hill, with a reported 8,000 to 12,000residents. Nor is there mention of the Hampton Elementary School and athletic fieldsimmediately outside the northeast perimeter of the NSA.
  14. Response: Thank you. ATSDR has added the information to the Demographic Section of the PHA.

  15. Comment: The municipal park to the west of NSA is the Mechanicsburg Borough park.
  16. Response: Thank you. ATSDR has added the information to appropriate sections of the PHA.

  17. Comment: The NSA and the U.S. Department of Public Health and Human Services say thatthere is no public health hazards involving the NSA. It is proven, however, that the type andseverity of health effects that occur in an individual from contact with contaminants dependon the exposure concentrations, the route or pathway of exposure, and the multiplicity ofexposure.
  18. Response: ATSDR's primary goal in its PHA is to put possible exposures to environmentalcontaminants into meaningful perspective for the public. ATSDR scientists reviewedenvironmental data to see how much contamination occurred at and near NSA and howpeople might come into contact with it. Exposures are only possible if people come incontact with contaminated media (e.g., drinking, touching, inhaling). For cases whereexposure was or is possible, ATSDR tried to explain the likelihood that exposure to thedetected level of a particular chemical may or may not cause harm. As for the NSA area,ATSDR did not find reason to suspect that people working at or living around NSA havebeen or could be exposed to harmful levels of contaminants.

  19. Comment: ATSDR should refrain from using "never" when discussing the possibility ofcontact with contamination. It is clear that children play in the area and thus contact occurs."No supporting evidence of impact at this time" is more useful and reflective of the actualsituation.
  20. Response: In its PHA, ATSDR uses "never" only in relation to the use of the groundwaterbeneath NSA as a source of drinking water. ATSDR's review of site information anddiscussions with site personnel found that the groundwater has not ever been used fordrinking water. ATSDR believes its use of "never" in this context is both unambiguous andaccurate.

  21. Comment: The warning about consuming fish caught from Trundle Spring Run needsstronger language. Also, the warning signs are difficult to read because the print is too small.
  22. Response: ATSDR's evaluation of available fish sampling data from Trundle Spring Runsupports the PADEP current limited advisory. The advisory for Trundle Spring Runrecommends for people to limit their consumption of rainbow trout from the run to one fishmeal per month and encourages sensitive individuals, such as children, women of child-bearing age, and pregnant women, to follow more stringent limitations. Along with theadvisory, the PADEP provides instructions to further reduce exposure to PCBs whenpreparing and cooking trout. ATSDR's very conservative evaluation found that people couldsafely eat on average one Trundle Spring Run trout meal each month without encountering agreater likelihood of developing health effects. No evidence to date supports expanding thisadvisory to other species of fish or strengthening the current restrictions. If, however, newsampling data become available suggesting that the PCB levels are increasing in TrundleSpring Run fish, ATSDR will reevaluate the need for additional action protective of publichealth, such as recommending stronger restrictions in the advisory.

    If you have questions about the clarity or the physical posting of the signs you should contactthe PADEP (717) 787-9657.

  23. Comment: Provide additional information on the type and storage locations of the metalores received by NSA as part of war payment.
  24. Response: Stock piles of mineral ores have been maintained by the Defense NationalStockpile since the 1950s within the 14-acre Site 8 in the southwest portion of NSA.Chromite and manganese ores were stored in the north and west portion of Site 8; kyaniteand aluminum oxide were stored in the southeast portion of Site 8. Site 8 once contained upto 39 piles of ore. Today, this area consists of only four grass-covered piles and oneadditional pile staged on concrete. This information has been added to sections of the textand to Table 2 as needed.

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