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1. ATSDR > Public Health Assessments & Consultations

PUBLIC HEALTH ASSESSMENT

HANSCOM FIELD/HANSCOM AIR FORCE BASE
BEDFORD, MIDDLESEX COUNTY, MASSACHUSETTS

APPENDIX C: ESTIMATED EXPOSURE AND HEALTH EFFECTS

The Agency for Toxic Substances and Disease Registry (ATSDR) evaluated exposures to surface soil and surface water/sediment at Hanscom Field/Air Force Base (HF/HAFB). In addition, to address a community concern, ATSDR also evaluated past exposure to drinking water from the Hartwell Road well field. To do so, ATSDR evaluated available data to determine whether contaminants were above ATSDR's comparison values (CVs). For those that were, ATSDR derived exposure doses and compared them against health-based guidelines. ATSDR also reviewed relevant toxicological data to obtain information about the toxicity of contaminants of interest.

Comparing Data to ATSDR's CVs

CVs are derived using conservative exposure assumptions. CVs reflect concentrations that are much lower than those that have been observed to cause adverse health effects. Thus, CVs are protective of public health in essentially all exposure situations. As a result, concentrations detected at or below ATSDR's CVs are not expected to cause health concern. While concentrations at or below the relevant CV may reasonably be considered safe, it does not automatically follow that any environmental concentration that exceeds a CV would be expected to produce adverse health effects. CVs 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 (PHA), ATSDR evaluated data that were collected from surface soil, surface water and sediment, and water from the Hartwell Road well field to determine whether people were exposed to contaminant concentrations that exceeded ATSDR's CVs. The majority of detected contaminants fell at or below CVs. Contaminants that were above CVs necessitated further evaluation, prompting ATSDR to estimate exposure doses (i.e., the amount of chemical a person is exposed to over time) using site-specific exposure assumptions.

Deriving Exposure Doses

When estimating exposure doses, health assessors evaluate (1) contaminant concentrations to which people might have been exposed and (2) length of time and the frequency of exposure. Together, these factors influence an individual's physiological response to chemical contaminant 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 protective assumptions to estimate exposures for residents, recreational users, and trespassers.

Using Exposure Doses to Evaluate Potential Health Hazards

ATSDR performs weight of evidence analyses to determine whether exposures might be associated with adverse health effects (noncancer and cancer). As part of this process, ATSDR examines relevant toxicologic, medical, and epidemiologic data to determine whether estimated doses are expected to result in adverse health effects. As a first step in evaluating noncancer effects, ATSDR compares estimated exposure doses to standard health guideline values, including ATSDR's minimal risk levels (MRLs) and the U.S. Environmental Protection Agency's (EPA's) reference doses (RfDs). The MRLs and RfDs are estimates of daily human exposure to substances that are not expected 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 be protective of human health, MRLs and RfDs have built in "uncertainty" or "safety" factors that make them much lower than levels at which health effects have been observed. Therefore, if an exposure dose is higher than the MRL or RfD, it does not necessarily follow that adverse health effects will occur.

As a second screen, ATSDR estimated doses using the maximum detected concentration. If these doses exceeded the health guideline values, then ATSDR calculated a more realistic exposure scenario using the average concentration. This approach is taken because it is not expected that anyone would have contact with the maximum concentration on a daily basis and for an extended period of time because not every environmental sample contains the maximum detected concentration of any given chemical. A description of assumptions used for each medium follows.

Surface Soil

The following equation was used to estimate recreational exposure doses to contaminants in surface soil from incidental ingestion:

where:

* 1 10^-6 kg (kilogram) = 1 mg (milligram)
** Mean body weight for a child 1 to 5 years old.

ATSDR applied this equation to the maximum concentration of each of the contaminants measured above CV in soil. None of the contaminants were measured above health guidelines based on the stated exposure estimates (Table C-1). From this evaluation, ATSDR concluded that no adverse health effects are expected from contaminants in surface soil.

Surface Water

The following equation was used to estimate recreational exposure doses to contaminants in surface water from incidental ingestion:

where:

* Mean body weight for a child 1 to 5 years old.

ATSDR used this formula to evaluate each chemical present above CV in surface water (Table C-2). Vinyl chloride for children was the only contaminant to be present above health guidelines based the conservative exposure estimates presented above. The sample that yielded the maximum concentration of vinyl chloride used in the dose assessment was the only sample in which vinyl chloride was found. Vinyl chloride concentrations in each of the 17 other samples collected from the Shawsheen River were below the detection limit. The streams and wetlands surrounding HF/HAFB are shallow and not typically used for recreational purposes. ATSDR assumed an exposure frequency of 195 days per year to these media, although such a frequency is not expected (i.e. a child is not expected to swim in surface water in Massachusetts during the long, cold winter months). Consequently, the initial dose estimates were especially conservative (i.e., it is not realistic to assume a child would ingest 0.05 liter of surface water at the maximum concentration for 195 days a year). When the dose is reevaluated using the more realistic second highest concentration (or the detection limit), the dose is no longer above health guidelines. Therefore, ATSDR concludes that chemicals detected in surface water are not present at levels expected to cause adverse health effects.

Sediments

The following equation was used to estimate recreational exposure doses to contaminants in sediments from incidental ingestion:

where:

* 1 10^-6 kg = 1 mg
** Mean body weight for a child 1 to 5 years old.

Using the above exposures, none of the estimated doses were above health guidelines with the exception of iron in children (Table C-3). The maximum concentration of iron (95,500 ppm) was almost twice as high as any other sample. This exposure dose was, however, extremely conservative. Most of the other samples in which iron was analyzed were below CVs and; therefore, below levels of health concern. Reevaluating the exposure dose using an average iron concentration, the dose was well below health guidelines. This approach is more realistic because a child could not ingest sediment at the maximum concentration each day for 195 days, but would be expected to ingest an average concentration. Further, as stated above in the surface water section, the exposure frequency was extremely conservative as well, it is not expected that a child would play/access sediments at HF/HAFB for 195 days out of the year, especially considering the wetlands and streams in the area are not conducive to recreation. Consequently, ATSDR determined that contaminants in sediments are not expected to cause adverse health effects.

Groundwater from the Hartwell Road Well Field

The contaminants benzene, trichloroethylene (TCE), and dissolved iron were detected in the Hartwell Road production wells in 1983 and 1984 at concentrations greater than ATSDR CVs for drinking water (Table 11). The wells contained other VOCs, but at lower concentrations. The primary exposure pathway of concern was past exposure through consumption of the well water. No exposure via consumption is occurring now because the wells are not being used to supply drinking water.

The following equation was used to estimate exposure doses to contaminants in the Hartwell Road production wells:

where:

* Body weight for an infant.

ATSDR applied this equation to the maximum concentrations of TCE, benzene, and iron. The exposure doses for benzene were below health guidelines, whereas, the exposure doses for iron and TCE were above health guidelines, based on the stated exposure estimates (Table C-4). Calculated exposure doses higher than the health guideline do not automatically mean harmful health effects will occur. Rather, they are an indication that ATSDR should further examine the harmful effect levels reported in the scientific literature and more fully review exposure potential. Estimated doses that are less than these values, as in the case of exposure to benzene, are not considered to be of health concern.

TCE

Noncancer: TCE was detected in water collected from the Hartwell Road production wells at levels up to 33 ppb. Using this maximum concentration, ATSDR derived exposure doses to TCE in the well water of 0.0009 mg/kg/day for an adult and 0.0033 mg/kg/day for a child (Table C-4). These doses are well below the levels at which no harmful health effects have been observed in animals orally exposed to TCE for less than 1 year (doses ranging from 18 mg/kg/day to 3,200 mg/kg/day; ATSDR 1997). Although intermediate doses less than these have been observed to cause developmental health effects (0.18 mg/kg/day caused 5% increased fetal heart abnormalities in rats; Dawson et al. 1993 as cited in ATSDR 1997), this lowest-observed-adverse-effect level (LOAEL) is still two orders of magnitude higher than the estimated exposure doses that ATSDR derived. Therefore, drinking water containing this level of TCE from the Hartwell Road well field between 1983 and 1984, is not expected to have resulted in adverse noncancer health effects.

Cancer: EPA is currently reviewing the scientific literature pertaining to the carcinogenicity of TCE to determine its cancer classification (EPA 2003b). The link between TCE and cancer in people's drinking water is controversial. Available studies are inconclusive and the data are inadequate to establish an association. Some studies have shown that individuals drinking TCE-contaminated water with up to 220 ppb—a concentration about 10 times greater than the maximum level detected at Hartwell Road production wells—suffered no increased incidence of cancer (ATSDR 1997). ATSDR compared the estimated lifetime dose from consuming drinking water from the Hartwell Road well field (0.000013 mg/kg/day; Table C-4) to the cancer effects levels (CELs) for TCE, which are based on animal studies in which carcinomas were observed at 1,000 mg/kg/day (NTP 1990 as cited in ATSDR 1997). In comparison, the estimated exposure from ingesting water containing TCE at the well field would result in a dose millions of times below the CELs. On the basis of these results, ATSDR concludes that ingestion of TCE at the levels detected in the Hartwell Road production wells between 1983 and 1984, would not have caused an increased likelihood of developing cancer.

Dissolved Iron

Noncancer: Iron is a mineral that is often found in drinking water supplies. The presence of iron in drinking water is, however, generally not considered a health problem. In fact, iron in small amounts is essential to good health because it is used by the body to make hemoglobin, which carries oxygen in the blood from the lungs to other areas of the body. Iron can also help the body's resistance to stress and disease. Instead, iron is considered a secondary—or aesthetic—contaminant because it can impart an unpleasant metallic taste to the water while still being safe to drink. Water high in iron can also cause reddish-brown staining on bathroom fixtures and laundry. The iron in water from the Hartwell Road well field contained dissolved or soluble iron. This type of iron is most common to water systems and creates the most complaints from water users (NCCES 1996).

Generally, iron is not considered to cause harmful health effects except when swallowed in extremely large doses, such as in the case of accidental drug ingestion. Acute iron poisoning has been reported in children under 6 years of age who have accidentally overdosed on iron-containing supplements for adults. According to the FDA, doses greater than 200 mg per event could poison or kill a child (FDA 1997). However, doses of this magnitude are generally the result of children ingesting iron pills. For comparison, ATSDR calculated a daily consumption from exposure to the average concentration of the water by multiplying the concentration of iron (31 ppm or mg/kg) by the daily ingestion rate (2 liters of water for an adult and 1 liter for a child). Based on this assessment, drinking water from the Hartwell Road well field could have increased an adult's daily consumption of iron by 62 mg/day and a child's by 31 mg/day.

The median daily intake of dietary iron is roughly 11-13 mg/day for children 1 to 8 years old, 13-20 mg/day for adolescents 9 to 18 years old, 16-18 mg/day for adult men, and 12 mg/day for adult women (NAS 2001). Therefore, the daily increases in consumption (from drinking water from the Hartwell Road well field) are not expected to cause a person's daily dose to exceed levels known to induce poisoning (e.g., greater than 200 mg/event). Further, the body uses a homeostatic mechanism to keep iron burdens at a constant level despite variations in the diet (Eisenstein and Blemings 1998). Therefore, drinking water containing this level of iron from the Hartwell Road well field between 1983 and 1984, is not expected to have resulted in adverse noncancer health effects.

Cancer: Iron is not known to be a carcinogen.

Finally, the exposure doses that ATSDR calculated are expected to be overestimated by the use of maximum concentrations detected in the production wells. The water from the contaminated production wells was treated and diluted with water from other uncontaminated sources before being distributed to people's houses. Thus, the water people actually drank are expected to have contained much lower concentrations of these contaminants. Therefore, ATSDR concluded that no adverse health effects are expected from drinking water from the Hartwell Road well field in the past.

Table C-1. Exposure Doses for Soil Contaminants Greater than Comparison Values

Chemical	Maximum Concentration ppm	Non Cancer Dose		Health Guideline mg/kg/day	Health Guideline Source	Cancer Dose mg/kg/day	Slope Factor (mg/kg/day)-1	Increased Cancer Risk
		Child mg/kg/day	Adult mg/kg/day
Benzo(a)pyrene	23	1.5E-04	8.8E-06	NA	NA	3.8E-06	7.3	2.7E-05
Benzo(b)fluoranthene	24	1.6E-04	9.2E-06	NA	NA	3.9E-06	0.73	2.9E-06
Benzo(a)anthracene	31	2.1E-04	1.2E-05	NA	NA	5.1E-06	0.73	3.7E-06
Dibenzo(a,h)anthracene	2.6	1.7E-05	9.9E-07	NA	NA	4.3E-07	0.73	3.1E-06
Indeno(1,2,3-cd)pyrene	9.9	6.6E-05	3.8E-06	NA	NA	1.6E-06	7.3	1.2E-06
Arsenic	32	2.1E-04	4.7E-05	0.0003	MRL-chr	2.0E-05	1.5	3.0E-05
Lead	470	3.1E-03	1.8E-04	NA	NA	NA	NA	NA

Key:

MRL-chr — chronic minimal risk level
mg/kg/day — milligram per kilogram per day
NA — not available
ppm — parts per million

Table C-2. Exposure Doses for Surface Water Chemicals Greater than Comparison Values

Chemical	Maximum Concentration ppm	Non Cancer Dose		Health Guideline mg/kg/day	Health Guideline Source	Cancer Dose mg/kg/day	Cancer Slope Factor	Increased Cancer Rate
		Child mg/kg/day	Adult mg/kg/day
1,2-Dichloroethene (total)	0.13	2.3E-04	9.9E-06	0.009	RfD	NA	NA	NA
Benzene	0.0015	2.6E-06	1.1E-07	0.004	RfD	4.9E-08	0.055	2.7E-09
Chloromethane	0.041	7.1E-05	3.1E-06	0.004	RfD	NA	NA	NA
Methylene chloride	0.014	2.4E-05	1.1E-06	0.06	MRL-chr	4.6E-07	0.0075	3.4E-09
Trichloroethene	0.1	1.7E-04	7.6E-06	0.0003	proposed RfD	3.3E-06	0.4	3.1E-06
Vinyl chloride	0.019	3.3E-05	1.5E-06	0.00002	MRL-chr	6.2E-07	1.4	8.7E-07
Benzo(a)anthracene	0.0004	6.9E-07	3.1E-08	NA	NA	1.3E-08	0.73	9.6E-08
Benzo(a)pyrene	0.0005	8.7E-07	3.8E-08	NA	NA	1.6E-08	7.3	1.2E-07
Benzo(b)fluoranthene	0.001	1.7E-06	7.6E-08	NA	NA	3.3E-08	0.73	2.4E-07
Benzo(g,h,i)perylene	0.000048	8.3E-08	3.7E-09	NA	NA	1.6E-09	7.3	1.1E-08
Aldrin	0.000045	7.8E-08	3.4E-09	0.00003	MRL-chr	1.5E-09	17	5.8E-08
Heptachlor epoxide	0.000092	1.6E-07	7.0E-09	0.000013	RfD	3.0E-09	9.1	2.7E-08
Arsenic	0.108	1.9E-04	8.2E-06	0.0003	MRL-chr	3.5E-06	1.5	5.3E-06
Cadmium	0.0058	1.0E-05	4.4E-07	0.0002	MRL-chr	NA	NA	NA
Iron	175	3.0E-01	1.3E-02	0.3	RfD	NA	NA	NA
Manganese	1.63	2.8E-03	1.2E-04	0.05	RfD	NA	NA	NA
Lead	0.0281	4.9E-05	2.1E-06	NA	NA	NA	NA	NA
Vanadium	0.202	3.5E-04	1.5E-05	0.003	MRL-int	NA	NA	NA

Key:

MRL-chr — chronic minimal risk level
MRL-int — intermediate minimal risk level
mg/kg/day — milligram per kilogram per day
ppm — parts per million
NA — not available
RfD — reference dose

Table C-3. Exposure Doses for Sediment Contaminants Greater than Comparison Values

Chemical	Maximum Concentration ppm	Non Cancer Dose		Health Guideline mg/kg/day	Health Guideline Source	Cancer Dose mg/kg/day	Cancer Slope Factor	Increased Cancer Rate
		Child mg/kg/day	Adult mg/kg/day
Benzo(a)anthracene	2.2	1.5E-05	8.4E-07	NA	NA	3.6E-07	0.73	2.6E-07
Benzo(b)fluoranthene	3.4	2.3E-05	1.3E-06	NA	NA	5.6E-07	0.73	4.1E-07
Benzo(a)pyrene	2.2	1.5E-05	8.4E-07	NA	NA	3.6E-07	7.3	2.6E-06
Dibenzo[a,h]anthracene	0.29	1.9E-06	1.1E-07	NA	NA	4.7E-08	7.3	3.5E-07
Indeno[1,2,3-cd]pyrene	1.2	8.0E-06	4.6E-07	NA	NA	2.0E-07	7.3	1.4E-07
Heptachlor epoxide	0.1	6.6E-07	3.8E-08	0.000013	RfD	1.6E-08	9.1	1.5E-07
PCB-1248	1.9	1.3E-05	7.3E-07	0.00002	MRL-chr for PCB-1254	NA	NA	NA
PCB-1260	1.3	8.6E-06	5.0E-07	0.00002	MRL-chr for PCB-1254	NA	NA	NA
Arsenic	38.1	2.5E-04	1.5E-05	0.0003	MRL-chr	NA	NA	NA
Iron	95,500	6.3E-01	3.6E-02	0.3	RfD	NA	NA	NA

Key:

MRL-chr — chronic minimal risk level
mg/kg/day — milligram per kilogram per day
NA — not available
ppm — parts per million
PCB — polychlorinated biphenyl
RfD — reference dose

Table C-4. Exposure Doses for Contaminants in Hartwell Road Production Wells Greater than Comparison Values

Chemical	Maximum Concentration ppb	Non Cancer Dose		Health Guideline mg/kg/day	Health Guideline Source	Cancer Dose mg/kg/day	Cancer Slope Factor	Increased Cancer Rate
		Child mg/kg/day	Adult mg/kg/day
Benzene	30	3.0E-03	8.6E-04	0.004	RfD	1.2E-05	0.055	6.7E-07
TCE	33	3.3E-03	9.4E-04	0.0003	RfD	1.3E-05	0.4	5.4E-06
Dissolved Iron	31,000	3.1	0.89	0.3	RfD	NA	NA	NA

Key:

mg/kg/day — milligram per kilogram per day
NA — not available
ppb — parts per billion
RfD — Reference dose
Note: Bold means that the chemical exceeded the health guideline value.

APPENDIX D: ATSDR GLOSSARY OF ENVIRONMENTAL HEALTH TERMS

The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal public health agency with headquarters in Atlanta, Georgia, and 10 regional offices in the United States. ATSDR's mission is to serve the public by using the best science, taking responsive public health actions, and providing trusted health information to prevent harmful exposures and diseases related to toxic substances. ATSDR is not a regulatory agency, unlike the U.S. Environmental Protection Agency (EPA), which is the federal agency that develops and enforces environmental laws to protect the environment and human health. This glossary defines words used by ATSDR in communications with the public. It is not a complete dictionary of environmental health terms. If you have questions or comments, call ATSDR's toll-free telephone number, 1-888-42-ATSDR (1-888-422-8737).

General Terms

Acute :

Occurring over a short time [compare with chronic].

Acute exposure :

Contact with a substance that occurs once or for only a short time (up to 14 days) [compare with intermediate duration exposure and chronic exposure].

Adverse health effect :

A change in body function or cell structure that might lead to disease or health problems

Analyte :

A substance measured in the laboratory. A chemical for which a sample (such as water, air, or blood) is tested in a laboratory. For example, if the analyte is mercury, the laboratory test will determine the amount of mercury in the sample.

Biologic uptake :

The transfer of substances from the environment to plants, animals, and humans.

Cancer :

Any one of a group of diseases that occur when cells in the body become abnormal and grow or multiply out of control.

Cancer risk :

A theoretical risk for getting cancer if exposed to a substance every day for 70 years (a lifetime exposure). The true risk might be lower.

Carcinogen :

A substance that causes cancer.

CERCLA:

[see Comprehensive Environmental Response, Compensation, and Liability Act of 1980]

Chronic :

Occurring over a long time [compare with acute].

Chronic exposure :

Contact with a substance that occurs over a long time (more than 1 year) [compare with acute exposure and intermediate duration exposure]

Comparison value (CV) :

Calculated concentration of a substance in air, water, food, or soil that is not expected to cause harmful (adverse) health effects in exposed people. The CV is used as a screening level during the public health assessment process. Substances found in amounts greater than their CVs might be selected for further evaluation in the public health assessment process.

Completed exposure pathway:

[see exposure pathway].

Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) :

CERCLA, also known as Superfund, is the federal law that concerns the removal or cleanup of hazardous substances in the environment and at hazardous waste sites. ATSDR, which was created by CERCLA, is responsible for assessing health issues and supporting public health activities related to hazardous waste sites or other environmental releases of hazardous substances. This law was later amended by the Superfund Amendments and Reauthorization Act (SARA).

Concentration :

The amount of a substance present in a certain amount of soil, water, air, food, blood, hair, urine, breath, or any other media.

Contaminant :

A substance that is either present in an environment where it does not belong or is present at levels that might cause harmful (adverse) health effects.

Dermal :

Referring to the skin. For example, dermal absorption means passing through the skin.

Dermal contact :

Contact with (touching) the skin [see route of exposure].

Detection limit :

The lowest concentration of a chemical that can reliably be distinguished from a zero concentration.

Disease registry :

A system of ongoing registration of all cases of a particular disease or health condition in a defined population.

DOD :

United States Department of Defense.

Dose:

The amount of a substance to which a person is exposed over some time period. Dose is a measurement of exposure. Dose is often expressed as milligram (amount) per kilogram (a measure of body weight) per day (a measure of time) when people eat or drink contaminated water, food, or soil. In general, the greater the dose, the greater the likelihood of an effect. An "exposure dose" is how much of a substance is encountered in the environment. An "absorbed dose" is the amount of a substance that actually got into the body through the eyes, skin, stomach, intestines, or lungs.

Environmental media :

Soil, water, air, biota (plants and animals), or any other parts of the environment that can contain contaminants.

Environmental media and transport mechanism :

Environmental media include water, air, soil, and biota (plants and animals). Transport mechanisms move contaminants from the source to points where human exposure can occur. The environmental media and transport mechanism is the second part of an exposure pathway.

EPA :

United States Environmental Protection Agency.

Epidemiology :

The study of the distribution and determinants of disease or health status in a population; the study of the occurrence and causes of health effects in humans.

Exposure :

Contact with a substance by swallowing, breathing, or touching the skin or eyes. Exposure may be short-term [acute exposure], of intermediate duration, or long-term [chronic exposure].

Exposure assessment :

The process of finding out how people come into contact with a hazardous substance, how often and for how long they are in contact with the substance, and how much of the substance they are in contact with.

Exposure investigation :

The collection and analysis of site-specific information and biologic tests (when appropriate) to determine whether people have been exposed to hazardous substances.

Exposure pathway :

The route a substance takes from its source (where it began) to its end point (where it ends), and how people can come into contact with (or get exposed to) it. An exposure pathway has five parts: a source of contamination (such as an abandoned business); an environmental media and transport mechanism (such as movement through groundwater); a point of exposure (such as a private well); a route of exposure (eating, drinking, breathing, or touching), and a receptor population (people potentially or actually exposed). When all five parts are present, the exposure pathway is termed a completed exposure pathway.

Feasibility study :

A study by EPA to determine the best way to clean up environmental contamination. A number of factors are considered, including health risk, costs, and what methods will work well.

Groundwater :

Water beneath the earth's surface in the spaces between soil particles and between rock surfaces [compare with surface water].

Hazard :

A source of potential harm from past, current, or future exposures.

Hazardous waste :

Potentially harmful substances that have been released or discarded into the environment.

Indeterminate public health hazard :

The category used in ATSDR's public health assessment documents when a professional judgment about the level of health hazard cannot be made because information critical to such a decision is lacking.

Ingestion :

The act of swallowing something through eating, drinking, or mouthing objects. A hazardous substance can enter the body this way [see route of exposure].

Inhalation :

The act of breathing. A hazardous substance can enter the body this way [see route of exposure].

Intermediate duration exposure :

Contact with a substance that occurs for more than 14 days and less than a year [compare with acute exposure and chronic exposure].

mg/kg :

Milligram per kilogram.

Migration :

Moving from one location to another.

Minimal risk level (MRL) :

An ATSDR estimate of daily human exposure to a hazardous substance at or below which that substance is not expected to pose a measurable risk of harmful (adverse), noncancerous effects. MRLs are calculated for a route of exposure (inhalation or oral) over a specified time period (acute, intermediate, or chronic). MRLs should not be used as predictors of harmful (adverse) health effects [see reference dose].

National Priorities List for Uncontrolled Hazardous Waste Sites (National Priorities List or NPL) :

EPA's list of the most serious uncontrolled or abandoned hazardous waste sites in the United States. The NPL is updated on a regular basis.

No apparent public health hazard :

A category used in ATSDR's public health assessments for sites where human exposure to contaminated media might be occurring, might have occurred in the past, or might occur in the future, but where the exposure is not expected to cause any harmful health effects.

No public health hazard :

A category used in ATSDR's public health assessment documents for sites where people have never and will never come into contact with harmful amounts of site-related substances.

NPL:

[see National Priorities List for Uncontrolled Hazardous Waste Sites]

Plume :

A volume of a substance that moves from its source to places farther away from the source. Plumes can be described by the volume of air or water they occupy and the direction they move. For example, a plume can be a column of smoke from a chimney or a substance moving with groundwater.

Point of exposure :

The place where someone can come into contact with a substance present in the environment [see exposure pathway].

Population :

A group or number of people living within a specified area or sharing similar characteristics (such as occupation or age).

ppb :

Parts per billion.

ppm :

Parts per million.

Prevention :

Actions that reduce exposure or other risks, keep people from getting sick, or keep disease from getting worse.

Public comment period :

An opportunity for the public to comment on agency findings or proposed activities contained in draft reports or documents. The public comment period is a limited time period during which comments will be accepted.

Public health action :

A list of steps to protect public health.

Public health advisory :

A statement made by ATSDR to EPA or a state regulatory agency that a release of hazardous substances poses an immediate threat to human health. The advisory includes recommended measures to reduce exposure and reduce the threat to human health.

Public health assessment (PHA) :

An ATSDR document that examines hazardous substances, health outcomes, and community concerns at a hazardous waste site to determine whether people could be harmed from coming into contact with those substances. The PHA also lists actions that need to be taken to protect public health [compare with health consultation].

Public health hazard :

A category used in ATSDR's public health assessments for sites that pose a public health hazard because of long-term exposures (greater than 1 year) to sufficiently high levels of hazardous substances or radionuclides that could result in harmful health effects.

Public health hazard categories :

Public health hazard categories are statements about whether people could be harmed by conditions present at the site in the past, present, or future. One or more hazard categories might be appropriate for each site. The five public health hazard categories are no public health hazard, no apparent public health hazard, indeterminate public health hazard, public health hazard, and urgent public health hazard.

Public health statement:

The first chapter of an ATSDR toxicological profile. The public health statement is a summary written in words that are easy to understand. The public health statement explains how people might be exposed to a specific substance and describes the known health effects of that substance.

RCRA:

[see Resource Conservation and Recovery Act (1976, 1984)]

Receptor population :

People who could come into contact with hazardous substances [see exposure pathway].

Reference dose (RfD) :

An EPA estimate, with uncertainty or safety factors built in, of the daily lifetime dose of a substance that is not expected to cause harm in humans.

Registry :

A systematic collection of information on persons exposed to a specific substance or having specific diseases [see exposure registry and disease registry].

Remedial investigation :

The CERCLA process of determining the type and extent of hazardous material contamination at a site.

Resource Conservation and Recovery Act (1976, 1984) (RCRA):

This Act regulates management and disposal of hazardous wastes currently generated, treated, stored, disposed of, or distributed.

RFA :

RCRA Facility Assessment. An assessment required by RCRA to identify potential and actual releases of hazardous chemicals.

RfD:

[see reference dose]

Risk :

The probability that something will cause injury or harm.

Route of exposure :

The way people come into contact with a hazardous substance. Three routes of exposure are breathing [inhalation], eating or drinking [ingestion], or contact with the skin [dermal contact].

Safety factor:

[see uncertainty factor]

SARA:

[see Superfund Amendments and Reauthorization Act]

Sample :

A portion or piece of a whole. A selected subset of a population or subset of whatever is being studied. For example, in a study of people the sample is a number of people chosen from a larger population [see population]. An environmental sample (for example, a small amount of soil or water) might be collected to measure contamination in the environment at a specific location.

Solvent :

A liquid capable of dissolving or dispersing another substance (for example, acetone or mineral spirits).

Source of contamination :

The place where a hazardous substance comes from, such as a landfill, waste pond, incinerator, storage tank, or drum. A source of contamination is the first part of an exposure pathway.

Special populations :

People who might be more sensitive or susceptible to exposure to hazardous substances because of factors such as age, occupation, sex, or behaviors (for example, cigarette smoking). Children, pregnant women, and older people are often considered special populations.

Statistics :

A branch of mathematics that deals with collecting, reviewing, summarizing, and interpreting data or information. Statistics are used to determine whether differences between study groups are meaningful.

Substance :

A chemical.

Superfund:

[see Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) and Superfund Amendments and Reauthorization Act (SARA)

Superfund Amendments and Reauthorization Act (SARA) :

In 1986, SARA amended the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) and expanded the health-related responsibilities of ATSDR. CERCLA and SARA direct ATSDR to look into the health effects from substance exposures at hazardous waste sites and to perform activities including health education, health studies, surveillance, health consultations, and toxicological profiles.

Surface water :

Water on the surface of the earth, such as in lakes, rivers, streams, ponds, and springs [compare with groundwater].

Toxic agent :

Chemical or physical (for example, radiation, heat, cold, microwaves) agents that, under certain circumstances of exposure, can cause harmful effects to living organisms.

Toxicological profile :

An ATSDR document that examines, summarizes, and interprets information about a hazardous substance to determine harmful levels of exposure and associated health effects. A toxicological profile also identifies significant gaps in knowledge on the substance and describes areas where further research is needed.

Toxicology :

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

Uncertainty factor :

Mathematical adjustments for reasons of safety when knowledge is incomplete. For example, factors used in the calculation of doses that are not harmful (adverse) to people. These factors are applied to the lowest-observed-adverse-effect-level (LOAEL) or the no-observed-adverse-effect-level (NOAEL) to derive a minimal risk level (MRL). Uncertainty factors are used to account for variations in people's sensitivity, for differences between animals and humans, and for differences between a LOAEL and a NOAEL. Scientists use uncertainty factors when they have some, but not all, the information from animal or human studies to decide whether an exposure will cause harm to people [also sometimes called a safety factor].

Urgent public health hazard :

A category used in ATSDR's public health assessments for sites where short-term exposures (less than 1 year) to hazardous substances or conditions could result in harmful health effects that require rapid intervention.

Volatile organic compounds (VOCs) :

Organic compounds that evaporate readily into the air. VOCs include substances such as benzene, toluene, methylene chloride, and methyl chloroform.

Other glossaries and dictionaries:

Environmental Protection Agency (EPA) (http://www.epa.gov/OCEPAterms/ )
National Center for Environmental Health (CDC) (http://www.cdc.gov/nceh/dls/report/glossary.htm )
(National Library of Medicine (NIH) (http://www.nlm.nih.gov/medlineplus/mplusdictionary.html )

For more information on the work of ATSDR, please contact:

Office of Policy and External Affairs
Agency for Toxic Substances and Disease Registry
1600 Clifton Road, N.E. (MS E-60)
Atlanta, GA 30333
Telephone: (404) 498-0080

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Agency for Toxic Substances and Disease Registry, 1825 Century Blvd, Atlanta, GA 30345
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Department of Health and Human Services