PETITIONED PUBLIC HEALTH ASSESSMENT
(A.K.A. VIRGINIA SOLITE)
CASCADE, PITTSYLVANIA COUNTY, VIRGINIA
|ATSDR||Agency for Toxic Substances and Disease Registry|
|COC||contaminant of concern|
|CREG||Cancer Risk Evaluation Guide|
|DHHS||Department of Health and Human Services|
|EMEG||Environmental Media Evaluation Guide|
|EPA||Environmental Protection Agency|
|IARC||International Agency for Research on Cancer|
|mg/kg/day||milligrams per kilogram per day|
|MRL||Minimal Risk Level|
|NAAQS||National Ambient Air Quality Standard|
|NCAPS||National Corrective Action Prioritization System|
|NTP||National Toxicology Program|
|RBC||Region III Risk-based Concentration (EPA)|
|RCRA||Resource Conservation and Recovery Act (EPA)|
|RMEG||Reference Media Evaluation Guide|
|TEF||toxicity equivalence factor|
|VADEQ||Virginia Department of Environmental Quality|
Glossary of Selected Terms
Any substance that may produce cancer.
Estimated concentrations of environmental contaminants in specific media that are not likely to cause adverse health effects, given a standard daily ingestion rate and standard body weight. Comparison values are calculated from the scientific literature on exposure and health effects.
The amount of one substance that is dissolved or contained in a given amount of another. For example, sea water contains a higher concentration of salt than does fresh water. Concentrations of air pollution usually state the mass of a contaminant found in one cubic meter of air.
Any substance or material that enters a system (e.g., the environment, food, the human body) where it is not normally found.
The amount of a substance to which a person is exposed. Dose often takes body weight into account.
The presence of hazardous substances in the environment. From a public health perspective, environmental contamination is addressed when it potentially affects the health or welfare of people living and working near the contaminated areas.
Contact with a chemical by swallowing, by breathing, or by directly contacting (e.g., through the skin or the eyes). Exposure may be short term (acute) or long term (chronic).
A source of risk that does not necessarily imply potential for occurrence. A hazard produces risk only if an exposure pathway exists, and if exposures create the possibility of adverse consequences.
A written response from ATSDR to a specific question or request for information pertaining to potential exposure to hazardous substances. Health consultations generally focus on exposures to contaminants present in just one environmental medium (e.g., air, water, or soil).
Indeterminate Public Health Hazard
A public health conclusion category used for sites for which no conclusions about public health hazards can be made because data are lacking.
Breathing. Exposure may occur from inhaling contaminants because they can be deposited in the lungs, taken into the blood, or both.
Interim (Permit) Status
Period during which treatment, storage and disposal facilities coming under RCRA in 1980 are temporarily permitted to operate while awaiting a permanent permit. Permits issued under these circumstances are usually called "Part A" or "Part B" permits.
Soil, water, air, plants, animals, or any other part of the environment that can contain contaminants.
No Apparent Public Health Hazard
A public health conclusion category used for sites where human exposure to contaminated media is occurring or has occurred in the past, but the exposure is below a level of health hazard. This category is used when exposures do not exceed an ATSDR chronic MRL or other comparable value, data are available for all environmental media to which humans are being exposed, and there are not community-specific health outcome data to indicate that the site has had an adverse impact on human health.
The presence of chemical and/or hazardous substances in the environment. From the public health perspective, pollution is addressed when it potentially affects the health and quality of life of people living and working near it.
In risk assessment, the probability that something will cause injury, combined with the potential severity of that injury.
Route of Exposure
The way in which a person may contact a chemical substance For example, drinking (ingestion) and bathing (skin contact) are two different routes of exposure to contaminants that may be found in water.
As noted in the text of this public health assessment, ATSDR's comparison values are media-specific concentrations that are considered to be "safe" under default conditions of exposure. Theyare used as screening values in the preliminary identification of "contaminants of concern" at a site.The latter is, perhaps, an unfortunate term since the word "concern" may be misinterpreted as animplication of "hazard." As ATSDR uses the phrase, however, a "contaminant of concern" is merelya site-specific chemical substance that the health assessor has selected for further evaluation ofpotential health effects.
Generally, a chemical is selected as a contaminant of concern because its maximum concentration inair, water, or soil at the site exceeds one of ATSDR's comparison values. However, it cannot beemphasized strongly enough that comparison values are not thresholds of toxicity. Whileconcentrations at or below the relevant comparison value may reasonably be considered safe, it doesnot automatically follow that any environmental concentration that exceeds a comparison valuewould be expected to produce adverse health effects. Indeed, the whole purpose behind highlyconservative, health-based standards and guidelines is to enable health professionals to recognizeand resolve potential public health problems before they become actual health hazards. Theprobability that adverse health outcomes will actually occur as a result of exposure to environmentalcontaminants depends on site-specific conditions, individual lifestyle, and genetic factors that affectthe route, magnitude, and duration of actual exposure, not on environmental concentrations alone.
Screening values based on non-cancer effects are obtained by dividing the lowest concentrationsassociated with health effects found in animal or (less often) human studies by cumulative safetymargins (variously called safety factors, uncertainty factors, and modifying factors) that typicallyrange from 10 to 1,000 or more. By contrast, cancer-based screening values are usually derived bylinear extrapolation from animal data obtained at high doses, because human cancer incidence datafor very low levels of exposure simply do not exist, and probably never will. In neither case can theresulting screening values (i.e., EMEGs or CREGs) be used to make realistic predictions of healthrisk associated with low-level exposures in humans.
Listed and described below are the various comparison values and health guidelines that ATSDRused in this report to determine whether contaminants released from Virginia Solite might beassociated with adverse health effects.
Cancer Risk Evaluation Guides (CREGs) are estimated concentrations of contaminants that areexpected to cause no more than one excess cancer case for every million (1 x 10-6) persons who arecontinuously exposed to the concentration for an entire lifetime. These concentrations are calculatedfrom EPA's cancer slope factors, which indicate the relative potency of carcinogenic chemicals.Only chemicals that are known or suspected of being carcinogenic have CREG comparison values.It should be noted that exposures equivalent to CREGs are not actually expected to cause one excesscancer in a million persons exposed over a lifetime. Nor does it mean that every person in anexposed population of 1 million has a 1-in-a-million chance of developing cancer from the specifiedexposure. Although commonly interpreted in precisely these ways, the CREGs reflect only a roughestimate of population risks, which should not be applied directly to any individual.
Environmental Media Evaluation Guides (EMEGs) are estimates of chemical concentrationsthat are not likely to cause an appreciable risk of deleterious, noncancerous health effects for fixeddurations of exposure. These concentrations factor in estimates of receptor body weights and rates ofingestion. EMEGs may reflect several different types of exposure: acute (1 to 14 days), intermediate(15 to 365 days), and chronic (more than 365 days). These concentrations are ultimately based ondata published in ATSDR Toxicological Profiles for specific chemicals.
EPA Region III Risk-Based Concentrations (RBCs) are similar to ATSDR's CREGs andEMEGs in that they are risk-based concentrations derived for carcinogens and noncarcinogens fromRfDs and cancer slope factors, respectively, assuming default values for body weight, exposureduration and frequency, and so on. Unlike EMEGs, however, they are available for fish as well asfor water, soil, and air.
Minimal Risk Levels (MRLs) are derived by ATSDR to represent estimates of daily humanexposure to chemical substances (i.e., doses expressed in mg/kg/day) that the agency considersunlikely to cause any appreciable risk of noncancer effects over a specified duration of exposure.MRLs are calculated using data from human and animal studies and are reported for acute (1 to 14days), intermediate (15 to 365 days) and chronic (more than 365 days) exposures. MRLs arepublished in ATSDR Toxicological Profiles for specific chemicals.
National Ambient Air Quality Standards (NAAQS) are developed by EPA to protect people andthe environment from unhealthy and undesirable levels of air pollution. As of the writing of thisreport, EPA has promulgated NAAQS for seven pollutants (known as "criteria pollutants"). Thesestandards have been developed specifically to protect the health and welfare of humans. To beconservative, these standards were designed to be protective of all exposed persons, including"sensitive" populations (e.g., persons with asthma).
Reference Media Evaluation Guides (RMEGs) are derived from EPA's oral reference doses. TheRMEG represents the concentration in water or soil at which daily human exposure is unlikely toresult in adverse noncarcinogenic effects.
Reference Doses (RfDs) are derived by EPA to represent estimates of human daily exposure tochemical substances unlikely to cause any noncancer adverse health effects over a lifetime. Like ATSDR's MRL, EPA's RfD is a dose expressed in mg/kg/day.
The following section was not available in electronic format for conversion to HTML at the time of preparation of this document. To obtain a hard copy of the document, please contact:
Agency for Toxic Substances and Disease Registry
Division of Health Assessment and Consultation
Attn: Chief, Program Evaluation, Records, and Information Services Branch E-56
1600 Clifton Road NE, Atlanta, Georgia 30333
Dioxins and furans are two families of chlorinated compounds that include more than 200individual chemicals. Each of these chemicals has a similar structure and can be visualized as achain with ten outward facing spokes. Eight of these spokes have the capability of holding a chlorineatom. The difference in these individual chemicals stems from the number and location of thechlorine atoms. The group with only one chlorine atom is referred to as mono-chlorinated. Thegroups with two through eight chlorine atoms are referred to as di-, tri-, tetra-, penta-, hexa-, andocta-chlorinated, respectively. Chemicals with the same number of chlorine atoms are referred to asisomers.
The relative toxicity or potency of dioxins and furans varies depending on the chlorine number andlocations. 2,3,7,8-tetrachlorodibenzo--dioxin (2,3,7,8-TCDD), a compound with four chlorineatoms located in the 2, 3, 7, and 8 positions, has been shown to be the most toxic of thedioxins/furans. The toxicity of other dioxins and furans with chlorination in the 2, 3, 7, and 8positions ranges from slightly less toxic to 1,000 times less toxic. The U.S. EnvironmentalProtection Agency (EPA) has developed a system for evaluating the toxicity associated with amixture of different dioxin and furan groups. The toxicity of each group is expressed in relation to2,3,7,8-TCDD, using what are known as toxicity equivalent factors (TEFs). The TEFs applied toeach dioxin/furan group are listed below:
|Dioxin Group||TEF||Furan Group||TEF|
|Tetrachlorodibenzo--dioxin (TCDD) |
| ||Tetrachlorodibenzofuran (TCDF) |
|Pentachlorodibenzofuran (PeCDF) |
|Hexachlorodibenzo--dioxin (HxCDD) |
|Hexachlorodibenzofuran (HxCDF) |
2,3,7,8-HxCDF a other HxCDFs
|Heptachlorodibenzo--dioxin (HpCDD) |
|Heptachlorodibenzofuran (HpCDF) |
2,3,7,8-HpCDFa other HpCDFs
|Octachlorodibenzo--dioxin (OCDD)||0.001||Octachlorodibenzofuran (OCDF)||0.001|
In this public health assessment, TEFs were used to generate a TCDD-equivalent (TEQ). The TEQexpresses the total dioxin and furan concentration in relation to the toxicity of 2,3,7,8-TCDD. TheTEQ is calculated by first multiplying the concentration of a dioxin/furan by its TEF to generate atoxicity-weighted concentration. For example, 10 parts per billion (ppb) of 2,3,7,8-PeCDD ismultiplied by its TEF of 0.5 for a result of 5 ppb, the toxicity-weighted concentration. The toxicity-weighted concentrations for each dioxin/furan group are summed to calculated the TEQ.
The TEQ concentration is used to assess the potential health hazards associated with a dioxin/furanmixture. The TEQ is compared to the ATSDR (or other comparable) comparison value. If the TEQexceeds the comparison value, ATSDR further analyzes exposure to evaluate whether a publichealth hazard exists.
ATSDR. 1997. Toxicological Profile for Chlorinated Dibenzo--Dioxins (Draft for PublicComment). September 1997.
EPA. 1989. Interim procedures for estimating risks associated with exposure to mixtures ofchlorinated dibenzo--dioxins and dibenzofurans (CDDs and CDFs) and 1989 update. RiskAssessment Forum, Washington, DC. U.S. Environmental Protection Agency. EPA 625/3-89/4016.