PUBLIC HEALTH ASSESSMENT
EL DORADO, UNION COUNTY, ARKANSAS
Comparison values for ATSDR public health assessments are contaminant concentrations in specific media that areused to select contaminants for further evaluation. The values provide guidelines used to estimate a dose at whichhealth effects might be observed. Comparison values, along with acronyms and abbreviations, used in theEnvironmental Contamination and Other Hazards and the Public Health Implications sections of this public healthassessment are listed and described below.
| ||= Environmental Media Evaluation Guide|
| ||= Lifetime Health Advisory|
| ||= Minimum Risk Level|
| ||= Reference Dose (mg/kg/day)|
| ||= Reference Media Evaluation Guide|
| ||= Not detected|
| ||= Not analyzed or not reported|
| ||= Estimated value|
| ||= milligrams per liter (mg/l water) |
milligrams per kilogram (mg/kg soil)
| ||= micrograms per liter (µg/l water) |
micrograms per kilogram (µg/kg soil)
| ||= kilogram|
| ||= milligram|
| ||= microgram|
Environmental Media Evaluation Guides (EMEGs) are based on ATSDR minimal risk levels (MRLs) and factor in body weight and ingestion rates.
Lifetime Health Advisories (LTHAs) represent contaminant concentrations that the Environmental Protection Agency(EPA) deems protective of public health (taking into consideration the availability and economics of water treatmenttechnology) over a lifetime (70 years) at an ingestion rate of two liters of water per day.
EPA's Reference Dose (RfD) is an estimate of the daily exposure to a contaminant that is unlikely to cause adversehealth effects. However, RfDs do not consider carcinogenic effects.
Reference Media Evaluation Guides (RMEGs) are based on EPA's Reference Dose (RfD) and factor in body weightand ingestion rates.
Minimum Risk Level (MRL) is an estimate of daily human exposure to a contaminant below which non-cancer,adverse health effects are unlikely to occur. MRLs are developed for each route of exposure, such as ingestion andinhalation, and for the length of exposure.
The Benzo(a)pyrene (B(a)P) Equivalent concentration is a method used to estimate the carcinogenicity of a mixture ofpolycyclic aromatic hydrocarbons (PAHs) relative to the carcinogenicity of B(a)P.
Several PAHs, especially those with four of more benzene rings, have been established as carcinogens in animals. Among the most potent and best studied carcinogenic PAH is B(a)P. A significant amount of knowledge oftoxicological actions of PAHs is based on extrapolation of studies with B(a)P to other carcinogenic members of theclass. The U.S. EPA has classified several PAHs (B(a)P, indeno(1,2,3-cd)anthracene, dibenzo(a,h)anthracene,benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)anthracene, and chrysene) as Group B2 carcinogens, indicatingsufficient evidence of carcinogenesis in animals, but inadequate evidence in humans.
Because cancer potency factors for the carcinogenic PAHs other than B(a)P have not been developed, the potencyfactor for B(a)P is used as a basis for determining relative carcinogenic potential for the other carcinogenic PAHs. Accordingly, the U.S. EPA has developed toxicity equivalence factors (TEFs) to rank the relative carcinogenicpotential of other PAHs to B(a)P. The TEFs currently utilized by EPA Region VI for carcinogenic PAHs are listedbelow.
The TEFs can be used for estimating the relative carcinogenicity of an environmental mixture with a knowndistribution of PAHs. Specifically, the concentration of each carcinogenic PAH is multiplied by the appropriate TEFand then summed to provide an estimate of the B(a)P Equivalent Concentration.
June 1992; and Risk Assessment For The Popile, Inc. Site, July 1992.)
The 2,3,7,8-Tetrachlorodibenzo-p-dioxin Equivalent Concentration (TEC) provides a means of comparing the toxicityof a mixture of chlorinated dibenzo-p-dioxins (CDDs) and chlorinated dibenzofurans (CDFs) to an equivalentconcentration of 2,3,7,8-TCDD.
The EPA Chlorinated Dibenzo-p-dioxins/Chlorinated Dibenzofurans Technical Panel has developed the TEC as aninterim method for use in estimating the risk to human health from exposure to mixtures of these compounds. Thisprocedure generates toxicity equivalence factors (TEFs) which relate the toxicity of individual CDFs and CDDs to thetoxicity of 2,3,7,8-TCDD. 2,3,7,8-TCDD was chosen as the benchmark because it is the most toxic and extensivelystudied compound in this chemical class.
Current TEFs for CDD and CDF congeners are presented below. The TEF for 2,3,7,8-TCDD is defined as unity,whereas TEF values for all other CDD and CDF congeners are less than one (zero has been assigned to all non-2,3,7,8-substituted congeners), thus reflecting the lower toxicity potency of most CDD and CDD congeners. The TEFvalues will change over time as new toxicity information and data are obtained.
The TEFs generated can be used, assuming additivity of the toxic response, for estimating the toxicity of anenvironmental mixture with a known distribution of CDFs and/or CDDs. Specifically, the concentration of each CDDand CDF compound is multiplied by the appropriate TEF and then summed to provide an estimate of the TEC.