Risk assessment noncarcinogens

To assess tlie overall potential for noncarcinogenic effects posed by more dian one chemical, a liazard index (HI) approach has been developed based on EPA s Guidelines for Healdi Risk Assessment of Chemical Mixtures. This approach assumes that simultaneous subtlu eshold exposures to several chemicals could result in an adverse healtli effect. It also assumes tliat tlie magnitude of the adverse effect will be proportional to tlie sum of the ratios of the subtlireshold exposures to acceptable exposures. The non cancer hazard index is equal to tlie sum of the hazard quotients, as described below, where E and tlie RfD represent the same exposure period (e.g., subclironic, clironic, or shorter-term). 

Metal Emission Limits. Limits for metals, both carcinogenic and noncarcinogenic, are based on an adjusted stack height. Failure to meet these limits requires risk assessments using site specific factors and modeling to establish limits for each metal. The assessments are based on the probability of developing adverse health effects or cancer, based on an inhalation exposure pathway to maximum exposed individuals located near the incinerator (see Hazard ANALYSIS AND RISKASSESSL nt). 

The value for risk is the quantitative end point determined in risk assessment calculations it is commonly used in regulatory and management decisions regarding hazardous wastes. As with noncarcinogens, the risk term is calculated for each contaminant, each route of exposure, and for all sets of receptor populations each element of risk is then summed to provide the value of cumulative risk. 

Carlson-Lynch H, Price PS, Swartout JC, Dourson ML, and Keenan RE (1999) Application of quantitative information on the uncertainty in the R to noncarcinogenic risk assessments. HERA 5(3) 527-547. 

The risk assessment implications of hormesis are varied, complex, and may be seen whether the context is evaluating noncarcinogens or carcinogens. 

A hormetic dose-response model has the same dose-response for all biological models, endpoints, and chemical or physical agents. This means that hormesis can harmonize risk assessment procednres for both carcinogens and noncarcinogens. 

Beck, B. D., and Cohen, J. T. (1997). Risk assessment for criteria pollutants versus other noncarcinogens The difference between impUcit and explicit conservatism. Hum Ecol Risk Assess 3, 617-626. 

Calculation of risk from carcinogens and noncarcinogens are conducted differently. EPA uses a three-tiered approach for using data for risk assessments. They are ... 

Baseline Risk Assessment. The risk assessment is the foundation upon which site remediation goals are determined and is developed following two fundamental assessments. A toxicity assessment is performed to collect the most recent and pertinent toxicity data for carcinogenic and noncarcinogenic effects of chemical contaminants detected in site media. An exposure assessment is performed to quantify human intake of contaminated media. Subsequently, by measuring the concentrations of chemicals detected in the site media, the dose of chemical intake can then be quantified to complete the exposure assessment. Risk characterization is the final step, performed by coupling the results of the toxicity assessment with those of the exposure assessment to obtain an overall cumulative site risk. 

EPA also allows for the use of subchronic and developmental RfDs in specific cases where exposures are less than chronic. Subchronic RfDs are to be used for characterizing potential noncarcinogenic effects associated with shortterm exposures lasting from 2 wk to 7 yr (USEPA 1989). Developmental RfDs are used to evaluate the potential effects on the developing fetus following a single exposure event. Subchronic RfDs accepted for use in the preparation of Superfund risk assessments are available in EPA s Health Effects Assessment Summary Table (HEAST USEPA 1996a). 

The U.S. Environmental Protection Agency (EPA) divides the health effects of toxic chemicals into two broad categories for risk-assessment purposes risk of noncancer (noncarcinogenic) health effects and risk of cancer (carcinogenic risk) (Chapter 7). The same analysis of exposure is used for both noncarcinogenic and carcinogenic risk however, the relationship of exposure to effect is analyzed differently for noncancer and carcinogenic risks. 

In the case of noncarcinogenic substances, there exists a threshold this is an exposure with a dose below which there would not be adverse effect on the population that is exposed. This is the reference dose (RfD), and it is defined as the daily exposure of a human population without appreciable effects during a lifetime. The RfD value is calculated by dividing the no observed effect level (NOEL) by uncertainty factors. When NOEL is unknown, the lowest observed effect level (LOEL) is used. NOEL and LOEL are usually obtained in animal studies. The main uncertainty factor, usually tenfold, used to calculate the RfD are the following the variations in interspecies (from animal test to human), presence of sensitive individuals (child and old people), extrapolation from subchronic to chronic, and the use of LOEL instead of NOEL. Noncancer risk is assessed through the comparison of the dose exposed calculated in the exposure assessment and the RfD. The quotient between both, called in some studies as hazard quotient, is commonly calculated (Eq. 2). According to this equation, population with quotient >1 will be at risk to develop some specific effect related to the contaminant of concern. 

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