USEPA assessment factors

US Environmental Protection Agency [USEPA]. 2003. A summary of general assessment factors for evaluating the quality of scientific and technical information. Washington (DC) US Environmental Protection Agency, 18 p. 

USEPA, Exposure Factors Handbook, Report No. 600/C-99/001, US Environmental Protection Agency, National Center for Environmental Assessment, Cincinnati, OH, USA, February 1999. 

This section describes how the tj pes of to.xicity inforniation arc considered in the to.xicity assessment for carcinogenic effects. A slope factor and the accompanying weight of evidence determination are the toxicity data most commonly used to evaluate potential human carcinogenic risks. The methods the USEPA uses to derive these values arc outlined below. 

The USEPA estimates that over 6000 facilities are currently operated as treatment, storage, or disposal facilities (TSDFs) regulated under the Resource Conservation and Recovery Act (RCRA), which assigns the responsibility of corrective action to facility owners and operators and authorizes the USEPA to oversee corrective actions. Unlike the Superfund, RCRA responsibility is delegated to states. The USEPA and authorized states have completed initial assessment of potential environmental contamination at over 70% of RCRA facilities, as required by statute to address corrective action. Environmental contamination at many RCRA facilities is expected to be less severe than at Superfund sites however, the total number of RCRA facilities exceeds the number of Superfund sites. The USEPA developed a computer-based system known as the RCRA National Corrective Action Prioritization System (NCAPS) to help establish priorities for corrective action activities. Among the factors considered in NCAPS are the history of hazardous waste releases, the likelihood of human and environmental exposure, and the type and quantity of waste handle at the facility. 

The most recent USEPA dietary assessment for atrazine used 1.8mg/kg (chronic NOAEL from a 6-month rat study) with a 1000-fold safety factor (cRfD = 0.0018mg/kg/day). This analysis also confirmed that potential dietary exposure for all exposed population subgroups was less than 1% of the cRfD (USEPA, 2003). 

Integrating concentration- and effect-addition principles with (Q)SAR opens the door for (Q)SAR-based mixture assessments. As discussed above, linking interspecies correlations (Asfaw et al. 2004) with the USEPA s ECOSAR program allowed for the generation of species sensitivity distributions, hence a probabilistic estimate for aquatic community effects. Estimated HC5s for 4 chemicals were within a factor of 2 of published values, suggesting that current uncertainty factors overestimate NOECs established via data-based SSDs even SSDs derived... 

Guidelines for exposure assessment (USEPA, 1992a OECD, 1999 IPCS, 2000) and a handbook of child-specific exposure factors (USEPA, 2002a) have been published. Both list a number of references that are applicable to the quantitative estimate of exposure. Generally, the methods used for the quantitative estimate of exposure are not different for children and adults. The magnitude of exposure is a product of the exposure concentration as a function of... 

USEPA (1990) Exposure factors handbook. Washington, DC, United States Environmental Protection Agency, Office of Health and Environmental Assessment (EPA/600/8-98/043). 

Exposure assessment involves the specification of values for parameters, either for direct determination of the exposure or as input for mechanistic or empirical or distribution-based models that are used to fill the exposure scenario with adequate information. Numerical values for exposure parameters are obtained using various approaches, such as the USEPA s Exposure Factors Handbook (USEPA, 1997a), the European Union s (EU) Technical Guidance Document (EU, 2003), the German XProb project (Mekel, 2003) and the European KTL s ExpoFacts (Vuori et al., 2006). 

Simple models have been developed to screen for consequences of worst-case exposures (van de Meent et al., 1995 USEPA, 1997b). For example, these models calculate worst-case exposure by dividing the amount of active ingredient by the room size. When better estimates of exposure are needed, simple models are advanced based on mechanistic processes or statistical relations, in conjunction with experiments aimed at quantifying exposnre factors (Jayjock, 1994 Matoba et al., 1998a,c van Veen, 1996) (see the model overview below). These models describe the mechanisms of exposure and inclnde key factors that influence exposure, such as ventilation rates of rooms and vapor pressures of chemicals. In addition, they provide a more precise temporal and spatial scale of exposure and dose. These scales enable identification and exposnre assessment of persons at various distances from the application and of persons having varions time-intervals of contact with the pesticide. 

The cumulative assessment for endpoint (1) combines only those chemicals and routes that are associated with endpoint (1) via a common mechanism and incorporates only those No Observed Adverse Effect Levels (NOAELs), benchmark doses, uncertainty factors, etc. associated with endpoint (1). A similar cumulative assessment would be carried out for endpoint (2). Guidance on aggregate exposure and cumulative risk assessment has been recently published (USEPA, 2003). 

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