Data bases exposure, general population

There are insufficient data to determine potential daily inhalation and dermal exposure levels. However, based on the information presented in Seetions 6.3 and 6.4, exposure levels for the general population are probably very low by these routes. Inhalation exposure is not important for the general population, with the possible exception of those individuals living near areas where methyl parathion is frequently sprayed. Since methyl parathion is readily adsorbed through the skin, dermal eontact may be the most relevant exposure pathway. Dermal eontaet is most likely to oeeur in people who are occupationally exposed. 

Suppose there are several animal studies available for a chemical, including some which have involved long-term exposures, and some relating to possible reproductive and developmental effects. Assume data for both mice and rats are available, and that there are well-defined NOAELs for each of the identified toxicity endpoints. The lowest NOAEL from all those available derives from a chronic study, and is 10 mg/(kg day). Given such a data base, and the defaults listed above, a Dy for this chemical applicable to the general population, would be derived as follows... 

Inhalation is the predominant route of exposure to 1,4-dichlorobenzene for the general population. According to data from the TEAM study, 1,4-dichlorobenzene was found in 44-100% of air and breath samples from several U S. locations, and indoor air levels were up to 25 times higher than ambient outdoor levels for dichlorobenzene (1,3- and 1,4-dichlorobenzene) (Wallace et al. 1986b). The EPA has estimated that adult exposure to 1,4-dichlorobenzene is about 35 g/day, based on a mean ambient air concentration of 1.6 g/m (0.27 ppb) (EPA 1985a). Inhalation exposure may be considerably higher indoors where 1,4-dichlorobenzene space deodorants or moth repellents are used. 

Humans may be exposed to 2,3-benzofuran by inhalation, ingestion, or dermal absorption. Based on the limited data available, exposure of the general population to 2,3-benzofuran does not appear to be substantial. However, since this compound has been detected at hazardous waste sites, is reported to be a component of cigarette smoke, and is one monomer in a resin which may be used as a coating on citrus fruits and in packaging materials for foods, human exposure may be possible from these sources. People in Britain who had died in fires had 2,3-benzofuran in some blood samples, but no source of exposure was identified (Anderson and Harland 1980). 2,3-Benzofuran was... 

It is noteworthy that the styrene reference concentration (RfC) in the Integrated Risk Information System is based on the biomarker-response relationship found in workers (Mutti et al. 1984 EPA 1998). The Environmental Protection Agency (EPA) used the relationship of urinary biomarker to ambient-air concentration of workers to develop an RfC that was adjusted for the difference in exposure time between the workplace and the general population. That is a valid approach because it derives a workplace concentration-toxicity relationship in workers, which can then be adjusted for the general population to account for differences in exposure time and can take uncertainty factors into account. It is different from direct adjustment of the styrene BEI to evaluate human population biomonitoring data on styrene metabolites in urine, which would have the uncertainties described above and in Chapter 5. 

Currently, however, since PBBs are no longer produced, exposure of the general population to PBBs will likely only be from historical releases. Based on temporal data, it would appear that environmental levels have decreased substantially since the 1970s and current exposure, if any, will likely be at low levels. 

Most data on human responses to sulfate are based on short-term exposures that are obtained from controlled settings (i.e., studies and experimental trials). The risk of adverse health effects to the general population is limited and acute, and such effects occur only at high drinking water concentrations (>500mgl , and in many cases >1000mgH ). 

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