Exposure data factors

Stanners have designed a test rig (Fig. 19.12) which provides results that can be correlated with actual atmospheric exposure data. The rig has been designed to investigate a wide range of alloying elements in a development programme on slow-weathering steels for which it was essential to have a rapid, reliable and reproducible test that incorporated the specific atmospheric factors responsible for rust formation. 

Lack of exposure data for most organotins together with limited toxicity information for marine organisms preclude the calculation of risk factors for the marine environment. For dibutyltin, measured concentrations in seawater reflect the use of tributyltin as a marine anti-foulant rather than the use of dibutyltin in plastics. It is therefore not possible to conduct a reliable risk assessment for the current uses of the compormd. 

Although several data sets could be used to derive AEGL-3 values, the 1-h exposure data from the mouse study by Peterson and Bhattacharyya (1985) provided the most sound basis and were selected to derive AEGL-3 values. Due to the steep concentration-response curve for arsine, the 15-ppm exposure (where there was no lethality) was considered an estimate of the lethality threshold. An uncertainty factor of 30-fold was applied to account for interspecies extrapolation (10-fold) and intraspecies variability (3-fold) (see Section 6.3). 

The fundamental factors that govern the accuracy of primary reference standards are discussed in this chaptw. Even though an improved reference standard has been advocated, most of the existing air monitoring and laboratory-exposure data have as their reference the potassium iodide procedure used by either the carb, the laapcd, or the EPA. The relationship of these three variations of the potassium iodide procedure to the ultraviolet method is as follows ... 

Residue must be < 0.1 ppm in meat and < 10 ppb in milk and eggs. + - If teratogenic activity is demonstrated, the safety factor is 1,000 may also be < 100 when human exposure data are available or when a sensitive measurement is used to set a no-effect concentration. 

The authors also pointed out the connection between the duration of exposure extrapolation factor and the interindividual variance. If, e.g., young adult animals were exposed (normal case) and observed over 90 days, this might have to be assessed differently from a smdy on neonates or older animals. Therefore, it is necessary to examine which elements have already been included in the interindividual factor. If the time factor (children, elderly people) was considered as a separate subfactor in the interindividual factor, then the specific data on the exposure period must be considered in relation to the duration of exposure extrapolation factor in order to avoid double assessment. 

ECETOC emphasized that the scientific basis for establishing meaningful extrapolation factors in this area is still weak. Nevertheless, a provisional default value of 2-3 was considered to be consistent with the available scientific data when extrapolating from subchronic to chronic exposure. Eor extrapolation from short-term repeated to subchronic exposure, a factor of 3 was recommended as a provisional default value. 

TNO has, for differences between experimental conditions and exposure patterns for workers, suggested a number of default values (Hakkert et al. 1996). For extrapolation of data from subacute-to-subchronic exposure and from subchronic-to-chronic exposure, the factor ranges generally... 

The European Commission s Joint Research Centre (on behalf of DG S ANCO) has started a project known as European Information System on Risks from Chemicals Released from Consumer Products/Articles (EIS-ChemRisks) (EU 2004), which is designed as a network to collect exposure data, exposure factors, exposure models, and health-related data. The overall objective is to develop tools and reference data to enable harmonized exposure assessment procedures in the EU. A toolbox has been designed to collect exposure information from four reference systems to systematically support exposure assessors in the EU ... 

The US-EPA Child Specific Exposure Factors Handbook (US-EPA 2006), first published in 2002, consolidates all children s exposure factors data into one document. The document provides a summary of the available and up-to-date statistical data on various factors assessing children s exposures. These factors include drinking water consumption soil ingestion inhalation rates dermal factors including skin area and soil adherence factors consumption of fruits, vegetables, fish, meats, dairy products, homegrown foods, and breast milk activity patterns body weight consumer products and life expectancy. 

ECETOC (2001) has collected exposure data in the Exposure Factors Sourcebook for European Populations. For VRs, the Sourcebook presents the values, which are recommended by the US-EPA in the Exposure Factors Handbook (US-EPA 1997), see Table 7.3. ECETOC states that these values are probably representative of Europeans as well. 

The following examples illustrate some of the steps that occur in the collection of many data sets and the factors that can affect the accuracy of exposure data used to characterize particular exposures. 

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