Exposure assessments quantification

Exposure assessment, quantification or prediction of environmental concentrations of the substance based on on-site measurements (MEC) or its projected fate and behaviour (PEC), respectively. 

The extent of accommodation and characterization of uncertainty in exposure assessment must necessarily be balanced against similar considerations with respect to hazard, since the outcome of any risk assessment is a function of comparison of the two. If, for example, there is limited information to inform quantitatively on hazard and, as a result, a need to rely on defaults, there is limited benefit to be gained in developing the exposure analysis such that any increase in certainty is cancelled by uncertainties of greater magnitude associated with quantification of critical hazard, as a basis for a complete risk assessment. 

Currently, there are inconsistencies in the application and methodology for uncertainty analysis in exposure assessment. While several sophisticated quantitative techniques exist, their general application is hampered not only by their complexity (and resulting need for considerable supporting information) but also by the lack of methodology to facilitate the specification of uncertainty sources prior to the quantification of their specific weight. 

In view of the often considerable limitations of available data supporting exposure assessment, which sometimes limit the extent of uncertainty quantification and the need to explicitly identify sources of uncertainty prior to their quantification, this section provides an overview of existing concepts and proposes a harmonized approach for the qualitative analysis of uncertainty in exposure assessment. 

Exposure assessment a quantification of contaminant release, migration and fate characterization of exposure pathways and receptors and measurement or estimation of exposure point concentrations (USEPA, 1989c). 

USEPA (2009) Particulate Matter National Ambient Air Quality Standards scope and methods plan for health risk and exposure assessment. Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency. Research Triangle Park, NC 27711 Viana M, Amato F, Alastuey A et al (2009) Chemical tracers of particulate emissions from commercial shipping. Environ Sci Technol 43 7472-7477 Wallace LA, Emmerich SJ, Howard-Reed C (2004) Source strengths of ultrafine and fine particles due to cooking with a gas stove. Environ Sci Technol 38 2304-2311 Wardoyo AYP, Morawska L, Ristovski ZD et al (2006) Quantification of particle number and mass emission factors from combustion of Queensland trees. Environ Sci Technol 40 5696-5703... 

Considering the multi-route and multimedia exposure of pesticides, the exposure assessment can be considered from three aspects (i) external (or potential) dose, (ii) internal or absorbed dose and (iii) biologically active dose. The external dose measurements determine the potential exposure of individuals or population. It involves a proper monitoring of the exposed environment, including air, water, food consumptions and workplace environment, to achieve an accurate quantification of the potential exposure of individuals. This kind of monitoring does not give information about the absorption of pesticides into the body. 

Exposure assessment Development of qualitative scenarios describing potential exposures and quantification of predicted frequency, timing, and concentrations of exposure. 

Leaded dusts can occur in soils, in the household, on hard exterior surfaces such as streets, and as occupational dusts in the specific context noted above. The ability of lead in dusts to rapidly accumulate on hard surfaces produces both a problem for quantification and a potent potential factor in human lead exposure assessments (U.S. EPA, 1986, Ch. 7). The physical and chemical compositions of dusts as well as the levels of lead are determined in large measure by their origin. It is also typical of dusts that they can deposit onto an almost infinite array of hard surfaces, and as a consequence can accumulate to quite high levels over time. This accumulation can be depicted quantitatively as either concentration or as dust lead loadings. 

In vitro absorption-spectrophotometry techniques are available to assess a sunscreen s efficacy, but the preferred methods are in vivo procedures in which a small body site is irradiated with the desired wavelengths for different periods in the presence or absence of a uv protectant. Procedures vary from country to country to determine the incremental timing of the exposure that ultimately allows quantification via sun protective factor (SPE). In the United States, sunscreen preparations are considered OTC dmg products, and the SPE must be specified (54). Even in countries that do not identify these products as dmgs, SPE labeling has become customary. 

Today, when a pesticide with no detectable residues is registered for use, a Tolerance or maximum residue limit (MRL) is established at the lowest concentration level at which the method was validated. However, for risk assessment purposes it would be wrong to use this number in calculating the risk posed to humans by exposure to the pesticide from the consumption of the food product. This would be assuming that the amount of the pesticide present in all food products treated with the pesticide and for which no detectable residues were found is just less than the lowest level of method validation (LLMV). The assumption is wrong, but there is no better way of performing a risk assessment calculation unless the limit of detection (LOD) and limit of quantification (LOQ) of the method were clearly defined in a uniformly acceptable manner. 

A more recent Dutch report (Vermeire et al. 2001) provides a practical guide for the application of probabilistic distributions of default assessment factors in human health risk assessments, and it is stated that the proposed distributions will be applied in risk assessments of new and existing substances and biocides prepared at RIVM (the National Institute of Public Health and the Environment) and TNO. The report concentrated on the quantification of default distributions of the assessment factors related to interspecies extrapolation (animal-to-human), intraspecies extrapolation (human-to-human), and exposure duration extrapolation. 

There seems to be a desire among the workshop participants to develop a series of standard distributions, or distribution parameters, for exposure and effects variables that are generally used in risk assessments. In the case of toxicity data, for example, investigations leading to the quantification of a generic variance for between-species variation from pooled data for many pesticides may be useful (Luttik and Aldenberg 1997). 

The assessment of DNA adducts may provide a sensitive indicatCH of previous exposure. The enzyme-linked immunosorbent assay (ELISA) has a lower limit of detection of about 0.08 femtomol per microgram of DNA (Perera et oL, 1982). This assay requires (1) the development of an antibody specific for a certain chemical metabolite bound covalently to DNA and (2) the isolation of DNA from some tissue sample, ag., skin biopsy, or lymphocytes of an exposed individual. It is anticipated that further refinement of such immunologic techniques may lower the threshold of sensitivity by one or two orders of magnitude. One such refined test is the ifitrasensitive ymatic radioimmunoassay (USE-RIA), purported to be about five times more sensitive than ELISA (Hsu et oL, 1981 Shamsuddin et oL, 1985 Harris et oL, 1985). Quantification by the development of monoclonal antibodies to aflatoxin Bj metabolites bound to DNA (Groopman et oL, 1982 Sizaret et oL, 1982) has now been reported. 

The extent of development and characterization of uncertainty associated with estimating exposure should take into account the nature of quantification of hazard in any risk assessment to ensure comparability of the two. 

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