Exposure scenarios, general

Advantages of epidemiological studies include that often a heterogenous population is studied, and the exposure scenarios generally are realistic. 

EU (2005) Work Package 1. Development of the concept of exposure scenarios. General framework of exposure scenarios. Scoping study for technical guidance document on preparing the chemical safety report under REACH, final report. European Union, European Chemicals Bureau (REACH Implementation Project 3.2-1A Lot 1 Commission Service Contract No. 22551-2004-12 FISC ISP BE ... 

The relative importance of metabolic transformation of precursor compounds in exposure to PEGS and PFGA has been scarcely evaluated and, to our knowledge, the only study that afforded the problem by a Scenario-Based Risk Assessment (SceBRA) approach estimated the relative importance of precursor-based doses of PEGS and PFGA of 2-5% and 2-8% in an intermediate scenario and 60-80% and 28-55% in a high-exposure scenario. This indicates that these precursors are of low importance for the general population. 

In summary, for the general population, the common routes of exposure to environmental compounds are ingestion, dermal contact and inhalation. Many PEAS are environmentally persistent but not lipophilic rather they have mixed lipophobic and hydrophobic properties. The exposure scenario is complex as PEAS have a large variety of applications. Gral exposure from materials other than food, inhalation and dermal contact may be important exposure routes for certain segments of the population. Dust inhalation could also be a possible source of exposure. However, the information on concentrations of PEAS in indoor dust is very limited and the bioavailability of the current compounds from dust is unknown. 

In inhalation studies, laboratory animals are generally exposed to an airborne chemical for a limited period of time, e.g., 6 h a day, 5 days per week. Adjustment of such an intermittent exposure to a continuous exposure scenario is regularly applied as a default procedure to inhalation smdies with repeated exposures but not to single-exposure inhalation toxicity smdies. Operationally, this is accomplished by a correction for both the number of hours in a daily exposure period and the number of days per week that the exposures were performed. In an inhalation smdy in which animals were exposed to an airbome concentration of a substance at 5 mg/m for 6 h a day, for 5 days per week, the adjustment of this intermittent exposure concentration to a continuous exposure concentration would consider both hours per day and days per week 5 mg/m X 6/24 h X 5/7 days/week = 0.9 mg/m, with 0.9 mg/m being the concentration adjusted to continuous exposure. 

Development of a waste classification system based on considerations of risks to the public requires assumptions about generic exposure scenarios (i.e., exposure scenarios that are generally applicable at any disposal site). 

The waste classification system developed in this Report includes a general class of exempt waste. Waste in this class would contain sufficiently small amounts of hazardous substances that it could be managed in all respects as if it were nonhazardous (e.g., as household trash). NCRP intends that exempt materials could be used or disposed of in any manner allowed by laws and regulations addressing disposition of nonhazardous materials. However, exempt waste would not necessarily be exempt for purposes of beneficial use without further analysis of the risks associated with anticipated uses. Materials could be exempted for purposes of disposal or beneficial use based on similar considerations of acceptable risk. However, based on differences in exposure scenarios for the two dispositions, limits on the amounts of hazardous substances that could be present in exempt materials intended for beneficial use could be substantially lower than the limits for disposal as exempt waste. Thus, disposal may be the only allowable disposition for some exempt materials based on considerations of risk. In addition, some exempt materials may consist of trash, rubble, and residues from industrial processes that would have no beneficial uses and must be managed as waste. 

In general, calculation of the risk or dose from waste disposal in the numerator of the risk index in Equation 6.2 or 6.3 involves the risk assessment process discussed in Section 3.1.5.1. As summarized in Section 6.1.3, NCRP recommends that generic scenarios for exposure of hypothetical inadvertent intruders at waste disposal sites should be used in calculating risk or dose for purposes of waste classification. Implementation of models describing exposure scenarios for inadvertent intruders at waste disposal sites and their associated exposure pathways generally results in estimates of risk or dose per unit concentration of hazardous substances in waste. These results then are combined with the assumptions about allowable risk discussed in the previous section to obtain limits on concentrations of hazardous substances in exempt or low-hazard waste. 

Exposure Scenarios for Classifying Exempt Waste. Based on the definition of exempt waste as any waste that would be generally acceptable for disposal in a municipal/industrial landfill for non-hazardous waste, scenarios for inadvertent intrusion appropriate to this type of facility should be used in determining whether a waste would be classified as exempt. 

For each generic exposure scenario to be used in classifying waste, and taking into account all relevant exposure pathways in each scenario, calculate the dose per unit concentration of each hazardous substance in the waste. These doses generally would be the highest values calculated over an assumed time frame for the risk assessment (see Section 6.4.5.3), taking into account the time-dependence of the concentrations of hazardous substances in the waste. For example, the quantity calculated for radionuclides would be the annual effective dose (sievert) per unit activity concentration (Bq nr3), and the quantity calculated for hazardous chemicals would be the dose (intake, mg kg 1 d-1) per unit concentration (kg m 3). 

For substances that cause stochastic effects, the risk index can be expressed in terms of risk, rather than dose. In this case, the risk per unit dose would be incorporated in the calculated risk in the numerator, based on the assumed exposure scenario, rather than in the denominator. However, the effective dose provides a convenient surrogate for risk for radionuclides, because all organs at risk and all stochastic responses of concern are taken into account, and the use of dose for all substances that cause stochastic effects is consistent with the form of the risk index for substances that cause deterministic effects, which generally should be expressed in terms of dose based on the assumption of a threshold dose-response relationship. 

This Section provides example applications of the recommended risk-based waste classification system to a variety of hazardous wastes to illustrate its implementation and potential ramifications. Disposal is the only disposition of waste considered in these examples. In Section 7.1.1, a general set of assumptions for assessing the appropriate classification of hazardous wastes is developed, including a variety of assumed exposure scenarios for inadvertent intruders at waste disposal sites and assumed negligible and acceptable risks or doses from exposure to radionuclides and hazardous chemicals. Subsequent sections apply the methodology to several example wastes. 

A noteworthy result of NRC s analysis of its present exemptions is that doses to individual members of the public during use of exempt products or materials generally are higher than doses that arise from disposal (Schneider et al., 2001). This is due in part to differences in the assumed exposure scenarios for use and disposal the dilution... 

Because the objective of an exposure assessment is to characterize both the magnitude and the reliability of exposure scenarios, planning for an uncertainty analysis is a key element of an exposure assessment. The aims of the uncertainty analysis in this context are to individually and jointly characterize and quantify the exposure prediction uncertainties resulting from each step of the analysis. In performing an uncertainty analysis, typically the main sources of uncertainties are first characterized qualitatively and then quantified using a tiered approach (see chapter 4). In general, exposure uncertainty analyses attempt to differentiate between key sources of uncertainties scenario uncertainties, model uncertainties and parameter uncertainties (for definitions, see section 3.2). 

Environmental exposures form the basis for determining indirect exposures to the general public that will usually occur during a lifetime. Direct consumer exposure assessments prove equally challenging, and may vary from acute to chronic exposure scenarios. Ideally the data set for consumer exposure from a substance in a product should include [127] ... 

UK-POEM UK PREDICTIVE OPERATOR EXPOSURE MODEL General Description 183 Formulations and Use Scenarios 183 Use in Risk Assessment 184 Exposure Reduction Measures 186 Model Updates 186 Comments on the Model 186 DUTCH MODEL 187 General Description 187 Formulations and Use Scenarios 187 Use in Risk Assessment 188 Exposure Reduction Measures 189 Model Updates 189 Comments on the Model 189 EUROPOEM DATABASE 189 General Description 189 Formulations and Use Scenarios 190 Use in Risk Assessment 192 Exposure Reduction Measures 194 Model Updates 194 Comments on the Model 194... 

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