Estimated exposure values

Example 3. Butler et al. (2003) conducted a population-based case-control study that evaluated levels of HCAs, meat intake according to doneness and cooking method, and the risk of colon cancer. The study population consisted of participants selected from 33 counties in North Carolina who were part of the North Carolina Colon Cancer Study. Cases included 274 blacks and 346 whites, between the ages of 40 and 84 with invasive adenocarcinoma of the colon diagnosed from 1996 to 2000. Controls, 426 blacks and 611 whites, were randomly selected from the North Carolina Division of Motor Vehicles (under 65) and the Center for Medicare and Medicaid services (over 65). Exposure was assessed using a food-frequency questionnaire. Meat intake frequency data, cooking method, and level of doneness was used to estimate exposure values for three specific HCAs. (Results of this study are discussed in Section 26.2.2b.). Source Butler et al. (2003). 

Table 19 List of estimated exposure values (EEV), critical toxicity values (CTV) and RQs for SCCPs...

TLV Threshold fimit value, estimated exposure value, below which no ill health effects should occur to the individual. 

Thus, tlie focus of tliis subsection is on qualitative/semiquantitative approaches tliat can yield useful information to decision-makers for a limited resource investment. There are several categories of uncertainties associated with site risk assessments. One is tlie initial selection of substances used to characterize exposures and risk on tlie basis of the sampling data and available toxicity information. Oilier sources of uncertainty are inlierent in tlie toxicity values for each substance used to characterize risk. Additional micertainties are inlierent in tlie exposure assessment for individual substances and individual exposures. These uncertainties are usually driven by uncertainty in tlie chemical monitoring data and tlie models used to estimate exposure concentrations in tlie absence of monitoring data, but can also be driven by population intake parameters. As described earlier, additional micertainties are incorporated in tlie risk assessment when exposures to several substances across multiple patliways are suimned. 

Because the significance of exposure has only been considered over the past few years, there is not as wide a selection of exposure models available as that for fate models. The latter have been applied for several decades to the calculation of ambient exposure levels compared with some standard values. Papers illustrative of human exposure assessments in this symposium include one on airborne pollutant exposure assessments by Anderson (2), a generic approach to estimating exposure in risk studies by Fiksel (5), and a derivation of pollutant limit values in soil or water based on acceptable doses to humans by Rosenblatt, Small and Kainz (6). 

For AEGL-3, the 1-h LC50 of 82 ppm for squirrel monkeys (Haun et al. 1970) was reduced by a factor of 3 to estimate a lethality threshold (27.3 ppm). Temporal scaling to obtain time-specific AEGL values was described by C% t=k (where C=exposure concentration, t=exposure duration, and k=a constant). The lethality data for the species tested indicated a near linear relationship between concentration and exposure duration (n=0.97 and 0.99 for monkeys and dogs, respectively). The derived exposure value was adjusted by a total uncertainty factor of 10.2 An uncertainty factor of 3 was applied for... 

The adjusted exposure value estimated to be the threshold level of AEGL-2 effects (12 ppm for 15 min) was then scaled to AEGL time frames using the Cn xt=k relationship (ten Berge et al. 1986). For relatively brief exposures (i.e., <4 h), the data for dimethylhydrazine implied a linear concentration-response relationship (C1 t=k), which was used for AEGL derivations. LC50 data on... 

As a basis for the determination of risk it must be assumed that the colorants are properly handled and applied. It is not appropriate to estimate risk primarily on the basis of exposure values obtained under improper working conditions, or where appropriate plant and equipment are not available. Ensuring satisfactory operating conditions and training of operatives to handle products correctly is essential nowadays for technological success as well as for health and safety requirements. In this way, exposure levels can be kept below the threshold of unacceptable risk. It is reasonable to accept that for practical purposes levels of exposure exist below which the risk becomes trivial [67]. 

Generic Exposure Values (GEVs) are generic threshold values for occupational exposure (and derived dermal values) derived from OELs (Occupational Exposure Limits). The effects used to estimate GEVs are acute and repeated dose toxicity for a total of 63 organic and nonorganic substances, both volatile and nonvolatile. 

The outcome of low-dose extrapolation is the resulting lifetime cancer risk associated with estimated exposure for a particular population. An acceptable/tolerable lifetime cancer risk is often used as a reference value to compare with the estimated hfetime cancer risk. The important question is thus Which lifetime cancer risk is acceptable/tolerable ... 

If actual or potential exposure has been identified, a quantitative exposure assessment is necessary. Exposure levels/concentrations for each potentially exposed population need to be derived from the available measured data and/or from modeling. A range of exposure values to characterize different subpopulations and scenarios may result. These results are taken forward to the risk characterization where they are combined with the results of the effects assessment in order to decide whether or not there is concern for the human population exposed to the substance. In some cases all three types of exposure estimates may contribute to an overall exposure value (combined exposure), which should be considered in the risk characterization. 

Finally, the MOS should also take into account the uncertainties in the estimated exposure. For predicted exposure estimates, this requires an uncertainty analysis (Section 8.2.3) involving the determination of the uncertainty in the model output value, based on the collective uncertainty of the model input parameters. General sources of variability and uncertainty in exposure assessments are measurement errors, sampling errors, variability in natural systems and human behavior, limitations in model description, limitations in generic or indirect data, and professional judgment. 

Now let us estimate the value of t to the first approximation. If q 50P, K 10 dyne/cm2, 5 0.1 cm, H % 100 cm, then te p 1.094 s. Consequently, it may be safe to consider that several seconds of exposure to pressure upon moud filling will be sufficient for complete equalization of pressure over the entire plastisol moulding. 

The denaturation of GFPuv in buffer solutions at various pH values was measured by the loss of fluorescence intensity and expressed in the decimal logarithm of the decrease in native GFPuv concentration vs the time of exposure at constant temperature (Fig. 1). To estimate D-values at constant heating temperatures and pH values (Table 1), the interval of GFPuv concentrations considered was between 3.5 (acetate, pH 5.18) and... 

Default values have been published for use in estimating exposures — for example, from food and water consumption in adults and children, soil ingestion in children, and respiration rates in children and adults (USEPA, 1990). The Child-Specific Exposure Factors Handbook summarizes data on human behaviour and characteristics that affect children s exposure to environmental agents and recommends values to use for these factors (USEPA, 2002a). 

Although the advice is given mainly for the description of risk assessment results, it holds completely for exposure assessment, since the quantitative input for risk assessment is exposure assessment and uncertainty analysis. Since any description of the resulting exposure distribution(s) in terms such as very low , low , fair , moderate , high or extreme includes an evaluation, it must be defined and justified (EnHealth Council, 2004). Those communicating the results of an exposure assessment frequently use comparative reporting schemes, such as the 50%/majority/. .. /95% of data/measurements/individuals show exposure values/estimates/measurements lower than the tolerable daily intake... 

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