Exposure assessments case studies

Although the likelihood for biologically harm has not been assessed fully, for most EDCs the exposure concentrations in ambient environments (away from hotspots of chemical discharges) would suggest that they are insufficient to do so. Exceptions to this inclnde the case studies detailed in the previous section. It should, however, also be emphasized that most studies on the effects of EDCs under controlled laboratory conditions have not considered long-term chronic exposures encompassing full life cycles, and some wildlife species are exposed lifelong to some of the EDCs described earlier. 

The degree of confidence in the final estimation of risk depends on variability, uncertainty, and assumptions identified in all previous steps. The nature of the information available for risk characterization and the associated uncertainties can vary widely, and no single approach is suitable for all hazard and exposure scenarios. In cases in which risk characterization is concluded before human exposure occurs, for example, with food additives that require prior approval, both hazard identification and hazard characterization are largely dependent on animal experiments. And exposure is a theoretical estimate based on predicted uses or residue levels. In contrast, in cases of prior human exposure, hazard identification and hazard characterization may be based on studies in humans and exposure assessment can be based on real-life, actual intake measurements. The influence of estimates and assumptions can be evaluated by using sensitivity and uncertainty analyses. - Risk assessment procedures differ in a range of possible options from relatively unso-... 

Intermediate-Duration Exposure. Intermediate-duration studies in humans are fairly limited and virtually all are complicated by exposures to other chemicals as well as rarely being accompanied with adequate exposure assessment. Additional epidemiologic studies, particularly prospective or case-control, of populations exposed environmentally to various levels of hydrogen sulfide (where other pollutants are monitored and ideally, do not vary) are needed. 

DeRosa CT, Choudhury H, Peirano WB. 1991. An integrated exposure/pharmacokinetic-based approach to the assessment of complex exposures Lead A case study. Toxicol Ind Health 7(4) 231-247. 

This second volume of the book presents the results obtained during the RISKCYCLE project, paying special attention to a set of selected additives in the diverse industrial sectors (i.e., PFOS, DEHP, Pb). Different methodologies have been used to analyze aspects such as the fate, human and environmental exposure, and toxicity of these compounds. Case studies have been developed to assess their risk in developing countries such as China or Vietnam. The findings have been presented in the different RISKCYCLE workshops as well as at the final conference in Dresden. 

For human health risk assessment, it is necessary to elaborate realistic scenarios. Knowledge of real scenarios where the contaminant is emitted to the environment will help to obtain information about the fate and transport of the contaminant once emitted to the environment and the route of exposure for the human beings living in this scenario of concern. There are different types of exposure, i.e., direct, indirect (as is the case of food contaminated by the air, water, or soil contaminated by the emission), occupational exposure, and consumer goods coming from outside the scenario of concern. Depending on the objective of the study, it will be necessary to consider in the exposure assessment one or more types of exposure. 

In the case of noncarcinogenic substances, there exists a threshold this is an exposure with a dose below which there would not be adverse effect on the population that is exposed. This is the reference dose (RfD), and it is defined as the daily exposure of a human population without appreciable effects during a lifetime. The RfD value is calculated by dividing the no observed effect level (NOEL) by uncertainty factors. When NOEL is unknown, the lowest observed effect level (LOEL) is used. NOEL and LOEL are usually obtained in animal studies. The main uncertainty factor, usually tenfold, used to calculate the RfD are the following the variations in interspecies (from animal test to human), presence of sensitive individuals (child and old people), extrapolation from subchronic to chronic, and the use of LOEL instead of NOEL. Noncancer risk is assessed through the comparison of the dose exposed calculated in the exposure assessment and the RfD. The quotient between both, called in some studies as hazard quotient, is commonly calculated (Eq. 2). According to this equation, population with quotient >1 will be at risk to develop some specific effect related to the contaminant of concern. 

EUSES. As in the case of USEtox model, the present model provides outputs such as human intake fraction of a certain substance for different exposure pathways. In the present case study, estimation of the human intake doses for Guiyu was calculated. These results were compared with the incidence and severity of the effects (dose-response assessment). 

In the first part of this book, different models related to the assessment of the potential risk posed by the chemical additives are presented. These models come from different fields of expertise toxicology, risk assessment, chemicals fate and exposure, life cycle assessment, economics, etc. The potential benefits of the different models as well as their drawbacks are analyzed in order to select some of them for the application to particular case studies. 

EPA released the first case study of cumulative risks from 24 OPs in food for scientific review in mid-2000. Public comments were solicited and several scientific panel (SAP) meetings were held on various aspects of EPA s quantitative methods. In December 2001 a preliminary OP-CRA (cumulative risk assessment) was released, this time encompassing 30 OPs, additional foods, more residue data and all major routes of exposure. Public comments were solicited again and another series of SAP meetings were held. The revised final OP-CRA was issued in June 2002 after more than 20 SAP meetings and four rounds of public comment (US Environmental Protection Agency, 2002). It is the most sophisticated and data-rich pesticide risk assessment ever carried out. 

Many quantitative aspects of exposure pathways and their relevant application during environmental risk assessment depend on regional biogeochemical peculiarities and should be undoubtedly considered on the regional scale. Accordingly this part includes some characteristic examples and case studies from local up to regional and continental dimensions. We discuss the importance of the trans-boundary of pollutant exposure as well as the application of critical load methodology for risk estimates. 

Table 8.1 Component groups for gasoline based on C- number and main chemical composition. Reprinted with permission from Foster KL, Mackay D, Parkerton TF, Webster E, Milford L (2005) Five-stage environmental exposure assessment strategy for mixture gasoline as a case study. Environ Sci Technol 39 2711-2718. Copyright 2005 American Chemical Society...

Limitations include difficulties in performing a correct exposure assessment, in some cases even a lack of information on exposure, insufficient sample size (i.e., small number of subjects in the study), selected group of subjects (e.g., the workforce), short length of follow-up, exposure to more than one substance, and potential errors (bias, confounding). 

Immunotoxicity. No immunological effects were reported in case studies of human exposure. There was a decrease in spleen weight in rats orally exposed to p-cresol for 90 days (MBA 1988b), which, although unaccompanied by histopathological changes, suggests the possibility that cresols may affect the immune system. A battery of immune function tests would better enable assessment of the immunotoxicity of cresols in humans and animals. 

Seal, A. B. Bise, C. J. 2002. Case study using task-based, noise-exposure assessment methods to evaluate miner noise hazards. Mining Engineering, 54, 44-48. 

Crump, D., Brown, V., Carson, A. and Harrison, P. (2007) Assessment of risk from inhalation exposure to benzene-a case study. Proceedings of the Tenth Annual UK Review Meeting on Outdoor and Indoor Air Pollution Research, 1-2 May, IEH, Cranfield University, 1-2 May 2007. 

Calafat, A.M., and R.H. McKee. In press. Integrating biomonitoring exposure data into the risk assessment process Phthalates (diethyl phthalate and di[2-ethylhexyl] phthalate) as a case study. Environ. Health Perspect. [online]. Available http //ehp.niehs.nih.gov/docs/ 2006/9059/abstract.html [accessed Aug. 21, 2006]. 

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