Exposure assessments interpretive issues

The interpretation of uncertainty analysis results can cover a wide range of issues. Here, we consider the interpretation of results with regard to the needs of decision-makers who would use the results of uncertainty analysis in exposure assessment. The discussion is primarily based upon Morgan Henrion (1990), Bloom et al. (1993) and Thompson Graham (1996). The discussion is organized on the basis of key questions that decision-makers often ask, as reported by Bloom et al. (1993), based upon a survey of senior risk managers at the USEPA, and as described by Thompson Graham (1996) ... 

Besides meeting its assumptions, other problems in the application of SSD in risk assessment to extrapolate from the population level to the community level also exist. First, when use is made of databases (such as ECOTOX USEPA 2001) from which it is difficult to check the validity of the data, one does not know what is modeled. In practice, a combination of differences between laboratories, between endpoints, between test durations, between test conditions, between genotypes, between phenotypes, and eventually between species is modeled. Another issue is the ambiguous integration of SSD with exposure distribution to calculate risk (Verdonck et al. 2003). They showed that, in order to be able to set threshold levels using probabilistic risk assessment and interpret the risk associated with a given exposure concentration distribution and SSD, the spatial and temporal interpretations of the exposure concentration distribution must be known. 

Toxicokinetics is defined as the generation of pharmacokinetic data, either as an integral component in the conduct of nonclinical toxicity studies or in specially designed supportive studies, in order to assess systemic exposure. These data may be used in the interpretation of toxicology findings and their relevance to clinical safety issues (ICH Guidance Toxicokinetics 1994). 

The opinions issued by SCHER are basically scientific peer reviews, similar to a longer referee report for a piece submitted to a scientific journal. Just like any peer reviewer would do, SCHER comments on the data used in risk assessments, especially on the lack or reliability of data as well as on methods, approaches and interpretations. Uncertainty of exposure and effects and factors conditioning uncertainty are discussed, often resulting in statements such as firm conclusions cannot be reached . 

The studies of the Iraqi, Amazon, Seychelles, and Faroe Islands populations were reviewed by an expert panel that met in Raleigh, North Carolina, at the Workshop on the Scientific Issues Relevant to Assessment of Health Effects from Exposure to MeHg. A report of that workshop has been published (NIEHS 1998). In suggesting possible explanations for the discrepant findings of the Seychelles and Faroe studies, the panel pointed to differences in sources of exposures or exposure measures, differences in the neurobehavioral tests used or their administration or interpretation, influences of confounders and covariates, and biostatistical issues involved in the analysis of the data. The differences between those studies are discussed further in Chapter 6. 

This chapter discusses issues relevant to assessing exposure of military personnel to jet-propulsion fuel 8 (JP-8). The chapter begins with a description of various scenarios under which military personnel are exposed to JP-8, followed by a brief discussion of the challenges of quantifying human exposure to this distillate fuel. The next section contains a summary of data from studies that have measured concentrations of several components of JP-8 in ambient air at Air Force aircraft maintenance sites. Studies measuring body burden of several JP-8 components in workers involved in aircraft maintenance are also presented. The final section of this chapter describes how the physical and chemical properties of JP-8 affect uptake into the body from exposure by the inhalation, dermal, and oral routes. This last section also serves as a prelude to interpretation of animal toxicity studies conducted with distillate fuels (e.g., JP-8) that are described in later chapters. 

A central issue to carcinogenic risk assessment revolves around the ability to identify animal carcinogens and the interpretation of this data in terms of human risk. The vast majority of data on which decisions are made to protect the public from undue exposure to potential carcinogens are generated from animal bioassays. 

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