Biomonitoring techniques

Assessments of risks associated with the use of chlorpyrifos insecticide products for workers have been made. The assessments are based on the results of field studies conducted in citrus groves, a Christmas tree farm, cauliflower and tomato fields, and greenhouses that utilized both passive dosimetry and biomonitoring techniques to determine exposure. The biomonitoring results likely provide the best estimate of absorbed dose of chlorpyrifos, and these have been compared to the acute and chronic no observed effect levels (NOELs) for chlorpyrifos. Standard margin-of-exposure (MOE) calculations using the geometric mean of the data are performed however, probability (Student s f-test) and distributional (Monte Carlo simulation) analyses are deemed to provide more realistic evaluations of exposure and risk to the exposed population. 

Some of the biomonitoring techniques employed are discussed in the following sections. 

Lucaciu, A., Timofte, L., Culicov, O. et al. (2004) Atmospheric deposition of trace elements in Romania studied by the moss biomonitoring technique. Journal of Atmospheric Chemistry, 49(1-3), 533-48. 

Biomonitoring Techniques for Measuring the Biological Effects of Liquid Effluents... 

The range of biomonitoring techniques for point-source effluents includes ... 

Collectively, the data from Table 7 and Figures 1 through 3 lead to the conclusion that concurrent biomonitoring and passive dosimetry techniques can be achieved and are not divergent worker exposure assessment methods. The correlation between exposure levels measured by these methods is quite good. 

Prerequisites are (1) a biological test system that is capable of registering the observed effect in an environmental system and (2) an applied concentration technique that acts as an interface between the environment and the test system. If biomonitoring indicates an unwanted exposure to chemicals, it must be translated in chemical terms. This chemical information can be used for control purposes to eliminate the exposure, preferably to a real no-effect level, so that no risk evaluation has to be made. This method requires a bioassay that is specific for an effect in an environmental system and a concentration technique that is specific for the collection and transition of compounds causing the effect. 

The National Report on Human Exposure to Environmental Chemicals, produced by CDC, is based on a representative sample of the population and a large number of chemicals, and uses well-documented analytic techniques. However, not all biomonitoring studies are conducted with the... 

The widespread use of biomonitoring, as evidenced by reports citing chemical concentrations in human blood samples (CBRC 2005 IC Wales 2005 WWF 2002, 2003) or in initiatives for developing biomonitoring programs in such states as California and Minnesota (OMB Watch 2005 Risk Policy Report 2005), stems from improvement in analytic methods and laboratory techniques. It is possible to measure smaller concentrations of chemicals in the body and to do so with smaller quantities of biologic samples (such as blood and urine). 

Despite the powerful nature of biomonitoring (Wilhelm et al. 2004), the utility and interpretation of the data are controversial. The controversy stems in part from the fact that the pace at which biomonitoring data are being generated has eclipsed the development of basic epidemiology, toxicology, and exposure-assessment techniques that are needed to evaluate... 

Improvements in analytic techniques for sampling, including lower detection limits, will probably change how biomonitoring data are used. It... 

It is essential to develop and use noninvasive and ultrasensitive specimen-collection techniques for the biomonitoring of children and other groups that can provide only small samples. 

In the most straightforward risk-based approach, epidemiologic studies have developed exposure-response relationships based on biomarker measurements in hair, blood, urine, or other matrices (e.g., mercury, lead) (see Figure 5-2a). The relationships can be applied directly to new biomonitoring data to determine where on the exposure-response curve any person is. That may facilitate an understanding of risk, but it does not analyze sources of exposure, so other techniques (such as environmental sampling and behavioral surveys) may be needed to assess where the exposure came from. 

It may be possible to use Geographic Information Systems (GIS) to map biomonitoring results to determine whether there is a spatial pattern in exposure concentrations. This could be overlaid with GIS maps of environmental data (for example, air or water pollution or distribution of waste sites) to determine whether biomonitoring results correspond to specific environmental sources. However, mapping techniques are generally not useful for sporadic, localized sources such as food or consumer products. In such cases, survey questionnaires and sampling of the home environment are of more direct use in understanding exposure sources. 

Expand modeling approaches and case examples in which nonsteady-state biomonitoring data are simulated to explore the exposure conditions responsible for biomonitoring results this may provide exposure estimates that can be used in risk assessment (for example, Bayesian inference techniques and population behavior-exposure models). 

However, the communication challenge of results below the limit of detection is not quite so easily resolved. Each environmental-monitoring technique, including those of biomonitoring, has a limit in the amount of a chemical that it can reliably and validly measure in a given matrix. Below that limit, it is impossible to tell how much of the substance, if any, is in the sample. Experience with or modification of the technique or invention of a new one can lower the detection limit eventually, but in the short run it is fixed. That is one reason, when multiple biomonitoring methods are available, that the method chosen can have an appreciable effect on the results and their interpretation (Helsel 1990, cited by Bates et al. 2005). 

We do not imply here that scientists know all cause-effect relations for human biomonitoring in fact, the mental-model technique probably becomes more useful as it makes expert uncertainties and disagreements more explicit. However, experts mental models of the causal links are likely to be more comprehensive than those of nonscientists and thus provide a useful guide for topics on which to probe lay mental models about biomonitoring and biomarkers. 

In addition to developing a strategy for identifying specifically targeted chemicals, the committee recommends that population-based biomonitoring studies include a subset of samples to screen specific populations for untargeted analytes and to identify and quantify these chemicals. Such an approach is feasible with current analytic techniques that provide for the tentative identification of unknown analytes. 

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