Measurement of human exposure

In recent years there has been an upsurge in efforts to move from indirect measures of human exposure (obtained by measurements of chemicals in environmental media and estimation of dose accrued from contact with those media) to direct measures of the concentrations of chemicals in the body, typically in blood and in elimination pathways such as urine and hair. The most significant effort in this direction in the United States has been undertaken as part of the CDC s National Health and Nutrition Examination Survey (NHANES). 

Urine Urine is the principal route by which nonlactating humans excrete perchlorate [261, 262]. Urinary perchlorate provides a reasonable measure of human exposure because 70-95% of perchlorate dose is excreted unchanged in the urine with a half-life of 8 h [261-263]. Creatinine (CR) adjustment is typically used to minimize the effects of variation of analyte concentration in urine either among samples produced by different individuals or among samples produced by the same individual. 

D is readily absorbed through the skin therefore, measurements of ambient air concentrations do not necessarily reflect the total absorbed dose. Immunochemical determination of 2,4-D in urine has provided effective measurement of human exposure levels. 

Substances produced in quantities of less than 10 tonnes per year include most of the chemicals used as textile dyestuffs and auxiliaries (CEC, 2003b). This illustrates the inadequacy of using tonnage thresholds as a measure of human exposure. Chemicals used to dye or treat cloth are present in our clothes and may leach from clothes through our skin into our bodies. We may also inhale the chemicals, after the skin has flaked off and become part of household dust (ENDS, 1994). Clothes are probably one of the major routes of human exposure to synthetic chemicals and the long-term effects of those chemicals should surely be investigated. 

Steven R. Tannenbaum, a member of the Institute of Medicine, has a Ph.D. in food science and technology from the Massachusetts Institute of Technology, where he is currently the codirector and Underwood-Prescott Professor, Division of Bioengineering and Environmental Health, and professor of chemistry, Department of Chemistry. Dr. Tannenbaum s research interests include the chemistry and pathophysiology of nitric oxide, the quantitative measurement of human exposure to carcinogens, and tissue-based microsensors for toxin detection and drug metabolism. He has been a member of the NRC Board on Environmental Studies and Toxicology and has served on several NRC committees. 

Young AL. 1984b. Determination and measurement of human exposure to the dibenzo-p-dioxins. Bull Environ Contain Toxicol 33 702-709. 

Measurement of human exposure can be done either directly or indirectly. Direct measurement involves determination of the pesticide level in the media through which the exposure occurs. Examples of this are measurement of pesticides in breathing zone air or pesticides adsorbed onto pads or clothing worn by workers (1, 2). These techniques provide a direct and calculable measure of human exposure under actual conditions. Most often, however, direct measurement is not possible. In these situations indirect methods of exposure assessment must be used. 

Data to assess the potential of JP-8 to adversely affect reproduction and development are sparse. One study (Puhala et al. 1997) reported measurements of human exposures and the values for the components of jet fuels analyzed that were far below the TWA threshold limit values (see Tabel A-2). Data on the absorption of volatile hydrocarbon components of JP-8 suggest that systemic exposure is likely, by any route of exposure. The single published developmental toxicity study (Cooper and Mattie 1996) did not report an adverse effect on embryonic or fetal development in rats with oral treatment at up to 2,000 mg/kg/d on days 6-15 of pregnancy, except for a decrease in body weight of offspring. 

Cherrie JW, Aitken RJ. 1999. Measurement of human exposure to biologically relevant fractions of inhaled aerosols . Occup. Environ. Med. 56 747-752. 

Human Receptors for Surface Water. The following factors are scored to obtain a measure of human exposure to surface water pollution ... 

To ascertain whether a general population is at risk or not, it is necessary to estimate the actual dietary intake of a toxic metal by comparison with provisional tolerable weekly intakes (PTWIs) [1]. This estimation is a measure of human exposure to pollutant and thus indispensable for risk assessment... 

Dithiocarbamates are chemically characterized by the presence of metals in the molecule (iron, manganese, zinc, etc.) therefore, the measurement of these metals in urine has been proposed as an alternative approach to monitor exposure. For instance, increased urinary excretion of manganese has been reported in workers exposed to mancozeb (Canossa et al., 1993). Available data are at present insufficient to confirm the possibility of using metals as biomarkers of human exposure to DTC. 

Measurements of human serum concentrations of endrin following incidents of acute poisoning indicate rapid decline in concentration after exposure (Coble et al. 1967 Rowley et al. 1987). 

Studies are needed to clarify the importance of age, sex, ethnicity, familial elements, nutritional factors, and pharmacologic agents in determining response to oxidants. Because people with lung disease are thought to be more susceptible to oxidant pollutants, exposure studies are needed to quantify this. Better methods for measuring or estimating the actual dose of oxidants absorbed by each subject are needed. The usual time variation in measures of human response should be evaluated... 

It is noteworthy that in three species (monkeys, rats, and hens), 3-6 months of exposure to 2-hexanone at 100 ppm resulted in little or no effect on body weight parameters. Levels measured in the epidemiological study of exposed workers, however, were only 9.2-36 ppm (Allen et al. 1975). However, these levels were measured after the incident. If these low levels of 2-hexanone are a reasonably accurate indication of the conditions of human exposure that resulted in the observed weight loss, humans may be a very sensitive species with regard to this parameter. It is not clear whether the affected individuals had decreased appetites and/or food consumption levels in conjunction with their weight loss. 

Sexton, K. Ryan, P. B. Assessment of Human Exposure to Air Pollution Methods, Measurements and Models Air Pollution, the Automobile and Public Health Health Effects Institute, National Academy Press Washington, DC, 1988 pp 207-238. 

Kelly, T.H., Foltin, R.W., and Fischman, M.W., The effects of repeated amphetamine exposure on multiple measures of human behavior, Pharmacol. Biochem. Behav., 38, 417, 1991. 

Sexton K, Ryan PB (1988) Assessment of human exposure to air pollution methods, measurements and models. In Watson AY, Bates RR, Kennedy D (eds) Air pollution, the automobile and public health. National Academic Press, Washington... 

Blood proteins, such as hemoglobin, may be used in tests of human exposure because blood is readily and safely accessible. For example, the exposure of mice to ethylene oxide or dimethylnitrosamine was estimated by measuring alkylated residues in hemoglobin. The method was subsequently extended to people exposed occupationally to ethylene oxide by measuring 7V-3-(2-hydroxycthyl) histidine residues in hemoglobin. Similarly methyl cysteine residues in hemoglobin can be used as a measure of methylation. 

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