Environmental levels

The contamination of sediments may pose an unacceptable risk to aquatic organisms, which tend to bioaccumulate chlorinated and brominated POPs, and to wildlife and humans through the ingestion of contaminated fish and shellfish. During the last foiu decades a large amount of environmental data 

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Environmental Levels and Exposures. Barium constitutes about 0.04% of the earth s cmst (47). Agricultural soils contain Ba " in the range of several micrograms per gram. The Environmental Protection Agency, under the Safe Drinking Water Act, has set a limit for barium of 1 mg/L for municipal waters in the United States. 

Environmental exposures to PCBs are significantly lower than those reported in the workplace and are therefore unlikely to cause adverse human health effects in adults. However, it is apparent from the results of several recent studies on children that there was a correlation between in utero exposure to PCBs, eg, cord blood levels, and developmental deficits (65—68) including reduced bkth weight, neonatal behavior anomaUes, and poorer recognition memories. At four years of age, there was stiU a correlation between prenatal PCB exposure levels and short-term memory function (verbal and quantitative). In these studies the children were all exposed to relatively low environmental levels of PCBs. Although these effects may be related to other contaminants, it is clear that this is an area of concern regarding the potential adverse human health impacts of PCBs. 

PBPK models improve the pharmacokinetic extrapolations used in risk assessments that identify the maximal (i.e., the safe) levels for human exposure to chemical substances (Andersen and Krishnan 1994). PBPK models provide a scientifically sound means to predict the target tissue dose of chemicals in humans who are exposed to environmental levels (for example, levels that might occur at hazardous waste sites) based on the results of studies where doses were higher or were administered in different species. Figure 3-4 shows a conceptualized representation of a PBPK model. 

Ecotoxicology deals with the study of the harmful effects of chemicals in ecosystems. This includes harmful effects upon individuals, although the ultimate concern is about how these are translated into changes at the levels of population, commnnity, and ecosystem. Thns, in the conclnding sections of the chapter, emphasis will move from the distribntion and environmental concentrations of pollutants to conseqnent effects at the levels of the individnal, population, community, and ecosystem. The relationship between environmental exposure (dose) and harmful effect (response) is fundamentally important here, and full consideration will be given to the concept of biomarkers, which is based on this relationship and which can provide the means of relating environmental levels of chemicals to consequent effects npon individuals, populations, communities, and ecosystems. 

Thus, as with studies on the double-crested cormorant in the Great Lakes (see Chapter 16 in Walker et al. 2006), there is evidence of a continuing (although reduced) effect of p,p -DDE on reproductive success even after environmental levels had fallen and eggshell thinning was much less. This raises the possibility that p,p -DDE may have had toxic effects other than eggshell thinning on these species (Nisbet 1989). There is the further complication that other OCs such as PCBs, dieldrin, and hep-tachlor epoxide were present in the same samples and may have had toxic effects. 

The text is divided into three parts. The first deals with the basic principles underlying the environmental behavior and effects of organic pollutants the second describes the properties and ecotoxicology of major pollutants in reasonable detail the last discusses some issues that arise after consideration of the material in the second part of the text, and looks at future prospects. The groups of compounds represented in the second part of the book are all regarded as pollutants rather than simply contaminants, because they have the potential to cause adverse biological effects at realistic environmental levels. In most cases these effects have been well documented under environmental conditions. The term adverse effects includes harmful effects upon individual organisms, as well as effects at the level of population and above. 

Ziglio G, Beltramelli G, Pregliasio F. 1984. A procedure for determining plasmatic trichloroacetic acid in human subjects exposed to chlorinated solvents at environmental levels. Arch Environ Contam Toxicol 13 129-134. 

Weiner RE, Mclnroy JF, Wegst AV. 1985. Determination of environmental levels of Pu, Am, U and Th in human fetal tissue. Health Phys 49(1) 141. 

Exposures to hydraulic fluids occur mainly in workers using hydraulic equipment and in people who work on cars or tractors that use the fluids. Most people are exposed when fluids spill or leak on the skin, when the fluid is changed, or when the fluid reservoirs are filled. Low levels of hydraulic fluids may occur in the air near machines that use them. Understanding environmental levels of hydraulic fluids is very difficult because the ingredients in hydraulic fluids are used in many products other than hydraulic fluids. For example, mineral oil is an ingredient in both motor oil and mineral oil hydraulic fluids. In the environment, mineral oil from both sources would appear to be the same. Polyalphaolefin hydraulic fluids have chemical components and potential applications similar to mineral oil hydraulic fluids. 

Based on these data, it is not likely that acute exposure of humans to environmental levels of polyalphaolefln hydraulic fluids will result in dermal irritation. There is insufficient information to determine if long-term exposure to polyalphaolefln hydraulic fluids will result in dermal irritation in humans. 

Hutton M, Wadge A, Milligan PJ. 1988. Environmental levels of cadmium and lead in the vicinity of a maj or refuse incinerator. Atmos Environ 22 411 -416. 

A worktable that can be used to calculate a cumulative exposure estimate on a site-specific basis is provided in Table 2. To use the table, environmental levels for outdoor air, indoor air, food, water, soil, and dust are needed. In the absence of such data (as may be encountered during health assessment activities), default values can be used. In most situations, default values will be background levels unless data are available to indicate otherwise. Based on the U.S. Food and Drug Administration s (FDA s) Total Diet Study data, lead intake from food for infants and toddlers is about 5 pg/day (Bolger et al. 1991). In some cases, a missing value can be estimated from a known value. For example, EPA (1986) has suggested that indoor air can be considered 0.03 x the level of outdoor air. Suggested default values are listed in Table 3. 

Pharmacokinetic models have been developed that attempt to relate environmental levels to PbB levels (Leggett 1993 O Flaherty 1995). The Integrated Exposure Uptake Biokinetic Model (IEUBK) developed by EPA is one of the most extensive efforts to date to make population-based predictions of PbB levels based upon environmental data. The model incorporates both exposure/uptake parameters and a biokinetic component to estimate the PbB distribution in the exposed population (EPA 1994). 

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