Biological pathways exposure

Risk assessments may be conducted for individual chemicals or for complex mixtures of chemicals. In the case of complex mixtures such as hazardous waste sites, the process of risk assessment itself becomes quite complex. This complexity results from simultaneous exposure to many substances with the potential for numerous chemical and biological interactions, exposure through multiple media and pathways, and exposure to a wide range of target organisms with different susceptibilities (e.g., infants, adults, humans, animals, organisms). 

A report by the National Academy of Sciences proposed that future toxicity screens not be organ-based as they are today, but that they instead focus on detecting specific mechanisms of toxicity.86 Thus, a suite of such assays may be used to determine what toxicity pathways are triggered by exposure to specific chemicals. Similar approaches may be applied to developmental toxicity tests. In this way, we need not know all the relevant developmental biology pathways... 

The process for assessing environmental health risks Is complex Information regarding 1) the environmental agent, 2) the pathways by which exposure occurs, and 3) the biologic effects observed after exposure must be assembled and simultaneously evaluated Incomplete knowledge or Inadequate methodology In any of these three areas can severely Inhibit accurate or useful estimates of health risk ... 

Relevance. A key criterion in the selection of biological indicators is relevance to human and ecological health and to the development of policy. Fish are directly relevant, for example, given that consumption of fish is the primary pathway for exposure to MeHg. The concentration of MeHg in fish is also a key variable in the issuance of fish-consumption advisories. 

The dietary importance of benthic invertebrates to many species of fish, birds, and mammals (Vander Zanden and Vadeboncoenr 2002) signifies their importance in the trophic transfer of MeHg and their potential relevance as biological indicators. Some benthic invertebrates (e g., oysters, clams, shrimp, crabs, and crayfish) are consumed by humans, providing a direct pathway for exposure to MeHg. In the United States, shellfish rank below fish as a source of dietary MeHg in the human population (NRC 2000 Schober et al. 2003). 

Wildlife indicators can establish baseline conditions, act as early warning signals of environmental problems, identify the extent of contamination, define critical pathways and responses at multiple trophic levels, as well as integrate biological exposure with the physical and chemical environment (Farrington 1991). Indicator selection is based on a combination of criteria or characteristics that include (Jenkins 1981) ... 

Biological exposure pathway of sulfur movement in soils of forest ecosystems is related to microbial transformation of sulfolipids. Back conversion of sulfate-S into organic matter immobilizes the anion and potentially reduces soil cation leaching. Processes of sulfur mineralization and incorporation proceed rapidly in response to several factors, including temperature, moisture, and exogenous sulfate availability in soils and water. 

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