A Textbook of Modern Toxicology
نویسنده
چکیده
More than 100,000 chemicals are released into the global environment every year through their normal production, use, and disposal. To understand and predict the potential risk that this environmental contamination poses to humans and wildlife, we must couple our knowledge on the toxicity of a chemical to our knowledge on how chemicals enter into and behave in the environment. The simple box model shown in Figure 27.1 illustrates the relationship between a toxicant source, its fate in the environment, its effective exposure or dose, and resulting biological effects. A prospective or predictive assessment of a chemical hazard would begin by characterizing the source of contamination, modeling the chemical’s fate to predict exposure, and using exposure/dose-response functions to predict effects (moving from left to right in Figure 27.1). A common application would be to assess the potential effects of a new waste discharge. A retrospective assessment would proceed in the opposite direction starting with some observed effect and reconstructing events to find a probable cause. Assuming that we have reliable dose/exposure-response functions, the key to successful use of this simple relationship is to develop a qualitative description and quantitative model of the sources and fate of toxicants in the environment. Toxicants are released into the environment in many ways, and they can travel along many pathways during their lifetime. A toxicant present in the environment at a given point in time and space can experience three possible outcomes: it can be stationary and add to the toxicant inventory and exposure at that location, it can be transported to another location, or it can be transformed into another chemical species. Environmental contamination and exposure resulting from the use of a chemical is modified by the transport and transformation of the chemical in the environment. Dilution and degradation can attenuate the source emission, while processes that focus and accumulate the chemical can magnify the source emission. The actual fate of a chemical depends on the chemical’s use pattern and physical-chemical properties, combined with the characteristics of the environment to which it is released.
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