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Environmental+Toxicology+Tox+2000+notes (2)

Environmental+Toxicology+Tox+2000+notes (2) - 3.0...

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3.0 ENVIRONMENTAL TOXICOLOGY Objectives: The objective of this section of the course is to provide an understanding of the basic principles of toxicology as they apply to ecosystems and environmental issues. These principles will be illustrated in several case histories which will focus on environmental toxicology and the toxicology of pesticides. Students will be expected to understand the following concepts: Endpoints and measures in ecotoxicology Ecosystem health, resiliency, and redundancy Assessing toxicity in single organisms and in communities Factors which influence environmental responses Examples of several environmental processes and their effects on toxic substances Endocrine modulators in the environment 3.1 CHARACTERIZING TOXICITY Toxicologists often study and measure toxicity in the narrow sense of testing effects in organisms, however, in the broader sense, they also study impacts on human and environmental health and risks posed by toxic substances. Toxicity testing is thus a subset of the bigger picture that is risk assessment and provides essential data to this process( see Chapters 4 and 5 for more on this ). 3.1.1 Endpoints and measures in ecotoxicology An important process in the characterization of toxicity is the selection of endpoints and measures for ecotoxicological risk assessment. An assessment endpoint is what is to be protected. A measure is a characteristic of an organism and a substance (for example, the concentration that causes mortality) or the intensity of a general stressor, such as increased temperature (USEPA 1992a, 1998) that causes an effect. A test endpoint is what is observed in a toxicity test (mortality, lack of motion, etc.). Assessment Endpoints Are explicit expressions of the actual ecological value that is to be protected. These are the ultimate focus in risk assessment and act as a link to the risk management process (such as the policy goals). Assessment endpoints must have the following characteristics: They must be ecologically relevant , they should be susceptible to the toxicant/stressor and, more controversially, they should have societal value . This last criterion, social value must be treated with caution as it is subject to interpretation. For example, societal values may change over time, such as the public regard for wetlands (Suter et al. 2007). Before the 1970s, the public saw little value in
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wetlands and many were, in fact, drained to reduce nuisance from mosquitoes. Since risk assessors and activists have linked wetlands to the production of birds, waterfowl and flood protection, the social value of wetlands has increased and they are now accepted as a worthwhile assessment endpoint. Similarly, the impact of clear-cutting on the spotted owl in the Pacific North-West grabbed the attention of the public much more than a similar impact on stream invertebrates.
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