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

These methods have been extensively described in the

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Unformatted text preview: a, 1997b, a) . Oral Dermal Through gills Figure 3-18 4Routes of exposure in aquatic invertebrates Routes of exposure are usually through the matrix and the substance may enter the body through the oral, dermal or respiratory route (Figure 3-18). The endpoint is often mortality (usually assessed as morbidity or lack of movement after a stimulus). Probit analysis and non -quantal methods are used as statistical treatments. 3.2.6 Aquatic systems, vertebrates Bioassay methods for fish are well standardized (CFR 2004; OECD 1981, 1984; ASTM 1991; Parrish 1984; Environment Canada; 1990c, d, e; 1992 b, 1998). These standardized tests include acute, life cycle tests and early life stage tests. Some assays have been reported with amphibians (mostly larval) and non with marine mammals. Both freshwater and saltwater species are used in these assays. Dermal Routes of exposure are through the matrix in most cases but through food in some cases ( Figure 3-19). Measures of effect include acute lethality, growth and development. Statistical treatments include probit analysis and non quantal approaches. Oral Respiratory (gills) 3.2.7 Assessing the quality of ecotoxicity tests Figure 3-195 Routes of entry of toxic substances in fish Effects measurements may vary in quality from one testing laboratory to another and from one publication to anot her. Tests that follow specific guidelines that have been developed by regulatory agencies (see references above and, in particular, CFR 2004) are usually considered better than those that do not. This does not mean that the n on-guideline tests are always of poor quality nor does it mean that guideline tests are good science. In general, the following are preferred in toxicity tests. • • • 3.2.8 Tests which follow published guidelines. Tests in which the exposure concentrations a re measured rather than determined from the dilutions used (nominal concentrations). Tests for aquatic organisms where flow -through exposures have been used. Measuring effects in the ecosystem Most ecotoxicological risk assessments are aimed at protecting populations or communities of organisms from effects. These risk assessments, for the most part, are based on observations of toxicity that are extrapolated to the population level. This is not an easy task for the following reasons: ● The distribution of the population may not be the same as that of the toxicant. ● The impact of the toxicant may be confounded by other stressors (anthropogenic or natural). ● The population may be able to adapt to or co mpensate for the effects of the toxicant. The inherent properties of populations may have a significant effect of their response to a stressor. Experience of previous events in ecotoxicology shows that long -lived, low fecundity organisms such as predator y birds and whales are more susceptible to adult mortality than more fecund and short -lived organisms such as quail and anchovies ( Suter et al. 2007). Similarly, populations where reproduction and survival are strongly related to density are inherently les...
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This document was uploaded on 04/07/2014.

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