Population level effects organization

The dose or contaminant body residue in organisms is a key determinant of potential risk from contaminant uptake. For instance, metal body concentrations in small exposed organisms can be related to metal-induced effects at the organism and population levels of organization (Chapman et al., 2003). CBRs have been used, similar to TIEs, to establish causation as part of the SQT (Borgmann et al., 2001), and to provide additional information for predictions related to changes in contaminant loadings. 

Microcosms are composed of large chambers, terreria, aquaria, or artificial pools aquatic mesocosms include artificially constructed ponds or streams, while terrestrial mesocosms are large containers filled with soil, plants, and (sometimes) leaf litter. Microcosms and mesocosms typically contain more than one species of test organism, are located outdoors (but may also be located indoors), and often contain sediment and/or vegetation. The rationale is to produce a test system with similarities to the natural environment, but is more controllable. End points examined may include acute toxicity, suble-thal effects, or community/population level effects. 

Methods for Detecting Population-Level Effects of Toxicants in Field-Exposed Organisms... 

There are a variety of methods that can be used to examine population genetic structure. In Figure 3, methods for evaluating population-level effects of toxicants in aquatic organisms have been categorized... 

The analysis of environmental risk assessments of 50 pesticides revealed that risks to birds and mammals often were not fully addressed. EMs could be useful for filling this gap, but should also be useful for aquatic organisms and nontarget arthropods, particularly in relation to questions of recovery. A major obstacle to the full use of EMs is the lack of clear protection goals in terms of population-level effects. Validation is key to the acceptance of models in the regulatory context, and guidance is needed for the assessment of EMs and their outputs (Chapter 11). 

Figure 1. Conceptual model illustrating examples of major anthropogenic contaminant sources and contaminants, their distribution within the abiotic environmental media, their movement into biota with potential food chain contamination, and potential effects at the organismal, population, conmiunity and ecosystem level of organization.

Because of the high toxicity of pyrethroids to aquatic invertebrates, these organisms are likely to be adversely affected by contamination of surface waters. Such contamination might be expected to have effects at the population level and above, at least in the short term. In one study of a farm pond, cypermethrin was applied aerially, adjacent to the water body (Kedwards et al. 1999a). Changes were observed in the composition of the macroinvertebrate community of the pond that were related to levels of the pyrethroid in the hydrosoil. Diptera were most affected, showing a decline in abundance with increasing cypermethrin concentration. Chironimid larvae first declined and later recovered. 

The book takes a bottom-up approach, describing the mechanisms by which pollutants have harmful effects on living organisms and how these effects are translated into adverse changes at the population level. This mechanistic approach supplies the basis for development of new mechanistic biomarker assays, which in turn provide measures of toxic effect and not merely of exposure, and subsequently provide evidence of causality between pollutant levels and ecological changes. 

Another simple approach to predict effects at higher levels of biological organization through extrapolation is the HERBEST model (van den Brink and Kuyper 2001). HERBEST estimates direct effects and potential recovery of field populations of aquatic organisms from predicted or measured pesticide concentrations,... 

LOEC/L Lowest-observed-effect concentration/level. The lowest concentration of an agent used in a toxicity test that has a statistically significant effect on the exposed population of test organisms, compared with the controls. 

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