The role of ecotoxicity testing in assessing water quality

Abstract Ecotoxicology provides a basis for making decisions on the likely impact of a chemical or effluent on the aquatic environment. It encompasses laboratory ecotoxicity tests of various types to explore relationships between exposure and effect under controlled laboratory conditions, through to studies of the effects of chemicals or effluents under a variety of ecological conditions in complex field ecosystems. This paper will focus on the value of laboratory ecotoxicity tests as a tool in assessing water quality. Laboratory tests are valuable (i) in deriving and assessing water quality criteria, (ii) for screening and ranking chemicals and predicting their hazard and risk, (iii) for establishing dilution levels of chemicals or effluents prior to discharge into water bodies, (iv) in determining cause-effect relationships in post-impact studies, and (v) for establishing and validating field bioindicators. Both the advantages and deficiencies of using ecotoxicological testing for these purposes are illustrated from research with pesticides, metals and sediments. Use of a combination of both laboratory- and field-based ecotoxicology studies is important to gain a full understanding of the effects of chemicals at the ecosystem level.     

Cause-effect modeling as a general method for describing and studying phenomena in complex hierarchical systems

A strict definition of a cause-effect model of a complex phenomenon is given, and the rules for presenting such models in the form of cause-effect diagrams are formulated. The relationship between the cause-effect modeling and conventional methods of mathematical modeling is analyzed. Examples of the cause-effect models (diagrams) of phenomena of various physical nature are presented, and the application of these models to some specific problems is shown. In particular, the mechanism of renormalizing the rate constants of chemical reactions is considered in terms of dissipative resonance. An example of renormalizing the parameters of climate sensitivity and the relaxation time of the Earth’s climatic system in terms of a two-component (CO₂ + H₂O) greenhouse effect is considered.     

Midpoints versus endpoints: The sacrifices and benefits

On May 25–26, 2000 in Brighton (England), the third in a series of international workshops was held under the umbrella of UNEP addressing issues in Life Cycle Impact Assessment (LCIA). The workshop provided a forum for experts to discuss midpoint vs. endpoint modeling. Midpoints are considered to be links in the cause-effect chain (environmental mechanism) of an impact category, prior to the endpoints, at which characterization factors or indicators can be derived to reflect the relative importance of emissions or extractions. Common examples of midpoint characterization factors include ozone depletion potentials, global warming potentials, and photochemical ozone (smog) creation potentials. Recently, however, some methodologies have adopted characterization factors at an endpoint level in the cause-effect chain for all categories of impact (e.g., human health impacts in terms of disability adjusted life years for carcinogenicity, climate change, ozone depletion, photochemical ozone creation; or impacts in terms of changes in biodiversity, etc.). The topics addressed at this workshop included the implications of midpoint versus endpoint indicators with respect to uncertainty (parameter, model and scenario), transparency and the ability to subsequently resolve trade-offs across impact categories using weighting techniques. The workshop closed with a consensus that both midpoint and endpoint methodologies provide useful information to the decision maker, prompting the call for tools that include both in a consistent framework.