Toxicology and Laboratory Studies

Abstract

This chapter provides a chronological synthesis of the available literature and information on laboratory based studies of aquatic oligochaetes and has been organized into water-only vs. sediment toxicity tests, and acute vs. chronic toxicity tests. Toxicological studies have employed relatively few species. Absence of sediment in tests with aquatic oligochaetes is a source of stress and reduces realism in exposure conditions and most current toxicity work is performed in the presence of sediment. Thus, unless there is a requirement for water-only tests, for interspecies comparison of toxicity of chemical compounds, or for routine control of species sensitivity in laboratory cultures, these tests are considered inappropriate for oligochaete worms in ecological risk assessment. Field populations of several species have been demonstrated to vary genetically, and may have different tolerances to both environmental and anthropogenic stress. This suggests that test organisms should be obtained from cultures of a defined genetic strain, or alternatively the sensitivity of the populations should be intercalibrated with reference toxicants. Oligochaete worms are not uniformly more tolerant to contaminants than other test organisms. Comparative data for worms and other benthic invertebrates show that responses are species-specific and also contaminant-specific. Among the sublethal measurements, sexual reproduction seems to be the most easily standardised and informative endpoint, and has high ecological relevance, since reproductive impairment has the same long-term effect as mortality on the population. Sublethal, shortterm responses such as behavioural responses (avoidance behaviour, sediment reworking and sediment borrowing) need further standardization. In the future, in situ bioassays are promising tools in environmental risk assessment but will require the use of species characteristic of particular habitats or that are suitable for reproduction and toxicity assessment under different environmental conditions.