Utility and relevance of aquatic oligochaetes in Ecological Risk Assessment

Ecological risk assessment (EcoRA) provides both a process and a framework to evaluate the potential for adverse ecological effects occurring as a result of exposure to contaminants or other stressors. EcoRA begins with problem formulation/hazard identification, progresses to effects and exposure assessment, and culminates with risk characterization (an estimate of the incidence and severity of any adverse effects likely to occur). Key components of EcoRA include determining: stressors/contaminants of concern; sensitive, exposed biota; and, appropriate tests and organisms for evaluating effects. Aquatic oligochaetes are not generally used directly in EcoRA because of three major perceptions. First, EcoRA personnel are generally not familiar with or comfortable using this group of organisms. Second, there is believed to be a paucity of widely accepted toxicity tests with these organisms. Third, their taxonomy is considered difficult and uncertain. In fact, aquatic oligochaetes potentially have great utility and relevance to EcoRAs because of factors including: their importance in the aquatic food chain (e.g. prey to fauna including fish and waterfowl; as a vector for contaminant movement through the food chain from bacteria); many species are widely distributed and well studied; representatives include fresh, estuarine and marine species; as a group, they range from sensitive to insensitive over a wide range of environmental insults; they have a long history of use in pollution monitoring and assessment; and, relevant toxicity and biaccumulation tests exist. Toxicity testing under defined conditions is appropriate for problem formulation while more realistic testing for effects assessment (e.g. microcosms) is logistically easier with this group of organisms than with others due to their relatively small size. The importance of aquatic oligochaetes for EcoRA, in particular of sediments, is particularly compelling.