Earthworm culture, maintenance and species selection in chronic ecotoxicological studies: A critical review

A critical review of earthworm use in chronic ecotoxicological studies is presented. In laboratory studies, species selection has often been based on commercial availability or on field-collected earthworms. The validity of results employing earthworms of either unknown origin or previous exposures must be questioned. Many studies have relied heavily on methodologies adopted from acute testing where earthworm maintenance was not a priority. A number of studies have been published without reference to such critical factors as earthworm density, food, temperature or soil moisture levels. Earthworm death has been identified as a source of error particularly in reproduction tests where adult number is directly related to cocoon production. This has been partially addressed by growing individuals separately or culturing in pairs for reproduction studies. It is suggested that a further development could be the use of parthenogenetic species allowing reproduction to be assessed on an individual basis. The use of such species would also permit tests on genetically similar cohorts. It is (widely) recognised that there are problems of extrapolation from laboratory to field scale. However, field tests remain uncommon due to difficulties with experimental design and interpretation of results. Use of laboratory-reared earthworm cohorts and mark–release–recapture techniques may allow development of a standard comparative procedure across different sites. It is suggested that wider use of established culture techniques allied to ecological requirements and behaviour of species will increase the consistency and validity of sub-lethal earthworm toxicity tests.