Assessment of the earthworm, Eisenia fetida, as a biomarker species using selected dispositional processes and biological endpoints

The hypothesis tested in this research was that the earthworm E. fetida is an acceptable biomarker species based on disposition and biological effects resulting from chemical exposure. The dispositional processes examined were uptake, excretion, distribution, and metabolism. The biological endpoints studied were acid-soluble thiol levels and DNA strand breaks (as assessed by the alkaline unwinding assay) to develop biomarkers that could be used to ascertain earthworm exposure to classes of chemical contaminants. Two exposure media suggested for use by regulatory agencies, filter-paper exposure and artificial-soil exposure, were used for earthworm exposures.;Absorption of cadmium and benzo (a) pyrene occurred rapidly with filter-paper exposure and was affected by the physical characteristics of soil with artificial-soil exposure. Once absorbed, compartmentalization in earthworms occurred in a predictable manner, with the water-soluble metal cadmium localizing in the aqueous cytosol of the cell and the non-water-soluble organic compound benzo (a) pyrene localizing in the lipid portions (10 000xG pellet and microsomal fraction) of the cell. Coelomic fluid was used as a vehicle for localization. Cadmium exhibited a long half-life in earthworms, 77 hours for filter-paper exposure and 100 days for artificial-soil exposure.;Metabolism in earthworms was compound specific, dependent on the enzyme content, both qualitative and quantitative, of the earthworm. Earthworms metabolized aldrin extensively when compared to biphenyl, and did not metabolize benzo (a) pyrene.;Acid-soluble thiol level in earthworms upon chemical exposure is not a good candidate as a biomarker of exposure. The background acid-soluble thiol level widely fluctuated (0.31-1.32 ;This research has shown a genotoxic biomarker is possible using the alkaline unwinding assay, though it may not detect some compounds that must be metabolically activated. Methylmethane sulfonate and dimethylnitrosamine caused significant genotoxicity, while benzo (a) pyrene and 2-acetylaminofluorene did not.;The goal of such research is the establishment of the earthworm as a regulatory tool to assess chemical contamination of soils or soil leachates (using filter-paper exposure). The earthworm may have merit as a biomarker species. The bioindicator potential of the earthworm needs to be further explored with more research on the sublethal effects of xenobiotics to earthworms.