| Earthworms are a cornerstone of terrestrial ecosystems. Laboratory studies were conducted on the acute toxicity and effects of chemicals to investigate toxic insult to this soil invertebrate. Eisenia foetida were exposed to an array of compounds using a 48-hour contact toxicity test to assess and identify classes of chemicals that are potentially hazardous to earthworms. The acute contact toxicity data generated allowed chemicals to be categorized by a hazard rating system that identifies a compound as either super-toxic (< 1 (mu)g/cm('2)), extremely toxic (1-10 (mu)g/cm('2)), very toxic (10-100 (mu)g/cm('2)), moderately toxic (100-1000 (mu)g/cm('2) or relatively non-toxic (> 1000 (mu)g/cm('2)). Of the 120 compounds screened in this bioassay, phenols and N-methylcarbamates were the most toxic chemicals tested. From the acute toxicity data on parathion and carbaryl, their metabolites, degradation products and non-insecticidal analogs, it is apparent that for some pesticides phenolic degradation products are inherently as toxic or more toxic than the parent compound to earthworms. Furthermore, in studies on the uptake of chemicals by contact exposure, earthworms absorbed the major phenolic degradation products of carbaryl, carbofuran and parathion as readily as the more non-polar parent compounds.;In the course of investigating acute toxicity of chemicals, a small group of chemically diverse compounds were observed to induce a site-specific lesion in E. foetida. Carbaryl and nornicotine were the most potent inducers of this mid-segmental swelling phenomenon. Structure-activity studies and the ability to block the lesion with concurrent exposure to alcohol dehydrogenase inhibitors suggest highly reactive derivatives (e.g., nitroso formation) formed in vivo are responsible for the observed pathology.;A number of chemicals that are moderately or relatively non-toxic to mammals such as malathion, benomyl and cypermethrin were extremely toxic to earthworms. On the other hand, solvents that are very hazardous to mammals (e.g., carbon tetrachloride and methanol) were relatively non-toxic to earthworms in the 48-hour contact toxicity test. Results obtained in this study demonstrate the unpredictability of chemical toxicity to different animal species which complicates estimating environmental risk to one species based on data obtained with another animal model. |
