Relative toxicities of chemicals to the earthworm Eisenia foetida

Abstract

In the present study, 90 chemicals were tested against Eisenia foetida for the purpose of using this organism as the marker species to indicate the relative toxicities of chemicals to earthworms and other soil invertebrates. The worms were exposed to deposits of the chemicals on filter paper for 48 h and the mortality was recorded; concentrations were expressed in μg/cm². Based on the resulting LC₅₀ values, the chemicals were classified as supertoxic (< 1.0 μg/cm²), extremely toxic (1–10 μg/cm²), very toxic (10–100 μg/cm²), moderately toxic (100–1,000 μg/cm²) or relatively nontoxic (> 1,000 μg/cm²). Of the chemicals tested (pesticides, solvents, metals, drugs, carcinogens, etc.), only carbofuran and eserine salicylate, both carbamates, were supertoxic. The remaining chemicals were distributed about equally among the other toxicity categories. The most surprising results were that the phenolic hydrolytic products of parathion, carbaryl, 2,4‐D and 2,4,5‐T were as toxic, or more toxic, than the parent material, with all of these compounds falling within the extremely toxic and very toxic classifications. Several chemicals, considered only moderately or relatively nontoxic to mammals, were extremely or very toxic to earthworms; among these compounds were carbaryl, malathion, cypermethrin and benomyl. The results of this study further demonstrate the unpredictability of chemical toxicity to different animal species, a fact which complicates the assessment of environmental risk to one or more species based on data attained with another.