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 hand the mortality was recorded; concentrations were expressed in pgkm'. Based on the resulting LC,, values, the chemicals were classified as supertoxic (< 1.0 pglcm'), extremely toxic (1-10 pg/cm ' 1, very toxic (10-100 pg/cm2), moderately toxic (IOO-I,OOO pg/cm2) or relatively nontoxic (> 1,000 pg/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,S-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 basedon data attained with another.
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.
While great strides have been made in recent years regarding water quality criteria and hazard assessment of chemicals in the aquatic environment, the same is not true for the terrestrial ecosystem. This results in part from the magnitude of the problem and, perhaps, to some degree, from an attitude held by some that animals dwelling in and on the land can better cope with environmental stress than can their aquatic counterparts. Indeed, this sometimes may be the case, but results of our studies with the earthworm Eisenia foetida suggest otherwise. This organism is extremely susceptible to the toxic action of many common pesticides and other chemicals, and there is good evidence that this species is among the more hardy of all the earthworms. Although many facets of the terrestrial ecosystem must be addressed with regard to chemical hazards, practicality dictates that emphasis be directed toward specific organisms representing a given segment of the terrestrial population. This article discusses the vital role of earthworms in the environment and why they are particularly useful as test organisms, and summarizes chemical toxicity data obtained in laboratory and field investigations.
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