ACTION OF PESTICIDES ON EARTHWORMS .2. ELIMINATION OF PARATHION BY THE EARTHWORM EISENIA-FOETIDA (SAVIGNY)

The earthworm, Eisenia foetida, eliminated parathion and carbofuran at first order rates when continually rinsed in water after treatment with the pesticides. This experiment was also carried out on Lumbricus rubellus for comparison. Carbofuran which is more soluble in water, was eliminated quicker than parathion. The later rate of elimination was very similar for the two species, but immediately after injection the rate was much higher in E. foetida. The metabolism of 1‐ethyl14C labelled parathion and paraoxon (diethyl 4‐nitrophenyl phosphate) was studied in E. foetida. The worm was able to convert parathion to paraoxon by a rather slow process although this metabolite could not be detected in the worms due to its rapid transformation to diethyl hydrogen phosphate. Indirectly, paraoxon can be postulated as a parathion metabolite because of a progressive depression of cholinesterase level observed after treatment with parathion. Small amounts of diethyl hydrogen phosphate were detected as a metabolite of parathion; this is also an indication of paraoxon formation. During the 30 h following injection of parathion, only 4.4% of the applied dose was recovered as water‐soluble metabolites (2.8% in the worms and 1.6% in the sand surrounding them), while 52% was recovered as unmetabolised parathion. Because of inefficient injection, only 70‐59% of the dose thought to be injected was recovered. Therefore the part of the actual applied dose that remained unmetabolised was probably even greater (88%). Five days after injection of parathion, 15 and 9.3 % of the recovered radioactivity in the surrounding sand and in the worm extracts, respectively, was identified as O,O‐diethyl O‐hydrogen phosphorothioate, 3.7 and 7.0% as diethyl hydrogen phosphate, 8.8 and 3.3% as O‐ethyl O‐4‐nitrophenyl O‐hydrogen phosphorothioate (desethylparathion) and/or O‐4‐aminophenyl O,O‐diethyl phosphorothioate, while 70.3 and 80.4% was unmetabolised parathion. Paraoxon was very quickly hydrolysed to diethyl hydrogen phosphate in vivo and in vitro. The in‐vitro hydrolysis was associated with a microsomal fraction and was not inhibited by ethylenediaminetetra‐acetic acid or 4‐(chloromercuri)benzoic acid, and incompletely by aldicarb. Cholinesterase and arylesterase were therefore excluded as enzymes responsible for the activity. Copyright © 1979 John Wiley & Sons, Ltd