Toxicity of azodrin on the morphology and acetylcholinesterase activity of the earthworm Eisenia foetida.

The acute toxicity of azodrin (monocrotophos, an organophosphorus insecticide) was determined on a soil organism, Eisenia foetida. The median lethal concentrations (LC50) were derived from a 48-h paper contact test and from artificial soil tests. The LC50 of azodrin in the paper contact test was 0.46 +/- 0.1 microg cm(-2) (23 +/- 6 mg L(-1)) and those in the 7- and 14-day artificial soil tests were 171 +/- 21 and 132 +/- 20 mg kg(-1), respectively. The neurotoxic potentiality of azodrin was assessed by using a marker enzyme, acetylcholinesterase (AChE; EC 3.1.1.7) in both in vitro and in vivo experiments. The progressive signs of morphological destruction are correlated with percentage inhibition of AChE in the in vivo experiments. The kinetics of AChE activity in the presence and absence of azodrin indicated that the toxicant is competitive in nature. This study demonstrated that azodrin causes concentration-dependent changes in the morphology and AChE activity of the earthworm E. foetida.