A Comparative Study on the Relationship Between Various Toxicological Endpoints in Caenorhabditis elegans Exposed to Organophosphorus Insecticides

Abstract

The toxicity of 10 organophophorus (OP) insecticides—acephate, dimethoate, dichlorvos, dicrotophos, monocrotophos, methamidophos, phosphamidon, omethoate, phosdrin, and trichlorfon—was evaluated in Caenorhabditis elegans using lethality, movement, and acetylcholinesterase (AChE) activity as the endpoints after a 4-hr- exposure period. The OP insecticides tested showed LC50 values ranging from 0.039 mM (for dichlorovs) to 472.8 mM (for methamidophos). The order of toxicity for lethality and movement was not significantly different when tested using the rank order correlation coefficient. AChE activity was markedly affected by all the OP insecticide exposures that caused significant inhibition in movement, indicating that the mechanism of toxicity of OP insecticides in C. elegans is the same as in higher animals. All OP insecticides induced greater than 50% inhibition of AChE at the lowest tested OP insecticide concentration resulting in inhibition in movement. While a significant correlation was evident between LC50 values in C. elegans and the LD50 values in rats for the 10 OP insecticides studied, a correlation was not evident between EC50 values in C. elegans and LD50 values in rats. Overall, the two endpoints, LC50 and movement, were more reliable and easier to perform than measurement of AChE activity in C. elegans for determining the toxicity of OP insecticides. Further, ranking of these endpoints with respect to the OP insecticides studied indicates that these parameters in C. elegans are predictive of OP insecticides mammalian neurotoxicity.

Acknowledgements

The first author acknowledges the Department of Biotechnology, Government of India, for the award of overseas Associateship. We also thank Dr. David Dusenbery for permitting use of the computer tracking software program. Finally, we would like to thank the Caenorhabditis Genetics Center, which is funded by the NIH National Center for Research Resources (NCRR), for supplying the nematode strain used in this research.

Notes

Dusenbery, D. 1996. NIH Image, Version 1.59. Computer tracking program modified by Dr. David Dusenbery, School of Biology, Georgia Institute of Technology, Atlanta.