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

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-hrexposure
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.