Comparison of the delayed neurotoxicity of O-methyl and O-ethyl analogs of EPN, leptophos, and cyanofenphos.

Eight pairs of O-methyl and O-ethyl O-(substituted-phenyl) phenylphosphonothionates were evaluated with respect to their delayed neurotoxic activity in hens. O-methyl compounds were in all cases more active than their O-ethyl analogs. The neurotoxic potential of the O-methyl phenylphosphonothionates was 2,5-diCl greater than 4-NO2 greater than 2,4,5-triCl and 2,4,6-triCl greater than 2,4-diCl greater than 2,5-diCl-4-Br greater than 4-CN, when single oral doses were given. Both EPN-ethyl and leptophos-methyl were more neurotoxic in multiple dermal than multiple oral dosing regimens. LD50s for mice and flies were established.