Effects of monocrotophos and its analogs in acetylcholinesterase activityʹs inhibition and its pattern of recovery on euryhaline fish, Oreochromis mossambicus

Acute toxicity of monocrotophos (MCP) and its newly synthesized thiol analogs 2-butenoic acid-3-(diethoxyphosphinothionyl) methyl ester (RPR II) and 2-butenoic acid-3-(diethoxyphosphinothionyl) ethyl ester (RPR-V) was studied on euryhaline fish, Oreochromis mossambicus. The median lethal concentrations of MCP, RPR-II, and RPR-V are 11.506, 0.167, and 0.174 mg L−1, respectively. Both the analogs were found to be 65-fold more toxic than MCP. Inhibitory and recovery patterns of brain, gill, and muscle acetylcholinesterase (AChE) was studied in vivo after exposure to LC50 (96 h) concentrations. Recovery study was performed of regular intervals of day-1, -7, -14, -21, and -28 to establish the time course of 50% and 100% recovery in neurotransmitter enzyme of brain, gill, and muscle tissues. The sensitivity of the tissue AChE was in the order gill>brain>muscle. The relative toxicity of these compounds with regard to AChE was RPR-II>RPR-V>MCP. The MCP-treated fishes recovered at a faster rate than for RPR-V, followed by RPR-II.