Comparative methyl parathion toxicity between three feral rodent species and their laboratory animal counterparts

Abstract

Lethal methyl parathion (MP) intoxication and recovery from nonlethal MP intoxication was investigated in 3 feral rodent species as well as their laboratory animal counterparts. The study animals were laboratory Sprague-Dawley rats and ICR mice as well as feral cotton rats (Sigmodon hispidus), deer mice (Peromyscus maniculatus), and house mice (Mus musculus). The feral rodents were investigated as captive feral (CF) and/or colony reared feral (CRF) animals. The lethality investigation revealed that females were significantly more resistant than males only among laboratory rodents and CRF house mice. The CRF rodents were more susceptible to MP lethality than their CF counterparts; however this difference was significant only among female deer mice. Both CF and CRF cotton rats were significantly more resistant to MP lethality than their corresponding laboratory rats. Lethal MP intoxication among CRF and CF deer mice as well as among male CRF house mice was not significantly different from their laboratory animal counterparts. In contrast, female CRF house mice were significantly more resistant to MP lethality than female laboratory mice. Brain acetylcholinesterase (ACHE) activity recovery (BAAR) following acute nonlethal MP intoxication was investigated in laboratory rodents and CRF cotton rats and house mice. Comparisons were made with respect to sex between feral species and their laboratory animal counterparts. Male laboratory rats recovered significant brain ACHE activity much more rapidly than did male CRF cotton rats; whereas female laboratory rats and female CRF cotton rats attained significant recovery on the same day. However, at a subsequent time interval, female CRF cotton rats did not maintain significant recovery whereas female laboratory rats did. Both male and female laboratory mice attained significant recovery of brain ACHE activity sooner than their feral counterparts. Overall, laboratory mice accurately predicted MP lethality in the investigated feral counterparts whereas laboratory rats did not. However, laboratory rats erred on the side of safety. Laboratory rodents underestimated the time required for feral rodents to obtain significant recovery from acute nonlethal MP intoxication. Feral rodents may be at significant risk if subjected to repetitive organophosphorous pesticide (OP) exposure intervals calculated on the basis of laboratory rodent data.