Abstract

The use of pesticide mixture to combat increased resistance by pest, to single chemical insecticide has brought about an increase in the use of pesticide mixture from different class, with its attendant toxicity. The objective of this study was to evaluate the maternal and foetal toxicity associated with dimethoate and cypermethrin, the two insecticides that are normally mixed to reduce pest resistance. 100 confirmed-mated (gravid) females were assigned at random among the four groups (control – tap water only):   group 1- very low dose-10 mg/kg/day of Cypermethrin (5.3% LD50) + 1.0 mg/kg/day Dimethoate (0.7% of LD50); group 2- intermediate dose- 19 mg/kg/day of Cypermethrin (10% LD50) + 1.4 mg/kg/day  Dimethoate (0.9% of LD50); and group 3- high dose-  38 mg/kg/day of Cypermethrin (20% LD50) + 12.8 mg/kg/day  Dimethoate (8.5% of LD50). The regimens were administered orally at gestation days (GD) 6-20 to pregnant rats. The dams were examined for mortality, moribundity, pertinent behavioural changes and signs of overt toxicity. Animals were weighed on day 0, and once at every 3-day intervals during the dosing period and on GD 21. The pregnant rats were sacrificed by decapitation on GD 21, the uteri were removed and the fetuses examined for litter weight, size, resorption, sex ratio, absolute and relative organ weight. The results showed that combined pesticide exposure caused overt toxic signs in the dams. However, the maternal body weight and relative organ weight were not adversely affected except in the heart that showed significant alteration. Although, the litter weight was not adversely compromised, the result showed that the prenatal exposure to pesticide mixture caused increased foetal resorption, decreased the litter size and offsprings’ male/female ratio. The study concludes that prenatal co-exposure to cypermethrin and dimethoate has adverse consequences on some maternal and foetal parameters in albino rats.

Key words: Pesticide mixture, litter size, sex ratio, litter weight, maternal relative organ weight.