Abstract:
This paper reports the histopathological responses of the gill, liver and tail muscle tissues in
tadpoles of the Asian Common Toad Duttaphrynus melanostictus (Schneider, 1799) exposed to
chlorpyrifos a common organophosphorus pesticide. Tadpoles of Gosner stages 24-26 were continuously
exposed to low, mid and high (500, 1000 and 1500 μgl–1) concentrations of chlorpyrifos for two weeks.
Histological alterations in the tissues of the surviving larvae were microscopically examined both at the
end of the exposure period and after a week following the final exposure. Several histological alterations
were noted in the gills, liver and tail muscles of the larvae exposed to 1500 μgl–1 of chlorpyrifos. The gills
of exposed larvae showed architectural distortion resulting from reduced primary and secondary gill
lamellae and blood vessels, and alterations in the gill epithelium. In the liver sinusoidal congestion and
dilation, cytoplasmic vacuolation and changes in hepatocytes such as hyperchromatic nuclei and nuclear
fragmentation were observed. The tail muscle tissue suffered from severe atrophy and myotomal
disintegration. Although histological alterations in the gill and liver tissues were noted only at the high
concentration, changes in the muscle tissue i.e. muscle degeneration and atrophy, were apparent at both
low and mid concentrations. The degree of damage in surviving larvae in a week following the final
exposure was lower than that observed during the exposure, probably indicating recovery or resistance.
The findings of the present study emphasize the need to investigate possible sublethal damage induced by
pesticides in amphibians inhabiting agricultural habitats.
