Abstract:
The toxicity of the herbicide paraquat upon two larval stages of rainbow trout (Salmo gairdneri) was studied. The histopathological effects and tissue accumulation of l4C-labeled paraquat were also investigated. Static bioassays were conducted for 24 and 48 hours at concentrations of ISO, 205, 281, 385 and 528 ppm paraquat. Using four replicates, prolarval fish (12 days old) had LC50 values of 282, 313, 366 And 329 ppm paraquat. In another experiment with postlarval fish (53 days old), 50% died after 48 hour exposure to 528 ppm paraquat (noreplicates). Results of these experiments indicate that toxicity is both time and age dependent. Tissues from the skin, gills, intestine, kidney and liver of postlarval fish were examined after exposure to 724 ppm paraquat for 48 hours. Microscopic examination revealed no evidence of tissue degeneration,
hypertrophy or lesions. Whole-body autoradiographs were used to locate any sites of paraquat
accumulation in the tissue. Prolarval fish (24 days old) were exposed to 20 ppm l4C-paraquat dichloride (50 pCi) in 250 ml of water for 48 hours. Autoradiograms revealed extensive grain around the columnar epithelium of pyloric cecae. Extensive study of other organ systems failed to show any dense grain development which could be interpreted as paraquat localizations.
