Metabolism of parathion and brain cholinesterase inhibition in aroclor 1254-treated and untreated Caspian terrapin (Mauremys caspica rivulata, Emydidae, Chelonia) in comparison with two species of wild birds.

The mean level of PCB residues in the liver of the Caspian turtle collected in nature was 23 ppm, or approximately 20-fold greater than that detected in the two bird species tested. Treatment of the turtles with aroclor 1254 resulted in a 30-fold increase in the level of PCB residues in the liver but did not cause any increase in the content of cytochrome P-450 and the desulfurase activity of this hemoprotein. The Ki value for acetylcholinesterase inhibition by paraoxon in brain homogenate of the Caspain terrapin was 3 and 2 orders of magnitude higher than that found in the African bulbul and the barn owl, respectively.