Effect of Temperature and Pirimiphos Methyl on Biochemical Biomarkers in Chironomus riparius Meigen

Fourth-instar Chironomus riparius Meigen larvae were exposed to the organophosphate (OP) insecticide pirimiphos methyl (0, 0.1, 1.0, and 10 μg/L) for 48, 72, or 96 h at three temperatures (3, 12, or 22°C). Two biochemical biomarkers, acetylcholinesterase (AChE) and glutathione S-transferase (GST), were measured in individual larvae from each treatment. AChE activity was inhibited by the OP in a dose-responsive fashion. This response remained similar at all three temperatures, demonstrating that AChE is a robust and specific biomarker. Exposure duration had little effect on AChE activity. In contrast, GST activity was induced at the highest OP insecticide concentration, but induction was also evident at 3°C. There was a significant effect of exposure duration, with an overall decline in GST activity over time. This result agrees with previous work suggesting that GSTs are not particularly suitable for use as a biomarker of pesticide exposure or effect in Chironomus.