Variability in acetylcholinesterase and glutathione S-transferase activities in Chironomus riparius Meigen deployed in situ at uncontaminated field sites.

An in situ system was used to expose fourth instar Chironomus riparius Meigen larvae for 48-h at 13 uncontaminated river sites across southeast England. Acetylcholinesterase (AChE) and glutathione S-transferase (GST) activities were measured in individual larvae recovered from these sites. Activities of both biomarkers varied almost twofold across the sites, with statistically significant differences detectable between sites. There were no clear relationships between biomarker activities and physical or chemical characteristics measured at each site. This study shows that biomarker measurements can be used successfully in conjunction with an in situ system. However, the results of statistically significant biomarker results must be treated with caution because natural variability in responses can occur even in the absence of toxicant exposure.