Acetylcholinesterase Activity in Daphnia: is It a Good Biomarker of Environmental Contamination?

Abstract

Acetylcholinesterase (AChE) activity has been employed as a biomarker of environmental contamination. However, for invertebrates, additional studies are required to determine the role of AChE activity in biological monitoring. Thus, a series of experiments was performed to evaluate the interference of developmental and environmental factors on AChE activity in D. magna and D. similis. In addition, the relationships between AChE activity, acute toxicity and population level effects were evaluated for D. magna. An inverse relationship between body length and AChE activity has been demonstrated for D. magna. Also, juveniles of D. similis (= 72 h) kept in diluted mineral water had lower AChE activity than those kept in ASTM water. Our findings have as well indicated that the associations between AChE activity and higher level effects in D. magna are not always straightforward. Exposure to parathion, propoxur, malathion, chlorpyrifos, and acephate resulted in the ratio between EC50 and IC50 varying from 0.31 to 0.90. Furthermore, we found that genotypic variation will interfere with the link between AChE activity and population growth rate in D. magna pos-exposed to acephate. Therefore, the use of this biomarker in environmental assessment programmes should be made with caution. On one hand, it is very sensitive, and keeping strict standard conditions it can give a good indication of exposure to organophosphates and carbamates. On the other hand, its use as a predictive tool is limited, and should only be made in association with complementary measurements.