Acetylcholinesterase, an old biomarker with a new future? Field trials in association with two urban rivers and a paper mill in Newfoundland

Biological markers are sensitive, cost effective tools for identifying risks of environmental contamination. The cytochrome P450-linked mixed-function oxygenase (MFO) system has been extensively validated in the environment, not only in association with point sources of pollution, but also in association with contamination over broad geographical areas. However, there is a recognized need for the establishment of biomarkers for assessing a variety of toxicological endpoints. With respect to neuromuscular functions, a recent study in the North Sea has indicated that the ‘old’ biomarker, acetylcholinesterase (ACHE), which is sensitive to selected organophosphate and carbamate pesticides, may be responding to low levels of contaminants in the environment, putatively by compounds other than, or in addition to, pesticides. We now provide evidence for such a possibility. A distinct depression of ACHE was found in muscle tissues of trout (Salmo trutta) taken from two urban rivers in St. Johnʹs (Virginia River and Rennieʹs Mill River), in comparison with a nearby reference river (South Brook). Most striking was the fact that depression was observed in the 50% range. A similar high level of enzyme depression was observed in muscle tissues of flounder (Pleuronectes americanus) taken in the area of a pulp and paper mill (Birchy Bay in the Bay of Islands), in comparison with a nearby reference site. Depression of ACHE was associated with induction of MFO enzyme activity (ethoxyresorufin-O-deethylase) in liver tissues of both trout and flounder. We provide evidence and discussion that contaminants other than pesticides, including compounds in complex mixtures of combustion hydrocarbons and natural wood leachate, could be responsible for the depressed ACHE levels observed in our studies (as well as those in the North Sea) and suggest that this old biomarker may have a new future in biological monitoring and assessment programmes.