Acetylcholinesterase inhibition as a biomarker of adverse effect. A study of Mytilus edulis exposed to the priority pollutant chlorfenvinphos

The inhibition of acetylcholinesterase (AChE) activity has been used widely as a biomarker of exposure to organophosphorous pesticides (OPs). However, scientific uncertainty about the risk assessment implications of data describing inhibition of cholinesterases in diverse species and tissues has hampered the use of AChE activity as a biomarker of adverse effect. Here, haemolymph AChE activity was combined with biomarkers of cellular integrity, immunotoxicity and physiological status in order to measure exposure to and the effects of the priority pollutant chlorfenvinphos. Laboratory exposures of the blue mussel Mytilus edulis to commercial grade chlorfenvinphos (Sapecron) were conducted over 24, 48 and 96 h. AChE activity in haemolymph of M. edulis was highly variable and bore no relationship to either sublethal effects or lethality over the range 0.003-0.03 mg/l chlorfenvinphos. In comparison, concentration dependent inhibition was evident for each of the remaining biomarkers (phagocytic activity, spontaneous cytotoxicity, neutral red retention time, total haemolymph protein). Mussels at the highest exposure concentration showed visual signs of neurotoxicity (impaired neuromuscular control). Haemocyte phagocytic activity and spontaneous cytotoxicity responses were highly sensitive to chlorfenvinphos with significant modulation evident after 24 h exposure to environmentally realistic concentrations of 0.007 mg/l (P = 0.0003). Thus the immune function and well being of the mussels was significantly impacted in the absence of measurable inhibition of haemolymph AChE.