Potential use of cholinesterase in monitoring low levels of organophosphates in small streams: Natural variability in three-spined sticleback (Gasterosteus aculeatus) and relation to pollution

The potential use of cholinesterase (ChE) in body muscle of three-spined st ickleback (Gasterosteus aculeatus) as a biomarker of organophosphate (OP) c ontamination was investigated. Fish were sampled from nine headwater stream s directly after the main application period (July 1995) and 2 months after the end of OP use (October 1995). Cholinesterase activity was inversely re lated to fish weight. Muscle ChE was comprised of both acetylcholinesterase and pseudocholinesterase. In July, fish from two sites (A and B) had signi ficantly lower (similar to 30%) ChE activities than fish from all but one o f the other sites. In October, the range of ChE activities was similar to t hat observed in July; however, no site significantly differed from the majo rity of other sites. The OP parathion was detected in suspended particulate s at sites A and B. This suggests that decreased ChE in July reflects OP ex posure. Because sampling of suspended particulates at site A occurred with a higher resolution than at the other sites and because decreases were clos e to the natural variability, however, this relationship cannot be demonstr ated with certainty. The reported characteristics of ChE and its natural va riability in stickleback represent baseline data for its use in the monitor ing of OP contamination of small streams.