Comparative thresholds for acetylcholinesterase inhibition and behavioral impairment in coho salmon exposed to chlorpyrifos

Abstract

Chlorpyrifos is a common organophosphate insecticide that has been widely detected in surface waters that provide habitat for Pacific salmon in the western United States. Although chlorpyrifos is known to inhibit acetylcholinesterase (AChE) in the brain and muscle of salmonids, the relationship between sublethal AChE inhibition and more integrative indicators of neuro-behavioral impairment are poorly understood. This is particularly true for exposures that reflect the typical range of pesticide concentrations in the aquatic environment. To directly compare the effects of chlorpyrifos on AChE activity and salmon behavior, we exposed juvenile coho salmon (Oncorhynchus kisutch) to chlorpyrifos (0-2.5 microg/L) for 96 h. A computer-assisted, three-dimensional video imaging system was used to measure spontaneous swimming and feeding behaviors in control and chlorpyrifos-exposed fish. After the behavioral trials, brain and muscle tissues were collected and analyzed for AChE activity. Chlorpyrifos inhibited tissue AChE activity and all behaviors in a dose-dependent manner. Moreover, brain AChE inhibition and reductions in spontaneous swimming and feeding activity were significantly correlated. Benchmark concentrations for sublethal neurotoxicity (statistical departure values) were <0.5 microg/L and were similar for both neurochemical and behavioral endpoints. Collectively, these results indicate a close relationship between brain AChE inhibition and behavioral impairment in juvenile coho exposed to chlorpyrifos at environmentally realistic concentrations.

Maternal transfer of xenobiotics and effects on larval striped bass in the San Francisco Estuary

“…Concentrations of individual contaminants and mixtures determined in this study have been shown to have adverse effects in a wide range of animals, including mammals, reptiles, amphibians, and fish (20)(21)(22)(23). Some of the effects described are as follows: alterations of growth and development (24), poor hatching success (22), alterations of the reproductive and nervous system (25,26), learning and behavioral deficits retained throughout life (27,28), abnormalities of the liver and other organ systems (29,30), and endocrine disruption (29,31). Studies have also shown that these contaminants in combination can increase adverse effects by several orders of magnitude (32,33).…”

Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States

“…Several studies have linked effects of CPY on the sensory epithelium and behavior to inhibition of AChE. Working with juvenile Coho salmon ( Oncorhynchus kisutch ) exposed to CPY at concentrations between 0.6 and 2.5 μg L −1 , Sandahl et al ( 2005 ) showed that spontaneous swimming rate and food strikes were correlated (r 2 0.58 and 0.53, respectively) with inhibition of AChE activity in the brain. Other studies of effects of CPY in the same species showed that thresholds for different behaviors were related to inhibition of AChE (Tierney et al 2007 ).…”

Risks of carbamate and organophosphate pesticide mixtures to salmon in the Pacific Northwest

“…Although herbicides could indirectly affect salmonids via effects to algae and plants, direct effects to fish from these pesticides are much less likely. In contrast to the other pesticide groups, carbamates and organophosphate pesticides are highly toxic to salmonids (Beauvais et al 2000(Beauvais et al , 2001Sandahl and Jenkins 2002;Sandahl et al 2005;Laetz et al 2009;NOAA 2009) and were frequently detected in the Washington State WRIAs from 2003 to 2007. Thus, carbamate and organophosphate pesticides are the pesticides of greatest concern for direct effects to Pacific salmonids.…”

“…Inhibition of AChE activity occurs in the central nervous system (CNS) and in the plasma and muscle of fish (Perkins and Schlenk 2000). Studies with a number of carbamate and organophosphate pesticides (e.g., azinphosmethyl, chlorpyrifos, malathion, diazinon, carbaryl) have demonstrated an association between inhibition of brain AChE activity and behavioral endpoints such as reduction in spontaneous swimming and feeding rates, swimming stamina, predator detection, and homing behavior (Post and Leasure 1974;Moore and Waring 1996;Van Dolah et al 1997;Beauvais et al 2000Beauvais et al , 2001Scholz et al 2000;Sandahl et al 2005;Labenia et al 2007).…”