Effects of terbufos on juvenile red swamp crayfish (Procambarus clarkii): differential routes of exposure

During rain events, terbufos may be transported into aquatic ecosystems via agricultural runoff. Because crayfish are closely associated with sediment, they may be exposed to aqueous terbufos through the gills or by ingesting contaminated sediment, detritus, or plants. Bioavailability of terbufos in food and toxicity of terbufos to crayfish were examined by measuring mortality and acetylcholinesterase (AChE) inhibition and by observing behavior. A 96-h aqueous exposure and a 12-h dietary exposure of juvenile red swamp crayfish, Procambarus clarkii, to terbufos produced median lethal concentrations (LC50s) of 5.9 microgram/L (95% CI: 4.4, 8.1) and 4.4 microgram/g pellet (95% CI: 2.9, 6.7), respectively. Aberrant behavior, such as loss of motor control and equilibrium, was noted at concentrations almost 50% of the aqueous LC50 and 80% of the dietary LC50. As concentration increased, AChE activity decreased and mortality and aberrant behavior increased. I50s, the percentage of AChE inhibition at which 50% of the crayfish died, for aqueous and dietary exposures were 76.5% (95% CI: 67.4, 85.6) and 86.1% (95% CI: 78.1, 94.1) of control activity, respectively. Based on present study results, terbufos is available for uptake by crayfish through ingestion and causes detrimental effects at concentrations less than expected in agricultural runoff