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Filtered extracts were partitioned in acetonitrile, cleaned in a florisil column and concentrated foranalysis according to the methodology described by Robinson (1997). Identification andquantification of residues were done by a Shimadzu 9A gas chromatograph equipped with an FPD.Analytical conditions were: glass column, 1.6 m by 2 mm packed with OV-17; carrier gas, nitrogen,at a flow rate of 30 - 35 mL/min; temperature settings - column 230 o C, injector and detector 260 o C.Detection levels ranged from 0.001 - 0.002 ng.Fish exposed to 0.005 mg/L chlorpyrifos in fresh water accumulated only 35% (1.35 mg/g) of theinsecticide within the first 2 hr. Accumulation fluctuated thereafter, reaching a maximum of 3.87mg/g after 48 hr of exposure followed by a decline within the next 48 hr to 2.45 mg/g. At higherconcentration (0.05 mg/L), there was rapid accumulation of chlorpyrifos by the fish as 51% (0.86mg/g) of the total 72-h accumulation of the insecticide was achieved after 1 hr of exposure. Uptakethen fluctuated before rapidly increasing to1.68 mg/g at the end of the 72-hr exposure period.There was a two-fold accumulation of chlorpyrifos by fish in brackish water compared with freshwater as maximum bioconcentration (0.96 mg/g) in brackish water was achieved after 1 hr ofexposure. Accumulation of the insecticide subsequently declined to 0.39 mg/g at the end of the 72-hrexposure period (Table). An unidentified organophosphorus metabolite of chlorpyrifos was alsodetected within 1 - 2 hr of exposure to the insecticide in fresh and brackish water.The rapid uptake of chlorpyrifos by Tilapia is consistent with the relatively high octanol-waterpartition coefficient (logKow = 4.82) of the insecticide which suggests that it readily partitions in fishtissues. Although the rapid formation of the metabolite implies that the chemical is quicklybiotransformed, the toxicity of this metabolite to the fish is unknown. Thus, further studies areneeded, including the elimination of the parent compound and its metabolite by the fish.ReferencesMansingh, A., Robinson, D.E. and Dalip, K.M. (1997). Insecticide contamination of the Jamaicanenvironment, Trends in Anal. Chem. 16 (3): 115-123.Robinson, D. E., Mansingh, A. and Dasgupta, T. P. (1997) Fate of endosulfan in river and coastalwaters of Jamaica. Proc. Int. Symp. on the Use of nuclear and related techniques forstudying environmental behaviour of crop protection chemicals, IAEA, Vienna, July 1 - 5,1996. pp. 301-311.Robinson, D.E. (1997). The fate, biological impact and management of endosulfan andethoprophos in the Jamaican environment. Ph. D. Thesis. Univ. West Indies, Mona,Jamaica. 289 pp.Witter, J.V., Robinson, D.E., Mansingh, A. and Dalip, K.M. (1998). Insecticide contamination ofJamaican environment. V. Island-wide rapid survey of residues in surface and groundwater. Environ. Monitor. & Assess. (In press).33