GAMMA-AMINOBUTYRIC-ACID RADIORECEPTOR ASSAY - A CONFIRMATORY QUANTITATIVE ASSAY FOR TOXAPHENE IN ENVIRONMENTAL AND BIOLOGICAL SAMPLES

Toxaphene is a complex mixture of polychlorinated monoterpenes. Before its ban in 1982, it was the most heavily used insecticide with a cumu lative world use of 409,000 metric tons. Toxaphene was found to be acu tely and chronically toxic to aquatic and wild life and poses a carcin ogenic risk to humans. Although the use of toxaphene has been severely limited or eliminated, it is still found in the environment due to it s relative persistence with an estimated half life time of about 10 ye ars in soils. Residue analysis of toxaphene in environmental and biolo gical samples rely mostly on instrumental analysis such as gas chromat ography (GC) and gas chromatography with mass spectrometry. These requ ire extensive sample clean up. These instrumental analyses still have a problem of interference from other chlorinated hydrocarbons, mainly PCBs and DDT metabolites, and may not detect environmentally altered t oxaphene products. Although toxaphene is a mixture of more than 200 is omers its neurotoxicity is only attributed to few isomers with a mode of action through binding to the chloride channel of the gamma-aminobu tyric acid (GABA) receptor ionophore complex. [S-35] tertiary butylbic yclophosphorothionate (TBPS) with specific activity higher than 60 Ci/ mmole has a high binding affinity to the same sites and is now commerc ially available and can be used to label the GABA receptor for the dev elopment of radioreceptor assay technique. The GABA receptor was prepa red by a sequence of ultra centrifugation and dialysis of mammalian (r ats, cows, catfish and goats) brain homogenates. The receptor is then labeled with [S-35] TBPS and the assay was conducted by measuring the displacement of radioactivity following incubation with the sample con taining the analytes. The assay is fast, sensitive and requires very l ittle or no sample preparation prior to the analysis.