Gamma aminobutyric acid radioreceptor assay: A confirmatory quantitative assay for toxaphene in environmental and biological samples

Abstract

Toxaphene is a complex mixture of polychlorinated monoterpenes. Before its ban in 1982, it was the most heavily used insecticide with a cumulative world use of 409,000 metric tons. Toxaphene was found to be acutely and chronically toxic to aquatic and wild life and poses a carcinogenic risk to humans. Although the use of toxaphene has been severely limited or eliminated, it is still found in the environment due to its relative persistence with an estimated half life time of about 10 years in soils. Residue analysis of toxaphene in environmental and biological samples rely mostly on instrumental analysis such as gas chromatography (GC) and gas chromatography with mass spectrometry. These require 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 toxaphene products. Although toxaphene is a mixture of more than 200 isomers its neurotoxicity is only attributed to few isomers with a mode of action through binding to the chloride channel of the gamma-aminobutyric acid (GABA) receptor ionophore complex. [ 35S] tertiary butylbicyclophosphorothionate (TBPS) with specific activity higher than 60 Ci/mmole has a high binding affinity to the same sites and is now commercially available and can be used to label the GABA receptor for the development of radioreceptor assay technique. The GABA receptor was prepared by a sequence of ultra centrifugation and dialysis of mammalian (rats, cows, catfish and goats) brain homogenates. The receptor is then labeled with [ 35S] TBPS and the assay was conducted by measuring the displacement of radioactivity following incubation with the sample containing the analytes. The assay is fast, sensitive and requires very little or no sample preparation prior to the analysis.