Screening of Fish Tissue for Methyl Mercury Using the Enzyme Invertase in a Solvent Interface

Abstract.

This paper describes a simple and rapid screening system for the extraction and determination of methyl mercury in tissue samples from fish. A novel clean-up procedure based on the use of two immiscible phases, an organic one containing methyl mercury and an aqueous one containing invertase, was developed. Methyl mercury was selectively extracted from the organic into the aqueous phase by its irreversible reaction with thiol groups of invertase, and the resulting inhibition of enzymatic activity served as a measure of methyl mercury concentration. Enzyme activity was measured with a spectrophotometric method using 3,5-dinitrosalicylic acid as a reagent. After parameter optimisation including pH, substrate concentration, and enzyme reaction time, it was possible to determine methyl mercury in the ppb range with this technique. Concentrations as low as 10 ppb of methyl mercury in the extract, corresponding to 0.2 ppm of methyl mercury in fish, were detected. The proposed procedure was successfully demonstrated as a simple screening method for methyl mercury in fish samples.