Comparison of enzyme-based and instrumentation-based measurement of methyl mercury in lepomis sunfish tissue

Mercury levels have increased in our atmosphere and hydrosphere with anthropogenic inputs from burning fossil fuels and wastes.   In aquatic systems, inorganic mercury is converted by bacteria into methyl mercury, a pollutant of tremendous concern because it can be introduced and biomagnified into many trophic levels. We have measured the amounts of methyl mercury in fish tissue using a protocol based on the inhibition of Invertase enzymatic activity by the binding of methyl mercury (Mohammadi et al. (2005) Microchim Acta 149: 251- 257).  As part of the protocol, methyl mercury chloride (mmc) standards, dissolved in toluene, were layered over Invertase solutions and allowed to equilibrate before enzyme activity was measured. The inhibition curve of enzyme activity versus mmc standards when plotted as reciprocals (modified Lineweaver-Burk plot) was linear from 20 ppb up to 100 ppb, but showed different sensitivity at lower concentrations. Determination of the methyl mercury from fish tissue followed similar protocols; however, the amounts of methyl mercury extracted from tissue and observed with the enzymatic assay were not as high as mercury measurement obtained by direct mercury analysis of tissue using a Milestone DMA-80. The results of these experiments and future options will be discussed.