BIOTRANSFORMATION OF MERCURY COMPOUNDS BY ENVIRONMENTAL MICROORGANISMS

Abstract

Forty bacteria species commonly found in soil, sediments, and sewage effluent were exposed for acclimation to inorganic and organic mercury compounds using sterilized sediments as the culture medium. Screening tests for the ability of microorganisms to methylate inorganic mercury were made on all 40 species after acclimation to 13.5 mg/I mercuric chloride. Additional screening tests for demethylation of methylmercuric chloride were carried out with 21 acclimated microorganisms in sediments containing 2.5 mg/I methyI-mercuric chloride. Sediments and trap solutions were tested for total mercury, alkylmercury and dialkylmercury compounds using flameless atomic absorption, gas chromatography and a combination of gas chromatography-atomic absorption, respectively. 22-52% reduction in total inorganic mercury was observed in some bubblers containing microorganisms, indicating vaporization of metallic mercury. None of the microorganisms screened was able to methylate mercury; however, 16 aerobes and 1 anaerobe demonstrated the ability to demethylate methylmercuric chloride. Demethylation by individual organisms ranged from 32% to 84% of the initial dose after 16 days of experimentation. Tests for the formation of alkylmercurials and dialkylmervury compounds were negative in all cultures.