ACCUMULATION OF MERCURY(II) AND METHYLMERCURY BY MICROBIAL BIOFILMS

Several experiments were carried out in order to investigate the interactions of mercury(II) and methylmercury with microbial biofilms. The biofilms, mainly consisting of polysaccharides, were produced on glass slides in bacterial cultures spiked with different mercury compounds. The formation of the biofilm was determined as carbohydrate by the phenol-sulfuric acid method. Total mercury was measured after BrCl oxidation by CVAAS and methylmercury was extracted by a modified procedure and quantified by HPLC-u.v. Mercury(II) as well as methylmercury were accumulated by microbial biofilms, but no significant differences could be detected regarding the uptake of these compounds during the observation period of 2 weeks. The methylmercury content in the bacterial cultures declined after spiking. The reason for the decrease can be explained either by adsorption processes or by demethylation/reduction reactions followed by volatilization of produced Hg(O). Bioconcentration factors (BCF) for methylmercury were determined and are in the range 20,000-50,000. The BCF is calculated as the ratio of the methylmercury content in the biofilm expressed as carbohydrate and the actual concentration of methylmercury in the bacterial culture.