TOXIC ELEMENT CONTAMINATION AND THE OCCURRENCE OF MERCURY-RESISTANT BACTERIA IN HG-CONTAMINATED SOIL, SEDIMENTS, AND SLUDGES

River sediment, sludge, and soil samples were collected and analyzed for Hg, MeHg, Cd, Cr, Cu, Ni, Pb, and Zn. Volatile solids, chloride, sulphate, and sulphide were also assessed. Heavy metal contamination was present in all the samples, particularly soil and sediment. The 'k values for Cu were less than those for Hg and lower for soil than for river sediment. Complexation may be a major factor in Hg methylation as high 'k values reflected low MeHg levels. High chloride concentration was associated with low ratios of methyl to total Hg. Using DNA probe technology, the occurrence of DNA sequences typical of transposons Tn21 and Tn501 were determined for the samples. Observable (phenotypic) Hg resistance was greatest at sites of high Hg and chloride concentrations although genetic variation was greatest in soil and sediment samples with lower Hg concentrations. Isolation of Tn501-like elements increased when Hg was added to the medium. Mercury resistance systems which are not homologous at high stringency to the mer operon appear to be common in soil, activated sludge, and river sediments.