Isolation of mercury resistant bacteria and influence of abiotic factors on bioavailability of mercury -- a case study in Pulicat Lake North of Chennai, South East India.

Pulicat Lake sediments are often severely polluted with mercury compounds and other toxic heavy metals. Several mercury-resistant bacteria were isolated and identified from the sediments and all the isolates exhibited broad spectrum resistance (both organic and inorganic mercuric compounds). Mercury volatilization showed that four of the isolated Bacillus cereus strains were able to reduce water soluble ionic form of mercury into volatile form via the well known enzymatic reduction. The effect of increasing concentration of mercuric chloride and phenyl mercuric acetate in the growth of this mercury reducing strain was also determined. To study the native physico-chemical parameters, which influence the bioavailability of mercury to bacteria in Pulicat Lake ecosystem, a total of 60 water and 30 sediment samples were collected and analyzed for pH, temperature, dissolved oxygen, salinity, nitrate, nitrite, silicate, phosphate, organic matter and organic carbon. Increased levels of phosphate, nitrite, nitrate, silicate, organic matter and organic carbon during the post monsoon reduce the bioavailability of mercury by forming complexes which may increase the concentration of mercury in the sediments during post monsoon.