Is the methylmercury paradox real ?
Some researchers report that fish swimming in waters with very different levels of mercury contamination can often have similar methylmercury concentrations. Researchers from Rutgers University at New Brunswick believe to have some explanation for such paradox. They have found that the proportion of mercury present as methylmercury is inversely related to the total mercury concentration in natural water.
The authors hypothesize that such methylmercury accumulation paradox is explained by the quantitative induction of bacterial enzymes by inorganic mercury (Hg(II)). The hypothesis was further investigated at two different surface water sites, and it was found that bacteria that efficiently break down methylmercury thrive in the waters of the more contaminated site but are largely absent at the more prestine site. By demethylating mercury, these bacteria can significantly reduce the uptake of mercury into the food web and hence into fish. The action of the water column bacteria may well serve as a kind of natural mercury defense mechanism, reducing the proportion of the methylated mercury. The authors also showed that the absolute concentration of methylated mercury in contaminated water is still higher than in pristine waters.
Jeffra K. Schaefer, Jane Yagi, John R. Reinfelder, Tamara Cardona, Kristie
M. Ellickson, Shoshana Tel-Or, Tamar Barkay, Role of the Bacterial Organomercury Lyase (MerB) in Controlling Methylmercury Accumulation in Mercury-Contaminated Natural Waters, Environ. Sci. Technol., 38/16 (2004) 4304-4311. DOI: 10.1021/es049895w
University of Montana: Biomethylation of metals and metalloids
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Related News Scientific America, March 19, 2002: Organisms in Algae-Rich Lakes May Absorb Less Mercury
last time modified: August 3, 2006