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Mercury methylation in macrophytes, periphyton, and water - comparative studies with stable and radio-mercury additions

“…The radiolabelled mercury assay, in accordance with previous mercury methylation studies [5,6,7,8,9,11,45], revealed that large amounts of methylmercury were formed for the four aquatic macrophytes species studied (Fig. 1).…”

“…Investigations in Brazilian wetlands suggest that methylmercury formation might be considerably higher in the tropics. The presence of the roots of different species of living or decomposing, floating or rooted macrophyte mats particularly enhances Hg methylation compared with the surface of underlying lake sediments or floodplain sediments [5,6,7,8,9]. In the Tapajós river floodplain determination of natural methylmercury, and net 203 Hg(II) methylation essays, applied to the same lake-forest transect, both suggested that production and accumulation of methylmercury were highest in macrophyte mats and flooded forest soils [10,11].…”

“…The macrophyte roots provide a suitable environment for dense periphyton growth, including sulfate-reducing bacteria [9] which are considered the most important biotic mercury methylators [12]. In this context, the term periphyton is defined as the "living, senescent and dead autotrophic (microalgae) and heterotrophic microorganisms (bacteria, fungi, protozoa and micrometazoa) and fine particulate matter, enveloped in a polysaccharide matrix of biological origin" [13].…”

“…In this context, the term periphyton is defined as the "living, senescent and dead autotrophic (microalgae) and heterotrophic microorganisms (bacteria, fungi, protozoa and micrometazoa) and fine particulate matter, enveloped in a polysaccharide matrix of biological origin" [13]. The macrophytes can thus be regarded as a relevant mercury methylation site for tropical ecosystems [5,6,7,8,9], and this might also explain the high methylmercury formation and bioaccumulation potential of temperate wetland areas [14,15].…”

“…Studies have also been conducted in a freshwater lagoon in SE Brazil, the Lagoinha [8,9], using the water-hyacinth Eichhornia crassipes, which is also one of the macrophytes present in the ENR. It should be noted that hitherto all mercury methylation studies using aquatic macrophytes have been performed using a radiochemical technique.…”