engleski

Methyltins distribution and behaviour in marine environment; In situ study of tin methylation in sediment and porewater

The speciation of Sn plays a crucial role in its ecotoxicological behaviour ; while inorganic Sn is considered as non-toxic, the organotin compounds (OTCs), especially trisubstituted species, are highly toxic to living beings. Among all OTCs, only methyltins (MeTs) are not exclusively of anthropogenic origin because they can be formed in nature by the methylation process. Although it is known that some microorganisms successfully perform biomethylation of Sn, this process and its significance in the environment have not been fully elucidated so far. The aim of this study was to evaluate the behaviour of MeTs in the marine environment. This was accomplished by in situ investigation of methylation of Sn in surface sediments and corresponding porewaters, both in oxic and anoxic conditions. In addition, the distribution of MeTs in surface sediment and seawater collected at 59 locations along the Croatian Adriatic coast was determined. To access the Sn methylation activity in marine sediments, the MeTs transformations were determined in incubated sediment and porewater samples, isolated from surface oxic (0-2 cm) and anoxic (10-12 cm) sediment layers of two different cores. The results obtained after three days of incubation demonstrated that methylation of Sn in marine sediments occurred under both oxic and anoxic conditions, being particularly efficient in porewaters, while the methylation activity decrease with increasing number of methyl groups bound to Sn atom. The methylation rate constants, calculated following a first-order kinetic model, demonstrated that the methylation of inorganic Sn to MMT is 5-15 times faster than the methylation of MMT to DMT, while the methylation process is more successful in oxic than in anoxic conditions. The determination of MeTs concentrations in surface sediments and seawater samples collected at various coastal areas revealed that MeTs, mostly MMT and DMT, were present only in seawater, in the concentrations ranging from 0.38 to 14.3 ng(Sn) L-1, but not in sediments (they were detected in sediments at only two locations). This finding strongly suggests that MeTs, due to their solubility and low affinity for adsorption onto particulate matter, are transferred into the water column shortly after being formed in sediments.

methyltins (MeTs) ; biomethylation ; sediments ; porewater

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