Methylated arsenic, antimony and tin species in soils.
Methylated species of antimony, arsenic and tin were examd. in urban soils of the Ruhr basin, near the cities of Duisburg and Essen, Germany. The main aim of this study was to study the occurrence of mono-, di- and trimethylated species of these elements in urban soils. The influence of historical and present land use upon the species content was examd. The distribution of inorg. As, Sb and Sn and their methylated species along the profile depth was studied. As, Sb and Sn speciation was performed by pH-gradient hydride generation purge and trap gas chromatog., followed by inductively-coupled plasma mass spectrometry (HG-PT-GC/ICP-MS). Species' structures were confirmed by GC-EI/MS-ICP-MS. Monomethylated Sb and As were the dominant species detected: the concn. of these metal(loid) species varied between <0.07-56 mg/kg per dry mass. All dimethylated species and monomethyltin concns. were between <0.01-7.6 mg/kg per dry mass, and for the trimethylated species of all examd. elements, concns. between <0.001-0.63 mg/kg per dry mass were detected. The highest organometal(loid) concns. were obsd. in agricultural soils and garden soils; lower concns. were found in the soils of abandoned industrial sites (wasteland, primary forest and grassland) and a flood plain soil of the Rhine. This result can be ascribed to both the cultivation and the increased biol. activity of the agricultural soils, and the generally higher contamination, the disturbed structure and the artificial substrates (deposits from industrial sources) of the abandoned industrial soils. Due to periodical sedimentation, the flood plain profile was the only one where no depth dependence of organometal(loid) species concn. was detected. The other soil profiles showed a decrease of species content with increasing depth; this was particularly noticeable in soils with a clear change from a horizon with an org. character towards a mineral horizon, i.e. decreasing vitality from profile top to bottom. It is not as yet clear whether the organometal(loid) species are formed in the mineral horizons of the profiles or whether they are displaced from the org., biol.-active horizons towards the mineral horizons. Field studies revealed that soil parameters like pH, water content or temp. did not correlate significantly with the degree of biomethylation obsd. In contrast to the lower in vitro biomethylation efficiency of Sb vs. As in microbial incubations, the authors consistently detected higher proportions of transformed Sb compds. in situ in soil samples. These data may indicate a need to reexamine the currently accepted model of Sb biogeochem. cycling in the real environment.
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