DETERMINATION OF MONOMETHYLCADMIUM IN THE ENVIRONMENT BY DIFFERENTIAL-PULSE ANODIC-STRIPPING VOLTAMMETRY

A differential pulse anodic stripping voltammetric (DPASV) method was used to differentiate between the cadmium species Cd2+ and MeCd(+) (Me = methyl) in aquatic systems. These two species show peaks in the DPA SV voltammogram which differ by 112 mV. In model experiments, it was d emonstrated that monomethylcadmium is not stable at pH 2, but under hi gher pH conditions, normally found in fresh and ocean water samples, t he identity of MeCd(+) was verified by different investigations, inclu ding cyclic voltammetry, selective extraction of a complex of diethyld ithiocarbamate with MeCd(+) into n-hexane, and photochemical dissociat ion of MeCd(+) by UV irradiation. It was also shown that humic acids d o not influence the voltammetric determination of monomethylcadmium, F or the first time, it was possible to analyze MeCd(-) in environmental samples. During different expeditions with the German research vessel Polarstern, monomethylcadmium could be determined above the detection limit of 470 pg L(-1) in nearly all surface water samples of the Sout h Atlantic with spot concentrations of up to about 700 pg L(-1), where as in the North Atlantic only 15-30% of the total samples showed MeCd( +) concentrations above this limit. The existence of MeCd(+) in the re mote area of the South Atlantic, as well as positive correlations with the local bioactivity in the ocean, indicates biomethylation as the m ost probable formation process for this methylated cadmium species. Th is assumption is supported by the simultaneous occurrence of other met hylated heavy metal compounds, such as Me(3)Pb(+). Up to 48% of the to tal cadmium was found to be monomethylcadmium in some Arctic meltwater ponds.