抄録
The microbial activities in aquatic environments significantly influence arsenic cycles such as turnover between inorganic arsenic and organoarsenic compounds. In Lake Kahokugata, the inorganic arsenic was detected through all season, while the dimethylarsinic acid (DMAA) produced by microorganisms such as phytoplankton detected only at winter. Consequently, the changes in the methylarsenic species concentration did not correlate with the changes in phytoplankton abundance (chlorophyll a contents). The lake water spiked with 1 μmol/l of DMAA indicated the DMAA-diminish and the increase of inorganic arsenic under dark and anaerobic condition. Contrary, the lake water under aerobic or light condition did not show the DMAA-diminish. The lake water that bacterial activities were eliminated by filtration, NaN3 addition and autoclave-sterilization also did not show the DMAA-diminish, indicating that anaerobic bacteria would degrade DMAA in the lake water. Moreover, the incubation at 30 °C, the water samples collected in summer rapidly degraded 1 μmol/l of DMAA within 7days. In the lake water collected in winter incubated at 4 °C, DMAA-degradation did not observed. Presumably, the DMAA-biodegradation activities in the natural lake water of Kahokugata seasonally change depending on water temperatures and several degrees of DMAA-degradation activities influence the seasonal changes of concentrations of arsenic compounds.
