Geochemistry of porewater and sulfate-reducing bacteria in sediment cores from the Chianan Plain, Taiwan

High concentrations of arsenic and humic substances in groundwater from the southwestern coastal plain of Taiwan were well known for their probable relationships with black-foot disease. In order to realize the relationships between the concentrations of humic substances and arsenic in this area, 24 well water samples were analyzed. After filtered through 0.45 μm glass fiber membrane in the field, samples were kept in the dark at 4℃ and then separated into six fractions with varying range of molecular weight （〈0.5, 0.5-1, 1-5, 5-10, 10-50 and 〉50 k Da） by ultrafiltration apparatus （Molecular/Por Stirred Cell system） in the lab. Concentrations of humic substances were measured by fluorescence spectrometer （HITACHI F-2000, ex=370, em=445） and arsenic by FIAS-AA （Perkin Elmer AAnalyst 100, FIAS-400）. On average, only 6.2% of the total arsenic in water existed in the fraction of 〉0.5 k Da. and the others were complexed with humic substances （including humic acid and fulvic acid）. The results demonstrated a distinct positive correlation between the concentrations of humic substances and arsenic.

Geochemistry of porewater and sulfate-reducing bacteria in sediment cores from the Chianan Plain, Taiwan

Putai was one of the four main areas with endemic blackfoot disease in the southwestern coast of Taiwan. It was reported that the disease was caused by drinking groundwater with high concentrations of arsenic and/or humic substances. Recently, many studies have suggested that sulfate-reducing bacteria might be the causative agents involved in arsenic geocycle and the reduction of humic substances. The core sediments collected from Putai were investigated with sulfate-reducing bacteria by PCR amplification of 16S rRNA gene. The results show the common presence of sulfate-reducing bacteria in the depth range from 20 to 248 m. High concentrations of sulfate and organic matter within the densely intercalated layers of clay, silt and fine sand might provide suitable nutrients for the growth of sulfate-reducing bacteria. Three groups of sulfate-reducing bacteria, Desulfovibrio, Desulfomicrobium and Desulfotomaculum, which can reduce arsenate to arsenite, seem common in the sediments containing porewater with high concentrations of arsenic and humic substances. In addition, Desulfobulbus propionicus,