ARSENATE INHIBITION OF DENITRIFICATION IN NITRATE CONTAMINATED SEDIMENTS

Short-term and chronic exposure effects of arsenic on sediment denitrification were evaluated. N2O production rates were determined for As-contaminated (chronic treatment) and uncontaminated (short-term treatment) sediments exposed to a range of As concentrations. The As-containing sediments, collected from an herbicide-contaminated shallow aquifer, exhibited significantly lower rates of denitrification with increasing As concentration. With glucose amendment, denitrification rates were ca 10 nmol N2O g-1 h-1 higher than in unamended treatments, but a similar trend of decreasing N2O production with increasing As concentration was observed. For the uncontaminated sediment, short-term increases in As concentration reduced the rate of denitrification only under glucose amended conditions. This response suggests that carbon limitation is also an important factor influencing denitrification in these sediments. These results indicate that by inhibiting the denitrification potential of the in situ microbial community, As contamination may contribute to nitrate accumulation in shallow aquifers, which underlie cultivated land.