Hollibaugh, J T; Miller, L G; Maest, A S; Steinberg, N A; Oremland, R S 



Measurement of In Situ Rates of Selenate Removal by Dissimilatory Bacterial 
Reduction in Sediments|



Vol. 24, No. 8, p 1157-1164, August 1990. 6 fig, 4 tab, 35 ref. 1990|



   Oxyanions of selenium have been identified as toxic constituents in 
drainage waters from irrigated, seleniferous agricultural soils. Recently a 
novel process was reported by which anaerobic bacteria respire selenate, which 
in turn biochemically reduces this oxyanion to selenite and ultimately to 
elemental selenium. An understanding of how this process of dissimilatory 
selenate reduction operates should ultimately aid in the design of treatment 
schemes and the rehabilitation of selenate contaminated regions. 
Accordingly, a radioisotope method for measurement of bacterial respiratory 
reduction of selenate to elemental selenium in aquatic sediments was 
devised. Sediments were labeled with Se75 selenate, incubated, and washed, and 
Se75(s) was determined as counts remaining in the sediment. Core profiles of 
selenate reduction, sulfate reduction, and denitrification were made 
simultaneously in the sediments of an agricultural wastewater evaporation 
pond. Most of the in situ selenate reduction (85%) and all the denitrification 
activities were confined to the upper 4 to 8 cm of the profile whereas sulfate 
reduction was greatest below 8 cm (89% of total). The integrated areal rate of 
selenate reduction was 301 micromoles/sq m/day, which results in a turnover of 
water column selenate in 82.4 days. The rate of selenate reduction in 
sediments was enhanced in laboratory experiments by provision of the proper 
electron donors (e.g., acetate, lactate, hydrogen, etc.). When this is done in 
conjunction with removal of competitive electron acceptors like fertilizer-
derived nitrate, a treatment scheme can be envisioned.

 

Anaerobic bacteria Drainage water Fate of pollutants Path of; pollutants 
Radioactive tracers Sediment chemistry Selenium; Wastewater treatment Water 
pollution treatment Agricultural; water Denitrification Heavy metals 
Radiochemical analysis; Selenium radioisotopes Soil treatment.