Bioaugmentation of Atrazine and Fenamiphos Impacted Groundwater: Laboratory Evaluation

Abstract

After the failure of a three-month pump-and-treat exercise to clean up an aquifer contaminated with the pesticides atrazine and fenamiphos, microcosm experiments using ¹⁴C-labeled compounds were undertaken to determine under what conditions bioremediation would be most effective, and to investigate the prospects for the use of bioaugmentation. The calculated half-lives for atrazine and fenamiphos mineralization to carbon dioxide in unamended, anaerobic aquifer material were 730 and 1,000 years, respectively. Oxygenation, coupled with bioaugmentation with enrichments of atrazine-mineralizing bacteria obtained from the contaminated site or an imported, atrazine-mineralizing pure strain, Pseudomonas sp. strain ADP, decreased the half-life of atrazine mineralization, to >20 days. Although strain ADP does not use atrazine as a source of carbon and energy, amendment of the aquifer material with citrate, which strain ADP uses as a source of carbon and energy, did not appreciably stimulate the mineralization rate of atrazine in the microcosms, suggesting that the aquifer contains enough natural organic carbon for atrazine mineralization. Aerobic enrichments of fenamiphos-degrading bacteria were prepared; however, oxygenation and bioaugmentation of aquifer material with these strains did not enhance mineralization of fenamiphos within the time constraints of the experiments. The shortest calculated half-life of fenamiphos mineralization in the microcosms was 6.8 years, which is exceedingly long compared with the half-life of fenamiphos in most surface soils.