Background

Perchlorate (ClO4-) is a rapidly emerging environmental contaminant in California. In the past several years, perchlorate contamination has been found in soil and water resources throughout the U.S., mainly in the Southwest and California. Past improper disposal of ammonium perchlorate, an oxygen additive in solid rocket propellants, has resulted in groundwater and soil contamination. Perchlorate salts also have been manufactured for various uses including highway safety flares, airbags, fireworks, matches, etc. Perchlorate is very mobile and persistent in the environment and known to interrupt thyroid hormone production.

Currently, biological treatment is one of the most promising technologies to clean-up perchlorate contamination. Pure culture and bioreactor studies have demonstrated the biodegradation (reduction) of perchlorate to innocuous chloride under anaerobic conditions. However, although the vadose (unsaturated) zone is a substantial source of groundwater and surface water perchlorate contamination, little is known about the potential perchlorate-reducing microorganisms in native soil microbial communities in this vadose zone.

Aim

Our research goals are 1) to evaluate the potential of native vadose zone microbial communities to reduce perchlorate to chloride, in conjunction added electron donors such as acetate and hydrogen, 2) to detect, identify, and quantify growth of microbial populations involved in perchlorate degradation under different conditions, 3) to measure the inhibitory effect of nitrate, a competitive electron acceptor for perchlorate reduction, and 4) to explore the relationship between nitrate-reducing (denitrifying) and perchlorate-reducing microorganisms.