Effects of Aquifer Environmental Factors on Biodegradation of Organic Contaminants

Aquifers in New Mexico are contaminated with a wide variety of organic compounds. Benzene and 1,1,1-trichloroethane (TCA) are frequently detected and represent two major structural contaminant classes, aromatic and chlorinated aliphatic organic compounds, respectively. Important environmental effects on the biodegradation of these two compounds were examined in laboratory batch incubations of regional aquifer material with l4C-radiolabelled benzene and TCA. Redox status, changes in redox conditions, and long and short pre-exposure periods were investigated for their effects on complete biodegradation as indicated by l4CO2 generation over time. Additional variables which were quantified include residual organics in aquifer material, residual volatile organics, and 14C02 incorporated into microbial biomass.

Results showed that significant biodegradation of each contaminant occurred within 40 and 120 days for benzene and TCA, respectively. Starting levels of benzene present in batch aquifer material were reduced by approximately 90% during the incubation period, and TCA levels decreased approximately 80%. Disappearance of both contaminants occurred under aerobic and anaerobic conditions, but the specific biochemical fate of each compound was influenced by the prevailing redox conditions and the length of contaminant pre-exposure.

These results may be useful in establishing boundary conditions to predict biodegradation rates for benzene and TCA by native microbial communities in comprehensive ground water hydrologic models which track the fate of contaminants in New Mexico’s aquifers. Biodegradation is a factor requiring consideration when evaluating the fate of organic contaminants in New Mexico’s aquifers.