HETEROTROPHIC ACTIVITY OF MICROORGANISMS IN SOILS TREATED WITH QUATERNARY AMMONIUM-COMPOUNDS

In situ soil modification using quaternary ammonium compounds (QACs) enhances the immobilization of organic contaminants. The feasibility of coupling contaminant immobilization with subseqeunt bioremediation was assessed in biodegradability tests of C-14-labeled organic compounds in QAC-treated soils. Aqueous hexadecyltrimethylammonium (HDTMA) bromide added to soils caused increased lag periods and decreased rates and extents of mineralization of test compounds as a result of selective toxicity toward Gram-negative soil microorganisms. Toxic effects were more pronounced at higher HDTMA treatment levels and with more complex test substrates. Once bound to soil or clay, HDTMA toxicity was greatly reduced. Hence, biodegradation improved when HDTMA was introduced to soil in a prebound form, when sterile soils preequilibrated with HDTMA were reinoculated with active soil organisms, or when an HDTMA-degrading bacterial isolate was introduced to scavenge residual, unbound HDTMA. Dioctadecyldimethylammonium (DODMA) bromide was approximately 10-fold less toxic to the Gram-negative organism, Pseudomonas putida, and was less inhibitory to native naphthalene-degrading organisms in soil than HDTMA.