Phytoremediation of Soil Contaminated with Used Motor Oil: I. Enhanced Microbial Activities from Laboratory and Growth Chamber Studies

Abstract

Used motor oil is a common and toxic environmental contaminant, and technologies for its remediation vary in success. The degradation of used motor oil in soil as affected by plant treatment ("phytoremediation") was assessed in a growth chamber study. Seed germination of several grass, legume, and cereal species declined with an increase in used oil concentration; at oil rates greater than 1.0% (w/w), decreases in germination for most species were significantly (p < 0.05) below control rates. Green beans (Phaseolus vulgaris), soybeans (Glycine max), and maize (Zea mays) germinated better than other treatments at used oil concentrations up to 10% (w/w). In terms of both germination and overall growth, leguminous plants were generally more resistant to used oil contamination than nonleguminous species. The used oil contained lead, cadmium, barium, and other potentially toxic metals; however, uptake by the study plants was negligible. Bacteria were the most abundant microbial group in oil-contaminated soil (factor 10⁸) compared to actinomycetes and fungi (10⁷ and 10⁶, respectively). Soil microbial populations experienced exponential growth until 50 days, after which numbers returned to precontamination levels. Grampositive bacteria predominated in contaminated soils under mixed clover, mixed grass, and alfalfa (Medicago sativa) treatments. A number of hydrocarbon-degrading species were identified. Species of Brevibacterium and Bacillus were common in most treatments. Cumulative soil respiration increased by 43% over 28 days when used oil was added to soil microcosms. Respiration was not, however, significantly enhanced in the presence of either raw or autoclaved root tissue.