Controlled laboratory microcosms were used to research the phytoremediation potential of lupines (Lupinus chamissonis) for hydrocarbon-contaminated groundwater at a former oil field near Guadalupe, California. During oil production in the Guadalupe Oil Field, a kerosene-like
hydrocarbon mixture was used as a diluent to improve the flow of the heavy crude oil. Leaking tanks and pipes resulted in diluent contamination in the soil and groundwater. Native plant species were planted at a pilot-scale field site to investigate the feasibility of using phytoremediation
to remediate the groundwater contamination. In the field, biological and hydrological factors make it difficult to determine the specific contributions of individual plant species to hydrocarbon degradation. To overcome the variability of the field site, laboratory experiments with plants
grown in glass containers were conducted to examine and quantify the role of plants in contributing to hydrocarbon biodegradation. Earlier experiments, using Salix lasiolepis (Arroyo willows), indicated increased hydrocarbon biodegradation with willows present. Since L. chamissonis
plants are a prevalent native species at the site, and because of their potential for nitrogen fixation, the present laboratory study was undertaken to evaluate the contribution of L. chamissonis to phytoremediation and to compare L. chamissonis and S. lasiolepis results.
Hydrocarbon-contaminated groundwater from the field site with an initial total petroleum hydrocarbon (TPH) concentration of 5.5 mg/L was recirculated through 1-gallon glass soil chambers for 105 days under conditions mimicking site conditions. Chambers were established in triplicate with
1) soil with active bacteria and one L. chamissonis plant, 2) soil with active bacteria, and 3) sodium azide inhibited soil. Biodegradation was monitored using gas chromatography/mass spectrometry (GC/MS) to determine TPH concentrations on days 0, 24, and 105. TPH concentrations
in the L. chamissonis and soil-only chambers were not significantly different from each other after 24 days, suggesting the L. chamissonis did not contribute to bioremediation under these conditions. After 105 days, the final TPH concentrations were 0.95 ± 0.22 for the
sodium azide inhibited, 0.67 ± 0.085 for the soil only, and 0.33 ± 0.12 mg/L for the L. chamissonis chambers. Thus, final residual TPH concentrations in the chambers planted with L. chamissonis were less than half of those in the soil-only chambers, and this
difference was statistically significant at the 95% confidence level. These results are similar to those for the willows grown under the same conditions, indicating that the nitrogen-fixing ability of the lupines did not lead to enhanced bioremediation relative to willows. Nonetheless,
this research shows that lupines enhance biodegradation, most likely by stimulating the hydrocarbon-degrading microorganisms in the soil. Since lupines easily establish themselves at the site they are excellent candidates for use in ecological restoration and phytoremediation at the former
Guadalupe Oil Field.
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