Effect of heavy metals on the bioremediation of petroleum hydrocarbons

A relatively clean soil was amended with dodecane, pristane and phenanthrene at a final concentration of 3% (w/w). The contaminated soil was then seeded with hydrocarbon-degrading microorganisms and the biodegradation of the hydrocarbons investigated in the presence of either one (Cd) or two (Cd and Pb) heavy metals. Under abiotic conditions, the loss of the hydrocarbons was in the order dodecane > phenanthrene > pristane. Under biotic conditions, however, the rate was in the order dodecane > pristane > phenanthrene. The presence of Cd at 130 ppm had no appreciable effect on the biodegradation of dodecane and pristane. However, higher concentrations of Cd singly or in combination with Pb at 800 and 1300 ppm, led to reduced rates of biodegradation of dodecane and pristane, being more pronounced for dodecane. No significant effect on phenanthrene degradation was observed. Taken together, the results indicate that Cd, compared to Pb, had a more deleterious effect on microbiota, and thus had a more important role in hydrocarbon bioremediation. However, the effects of heavy metals become less apparent with increasing recalcitrance of the hydrocarbon compound.