Influence of heavy metals on the microbial degradation of diesel fuel

The degradation of diesel fuel by a microbial community from a soil polluted by heavy metals (h.m.) in the presence of Cu, Ni, Zn, Pb, Cd, Hg and Cr (as chromate) was investigated. Experiments were conducted with soil slurries and the extracted community in liquid cultivation. The concentrations applied were in the sub-mM and mM range. Whereas the slurries displayed no significant effect, degradation in liquid culture was increasingly inhibited by higher metal concentrations. The course of degradation in suspension was demonstrated by the oxygen consumption. The order of toxicity was found to be: Hg > Cr(VI) > Cu > Cd > Ni > Pb > Zn. The absence of any effect for slurries was due to the non-availability of the metals in the soil, and to precipitation or adsorption to the soil in the case of amendment. The paper also includes results on the availability of h.m. and changes to the community after exposure.