INVESTIGATIONS INTO THE TOXICITY OF PERSISTENT FRACTIONS OF MINERAL-OILS

The paper deals with the question whether toxicity could be a reason f or the incomplete microbial degradation of mineral oils in the laborat ory and the environment, especially in soils contaminated over a long period. The luminescence test showed inhibition by the nondegradable r esidues as well as by the water phase from degradation experiments. Th is most frequently applied test reaches its limits in the case of subs tances with very low solubility in water. Conclusions relating to the impact on the microbial community of a contaminated ecosystem are not admissible. Neither nondegradable residues from raffinates nor extract s from long-term contaminated soils showed inhibiting effects on the d ehydrogenase activity of Acetobacter methanolicus and a mineral oil-ad apted consortium. Inhibition of the respiration of the pure strain A. methanolicus and of the consortium growing on glucose and spindle oil respectively was not observed either. The residues evidently contain m ainly highly stable compounds which withstand microbial attack. The to xicity of such compounds per se is unlikely. Moreover, toxicity invest igations with aqueous phases from degradation experiments gave no indi cation of the formation of metabolites, which could be responsible for the stagnation of the process. Copyright (C) 1996 Elsevier Science Lt d