There is a need for cheap and reliable methods for assessing the efficiency of bioremediation processes.Could often expensive chemical analysis be supported or partly replaced by cheaper microbiological toxicity tests?

The biodegradation of polycyclic aromatic hydrocarbons (PAH's) was followed in two creosote oil contaminated outdoor composts by chemical analysis and by bacterial toxicity tests.Both of the two compost piles were otherwise similarity treated during the composting period but the other pile was inoculated with PAH degrading mycobacteria.Chemical analysis and toxicity assessments were carried out in the beginning and in the end of four month composting period.

The pooled soil samples were homogenized and PAH's were quantified and identified by a chromatographic (GC/MS) method.Also the metal contamination (Cu, Cr and As) was evaluated by AAS method.The toxicity of the soil samples was assessed by the direct contact modification of the standard Vibrio fisheri luminescent bacteria test and the toxicity of water extracts from these soil samples was also evaluated by luminescent bacteria test and by the automated modification of Pseudomonas putida growth inhibition test.

Total amount of PAH's was reduced in both piles and especially the loss of 2 and some 3 ring compounds was almost 90 per cent.However the concentrations of some PAH's increased during composting.Toxicity assessments support clearly chemical data.There was an apparent decrease in toxicity in both piles after the four month period but the inoculated pile containing more 3 and 4 ring compounds was clearly more toxic.The direct contact modification of V. fisheri luminescent bacteria test appears to be a cheap and suitable tool for assessing toxicity changes during bioremediation processes.