an in vitro approach was used to measure the genotoxicity of creosote - contaminated soil before and after four bioremediation processes . 
 the soil was taken from the reilly tar site , a closed superfund site in saint louis park , minnesota . 
 the creosote soil was bioremediated in bioslurry , biopile , compost , and land treatment , which were optimized for effective treatment . 
 mutagenicity profiles of dichloromethane extracts of the five soils were determined in the spiral technique of the salmonella assay with seven tester strains . 
 quantitative mutagenic responses in the plate incorporation technique were then determined in the most sensitive strains , yg1041 and yg1042 . 
 mutagenic potency ( revertants per microgram extract ) in yg1041 suggested that compost , land treatment , and untreated creosote soil extracts were moderately mutagenic with arochlor - induced rat liver ( s9 ) but were nonmutagenic without s9 . 
 however , the bioslurry extract was strongly mutagenic and the biopile extract was moderately mutagenic either with or without s9 . 
 a similar trend was obtained in strain yg1042 . 
 the strong mutagenic activity in the bioslurry extract was reduced by 50% in ta98nr , which suggested the presence of mutagenic nitrohydrocarbons . 
 variation in reproducibility was 15% or less for the bioassay and extraction procedures . 
 bioavailability of mutagens in the biopile soil was determined with six solvents ; water - soluble mutagens accounted for 40% of the total mutagenic activity and they were stable at room temperature . 
 the mutagenic activity in the bioslurry and biopsile samples was due to either the processes themselves or to the added sludge / manure amendments . 
 the in vitro approach was effective in monitoring bioremediated soils for genotoxicity and will be useful in future laboratory and in situ studies.imagesfigure 1figure 2