Reduction in genotoxic effects of explosives-contaminated soil by composting as determined by the Salmonella typhimurium microsomal mutagenicity assay

Composting of soils contaminated with the explosives 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro- 1,3,5,7-tetraazocine (HMX) was evaluated in a field study for its ability to detoxify and decontaminate the soil. Soil volumes of 7, 10, 20, 30, and 40% were used in separate compost piles to determine the loading efficiency of the compost. Organic extracts and synthetic precipitation leachates of the various compost piles were subjected to the Salmonella typhimurium microsomal mutagenicity assay (Ames test) to monitor reduction in mutagenicity as a result of composting. Composting effectively lowered the mutagenicity for the composts piles containing up to and including 30% soil. Results from the Ames test were compared to results obtained from chemical analysis and Ceriodaphnia dubia toxicity tests. The results correlated well as these tests also showed that 30% soil was the maximum loading volume to lower chemical concentration and leachate toxicity. However, an attempt to predict mutagenicity based on chemical concentration showed that the majority of mutagenic activity is unaccounted for by chemical concentration. A risk assessment of the final concentrations of explosives in the composts showed that TNT concentrations were effectively reduced in the composts containing up to and including 30% soil such that the soil could be returned to the environment under an industrial use scenario. However, the RDX concentrations for all but the 7% and 10% soil composts exceeded industrial use scenario risk numbers.