Influence of TNT transformation on microbial community structure in four different lake microcosms

After World War II, large amounts of obsolete ammunition were dumped in var ious lakes in Sweden. Trinitrotoluene, TNT, was one of the main components of the dumped explosives. In this study, four different lake microcosms ori ginating from lakes where relatively large amounts of ammunition were dumpe d were used to mimic the effect of TNT release on the natural microbial com munity. Increased microbial growth was found in lake microcosms amended wit h TNT. However, negligible mineralization of TNT was detected, suggesting t hat TNT was not utilized as a carbon source, but as a nitrogen source. Rand om amplified polymorphic DNA (RAPD) analysis indicated that the TNT induced no significant differences in microbial community composition and therefor e, no major changes in natural selection, despite the increased microbial g rowth in the presence of the compound. More than 95% of the added TNT bound irreversibly to the sediments, possibly as a result of microbial transform ation to reactive metabolites that subsequently bound covalently to compone nts of the sediment. The results, taken together, suggest that no permanent change in the microbial ecology occurred as a result of the TNT amendment. This was probably due partly to the transient exposure of the microbial co mmunities to the TNT before it became irreversibly bound to the sediment, a nd partly to the fact that TNT was not a primary growth substrate that stro ngly affects natural selection.