Influence of clay minerals, humic substances, and soil aggregation on the fate and bioavailability of 2,4,6-trinitrotoluene (TNT)
Pillar, Gregory D.
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Over the last several decades the production, use, and disposal of munitions has resulted in widespread contamination of nitroaromatic explosives, including 2,4,6-trinitrotoluene (TNT). In this dissertation, the environmental fate of TNT in soil, soil aggregates, and primary soil particles was investigated. In the first experiment, the objective was to characterize the influence of humic acid on TNT sorption to clay minerals. TNT sorption to humic acid was significant and increased with a decrease in humic acid concentration. Additionally, humic acid complexed with a high and low charge smectite and kaolinite resulted in greater TNT sorption compared to the corresponding homo-ionic clay minerals. The fractionation of humic acid during adsorption to a low-charge smectite was observed and sequential humic-clay complexation resulted in a reduction in TNT sorption. The objective of the next study was to characterize how the soil fractionation method used to obtain soil aggregates influences soil properties and processes. Wet- and dry-sieving of three different soils indicated that the particle size distribution, inherent clay mineralogy, and organic matter content determined to what extent the sieving method altered the aggregate size distribution and aggregate specific soil properties. In all three soils, wet-sieving resulted in a greater distribution of aggregates < 250 ¼m and a redistribution of organic matter and sand particles from large aggregates to microaggregates. Additionally, wet-sieving significantly altered the microbial community structure of aggregates < 250 ¼m. The objective of the third and final study was to determine if earthworms could influence the fate of TNT within soil aggregates and to what extent TNT and earthworms altered the soil microbial community. After 21 d 15.5 to 19.6% of the initial (§ 100 mg kg) TNT was recovered from two soils. After 7 d earthworm activity resulted in a 0 to 45% reduction in TNT depending on the soil type. With time, earthworm influence on TNT disappearance decreased due to the formation of irreversibly bound residues. Additionally, earthworms were able to absorb and transform TNT within their body and alter the distribution of TNT and metabolites among different sized aggregates, and along with TNT alter the microbial community structure.