The binding and availability of 2,4,6-trinitrotoluene (TNT) from sand, clay minerals, and soils: The effects of aging and the implications for biotreatment

For many years, the ultimate fate of the most important explosive, 2,4,6-trinitrotoluene (TNT), has been of interest to the scientific community. Despite its importance, the fate of TNT in the environment remains unknown. The objective of this research was to better understand the binding and physical availability of TNT from geosorbents including sand, clay minerals, and soils---the effects of aging and the implications for biotreatability. The physical availability of freshly-spiked TNT from geosorbents was investigated using sorption isotherm and thermal programmed desorption-mass spectrometry (TPD-MS) experiments. TPD-MS experiments demonstrated for the first time that TNT release is dependent upon the character of the geosorbent and that release energy values increase with increasing complexity of the geosorbent (i.e., montmorillonite > kaolinite > sand). Similarly, sorption coefficients indicated a stronger binding affinity and thus a decreased availability with increasing geosorbent complexity. The geosorbents were then aged to assess the effects of aging on the physical availability of TNT. Chemical extractions revealed that a small fraction of TNT was bound to the soils after only 30-60 days while TNT remained fully extractable from the clay minerals. In contrast, aqueous desorption experiments demonstrated a reduced availability of TNT with only 30 days of aging for all geosorbents, suggesting that sequestration was the dominant mechanism of interaction.; The biotreatability of TNT was investigated by composting. Anaerobically digested biosolids were used for the first time as a sole amendment by blending/composting with the geosorbents. TNT was effectively removed in systems amended with only 2.5% biosolids. Microbial growth corresponded to TNT degradation. The organic matter and the active microbial community in the soils were factors for the increased TNT removal in comparison to the clay minerals; thus, the type of geosorbent does affect the availability of TNT for treatment. Geosorbents were then aged for 30 days and subjected to composting. The soils did bind a fraction of the TNT in 30 days, but the remaining TNT was available for biotreatment. In contrast, the individual clay minerals did not bind TNT after aging for 30 days, but the TNT was less available for biotreatment from the aged than freshly-spiked clay minerals due to reversible sorption processes.