Role of soil organic carbon and colloids in sorption and transport of TNT, RDX and HMX in training range soils

Contamination of soils and groundwater by munitions compounds (MCs) is of significant concern at many U.S. Department of Defense sites. Soils were collected from operational training ranges in Maryland (APG), Massachusetts (MMR-B and MMR-E) and Washington (JBLM) and sorption and transport studies were conducted to investigate the effects of soil organic carbon (OC) and textural clay content on fate of dissolved MCs (TNT, RDX, HMX). Sorption experiments showed higher distribution coefficients [TNT:42-68 L kg−1, RDX:6.9-8.7 L kg−1 and HMX:2.6-3.1 L kg−1] in OC rich soils (JBLM, MMR-E) compared to clay rich soils (MMR-B and APG) [TNT:19-21 L kg−1, RDX:2.5-3.4 L kg−1, HMX:0.9-1.2 L kg−1]. In column experiments, breakthrough of MCs was faster in MMR-B and APG compared to MMR-E and JBLM soils. Among TNT, RDX and HMX, breakthrough was fastest for RDX followed by HMX and TNT for all columns. Defining the colloidal fraction as the difference between unfiltered samples and samples filtered with a 3 kDa filter, ∼36%, ∼15% and ∼9% of TNT, RDX and HMX were found in the colloidal fraction in the solutions from sorption experiments, and around 20% of TNT in the effluent from the transport experiments. Results demonstrate that OC rich soils may enhance sorption and delay transport of TNT, RDX and HMX compared to clay-rich soils. Further, transport of TNT may be associated with soil colloid mobilization.