Batch soil adsorption and column transport studies of 2,4-dinitroanisole (DNAN) in soils

Abstract

The explosive 2,4,6-trinitrotoluene (TNT) is currently a main ingredient in munitions; however the compound has failed to meet the new sensitivity requirements. The replacement compound being tested is 2,4-dinitroanisole (DNAN). DNAN is less sensitive to shock, high temperatures, and has good detonation characteristics. However, DNAN is more soluble than TNT, which can influence transport and fate behavior and thus bioavailability and human exposure potential. The objective of this study was to investigate the environmental fate and transport of DNAN in soil, with specific focus on sorption processes. Batch and column experiments were conducted using soils collected from military installations located across the United States. The soils were characterized for pH, electrical conductivity, specific surface area, cation exchange capacity, and organic carbon content. In the batch rate studies, change in DNAN concentration with time was evaluated using the first order equation, while adsorption isotherms were fitted using linear and Freundlich equations. Solution mass-loss rate coefficients ranged between 0.0002 h −1 and 0.0068 h −1 . DNAN was strongly adsorbed by soils with linear adsorption coefficients ranging between 0.6 and 6.3 L g −1 , and Freundlich coefficients between 1.3 and 34 mg 1 − n L n kg −1 . Both linear and Freundlich adsorption coefficients were positively correlated with the amount of organic carbon and cation exchange capacity of the soil, indicating that similar to TNT, organic matter and clay minerals may influence adsorption of DNAN. The results of the miscible-displacement column experiments confirmed the impact of sorption on retardation of DNAN during transport. It was also shown that under flow conditions DNAN transforms readily with formation of amino transformation products, 2-ANAN and 4-ANAN. The magnitudes of retardation and transformation observed in this study result in significant attenuation potential for DNAN, which would be anticipated to contribute to a reduced risk for contamination of ground water from soil residues.

Dissolution and transport of insensitive munitions formulations IMX-101 and IMX-104 in saturated soil columns

“…DNAN also had the lowest effluent concentrations. Previous research has shown that DNAN adsorbs to soil and that its adsorption is influenced by the soil OC and clay content (Hawari et al, 2015;Arthur et al, 2017). Linear adsorption coefficient values estimated by HYDRUS-1D for DNAN (Table s1) were similar for the two soils (0.63 ± 0.21 L•kg −1 for Camp Swift and 0.53 ± 0.07 L•kg −1 for Camp Guernsey).…”

“…Camp Swift (Bergstrom sandy clay loam, mixed, superactive, thermic Cumulic Haplustolls) collected at Camp Swift, TX and Camp Guernsey (Keeline-Turnercrest loam, mixed, superactive, calcareous, mesic Ustic Torriorthents) collected in Camp Guernsey, WY were the soils used for this study. These two soils were previously used in batch and column transport experiments conducted with NTO and DNAN (Dontsova et al, 2014;Mark et al, 2016;Arthur et al, 2017;Mark et al, 2017). These soils were selected for their relatively low organic matter content to provide conservative estimates of soil attenuation of IM compounds.…”

“…The following parameters were optimized for the munitions constituents: K d (L•kg −1 ) and dissolution parameters, Υ max , χ, and constant, a, which multiplied by Υ max gives the steady-state dissolution rate (Υ min ) (mg•L −1 •h −1 ). The mass-loss rate coefficient for dissolved phase, k (h −1 ) (transformation rate constant) was set to values determined from batch studies for DNAN and NTO (Mark et al, 2016;Arthur et al, 2017) and derived from literature for NQ, RDX, and HMX. Conversely, they were optimized via HYDRUS-1D for 2-ANAN.…”

“…DNAN has a higher K ow value than NQ, NTO and RDX, and thus is anticipated to be less mobile in soil (Table 1). Batch and column soil adsorption experiments for DNAN (Arthur et al, 2017) indicated that DNAN strongly adsorbed to soils, resulting in significant retardation during transport. Linear adsorption coefficients measured in batch studies for 11 different soils ranged between 0.6 and 6.3 L•kg −1 , and Freundlich coefficients between 1.3 and 34 mg 1 − n •L n •kg −1 and positively correlated with cation exchange capacity and the amount of OC in the soil.…”

“…Linear adsorption coefficients measured in batch studies for 11 different soils ranged between 0.6 and 6.3 L•kg −1 , and Freundlich coefficients between 1.3 and 34 mg 1 − n •L n •kg −1 and positively correlated with cation exchange capacity and the amount of OC in the soil. It was also shown that DNAN is readily reduced to amino transformation products 2-amino-4-nitroanisole (2-ANAN) and 4-amino-2-nitroanisole (4-ANAN) (Hawari et al, 2015;Arthur et al, 2017). RDX has intermediate behavior with higher K d , K OC , and K ow values than NTO and NQ, but lower than for DNAN (Haderlein et al, 1996;Singh et al, 1998).…”