Removal of munition constituents in stormwater runoff: Screening of native and cationized cellulosic sorbents for removal of insensitive munition constituents NTO, DNAN, and NQ, and legacy munition constituents HMX, RDX, TNT, and perchlorate.
Graphical Abstract
Introduction
Testing and training activities undertaken by the U.S. Department of Defense has resulted in contamination of soil and groundwater at military installations (Pennington and Brannon, 2002, Clausen et al., 2004). The primary legacy explosives of concern include octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5-trinitro-s-triazine (RDX), and 2,4,6-trinitrotoluene (TNT), as well as the energetic compound perchlorate. Additionally, several new explosive compounds are being phased in for use in insensitive munition (IM) formulations, including 3-nitro-1,2,4-triazol-5-one (NTO), 2,4-dinitroanisole (DNAN), and nitroguanidine (NQ). Soil concentrations of the legacy explosives range from the low µg/kg range to the high mg/kg range (Pichtel, 2012), and include the presence of actual undetonated explosive residues (Walsh et al., 2011). Explosives concentrations in stormwater surface runoff have not been widely reported, but we have observed low ug/L concentrations of HMX and RDX, and perchlorate up to more than 0.5 mg/L (unpublished data). As the IM are only now starting to come into wider use in testing and training, environmental concentration data are not available. Surface runoff concentrations are likely controlled by dissolution kinetics, total precipitation volume, and precipitation intensity, the latter controlling the entrainment and transport of small explosive residues as an undissolved solid phase. Previous work in our laboratory demonstrated dissolution and further disintegration of explosives of Composition B detonation residues under simulated precipitation, with average concentrations of approximately 0.5, 4, and 10 mg/L of HMX, RDX, and TNT, respectively, in the resulting solution (Fuller et al., 2015), highlighting that these compounds have a reasonable pathway as soil contaminants into surface runoff.
While the fate, transport, and toxicity of the legacy compounds have undergone considerable study (Pichtel, 2012, Chatterjee et al., 2017, Juhasz and Naidu, 2007), similar studies with the IM constituents have only begun relatively recently (Indest et al., 2017, Mark et al., 2016, Taylor et al., 2015, Temple et al., 2018). Although the IM constituents provide a higher level of safety for DoD personnel, they are also more water-soluble than the legacy explosives. This could result in lower retention in surface soil and higher transport to groundwater, as well as a higher probability of significantly higher concentrations in surface runoff during storm events. Additionally, the pKa of NTO (3.7) indicates it will be negatively charged at environmentally relevant pH levels, and its low estimated KOW (0.4–1.0) and Kd (avg. 0.6–1.5 across eight soils) values (Mark et al., 2016) indicate that hydrophobic sorption will likely not be effective. Rather, approaches more akin to anion exchange may be needed.
This research was undertaken to develop and evaluate sorbents and/or sorbent mixtures that effectively remove dissolved explosive and energetic compounds, with a focus on identifying materials that would be effective in remediation technologies for contaminated surface runoff. A range of inexpensive and sustainable materials were identified as effective sorbents, including cationized derivatives of several cellulosic biopolymers.
Section snippets
Chemicals and media
TNT, RDX, HMX, and NTO were purchased from Accurate Energetic Systems LLC (McEwen, TN). DNAN, NQ, and the cationizing agent 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHPTAC) were purchased from Sigma-Aldrich (St. Louis, MO, USA). All chemicals were reagent grade or higher.
An artificial surface runoff (ASR) used for this work was based on the analysis of the major anions and cations in stormwater collected from an east coast U.S. Navy facility, and consisted of (mg/L): Na2SO4, 16; MgCl
NTO removal
None of the native materials sorbed NTO, but cationization (designated as CAT henceforth) of all the materials demonstrated increased removal of NTO (Fig. 1), albeit only slightly in the case chitin. CAT cotton linters and CAT pine shavings performed quite well, resulting in sorption of more than 70% of the initial NTO. Sorption of NTO by CAT pine, CAT burlap, and CAT cotton in real stormwater runoff was similar to results in ASR (data not shown). The NTO removal reported herein by cationized
Conclusions
The identification of cationized materials for the removal of the insensitive MC compound NTO from aqueous solution, combined with the previous findings regarding the effectiveness of peat moss for removal of the legacy MC compounds HMX, RDX, and TNT, provide a foundation for further development of a passive treatment technology for MC in surface runoff. These data indicated that a combination of peat moss and CAT pine would be required to effectively remove both insensitive and legacy MC from
CRediT authorship contribution statement
Mark E. Fuller: Conceptualization, Project administration, Investigation, Formal analysis, Writing - original draft, Writing - review & editing. Erin Farquharson: Investigation. Paul C. Hedman: Investigation. Pei Chiu: Investigation, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The investigators acknowledge and thank the Strategic Environmental Research and Development Program for support of this research under project ER19–1106 (grant W912HQ-19-C-0014). Views, opinions, and/or findings contained herein are those of the authors and should not be construed as an official United States Department of Defense position or decision unless so designated by other official documentation. We would like to thank Danhui Xin and Julian Giron Pinto for their work determining the
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