Application of POCIS for exposure assessment of munitions constituents during constant and fluctuating exposure

Abstract

The present study examined the potential use of polar organic chemical integrative samplers (POCIS) for exposure assessment of munitions constituents, including 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and their breakdown products (aminodinitrotoluenes [ADNTs], diaminonitrotoluenes [DANTs], and hexahydro-1,3,5-trinitroso-1,3,5-triazine [TNX]). Loss of munitions constituents from the sorbent phase after uptake was observed for the "pesticide" POCIS configuration but not for the "pharmaceutical" configuration. Therefore, the latter was selected for further investigation. Under constant exposure conditions, TNT, ADNTs, DANT, RDX, and atrazine (a common environmental contaminant) accumulated at a linear rate for at least 14 d, with sampling rates between 34 mL/d and 215 mL/d. When POCIS were exposed to fluctuating concentrations, analyte accumulation values were similar to values found during constant exposure, indicating that the sampler was indeed integrative. In contrast, caffeine (a common polar contaminant) and TNX did not accumulate at a linear rate and had a reduction in accumulation of greater than 50% on the POCIS during fluctuating exposures, demonstrating that POCIS did not sample those chemicals in an integrative manner. Moreover, in a flow-through microcosm containing the explosive formulation Composition B, TNT and RDX were readily measured using POCIS, despite relatively high turnover rates and thus reduced water concentrations. Mean water concentrations estimated from POCIS were ± 37% of mean water concentrations measured by traditional grab sample collection. Thus, POCIS were found to have high utility for quantifying exposure to most munitions constituents evaluated (TNT, ADNTs, and RDX) and atrazine.

Field validation of POCIS for monitoring at underwater munitions sites

“…The POCIS‐derived time‐weighted average water concentrations ( C w ) for the field site were calculated as follows: where N is the amount of the chemical accumulated by the sampler (ng), R s is the sampling rate (L/d), and t is the exposure time (d). Sampling rates for TNT, 2‐ADNT, 4‐ADNT, 2,4‐dinitrotoluene (2,4‐DNT), DANT, and RDX (0.105, 0.097, 0.104, 0.066, 0.034, and 0.284 L/d, respectively) were calculated for munitions constituents in laboratory calibration experiments under low flow conditions (<9 cm/s; Belden et al ; Rosen et al , Lotufo et al ).…”

“…Because environmental conditions such as flow rate, orientation of the POCIS relative to flow, salinity, temperature, and biofouling have the potential to cause variations in R s (Söderström et al ; Harman et al ; Lissalde et al ; Lotufo et al ), R s should be derived under conditions that reasonably match those for the site of deployment. Our earlier work with POCIS for detection of munitions constituents under water (Belden et al ; Rosen et al ; Lotufo et al ) showed that R s increases with increasing flow velocities for most munitions constituents.…”

“…Integrative passive sampling techniques, specifically polar organic chemical integrative samplers (POCIS; Alvarez et al ), have recently been demonstrated in laboratory‐based experiments as a means of improving the environmental exposure assessment of munitions constituents (Belden et al ; Lotufo et al ). The POCIS technique offers an advantageous alternative to traditional sampling methods (e.g., collection of discrete grab samples) at sites where fluctuations in concentrations or low‐level concentrations are expected to occur, such as in the vicinity of underwater munitions.…”

“…Integrative samplers predict in situ time‐weighted water concentrations using sampling rates ( R s ) determined by deploying samplers for a prescribed period of time to known concentrations in the water, as recommended by Morin et al () and Harman et al (). Sampling rates are typically empirically derived during laboratory studies employing a closed system in which the contaminants are spiked only at the beginning of the experiment or at constant time intervals (e.g., Mazzella et al ; Arditsoglou and Vousta ; Belden et al ). Because environmental conditions such as flow rate, orientation of the POCIS relative to flow, salinity, temperature, and biofouling have the potential to cause variations in R s (Söderström et al ; Harman et al ; Lissalde et al ; Lotufo et al ), R s should be derived under conditions that reasonably match those for the site of deployment.…”

Review and synthesis of evidence regarding environmental risks posed by munitions constituents (MC) in aquatic systems

“…In May and October 2007, sediment samples were collected from the nearshore waters surrounding Isla de Vieques, including Bahia Salinas del Sur, for chemical analysis (Pait et al 2010 (Belden et al 2015); 15 spatially located on a grid across Bahia Salinas der Sur, hereafter referred to as "grid" samplers, and 15 spatially located near observed UWMM items, hereafter referred to as "target" samplers. When feasible, the target samplers were placed in close proximity (e.g., 15 cm) to visible breaches.…”