Compound specific isotope analysis (CSIA) is an established tool to demonstrate <i>in situ</i> degradation of traditional groundwater contaminants. To date, CSIA is mainly limited to heavily contaminated sites due to the high detection limit of isotope ratio mass spectrometers. Recently, CSIA has been reported for μg/L to higher ng/L by extracting 10-100 L of water using solid-phase extraction (SPE), which often resulted in significant method-induced isotope fractionation. This work evaluated the compatibility of polar organic chemical integrative sampler (POCIS) with CSIA for substituted chloronitrobenzenes, chloroanilines, and nitrotoluenes at low μg/L. Method-induced isotope fractionation evaluated using 60-day laboratory kinetic experiments demonstrated that neither diffusion towards and through the membrane and sorbent nor adsorption onto the membrane and sorbent phases resulted in significant carbon isotope fractionation (&lt;0.7‰), except for 3,4-dichloronitrobenzene (1.6‰). Results also suggested one POCIS can accumulate the target analytes for CSIA at concentrations down to 1-10 μg/L, which would require up to 10 L of water using SPE. Moreover, POCIS could theoretically be used to apply CSIA at ng/L range by combining multiple POCIS together or increasing sorbent mass. The performance of the POCIS-CSIA method was evaluated in a field pilot constructed wetland. The obtained δ<sup>13</sup>C of two substituted chloroanilines were within ±0.6‰ to the isotope signatures obtained from SPE using 4 L grab sampling during POCIS retrieval. Negligible membrane biofouling of the field deployed POCIS was observed. This work opens a new avenue for CSIA in low concentration environments, e.g., rivers, wastewater treatment plants, constructed wetlands, and long-term remediation sites. Because POCIS is specifically designed for polar compounds, this work also enables CSIA to the polar emerging contaminants present in the environment, such as pesticides, pharmaceuticals, and flame-retardants.

Compound specific isotope analysis of substituted chlorobenzenes at sub-μg/L concentrations using polar organic chemical integrative samplers

ACS Spring 2022

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