Investigating Potential Limitations of Current Diffusive Gradients in Thin Films (DGT) Samplers for Measuring Organic Chemicals.

The diffusive gradients in thin films (DGT) passive sampler has emerged as a powerful tool for measuring in situ concentrations of organic contaminants in waters with appropriate spatial and temporal resolution at low cost. This study addresses the property range of compounds which can be routinely sampled with the present design of DGT device. Sorption experiments and DGT deployment with 9 model chemicals [organophosphate esters with a wide range of log KOW (0.8-9.5), molecular weight (182-435 Da)] and different functional groups showed compounds with high hydrophobicity and aromatic rings are prone to retention on membrane filters, which slows the supply of chemical to the binding resin of the sampler. The current DGT sampler (PTFE membrane filter, agarose gel diffusion layer, and HLB binding layer) is potentially reliable for measuring hydrophilic [log KOW (0.8-2.6)] and nonaromatic-ring chemicals. For compounds of higher values of KOW or with aromatic rings, knowledge of the lag phase is necessary to optimize sampling times to avoid biasing subsequent laboratory analyses. A standard procedure is used to measure lag times (from minutes to days) by exposing a series of DGT samplers in waters until linear mass accumulation in samplers is achieved. We discuss how monitoring of a wide array of organic contaminants across classes should be possible in the future with a range of validated new DGT devices, optimized for the choice of membrane filter, diffusive material, and binding resin.

Novel Method for in Situ Monitoring of Organophosphorus Flame Retardants in Waters.

Widespread use of organophosphorus flame retardants (OPFRs) and their ubiquity in water results in the need for a robust and reliable monitoring technique to better understand their fate and environmental impact. In situ passive sampling using the diffusive gradients in thin-films (DGT) technique provides time-integrated data and is developed for measuring OPFRs here. Ultrasonic extraction of binding gels in methanol provided reliable recoveries for all tested OPFRs. Diffusion coefficients of TCEP, TCPP, TDCPP, TPrP, TBP, and TBEP in the agarose diffusive gel (25 °C) were obtained. The capacity of an HLB binding gel for OPFRs was >115 µg per disc, and the binding performance did not deteriorate with time up to 131 days. DGT performance is independent of typical environmental ranges of pH (3.12-9.71), ionic strength (0.1-500 mmol L-1), and dissolved organic matter (0-20 mg L-1), and also of diffusive layer thickness (0.64-2.14 mm) and deployment time (3-168 h). Negligible competition effects between OPFRs was found. DGT-measured concentrations of OPFRs in a wastewater treatment plant (WWTP) effluent (12-16 days) were comparable to those obtained by grab sampling, further verifying DGT's reliability for measuring OPFRs in waters.