Systematic evaluation of membrane filter materials for determination of mercury species using DGT

The accurate assessment of mercury bioavailability in aquatic environments requires reliable tools for determining labile inorganic mercury (Hg 2+ ) and methylmercury (CH 3 Hg + ). The diffusive gradients in thin-films (DGT) technique is increasingly applied for this purpose. Because mercury species exhibit a strong affinity for surfaces, membrane filters may affect diffusive transport and analyte accumulation within DGT devices. However, despite the routine use of membrane filters, their influence on DGT determination of Hg 2+ and CH₃Hg + has not been systematically investigated. Time-series DGT experiments were conducted in well-defined solutions containing Hg 2+ and CH 3 Hg + to compare conventional and chemically modified membrane filters. All untreated filters exhibited linear mercury accumulation in resin gel over time, with uptake rates in agreement with theoretical predictions (α = 0.05), confirming valid diffusive transport. For Hg 2+ , nylon and mixed cellulose ester filters showed the best agreement with theoretical fluxes, whereas polyvinylidene difluoride (PVDF) filters provided the most accurate performance for CH 3 Hg + . Among the untreated membranes, polyethersulfone (PES, AllPure) showed the lowest Hg 2+ adsorption, with a median value of 28.1 ng, while PVDF exhibited minimal interaction with CH 3 Hg + , with a median adsorption of 10.5 ng. In contrast, silver- and copper-modified filters strongly accumulated mercury on the membrane surface (681.9–5416 ng), disrupting linear uptake of mercury species into the resin gel and causing significant analytical bias. These results demonstrate that membrane filter selection represents a critical but previously underestimated factor in DGT-based mercury determination and provide practical recommendations for improving the accuracy and reliability of Hg 2+ and CH 3 Hg + bioavailability measurements in aquatic systems.