Determination of the Isotopic Composition of Aqueous Mercury in a Paddy Ecosystem Using Diffusive Gradients in Thin Films

Measuring the isotopic composition of Hg in natural watersis challengingdue to the ultratrace level of aqueous Hg (ng L-1). At least 5 ng of Hg mass is required for Hg isotopic analysis.Given the low Hg concentration in natural waters, a large volume ofwater (>10 L) is typically needed. The conventional grab samplingmethod is time-consuming, laborious, and prone to contamination duringtransportation and preconcentration steps. In this study, a DGT (diffusivegradients in thin films) method based on aminopropyl and mercaptopropylbi-functionalized SBA-15 nanoparticles was developed and extendedto determine the concentration and isotopic composition of aqueousHg for the first time. The results of laboratory analysis showed thatHg adsorption by DGT induces & SIM; -0.2 & PTSTHOUSND; mass-dependentfractionation (MDF) and little mass-independent fractionation (MIF).The magnitude of MDF exhibits a dependence on the diffusion-layerthickness of DGT. Since Hg-MDF can occur in a broad range of environmentalprocesses, monitoring the & delta;Hg-202 of aqueous Hg usingthe DGT method should be performed with caution. Field results showconsistent MIF signatures (& UDelta;Hg-199) between the DGTand conventional grab sampling method. The developed DGT method servesas a passive sampling method that effectively characterizes the MIFof Hg in waters to understand the biogeochemical cycle of Hg at contaminatedsites.