Intercomparison and applicability of some dynamic and equilibrium approaches to determine methylated mercury species in pore water

To assess adequately the impact of methylmercury (MeHg) on sensitive wetland ecosystems, accurate measurements of MeHg in pore water are required. In the present study, the feasibility of three methods for porewater sampling was investigated with respect to MeHg in sediments and rice paddy fields. The performance of dialysis samplers (peepers), sediment core sectioning followed by porewater separation by centrifugation (core), and the thin film diffusive samplers (DGT) were evaluated. These methods were intercompared in field experiments at two sites in Guizhou province, SW China disparately impacted by mercury pollution. All the methods report that the concentrations of MeHg in the soils of the Gouxi (GX) rice paddy near Wanshan were much higher than that in the sediment of the Hongjiadu Reservoir (HR), which is located within the Wujiang River basin. The three methods also report different MeHg profiles at the same site. However, these methods exhibit different temporal and spatial resolution scales, due to the differing operations involved with the sampling methods, may also reflect different states of MeHg in pore water. This corresponds to MeHg derived from diffusive flux, equilibrium concentration, and bulk concentration in pore water detected by DGT, peeper, and sediment core, respectively. The advantages and limits of the three methods are also presented.