322 - Use of a Novel Equilibrium-Based Passive Sampler to Measure Aqueous MeHg in Surface Waters and in a Sediment Microcosm

Accurate measurement of methylmercury (MeHg) is needed for adequate site risk assessment and for the design and evaluation of remedial practice. The transformative nature, temporal and spatial heterogeneity, and often non-detectable concentrations of MeHg make aqueous measurements by traditional grab sampling difficult. Previously, a novel, polymeric, equilibrium-based passive sampler comprising activated carbon particles suspended in agarose gel (ag+AC) was developed to provide time integrative and detectable MeHg concentrations [1]. The present work showcases the application of the ag+AC sampler to predict aqueous MeHg concentrations in environmentally relevant settings and produce spatial MeHg measurements across a sediment-water interface. Samplers deployed at two locations in East Fork Poplar Creek in Oak Ridge, TN, USA predicted surface water concentrations within a factor of 1.6 of direct measurements at both locations, demonstrating that the ag+AC samplers are a reliable tool for measuring aqueous MeHg concentrations. In a sediment microcosm experiment using a mixture of several Hg-contaminated sediments, a single sampler inserted partially within the sediment column and partially in the overlying water predicted both porewater and overlying water concentrations within a factor of four of direct measurements. Samplers provided simultaneous measurements of porewater and surface water, which are critical to determine sediment to surface water flux. Furthermore, the samplers’ ability to provide spatially resolved MeHg measurements forecasts their ability to detect depth profiles within sediment porewaters, which are crucial for understanding MeHg fate and transport. The deployments demonstrate that the ag+AC equilibrium samplers provide robust MeHg predictions across multiple environments. Future work will explore the samplers’ ability to provide spatially resolved MeHg depth profiles at a finer scale as well as in situ sediment deployments. [1] Sanders et al., Environmental Toxicology and Chemistry, 2020, 39:323-334

Authors: Jada Damond, Spencer Washburn, Cynthia Gilmour, Upal Ghosh, Scott Brooks, James Sanders