Recent advances in the field measurement of the diffusion flux of hydrophobic organic chemicals at the sediment-water interface

We describe and discuss recent advances in measurement of the diffusion flux of chemicals at the sediment-water interface. We analyze the key factors influencing diffusion flux (e.g., chemical-concentration gradient, mass-transfer resistance, sediment composition, hydrodynamics and temperature). We then discuss two main approaches to measure diffusion flux - two-point (i.e. chemical concentrations in sediment porewater and overlying water), and the traditional benthic chamber that can directly measure chemical-diffusion flux from sediment, but the measurement is done at the sorbent-water interface rather than the sediment-water interface. Finally, we present a recently-designed passive sampling device, which derives chemical-diffusion flux at the sediment-water interface from measured concentration profiles in overlying water and sediment porewater. Future work should be directed toward accurate determination of the chemical-diffusion coefficient in overlying water, which is still required for the new sampling device.