Novel Probe for in Situ Measurement of Freely Dissolved Aqueous Concentration Profiles of Hydrophobic Organic Contaminants at the Sediment–Water Interface

A novel pore water probe equipped with polyethylene passive samplers was used to measure the freely dissolved aqueous concentration profiles and diffusive flux profiles of DDT (dichlorodiphenyltrichloroethane) metabolites from 30 cm above to 30 cm below the sediment surface at 2.5 cm resolution intervals in a DDT-impacted lake. The probe was designed to be easily deployed in deep water without the need for divers, provide reliable indications of penetration depths, and minimize disturbance to water movement in the overlying water. The measured aqueous concentration profile allowed us to identify the peak in DDT concentration buried 15 cm below the sediment surface as a source for both upward and downward contaminant flux and to calculate the diffusive flux of freely dissolved DDT and DDT metabolites throughout the measured depths and across the sediment–water interface. The maximal upward flux of 4,4′-DDD (dichlorodiphenyldichloroethane), the major DDT metabolite, was 3.9 ng m^–2 day^–1, which would represent a <0.1% annual increase in average surficial sediment concentration. We propose that this approach can be used in field assessment of contaminated sediment to measure freely dissolved aqueous concentration profiles and estimate sediment-to-water fluxes of hydrophobic organic contaminants.