Feasibility of Short-Term and Flow-Weighted Long-Term Measurements Using Equilibrium Passive Sampling

Abstract

Short-term surface water measurements are often critical in assessing pollutant inputs from episodic events, while long-term flow-weighted measurements are needed for loading calculations. For either application involving hydrophobic pollutants, equilibrium passive sampling is currently less explored. In this paper, we first evaluate the feasibility of short-term sampling of polychlorinated biphenyls in polyethylene and polydimethylsiloxane samplers using a combination of mathematical modeling, laboratory-scale experiments, and field demonstration. Laboratory-scale experiments under a range of flow conditions revealed that short-term measurements of dissolved polychlorinated biphenyls using an 18 μm thick polyethylene sheet are possible with 24 h of exposure in high-flow conditions. The optimized samplers deployed at Anacostia River, Washington, DC, were able to measure the water concentration during a storm event and showed that the concentrations were not diluted by the high flow and that the loading during the storm event was substantial. Laboratory experiments revealed that with increasing flow velocity, the diffusive boundary layer thickness decreased and the resulting mass transfer rate increased for the sampler. The positive correlation between flow and exchange rate enables a passive approach for flow-weighted water quality sampling across changing flow conditions in a river.