IP06 Passive Samplers for POPs
B115 & B116
8:00 AM - 12:00 PM, Tuesday
(IP049) Semi-Permeable Membranes for Environmental Aqueous Sampling.
Seaman, J.1, Hardison, D.1, Walling, S.1, Kelsey-Wall, A.1, Hart, E.2, 1 University of Georgia/ Savannah River Ecology Lab, Aiken, SC, USA2 Westinghouse Savannah River Company, Aiken, SC, USA
ABSTRACT- The use of selectively permeable membrane bags has proven effective for sampling various constituents in monitoring wells, including the use of polyethylene bags in the sampling of VOCs and other organics from discrete aquifer screen zones within wells. However, a major disadvantage of polyethylene membranes is the limited suite of compounds that can penetrate the material. Often, there is a need to evaluate additional constituents, including inorganics and other organics that are not readily diffusible through polyethylene surfaces. In these cases, nylon screen and dialysis membranes may be a feasible option. To assess their potential use in groundwater sampling, a series of laboratory equilibration experiments were performed using these materials as diffusion samplers for various organic and inorganic compounds to determine the time required for equilibration under various conditions, i.e., pH, ionic strength, redox status, dissolved humics, agitation/water flow, etc. Surprisingly, incomplete equilibration was observed for the nylon screen materials at all pH levels, presumably due to the limited transfer area under stagnant flow conditions. Dialysis membrane results indicate a more complete equilibration for most metals under various conditions. In the most acidic solutions, (pH 2 to 3) concentrations in membrane samplers were similar to the surrounding matrix solution within 12 to 18 hours. Similar results were found for most metals at more environmentally realistic pHs, pH 4.5 to 6.5, excluding Cu, Cr, and Pb. This may reflect the formation of metal hydrolysis species at the higher pH that take longer to equilibrate. Near complete equilibration of organic carbon, chloride, and nitrate suggests that measurements of these constituents obtained from membrane samplers reflect concentrations within the environment. This data demonstrates that multiple particle size cutoffs and/or longer equilibration times may be required to allow for complete diffusion, depending on matrix composition.
Key words: diffusion, semi-permeable membrane, dialysis sampling, metals