Use of constrained DET probe for a high-resolution determination of metals and anions distribution in the sediment pore water

The constrained DET (diffusive equilibrium in thin films) probe filled with agarose gel was successfully used for measuring depth profiles of metals and anions in estuarine sediments at high-resolution (mm). The agarose gel was tested for equilibration times and recoveries. For manganese (10 mg l−1), the equilibration time between an aqueous solution and the agarose gel was reached after 60 min. In the presence of humic acids it was five times longer. As a consequence, for field applications a deployment time of 5–24 h was applied. The subsequent elution of manganese into nitric acid was completed in less than 10 min even without mixing. For agarose gel in contact with solutions of 10 mg l−1 ions (cadmium, copper and manganese, bromide, chloride, nitrate and sulfate), recoveries obtained were close to 100%. DET probes were applied in test laboratory sediment and in real sediment in the Authie (France) estuary. Depth profiles for 19 elements (Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se, Sr, Tl, V, and Zn) and four anions (bromide, chloride, nitrate and sulfate) were established for the test laboratory sediment. In the real sediment, the pore water concentrations of iron and manganese using gel probes were comparable with those obtained by a conventional method (box core-anoxic slicing followed by centrifugation).