Determination of Selenium Fractionation and Speciation in Wetland Sediments by Parallel extraction

Abstract

Selenium (Se) fractionation and speciation of wetland sediments is very important in understanding the bioavailability and bioaccumulation of Se in wetland systems. Sequential extraction of Se in sediments is often used in fractionation and speciation studies. Because of the difficulty to accurately determine Se fractions and species in sediment samples containing relatively low concentrations, high light materials and high clay texture by using a sequential extraction procedure, an alternative method was developed by parallel extraction of Se in sediments with deionized (DI) water, NaOH, Na 2 SO 3 and H 2 O 2 -HCl, and determination of Se species by differences. Results showed that adsorbed Se from spiked Se in sediments during DI water extraction can be quantitatively recovered with 0.1 M NaOH and 1 M Na 2 SO 3 . Mass recovery of Se from sediments between the parallel extraction and a sequential extraction was very close, indicating that sequential extraction can be replaced by parallel extraction in Se fractionation and speciation studies. Selenite [Se(IV)], elemental Se [Se(0)], organic material-related Se (OM-Se) and organic Se were the major forms of Se, respectively accounting for 31.2, 24.4, 25.2, and 11.6% of the total Se in Tulare Lake Drainage District wetland and Stewart Lake sediments. Reduction of selenate [Se(VI)] to reduced Se [Se(IV) + Se(0)] and Se uptake by wetland organisms with incorporation of these organisms into the sediment are two major immobilization processes that accumulate Se in wetland sediments.