Tenax extraction as a tool to evaluate the availability of polybrominated diphenyl ethers, DTT, and DTT metabolites in sediments

Solid-phase extraction with Tenax is one of the most used methods for determining the fraction of a pollutant that desorbs rapidly from sediment and thus is available for living beings. In the present study, this technique has been applied to sediment contaminated in the laboratory with polybrominated diphenyl ethers (PBDEs) and dichlorodiphenyltrichloroethane, dichlorodifenyldichloroethylene, and dichlorodifenyldichloroethane (generically, DDXs). The amount of chemical retained in sediment during the time of the experiment fit well with a three-phase exponential desorption model. The ratios between the rapidly desorbing fraction and the fraction desorbed during a fixed time (6 or 24 h) were calculated. The fraction desorbed in 6 h was lower than the rapidly desorbing fraction for most of PBDEs, whereas the fraction desorbed in 24 h exceeded the rapidly desorbing fraction for both groups of compounds. However, variability of these data suggests, when possible, a long time measure of desorption in order to achieve a more accurate estimation. Both the extent and the velocity of desorption were inversely related with the bromination degree and, consistently, with hydrophobicity and molecular size. In this way, low brominated PBDEs and DDXs showed a high availability relative to high brominated PBDEs.