Assessing desorption behavior of dechlorane plus and related compounds from laboratory-spiked sediment using Tenax extraction

PURPOSE: Dechlorane plus and its related compounds (DPs) are halogenated flame retardants. DP residues were widely detected in sediment because of its high hydrophobicity and extensive use in the electronics industry. In this study, Tenax extraction, a well-established method, was used to measure the effects of total organic carbon (TOC) content in sediment, aging time, and temperature on desorption behavior of DPs from sediment. Consequently, the bioavailability was estimated. MATERIALS AND METHODS: Three sediments (S1, S2, S3) with different TOC contents and particle-size distributions were collected from several different rivers and reservoirs in China. The sediments were spiked with a mix of DPs and extracted with Tenax resin. Desorption kinetics of DPs was obtained by measuring the amount of DPs that Tenax absorbed from sediments at 20 time points (1, 2, 3, 4, 6, 8, 10, 12, 24, 48, 72, 96, 144, 192, 240, 360, 480, 648, 816, or 1080 h). Then, the sediment (S1) with the highest TOC content was selected to study the effects of aging (14 days and 60 days) and temperature (30 °C and 50 °C). RESULTS AND DISCUSSION: Desorption kinetics were well described by a first-order three-compartment model. The content of TOC has different effects on the desorption of DPs. Desorption rates of dechlorane 602 (Dec 602) and Dec 604 decreased with the increase in TOC contents, while those of syn-DP and anti-DP were the largest in S2, which has an intermediate TOC content. The desorption of Dec 603 in S1 and S2 were similar, which may be attributed to similar contents of clay and silt in those two sediments. With the decreasing temperature and increasing aging time, the rapid fractions (Fᵣₐₚ) of DP, Dec 602, Dec 603, and Dec 604 decreased. The desorption of decachloropentacyclooctadecadiene (anti-Cl₁₀-DP) and undecachloropentacyclooctadecadiene (anti-Cl₁₁-DP) was unaffected by TOC contents, aging time, and temperature. CONCLUSIONS: The contents of TOC have different effects on desorption of DPs. After aging, DPs release from sediment more slowly, and high temperatures will speed up this process. According to Fᵣₐₚ and t₉₉.₉ values, DP is a group of halogenated flame retardants with low bioavailability, and Dec 602 has the highest bioavailability for biota among DPs.