Determining PCB Sorption/Desorption Behavior on Sediments Using Selective Supercritical Fluid Extraction. 3. Sorption from Water

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• 作者：Steven B. Hawthorne ; Erland Bjö ; rklund ; S//pubs.acs.org/images/gifchars/oslash.gif" border="0">ren B//pubs.acs.org/images/gifchars/oslash.gif" border="0">wadt ; and Le
• 刊名：Environmental Science & Technology
• 出版年：1999
• 出版时间：September 15, 1999
• 年：1999
• 卷：33
• 期：18
• 页码：3152 - 3159
• 全文大小：190K
• 年卷期：v.33,no.18(September 15, 1999)
• ISSN：1520-5851

文摘

Supercritical fluid extraction (SFE) with pure CO₂ wasused to quantitatively remove PCBs from historicallycontaminated sediments without substantially disturbingtheir bulk organic or inorganic matrix as evidenced by onlysmall or undetectable changes in thermal gravimetricbehavior, elemental (C, H, N, S) composition, ionic conductivity,and pH determined before and after SFE. The extractedPCBs were then spiked into water with the parent sediment,and sorption was allowed to occur for up to 18 days.The selective SFE conditions developed in part 1 wereused to determine the proportion of PCBs which could beextracted under four conditions of increasing stringency.Comparing the selective SFE behavior of the PCBs from thewater/sediment sorption samples to the original historicallycontaminated sediments demonstrated that 18 dayswas not sufficient for PCBs to migrate to the "slower"sediment-binding sites (those sites requiring more rigorousSFE conditions), which the PCBs had occupied in thehistorically contaminated sediments and that the adsorbedPCBs were primarly associated with the binding sitesmost easily extracted ("rapidly desorbed") by SFE. Sediment/water distribution coefficients at 18 days were similarfor sediments with low contamination levels (<50 ng/g ofindividual congeners) and high contamination levels (~300-4000 ng/g). Apparent distribution coefficients (K_ds) at 18 dayswere similar (within a factor of 2) for the various sedimentsregardless of congener molecular weight or concentration.K_ds increased by a factor of ~4-8 when exposure wasincreased from 2 h to 18 days, with the most rapidlysorbed molecules corresponding to those molecules mostrapidly desorbed by selective SFE.