Energy and Environmental Research Center, University of North Dakota, Box 9018, Grand Forks, North Dakota 58202-9018, USA.
Anal Chem. 2009 Nov 15;81(22):9472-80. doi: 10.1021/ac9019413.
Studies into bioaccumulation of polychlorinated biphenyls (PCBs) have increasingly focused on congeners that are freely dissolved in sediment interstitial pore water. Because of their low water solubilities and their tendency to persist and concentrate as they progress in the food chain, interest has grown in methods capable of measuring individual PCB congeners at low part-per-quadrillion (picogram per liter) concentrations. Obtaining large volumes of pore water is difficult (or impossible), which makes conventional analytical approaches incapable of attaining suitable detection limits. In the present study, nondepletive sampling is used to achieve very low detection limits of freely dissolved PCBs, while requiring no separation of the sediment and water slurry. Commercially available 76 microm thick polyoxymethylene (POM) coupons were placed directly into wet sediments and left to reach equilibrium with the pore water and sediment PCBs for up to 84 days, with 28 days found to be sufficient. Freely dissolved concentrations were then calculated by dividing the PCB concentration found in the POM by its POM/water partitioning coefficient (K(POM)). The K(POM) values required for determining water concentrations were measured using two spiked sediments and two historically contaminated sediments for all 62 PCB congeners that are present at greater than trace concentrations in commercial Aroclors. Log K(POM) values ranged from ca. 4.6 for dichloro-congeners to ca. 7.0 for octachloro-congeners and correlate well with octanol/water coefficients (K(OW)) (r(2) = 0.947) so that a simple linear equation can be used to calculate dissolved concentrations within a factor of 2 or better for congeners having no measured K(POM) value. Detection limits for freely dissolved PCBs ranged from ca. 20 pg/L (part-per-quadrillion) for dichloro-congeners down to ca. 0.2 pg/L for higher-molecular-weight congeners. Sorption isotherms were found to be linear (r(2) > 0.995) over at least 3 orders of magnitude for all congeners, demonstrating good quantitative linearity of the method for determining freely dissolved PCB concentrations at environmentally relevant levels.
对多氯联苯（PCBs）生物累积的研究越来越关注那些在沉积物间隙孔隙水中自由溶解的同系物。由于其低水溶性，以及随着食物链的发展而持续存在和浓缩的趋势，人们对能够测量低至万亿分之几（皮克/升）浓度的个别 PCB 同系物的方法产生了兴趣。获得大量的孔隙水是困难的（或不可能的），这使得传统的分析方法无法达到合适的检测限。在本研究中，非消耗性采样用于实现自由溶解 PCBs 的极低检测限，同时无需分离沉积物和水浆。商业上可用的 76 微米厚聚甲醛（POM）片直接放入湿沉积物中，让其与孔隙水和沉积物 PCBs 达到平衡，最长可达 84 天，28 天被认为是足够的。然后通过将 POM 中的 PCB 浓度除以其 POM/水分配系数（K(POM)）来计算自由溶解浓度。使用两种加标沉积物和两种历史上受污染的沉积物，为所有 62 种在商业 Aroclors 中以痕量以上浓度存在的 PCB 同系物测量了确定水浓度所需的 K(POM)值。K(POM)值的范围从约 4.6（二氯同系物）到约 7.0（八氯同系物），与辛醇/水系数（K(OW)）相关性很好（r(2) = 0.947），因此可以使用简单的线性方程在没有测量 K(POM)值的同系物的情况下，将溶解浓度计算在 2 倍或更好的范围内。自由溶解 PCBs 的检测限范围从约 20 pg/L（万亿分之一）的二氯同系物到约 0.2 pg/L 的高分子量同系物。发现所有同系物的吸附等温线至少在 3 个数量级上都是线性的（r(2) > 0.995），这表明该方法在确定环境相关水平下自由溶解 PCB 浓度时具有良好的定量线性。
