Environ. Sci. Technol. 2007, 41, 4600-4606
Bioaccumulation of Perfluorochemicals in Sediments by the Aquatic Oligochaete Lumbriculus variegatus C H R I S T O P H E R P . H I G G I N S , †,‡ PAMELA B. MCLEOD,† L A U R A A . M A C M A N U S - S P E N C E R , †,§ A N D R I C H A R D G . L U T H Y * ,† Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305-4020
Bioaccumulation of perfluoroalkyl sulfonates, perfluorocarboxylates, and 2-(N-ethylperfluorooctane sulfonamido) acetic acid (N-EtFOSAA) from laboratory-spiked and contaminated field sediments was assessed using the freshwater oligochaete, Lumbriculus variegatus. Semistatic batch experiments were conducted to monitor the biological uptake of these perfluorochemicals (PFCs) over 56 days. The elimination of PFCs was measured as the loss of PFCs in L. variegatus exposed to PFC-spiked sediment for 28 days and then transferred to clean sediment. The resultant data suggest that PFCs in sediments are readily bioavailable and that bioaccumulation from sediments does not continually increase with increasing perfluorocarbon chain length. Perfluorooctane sulfonate (PFOS) and perfluorononanoate were the most bioaccumulative PFCs, as measured by laboratory-based estimated steadystate biota sediment accumulation factors (BSAFs) and BSAFs measured using contaminated field sediments. Elimination rate constants for perfluoroalkyl sulfonates and perfluorocaroboxylates were generally smaller than those previously measured for other organic contaminants. Last, a PFOS precursor, N-EtFOSAA, accumulated in the worm tissues and appeared to undergo biotransformation to PFOS and other PFOS precursors. This suggests that N-EtFOSAA, which has been detected in sediments and sludge often at levels exceeding PFOS, may contribute to the bioaccumulation of PFOS in aquatic organisms.
Introduction Much attention has been paid to the bioaccumulation of perfluorochemicals (PFCs). The global distribution of PFCs in biota is well-documented (1), although much less is known about sources of PFCs to aquatic food webs. Some investigators suggest that sediments may be an important source of PFCs for benthic biota (2). Recent research in our laboratory shows that PFCs can accumulate in sediments via sorption (3), thereby increasing the potential exposure of benthic biota. Despite their widespread detection in sediments (4), very * Corresponding author phone: (650)723-3921; fax: (650)725-8662; e-mail:
[email protected]. † Stanford University. ‡ Current address: Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205. § Current address: Department of Chemistry, Union College, Schenectady, NY 12308. 4600
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little is known about the potential for bioaccumulation of PFCs from sediments. A recent field study suggested little accumulation of perfluorooctane sulfonate (PFOS) but considerable accumulation of perfluorooctanoate (PFOA) from sediments by benthic organisms (5). Complicating the study of PFC fate in natural systems is the presence of PFC precursors. While PFOS precursors have been detected in sediments and sludge (4), it is currently unclear whether they contribute to PFOS bioaccumulation or whether they are, in essence, a less bioavailable form of PFOS. As PFC precursors are larger than their respective endproduct PFCs, they may be more hydrophobic and therefore more likely to accumulate in sediments. Because of their contact with sediment and ease of laboratory culture, Lumbriculus variegatus is the organism recommended by the U.S. EPA for assessing bioaccumulation from freshwater sediments (6). L. variegatus is a deposit feeder and can serve as an entry point for sediment-bound contaminants into food webs. The fact that many investigators observe PFC trophic magnification (1) adds additional importance to gaining an understanding of PFC bioaccumulation and potential biotransformation of PFC precursors within lower trophic level organisms. The goal of this study was to evaluate the bioaccumulation of PFCs from sediments by L. variegatus. Semi-static bioaccumulation assays were conducted with PFCs of varying chain lengths for up to 56 days with both laboratory-spiked and contaminated field sediments. Bioaccumulation was also assessed for 2-(N-ethylperfluorooctane sulfonamido) acetic acid (N-EtFOSAA), a suspected PFOS precursor. Depuration of PFCs and PFOS precursors was followed for an additional 42-49 days after a 28 day exposure. Uptake and elimination rate constants as well as steady-state biota sediment accumulation factors (BSAFs) were calculated by fitting the data with generic bioaccumulation models.
Materials and Methods Materials. A purity corrected equimass stock standard solution containing PFOA, perfluorononanoate (PFNA), perfluorodecanoate (PFDA), perfluoroundecanoate (PFUnA), perfluorododecanoate (PFDoA), PFOS, and perfluorodecane sulfonate (PFDS) was prepared in a 70:30 (v/v) methanol/ aqueous ammonium hydroxide (0.01%) solution. When grouped, these chemicals will hereafter be referred to as endproduct PFCs. Individual and mixed stock solutions of N-EtFOSAA, perfluorooctane sulfonamidoacetate (FOSAA), N-ethylperfluorooctane sulfonamide (N-EtFOSA), perfluorooctane sulfonamide (FOSA), and PFOS were also prepared. Standard synthetic freshwater was prepared from MilliQ water. Additional information on the mass-labeled standards employed and the sources and purities of the standards and reagents is available in the Supporting Information. Sediments. For the laboratory-spiked experiments, a previously characterized freshwater sediment with nondetectable levels of PFCs was utilized (sediment 3 in ref 3). Two additional sediments (CA1 and CA2) were collected in June 2006 immediately downstream from two different municipal wastewater treatment plant discharge sites in California. Sediments were wet-sieved (1 cm), characterized for total organic carbon content, and briefly frozen at -80 °C to eliminate any indigenous macrobiota. After thawing, sediments were stored at 4 °C. For the laboratory-spiked sediments, small aliquots (
