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Polybrominated Diphenyl Ethers (PBDEs) in a Large, Highly Polluted Freshwater Lake, China: Occurrence, Fate, and Risk Assessment

Polybrominated diphenyl ethers (PBDEs) were extensively investigated in water, sediment, and biota samples collected from Chaohu Lake basin in China. The total concentrations of eight PBDEs (Σ8PBDEs) were in the ranges of 0.11–4.48 ng/L, 0.06–5.41 ng/g, and 0.02–1.50 ng/g dry weight (dw) in the water, sediment, and biota samples, respectively. The concentrations showed wide variations in the monitoring area, while the congener profiles in all the water, sediment, and biota samples were generally characterized by only a few compounds, such as BDE-47, BDE-99, and/or BDE-209. The spatial analysis depicted a decreasing trend of PBDEs from west to east Chaohu Lake, consistent with regional industrialization degree. The distributions of PBDE congeners in the biota samples were similar to the compositional profiles in the water, which were dominated by BDE-47 and/or BDE-99. Nevertheless, BDE-47 and BDE-153 in the brain tissue showed a higher accumulative potential than PBDEs in other tissues as well as the whole body, with 96% relative contribution of Σ8PBDEs. The noncarcinogenic risk values estimated for BDE-47, BDE-99, and BDE-153 indicated that the specific risk associated with the studied water and foodstuffs is limited. However, there is a potential mixture ecotoxicity at three trophic levels at some sampling points in the water, which should draw considerable attention.

* Correspondence: ghlu@hhu.edu.cn (G.L.); zfh168@163.com (F.Z.) Supplementary Information Table S1. Optimized MS/MS parameters of the eight PBDEs. Table S2. Recovery rates of the eight PBDEs in water samples. Table S3. Recover y rates of the eight PBDEs in sediment/biota samples. Table S4. Method detection limits (MDLs) for the eight PBDEs. Table S5. Regression equations, correlation coefficients and retention time of the eight PBDEs. Table S6. Contents of PBDEs in main rivers connected to Chaohu Lake (ng/L). Table S7. Contents of PBDEs in the effluents of main sewage treatment plants surrounding Chaohu Lake (ng/L). Table S8. Contents of PBDEs in water from Chaohu Lake (ng/L). Table S9. Contents of PBDEs in sediments of rivers flowing into Chaohu Lake and the sludge of sewage treatment plants (ng/g). Table S10. Contents of PBDEs in sediments from Chaohu Lake (ng/g). Table S11. Concentrations of PBDEs in aquatic species from Chaohu Lake (ng/g). Table S12. Estimated daily intake (EDI) and Hazard quotient (HQ) for BDE-47, BDE-99 and BDE-153. Table S13. The values of PNEC for fish, daphnia and green algae.
Table S14. The base set of acute toxicity for the calculation of MRQMEC/PNEC and MRQSTU.

Sample Extraction and Analyses
Water samples were filtered through 0.45 µm glass fiber filters (GF/F, Whatman, Clifton, NJ, USA) to remove particles. The water samples filtrate mixed with 0.1 volumes of methanol and sonicated for 5 min. Then the filtrate was extracted by solid phase extraction (SPE) on HLB cartridges (200 mg, Waters, Massachusetts, USA). The cartridges were preconditioned with 5 mL dichlormethane, 5 mL ethyl acetate, 5 mL methanol and 5 mL water. The samples were eluted from the cartridges using 3 mL dichlormethane and 3 mL ethyl acetate. The extracts were evaporated to dryness under a stream of nitrogen, reconstituted with 2 mL n-hexane.
Fish tissue (brain, liver, gills and muscle) samples were homogenized and weighed prior to extracting with an accelerated solvent extractor followed by an ASE 300 (Dionex Ltd., Sunnyvale, CA, USA). Weighed samples were mixed with 5 g of anhydrous sodium sulfate and were loaded into 33 mL ASE cells on top of 10 g of activated Florisil, which was used as a cleanup. Cells were spiked with 10 µL of 1 ng/µL 13 C12-labelled 2,2ʹ,4,4ʹ,5,5ʹ-hexa-BDE (BDE-153) as a recovery internal standard (RIS) solution. The fish sample was then extracted at 100°C with a mixture of n-hexane/dichloromethane (DCM) (4:1, v/v) working at a constant pressure of 1500 psi, a flush volume of 60% and a purge time of 90 s. Two static extraction cycles of 5 min each were applied to achieve the maximum recovery of the analytes. After extraction, the solvents were evaporated down to 1.0 mL and analyzed by GC/MS/MS.
The mass spectrometer was operated in negative electrospray ionization mode (ESI-) using MRM. The quantification of PBDEs was conducted using 13 C12-labelled BDE-153 as an internal standards.
A total of 39 PBDEs were analyzed by GC-MS/MS (EI, 70 eV). The GC-MS/MS was operated in pulsed splitless injection mode with an injector temperature of 340℃.The helium carrier gas flow rate was 1.3 mL/min, and the oven temperature program was as follows: 40°C, 230°C (20°C/min), 285°C (6°C/min), 340°C (25°C/min), held for 7 min. The interface, source and quadrupole temperature were set at 300, 300 and 40°C, respectively, and the MRM parameters are listed in Table S1.

Health Risk Assessment
The estimated daily intake (EDI, ng/kg-bw/day) of PBDEs by adult was calculated as follows: where C is the concentration of a PBDE congener in water (ng/L); V (mL/day) is the consumption rate of water (L); and BW (kg) is the adult body weight.
EDIwater= C×V/BW (2) where C is the concentration of a PBDE congener in fish (ng/g); R is the consumption rate of fish (g/day); and BW (kg) is the adult body weight.
To assess health risks associated with exposure to PBDEs concerning non-carcinogenic endpoints, hazard quotient (HQ) values were estimated and used. It can be calculated simply by dividing the estimated daily intake by the reference dose (RfD) of PBDEs reported by the Integrated Risk Information System (IRIS) of the USEPA as follows: where f is the transfer factor of unit (which is 0.001 in this case) According to the risk addition method, the total HQs of all PBDE congeners can be treated as the mathematical sum of the HQ values of single PBDE congener: Eco-toxicity assessment Eco-toxicity of target compounds in water was assessed using the risk quotient (RQ) on nontarget organisms. At three trophic levels, LC50 or EC50 for fish, daphnia and green algae associated with PBDEs were used for RQ calculation as Eq (6).

RQ = =
where PNEC is the predicted no effect concentration (mg/L),estimated as a quotient of toxicological relevant concentration (EC50 or LC50) with a security factor (f = 1000). The values of EC50 or LC50 for fish, daphnia and green algae for PNEC calculation were provided in the Table S13.
Two approaches for calculating the mixture risk quotient (MRQ) are outlined by Eq. (MRQSTU). The acute toxicity data EC50 and LC50 are represented by EC50 in Eqs. (7) and (8).
where TU and STU are the "toxic unit (MEC/EC50)" and the "sum of toxic unit", respectively.