AhR-mediated activities and compounds in sediments of Meiliang Bay, Taihu Lake, China determined by in vitro bioassay and instrumental analysis

Abstract

To better understand the historical deterioration and the recent restoration of the ecosystem in Meiliang Bay, Taihu Lake, the third largest freshwater lake in China, extracts of nine surficial sediments were analyzed for their ability to induce dioxin-like activities in vitro. The sediment samples were tested as raw extracts (REs), acid-treated extracts (AEs) and fractionated extracts (FEs), respectively. Based on the initial screening of the REs, all of the sediment samples exhibited significant dioxin-like activity in H4IIE-luc bioassay. Calculated from the raw extracts, the sediment contained 359–1018 pg TCDD-EQ (2,3,7,8-tetrachlordibenzo-p-dioxin toxicity equivalents) g⁻¹ DW (dry weight) derived from the concentration for 20% of maximal effect (EC20). Instrumental analysis of the FE samples revealed that moderately polar (F2) and maximum polarity (F3) fractions were responsible for the majority of the significant reporter gene expression in H4IIE-luc bioassay. Sediment associated with F2 and F3 samples was estimated to contain 94–260 pg TCDD-EQ g⁻¹ DW and 26–106 pg TCDD-EQ g⁻¹ DW respectively. Four F1 samples were either cytotoxic or caused morphological changes in H4IIE-luc cells. Similar toxicity was also observed in their corresponding REs and AEs, which indicated that the matter causing cytotoxicity was acid stable and cannot be removed by the Florisil adsorption process. By use of H4IIE-luc specific relative potencies (RePs), the toxicity equivalents (TEQs) of dioxin-like polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDFs), and polycyclic aromatic hydrocarbons (PAHs) with respect to TCDD were estimated to be 0.7–1.6 pg g⁻¹ DW, 2.7–6.9 pg g⁻¹ DW and 11.1–22.9 pg g⁻¹ DW, respectively. The total instrumental-derived TEQs (12.4–30.9 pg g⁻¹ DW) in sediment appeared to account for only a small portion of the dioxin-like responses observed in bioassay. Compared to the results of other studies, dioxin-like activities have decreased significantly in the past decade, which indicates that the large national ecological remediation project carried out in Meiliang Bay, Taihu Lake has been successful.