Dioxin-like toxicity in the Saginaw River Watershed: polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls in sediments and floodplain soils from the Saginaw and Shiawassee Rivers and Saginaw Bay, Michigan, USA.

Sediment and floodplain soils in the Saginaw River Watershed, Michigan, USA, have been demonstrated to be contaminated with a variety of organic compounds, including polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). Existing data indicate that, at some locations, the contamination exceeds human health risk-based regulatory levels and ecological risk-based screening levels. In this study, concentrations of PCBs including non-ortho coplanar congeners, PCDDs, and PCDFs were measured in more than 120 sediment and floodplain soil samples collected from the Shiawassee River (a tributary of the Saginaw River), the Saginaw River, and Saginaw Bay, to determine the sources and magnitude of contamination, and to elucidate the contributions from individual contaminant groups to the overall 2,3,7,8-tetrachlorodibezo-p-dioxin equivalents (TEQs). Sediment and soil extracts were also analyzed for total dioxin-like activity by means of the H4IIE-luc cell bioassay. Elevated concentrations of PCBs (>1000 ng/g, dry weight) were found in surface sediment and floodplain soil samples collected from the Shiawassee River near Chase Lake, from Middleground Island in the Saginaw River, and from subsurface sediments in Saginaw Bay. Concentrations of PCDDs and PCDFs in sediment and floodplain soils from the Saginaw River and Saginaw Bay were 2 to 3 orders of magnitude higher than concentrations in the samples from the Shiawassee River. The highest PCDD/F concentration (55,200 pg/g, dry weight in a subsurface layer) was found in sediment collected at the mouth of the Saginaw River. Concentrations of PCDFs were greater than the concentrations of PCDDs in sediment from the Saginaw River. 2,3,7,8-TCDF, 1,2,3,7,8-PeCDF, and 2,3,4,7,8-PeCDF were the major PCDF congeners found in sediments from the Saginaw River. The elevated concentrations of PCDFs, and the predominance of the less highly chlorinated PCDF congeners, in sediments from the Saginaw River were similar to previously determined characteristics of the PCDF contamination of the Tittabawassee River, another tributary of the Saginaw River. These results suggest the existence of a major source of PCDFs within the watershed. A few localized areas of high PCDD/F and PCB concentrations, with unique congener compositions, in the Saginaw River indicated the presence of other minor sources, such as wastewater treatment plants. PCDFs were the major contributors to TEQs in sediment and soils from the Saginaw River and Saginaw Bay. Approximately 30% of the samples analyzed in this study had values exceeding the screening level of 50 pg TEQ/g, dry wt, suggested for soils by the Agency for Toxic Substances and Disease Registry.

Polybrominated diphenyl ethers and polybrominated biphenyls in sediment and floodplain soils of the Saginaw River watershed, Michigan, USA.

Despite known historical release of polybrominated biphenyls (PBBs; brominated flame retardants) into the Pine River (St. Louis, MI, USA), a tributary of the Tittabawassee River which subsequently forms the Saginaw River and flows into Saginaw Bay-Lake Huron, little is known about spatial patterns of sediment contamination by PBBs in this watershed. In this study, concentrations of two groups of brominated flame retardants, polybrominated diphenyl ethers (summation PBDE; BDE-28, -47, -66, -100, -99, -85, -154, -153, -138, and -209) and PBBs were measured in more than 120 floodplain soil samples, surface sediment samples, and sediment cores collected in 2004 from the Shiawassee River, the Saginaw River, and Saginaw Bay, Michigan. In addition, sediment samples collected in 2002 from the Pine River and the Tittabawassee River were analyzed, to elucidate riverine transport and attenuation of PBBs and PBDEs in this watershed. The mean concentration of summation PBDE decreased from upstream to downstream, from the Shiawassee River and the Tittabawassee River to Saginaw Bay. BDE-209 was the predominant congener, accounting for 79% of the total PBDE concentration in the Shiawassee River and 90% in the Saginaw River. BDE-209 was followed, in order of decreasing abundance, by BDE-47, -99, and -100. The proportions of BDE congeners varied by water body, and by sample type, whether floodplain soil or sediment. High summation PBDE concentrations were found in floodplain soil collected from the Shiawassee River near Chase Lake (55 ng/g, dry weight) and in sediment from the Saginaw River near Middleground Island (49 ng/g, dry weight). There was a significant positive correlation between summation (9)PBDE (tri- to hexa-BDE) and BDE-209 in samples collected from the Shiawassee River and Saginaw Bay, but not in samples from the Saginaw River. Among PBBs, bromobiphenyl congener 153 (BB-153) was found in sediments from the Saginaw River but not in sediments from the Shiawassee River. An elevated concentration of BB-153 (13.5 ng/g, dry weight) was found in floodplain soil collected from the Pine River. The BB-153 concentration in sediment decreased by two to three orders of magnitude, from the Pine River downstream to Saginaw Bay. An elevated concentration of BB-153 (4.7 ng/g) was found in sediment collected from the mouth of the Saginaw River. Surface sediments collected near the mouth of the Saginaw River contained higher concentrations of both PBDEs and PBBs than did the subsurface sediments at these locations.