Distribution of mono- through hexa-chlorobenzenes in floodplain soils and sediments of the Tittabawassee and Saginaw Rivers, Michigan

Abstract

Chlorobenzenes are used as solvents or as feedstocks in the production of pesticide formulations, dyes, room deodorizers, moth-proofing agents, and de-inking solvents. Chlorobenzenes were produced by the Dow Chemical Company in Midland, Michigan, for several decades. In this study, concentrations of 12 chlorobenzene (CBz) congeners, from mono- to hexachlorobenzenes, were measured in more than 150 floodplain soil (FPS), surface sediment, and sediment core (SC) samples collected during 2002-2004 from the Pine River, Tittabawassee River, Shiawassee River, Saginaw River, and Saginaw Bay, Michigan. Five grams of wet sediment were homogenized with anhydrous sodium sulfate and extracted with 20% dichloromethane/hexane. The extracts were purified by silica gel column chromatography and analyzed by a gas chromatograph interfaced with a mass spectrometer (GC/MS). Mean concentrations of ΣCBz in FPS and surface sediment were seven to 30 times higher in the Tittabawassee River (80 and 60 ng/g dry weight (dw), respectively) than in the Saginaw River (2.4 and 8.1 ng/g dw, respectively) and Saginaw Bay (5.5 and 8.0 ng/g dw, respectively). Concentrations of ΣCBz were low in surface sediment and FPS from locations upstream of Midland, Michigan, on the Tittabawassee River. Concentrations of ΣCBz were higher in FPS than in surface sediment of the Tittabawassee River; on the contrary, surface sediment contained higher concentrations of CBz than FPS from the other rivers studied. High concentrations of hexachlorobenzene were found in FPS of the Tittabawassee River. All CBz congeners, except for dichlorobenzenes (DCBz), showed a trend of spatial decrease with downstream of the Dow Chemical Company in Midland. The CBz congener composition of the samples showed multiple patterns that reflected differences in historical emissions and environmental partitioning, arising from variations in physico-chemical properties of CBz. 1,4-Dichlorobenzene (1,4-DCBz) was found in all of the samples and accounted for a high proportion of total CBz. The relationship between concentrations of CBz and previously reported concentrations of PCDD/Fs for the same set of samples (Kannan et al. 2008) was significant, indicating similarities in sources and depositions of these two classes of compounds in the watershed.