| Summary: | Polybrominated diphenyl ethers (PBDEs) are added to many consumer products as flame retardants. Their hydrophobic characteristics and high n-octanol-water coefficients make them partition in organic media such us sludge and biosolids, by-products of wastewater treatment which are commonly applied to agricultural soils to promote crop growth or discarded in landfills. Biosolids-amended soils have been found to contain up to 7x10⁶ pg PBDEs/g dry weight, whereas leachates from biosolids and flame-retarded products in landfills, contained up to 4,000 pg PBDEs/litre. PBDEs in the environment could potentially cause serious health effects. Research was conducted to determine the concentration and mobility of PBDEs in biosolids, biosolids-amended soil, and clay liners used to retain PBDEs. A field study investigated the degree of PBDE contamination due to the application of biosolids at an agricultural site near Kamloops and an agricultural field in Totem Field at the University of British Columbia in Vancouver. PBDEs were found to migrate downwards to depths of at least 0.85 m. Laboratory experiments determined leachability of PBDEs from biosolids. PBDEs sorbed on fine particles suspended in the leachate, allowing PBDEs to exceed their aqueous phase solubilities. Concentrations were much higher on ultra-fine than on fine particles. Leaching column tests demonstrated that PBDEs leached from biosolids-amended soils and migrated through the soils. PBDEs in soils upgradient and downgradient of solid waste facilities in Northern Canada varied widely from location to location. There was evidence that PBDE contamination in Iqaluit is due to long-range atmospheric transport, whereas that found at Yellowknife is mainly from the solid waste facility. Laboratory experiments showed that sand-bentonite partially retained PBDEs. The hydraulic conductivity decreased with leaching, and then gradually increased. The decrease is attributed to swelling, whereas the increase is due to shrinkage of the clay interlayer, owing to the hydrophobicity of the permeant. The research may be helpful in establishing regulations on land application of biosolids, regulating waste disposal and landfill design requirements. Applied Science, Faculty of Civil Engineering, Department of Graduate
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