THE SPATIAL DISTRIBUTION AND HISTORIC CHANGES OF TRACE METAL IN ASBESTOS RICH SEDIMENT IN THE SWIFT CREEK/SUMAS RIVER WATERSHED: A CANADIAN PERSPECTIVE

Very high levels of asbestos fibers have been reported in the streamwater and sediments in the Swift Creek/Sumas River Watershed since the early 1980’s. High levels of Ni and Cr are also associated with the chrysotile rich serpentinitic bedrock formation which is the source of the asbestos fibers in the watershed. Trace metals are much easier and less costly to analyze that asbestos fibers and were used as a surrogate of asbestos fiber presence, and X-ray diffraction analysis were used to confirm the presence of chrysotile. In addition, the serpentinitic material also influences other water quality parameters such as high pH, excessive Mg and low Ca and P values at the source. The results show that Mg, Ni and Cr values in sediments reach up to 2000mg/kg for Ni, and 320mg/kg for Cr at the source area, diminish in the downstream direction but remain well above reference background levels. The data shows that the trace metal concentrations at the US/Canada border station have increased significantly between 1993 and 2009 and there is evidence that the contaminated sediments are moving through the system in a pulsed matter as a result of major storms events. Recent X-ray studies and fiber analysis have shown the presence of asbestos fibers in most of the downstream sampling stations on the Canadian side of the watershed. The main health concern is that airborne mobility of fibers in the area where sediments are deposited during flood events. Efforts to rehabilitate such sites and to establish vegetation cover have been difficult because of the unusual chemistry in the sediments. No conclusive results can be drawn from determining the potential effect on the aquatic ecosystem (fish and earthworm health, metal uptake and survival). Earthworms have difficulties surviving in these sediments but Sticklebacks are widespread but show elevated Cr and Ni levels in liver tissues. However, it is unclear whether the mortality of earthworms is due to the presence of asbestos fibers or the metals. Sequential extraction experiment are used to determine bioavailability and mitigation option for the sediment.