Metals risk in sewage sludge
Letters: Times Colonist, January 19, 2009
A major consequence of the B.C. environment minister's order for more land-based sewage treatment will be the generation of tens to hundreds of tonnes of sewage sludge per day that must be disposed of on land.
Sewage treatment does not destroy most contaminants of concern and will concentrate potentially toxic compounds in the sludge. A common mode of disposal of sewage sludge being considered by the Capital Regional Districts is using sludge in the form of "biosolids" as a fertilizer to be spread on parkland, boulevards and, potentially, forest and agricultural land.
In order to be spread as fertilizer on land, "biosolids" must meet Class A biosolids criteria for metals as dictated by the B.C. Organic Matter Recycling Regulation. Unfortunately, Class A biosolids can legally have higher concentrations of heavy metals than the deep-sea outfall sediments that the environment minister says are contaminated.
If, as the province contends, these metals are unsafe for marine mussels and worms, why are they OK to spread on my garden?
Evidence-based environmental policy should proceed by finding best answers for critical questions like: What are the environmental and public health impacts of "biosolid" disposal on land? How do these compare with our present practice of screening sewage and discharging effluent through long outfalls? Will more land-based sewage treatment benefit public and environmental health?
A thorough cost-benefit analysis should be done comparing our present liquid waste management plan to the total impact of more land-based treatment.
Jay T. Cullen
Saanich
Dr Jay Cullen is an Assistant Professor at the School of Earth and Ocean Sciences at the University of Victoria.
Dr. Cullen's research focuses on understanding the fate and function of trace elements in the marine environment and how natural and anthropogenic environmental perturbations affect trace element biogeochemical cycles. The laboratory utilizes inductively coupled plasma mass spectrometry and voltammetric techniques to investigate the distribution and chemical speciation of trace elements in seawater with special focus on the biogeochemistry of cadmium and iron.