| Cities are reservoirs of large stocks of materials, of which a very small fraction is persistent, bioaccumulative, and toxic substances (PBTs). This paper describes a study of the use in, and release from urban infrastructure of PCBs, perhaps the most infamous PBT. An assessment of PCB stocks in Toronto shows that most PCBs are contained in building sealants. Lesser stocks are contained within in-use transformers, the largest cluster of which is in large, electricity-intensive office towers. To support the estimate of high levels of PCBs in urban areas, soil and sediment samples were collected from ten riverside sites in the GTA. Sediment and soil concentrations of SigmaPCBs show 10-fold and 30-fold urban-rural gradients, respectively. The gradient of increasing concentrations from rural to urban areas peaks in downtown Toronto, and mimics the pattern of the stock of PCBs in building sealants and electrical equipment. |
