Investigation of lead content in Norway maple tree rings and soils in the vicinity of a secondary lead smelter in Toronto.

摘要

Two separate, but complimentary, studies were undertaken to investigate the extent of lead pollution in an urban environment. Changes in xylem lead concentrations in Norway maple (Acer platanoides) trees sampled from three municipal parkland sites in metropolitan Toronto were examined. One site was located less than a kilometer from a major secondary lead smelter, a second located 2 km from the smelter was adjacent to a major expressway, and a third site was chosen approximately 8 km from the smelter. Concentrations of lead in surface soil collected beneath sampled trees were elevated at the site near the smelter compared to the other sites, and the site located adjacent to the expressway had more lead than the third site. Lead concentrations in tree-rings were highest at the site near the smelter followed by the site adjacent to the expressway, and lead levels in trees at the third and furthest site were significantly lower than the other sites. A significant decline of lead in wood formed in the decade before 1977 to the present time was recorded, reflecting changes in lead deposition into the parklands. The results indicate that Norway maple trees can accurately record historical changes of lead in their environment.; In a second study, concentrations and total quantities of lead in Norway maple seedling roots, stems and leaves were determined after 10 weeks growth in soils with similar pH but different total and exchangeable lead levels. These soils were collected underneath the trees sampled from the three parklands and a site adjacent to the lead smelter. Roots accumulated most of the lead and its uptake increased as exchangeable lead in the soil increased. Significantly lower concentrations were observed in stems and leaves suggesting that lead was transported and deposited throughout the plant. In all four treatments, leaves had accumulated consistently higher lead levels than stems.