Heavy metals in urban soils

This thesis is focused on the investigation of heavy metal contaminated urban soils (especially lead and zinc). Soil samples from greater Montreal area were collected. The concentrations of lead and zinc of some soil samples were at elevated levels, with the highest concentration being 2000 mg/kg (the EPA standard limits for both metals is 300 mg/kg at residential soils). The physical and chemical properties of soils, including soil particle size distribution, soil cation exchange capacity (CEC), soil specific surface area (SSA), soil permeability coefficients, were determined. The majority of soil particles in the samples were found to have the texture of fine sand (loamy and silty sands). Selective sequential extraction (SSE) was performed to understand the affinities of heavy metals toward various fractions of soil. The results indicate that lead has the highest affinity toward soil fraction of organic matter, while zinc has the highest affinity toward soil oxides. Soil column leaching tests were carried out. SSE, together with soil leaching tests, explains the mobility of heavy metals. It shows that zinc has a higher mobility in soils than lead. With the knowledge of heavy metal mobility in soils, the soil decontamination scheme can be planned