Multivariate statistical analysis of urban soil contamination by heavy metals at selected industrial locations in the Greater Toronto area, Canada

A good understanding of urban soils metal contamination and locating their pollution sources due to industrialization and urbanization is important for addressing environmental problems. Urban soil samples near industrial locations in the Greater Toronto Area (GTA), Ontario, Canada were analyzed for metal (Cr, Mn, Fe, Ni, Cu, Zn, and Pb) contamination. Multivariate geo-statistical analysis (correlation matrix, cluster analysis, principal component analysis) was used to estimate the variability of the soil chemical content. The correlation matrix exhibits a negative correlation with Cr. The principal component analysis (PCA) displays two components. The first component explains the major part of the total variance and is loaded heavily with Cr, Mn, Fe, Zn, and Pb, and the sources are industrial activities and traffic flows. The second component is loaded with Ni, and Cd, and the sources could be lithology and traffic flow. The results of the cluster analysis demonstrate three major clusters: 1) Mn-Zn, 2) Pb-Cd-Cu and Cr, 3) Fe-Ni. The geo-accumulation index (I (geo)) and the pollution load index (PLI) were determined and show the main I (geo) values to be in the range of 0-1.67, indicating the studied soil samples are slightly to moderately contaminated with Cr, Fe, Cu, Zn, and Cd, and moderately contaminated with Pb, while Ni, and Mn fall into class 0. Regarding the PLI, the lowest values are observed at stations 6, 7, 9, 10, 11, 12, 25, 27 and 28, while the highest values are recorded for stations 1, 5, 6, 13, 14, 16, 17, 18, 20, 22 and 24, and very high PLI readings are seen for stations 5, 13, 16, 17, 18, 22 and 24. These data confirm that in addition to heavy traffic flows, the chemical and metallurgical type of industries are the major source for soil pollution in the GTA.