Multivariate statistical analysis of urban soil contamination by heavy metals at selected industrial locations in the Greater Toronto area, Canada
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Published:
Apr 24, 2015
Keywords:
Heavy metals, multivariate analysis, pollution loading index, Greater Toronto Area.
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Abstract
A good understanding of urban soil contamination with metals and the location of pollution sources due to industrialization and urbanization is important for addressing many environmental problems. The results are reported here of an analysis of the metals content in urban soils samples next toindustrial locations in the Greater Toronto Area (GTA) in Ontario, Canada. Theanalyzed metals are Cr, Mn, Fe, Ni, Cu, Zn, and Pb. Multivariate geostatistcalanalysis (correlation matrix, cluster analysis, principal component analysis) is used to estimate soil chemical content variability. The correlation matrix exhibits a positive correlation with Mn, Fe, Cu, Zn, Cd, and Pb. 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 andtraffic 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 and the pollution load index are determined and show the main I geovalues to be in the range of 0-1.67; the values indicate that the soil samples studied for industrial locations in the GTA are slightly to moderately contaminated with Cr, Fe, Cu, Zn, and Cd, and moderately contaminated with Pb,while Ni, and Mn fall in class "0". Regarding the pollution load ingindex (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 the type of industries, especially metallurgical and chemical related ones, in the study area, in addition to high traffic flows, are the main sources for soil pollution in the GTA.
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REFERENCES
ABU-RUKAH, Y.H. (2002): A study of soils along the Amman Aqaba highway contamination with heavy metal. Freiberger Forschungshefte, Geowissenschaften, C49, 53-62.
AKHTER, M.S., and MADANY, I.M. (1993): Heavy metals in street and house dust in Bahrain. Water, Air, and Soil Pollution, 66, 111-119.
AGRICULTURE AND AGRI-FOOD CANADA. (1996): Soil Landscapes of Canada. Version 2.2, National Soil Data Base. Ottawa, Ontario: Agriculture and Agri-Food Canada.
AGRICULTURE CANADA. (1987): The Canadian System of Soil Classification. 2nd ed. Publication No. 1646. Ottawa, Ontario: Agriculture Canada, Research Branch.
ALLOWAY, B.J. (1990): Heavy Metals in Soils. Glasgow: Blackie and Sons.
BADR, N.B.E., EL-FIKY, A.A., MOSTAFA, A.R., and AL-MUR, B.A. (2009): Metal pollution records in core sediments of some Red Sea coastal areas, Kingdom of Saudi Arabia. Environmental Monitoring Assessment, 155, 509-526.
BOSTOCK, H.S. (1970): Physiographic Subdivisions of Canada. In: Douglas, R.J.W. (ed.), Geology and Economic Minerals of Canada. Economic Geology Report No. 1. Ottawa, Ontario: Geological Survey of Canada, pp. 10-30.
CALMANO, W., and WELLERHAUS, S. (1982): Dredging of contaminated sediments in Weser estuary: chemical forms of some metals. Environmental Technology Letters, 3, 199-208.
CATTELL, R.B. (1966): The scree test for the number of factors. Multiple Behaviour Research, 1, 245-276.
CASTRIGNANO, A., COSTANTINI, A.C., BARBETTI, E.R., SOLLITTO. D. (2009): Accounting for extensive topographic and pedologic secondary information to improve soil mapping. Catena, 77, 28-38.
CHEN, X., XIA, X.H., ZHAO, Y., ZHANG, P. (2010): Heavy metal concentration in roadside soils and correlation with urban traffic in Beijing, China. Journal of Hazardous Materials, 181, 640-646.
CHEN, and DONGMEI. (2010): Geospatial analysis modelling of urban structure and dynamics. Springer e Book, springer.
CHEN, X., LU, X., YANG, G. (2012): Sources identification of heavy metals in urban topsoil from inside the Xi'an Second Ringroad, NW China using multivariate statistical methods. Catena, 98, 73-78.
DAO, L., MORRISON, L., and ZHANG, C. (2010): Spatial variation of urban soil geochemistry in a roadside sports ground in Galway, Ireland. Science of the Total Environment, 408, 1076–1084.
DE KIMPE, C.R., and MOREL, J.L. (2000): Urban soil management, a growing concern. Soil Science, 165, 31-40.
DYKE, A.S., VINCENT, J.S., ANDREWS, J.T., DREDGE, L.A., and COWAN, W.R. (1989): The Lauren tide ice sheet and an introduction to the quaternary geology of the Canadian Shield. In R.J. Futton (Ed.), Quaternary Geology of Canada and Greenland. Geology of Canada, publication No. 1 (pp. 178-189). Ottawa: Ontario Geological Survey of Canada.
ELLIS, J.B., and REVITT, D.M. (1982): Incidence of heavy metals in street surface sediments: solubility and grain size studies. Water, Air, and Soil Pollution, 17, 87-100.
FACCHINELLI, A., SACCHI, E., and MALLEN, L. (2001): Multivariate statistical and GIS based approach to identify heavy metal sources in soils. Environmental Pollution, 114, 313-324.
FERGUSSON, J.E., HAYES, R.W., YONG, T.S., and THIEW, S.H. (1980): Heavy metal pollution by traffic in Christchurch, New Zealand: lead and cadmium content of dust and soil, and plant samples. New Zealand Journal of Science, 23, 293-310.
FERGUSSON, J.E. (1990): The Heavy Elements: Chemistry, Environment Impact and Health Effects, vol. 9, Pergamon Press, Oxford.
FOREST LANDSCAPE ECOLOGY PROGRAM, ONTARIO MINISTRY OF NATURAL RESOURCES. (1996): Surficial Geology of Ontario: Digital Database and Viewing Software [CD-ROM]. Sault Ste. Marie, Ontario: Ontario Forest Research Institute, Ontario Ministry of Natural Resources.
FORSTNER, U., and WITTMAN, G.T. (1983): Metal pollution in the aquatic environment. Berlin: Springer.
GALLAGHER, F.J., PECHMANN, I., BOGDEN, J.D., GRABOSKY, J., and WEIS, P. (2008): Soil metal concentration and vegetative assemblage structure in an urban brownfield. Environmental Pollution, 153, 351-361.
GEE, G.W., and BAUDER, J.W. (1986): Particle-size analysis. In: Klute, A. (ed.), Methods of Soil Analysis, Part 1. American Society of Agronomy, Madison, pp. 383-412.
GRATANI, L., TAGLIONI, S., and CRESCENTE, M.F. (1992): The accumulation of lead in agriculture soil and vegetation along a highway. Chemosphere 24:941-949.
KAISER, H.F., and RICE,J. (1974): Little jiffy, mark IV Educ. Psychological Measurement, 34, 111-117.
HAMILTON, R.S., REVITT, D.M., and WARREN, R.S. (1984): Levels and physicochemical associations of Cd, Cu, Pb and Zn in road sediments. Science of the Total Environment, 33, 59-74.
HARRISON, R.M., LAXEN, D.P.H., and WILSON, S.J. (1981): Chemical association of lead and zinc in street dust and road side soils. Environ. Sci. Technol., 15, 1378-1381.
HOWARI, F.M., and BANAT, K.M. (2001): Assessment of Fe, Zn, Cd, Hg, and Pb in the Jordan and Yarmouk River sediments in relation to their physicochemical properties and sequential extraction characterization. Water, Air, and Soil Pollution, 132, 43-59.
HOWARI, F.M., ABU-RUKAH, Y., and GOODELL, O.C. (2004): Heavy metal pollution of soils along North Shauna-Aqaba Highway, Jordan. Int. J. Environment and Pollution, 22, 597-607.
GHREFAT, H.A., ABU-RUKAH, Y., and ROSEN, M.A. (2011): Application of geoaccumulation index and enrichment factor for assessing metal contamination in the sediments of Kafrain Dam, Jordan. Environmental Monitoring and Assessment, Vol. 178, pp. 95-109.
LI, J.L., HE, M., HAN, W., and GU, Y.F. (2009b): Analysis and assessment on heavy metal sources in the coastal soils developed from alluvial deposits using multivariate statistical methods. Journal of Hazardous Materials, 164, 976-981.
LU, X.W., WANG, L.J., LEI, K., HUANG, J.M, and ZHAI, Y.X. (2009): Contamination assessment of copper, lead, zinc, manganese and nickel in street dust of Baoji, NW China. Journal of Hazardous Materials, 161, 1058-1062.
JIRIES, A.G., HUSSEIN, H.H., and HALASH, Z. (2001): The quality of water and sediments of street runoff in Amman, Jordan. Hydrological Processes, 15, 815-824.
JOHNSTON, R.W., RALPH, J., and WISEN, S. (1985): The budget of Pb, Cu and Cd for a major highway. Science of the Total Environment, 46, 137-145.
MORTON-BERMEA, O., ALVAREZl, E., GONZALEZ-HERNANDEZ, G., ROMERO, F., LONZANO, R., and BERAMENDI-OROSCO, L. E. (2009): Assessment of heavy metal pollution in urban topsoils from three metropolitan areas of Mexico City. Journal of Geochemical Exploration, 101, 218-224.
MULLER, G. (1979): Schwermetalle in den Sedimenten des Rheins - Veränderungen seit 1971. Umschau, 24, 778-78.
NAZZAL, Y., ROSEN, M.A., AL-RAWABDEH, AM. (2012): Assessment of metals pollution in urban road dusts from selected highways of the Greater Toronto Area in Canada. Environ Monit Assess J, Springer. Doi: 10.1007/s10661-012-2672-3.
Nazzal, Y., HABES GHREFAT., and ROSEN, M.A. (2014): Application of multuivariate geostatistics in the investigation of heavy metal contamination of road side dusts from selected highways of the Greater Toronto, Canada. 71, 1409-1419.
NRIAGU, J.O., and PANCYNA, J.M. (1988): Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature, 133, 134-139.
POPULATION OF CENSUS METROPOLITAN AREAS. (2006): Census boundaries. Statistics Canada. http://www40.statcan.ca/l01/cst01/ demo05a-eng.htm. Retrieved 2010-03-02.
RAY, A.K., TRIPATHI, S.C., PATRA, S., and SARMA, V.V. (2006): Assessment of Godavary estuarine mangrove ecosystem through trace metal studies. Environmental International, 32, 2190-223.
SELVAM, A.P., PRIYA, L.S., BANERJEE, K.G.; HARIHARAN, G., PURVAJA, R., and RAMESH, R. (2012): Heavy metal assessment using geochemical and statistical tools in the surface sediments of Vembanad Lake, Southwest Coast of India. Environmental Monitoring and Assessment, 184, 5899-5915.
SOLLITTO, D., ROMIC, M., CASTRIGNANO, A., ROMIC, D., and BAKIC, H. (2010): Assessing heavy metal contamination in soils of Zagreb region (Northwest Croatia) using multivariate geostatistics. Catena, 80,182-194.
SOUMYA, HAJJI.KOLSI., SALEM, BOURI., WAFIK, HaACHICHA., and HAMED, BEN DHIA. (2013): Implementation and evaluation of multivariate analysis for groundwater hydrochemistry assessment in arid environmenr: a case study of Hajeb Elyoun-Jelma, Central Tunisia. Environmental Earth Sciences, 70; 2215-2224.
SUN, L.V., YANG, X.B., WANG, N.Q., and CHEN, S. (2008): Spatial distribution of Cd, and Cu, in soils in Shenyang Zhangshi irrigation area (SZIA), China Journal of Zhejiang University, Science, B, 9, 271-278.
TOMLINSON, D.L., WILSON, J.G., HARRIS, C.R., and JEFFREY, D.W. (1980): Problems in the assessment of heavy metal levels in estuaries and the formation of a pollution index. Helgolander Meeresuntersuchungen Helgolander Meeresunters, 33, 566-575.
THURSTON, P.C. (1991): Geology of Ontario: introduction. In P.C. Thurston, H.R. Williams, R.H. Sutcliffe, and G.M. Scott (Eds.), Geology of Ontario, special volume no. 4 (pp. 3–26). Toronto: Ontario Geological Survey.
TUREKIAN, K.K., and WEDEPOHL, K.H. (1961): Distribution of the elements in some major units of the earth's crust. Geological Society of America, 72, 175-192.
WEBSTER., ATTEIA, O., and DUBOIS, J.P. (1994): Coregionalization of trace metals in the soil in the Swiss Jura. Eur. J. Soil Sci., 45, 205-218.
WEDEPOHL, K.H. (1969): Composition and abundance of common igneous rocks. In: Handbook of geochemistry, K.H. Wedepohl, ed., vol. I., pp. 227-249. Berlin-Heidelberg-New York: Springer 1969.
WEI, B., and YANG, L. (2010): A review of heavy metal contamination in urban soils, urban roadside and agricultural soils from China. Microchemical Journal, 94, 99-107.
WEI, B., JIANG, F., LI, X., and MU, S. (2009): Spatial distribution and contamination assessment of heavy metals in urban road dusts from Urumqi, NW China. Microchemical Journal, 93, 147-152.
WONG, J.W.C., and MAK, N.K. (1997): Heavy metal pollution in children playgrounds in Hong Kong and its health implications. Environmental Technology, 18, 109-115.
XIA, X., CHEN, X, LIU, R., and LIU, H. (2011): Heavy metals in urban soils with various types of land use in Beijing, China. Journal Hazardous Materials, 186, 2043-2050.
XIAUYU, Li., LIJUAN, LIU., YUGANG, WANG., GEPING, LUO., XI, CHEN., XIAOLIANG, YANG., MYRNA, H. P. H., RUICHAO, GUO., HOUJUN, WANG., JIEHUA, CUI., and XINGYUAN, HE. (2013): Heavy metal contamination of urban soil in an old industry city (Shenyang) in Northeast China. Geoderma, 192, 50-58.
ABU-RUKAH, Y.H. (2002): A study of soils along the Amman Aqaba highway contamination with heavy metal. Freiberger Forschungshefte, Geowissenschaften, C49, 53-62.
AKHTER, M.S., and MADANY, I.M. (1993): Heavy metals in street and house dust in Bahrain. Water, Air, and Soil Pollution, 66, 111-119.
AGRICULTURE AND AGRI-FOOD CANADA. (1996): Soil Landscapes of Canada. Version 2.2, National Soil Data Base. Ottawa, Ontario: Agriculture and Agri-Food Canada.
AGRICULTURE CANADA. (1987): The Canadian System of Soil Classification. 2nd ed. Publication No. 1646. Ottawa, Ontario: Agriculture Canada, Research Branch.
ALLOWAY, B.J. (1990): Heavy Metals in Soils. Glasgow: Blackie and Sons.
BADR, N.B.E., EL-FIKY, A.A., MOSTAFA, A.R., and AL-MUR, B.A. (2009): Metal pollution records in core sediments of some Red Sea coastal areas, Kingdom of Saudi Arabia. Environmental Monitoring Assessment, 155, 509-526.
BOSTOCK, H.S. (1970): Physiographic Subdivisions of Canada. In: Douglas, R.J.W. (ed.), Geology and Economic Minerals of Canada. Economic Geology Report No. 1. Ottawa, Ontario: Geological Survey of Canada, pp. 10-30.
CALMANO, W., and WELLERHAUS, S. (1982): Dredging of contaminated sediments in Weser estuary: chemical forms of some metals. Environmental Technology Letters, 3, 199-208.
CATTELL, R.B. (1966): The scree test for the number of factors. Multiple Behaviour Research, 1, 245-276.
CASTRIGNANO, A., COSTANTINI, A.C., BARBETTI, E.R., SOLLITTO. D. (2009): Accounting for extensive topographic and pedologic secondary information to improve soil mapping. Catena, 77, 28-38.
CHEN, X., XIA, X.H., ZHAO, Y., ZHANG, P. (2010): Heavy metal concentration in roadside soils and correlation with urban traffic in Beijing, China. Journal of Hazardous Materials, 181, 640-646.
CHEN, and DONGMEI. (2010): Geospatial analysis modelling of urban structure and dynamics. Springer e Book, springer.
CHEN, X., LU, X., YANG, G. (2012): Sources identification of heavy metals in urban topsoil from inside the Xi'an Second Ringroad, NW China using multivariate statistical methods. Catena, 98, 73-78.
DAO, L., MORRISON, L., and ZHANG, C. (2010): Spatial variation of urban soil geochemistry in a roadside sports ground in Galway, Ireland. Science of the Total Environment, 408, 1076–1084.
DE KIMPE, C.R., and MOREL, J.L. (2000): Urban soil management, a growing concern. Soil Science, 165, 31-40.
DYKE, A.S., VINCENT, J.S., ANDREWS, J.T., DREDGE, L.A., and COWAN, W.R. (1989): The Lauren tide ice sheet and an introduction to the quaternary geology of the Canadian Shield. In R.J. Futton (Ed.), Quaternary Geology of Canada and Greenland. Geology of Canada, publication No. 1 (pp. 178-189). Ottawa: Ontario Geological Survey of Canada.
ELLIS, J.B., and REVITT, D.M. (1982): Incidence of heavy metals in street surface sediments: solubility and grain size studies. Water, Air, and Soil Pollution, 17, 87-100.
FACCHINELLI, A., SACCHI, E., and MALLEN, L. (2001): Multivariate statistical and GIS based approach to identify heavy metal sources in soils. Environmental Pollution, 114, 313-324.
FERGUSSON, J.E., HAYES, R.W., YONG, T.S., and THIEW, S.H. (1980): Heavy metal pollution by traffic in Christchurch, New Zealand: lead and cadmium content of dust and soil, and plant samples. New Zealand Journal of Science, 23, 293-310.
FERGUSSON, J.E. (1990): The Heavy Elements: Chemistry, Environment Impact and Health Effects, vol. 9, Pergamon Press, Oxford.
FOREST LANDSCAPE ECOLOGY PROGRAM, ONTARIO MINISTRY OF NATURAL RESOURCES. (1996): Surficial Geology of Ontario: Digital Database and Viewing Software [CD-ROM]. Sault Ste. Marie, Ontario: Ontario Forest Research Institute, Ontario Ministry of Natural Resources.
FORSTNER, U., and WITTMAN, G.T. (1983): Metal pollution in the aquatic environment. Berlin: Springer.
GALLAGHER, F.J., PECHMANN, I., BOGDEN, J.D., GRABOSKY, J., and WEIS, P. (2008): Soil metal concentration and vegetative assemblage structure in an urban brownfield. Environmental Pollution, 153, 351-361.
GEE, G.W., and BAUDER, J.W. (1986): Particle-size analysis. In: Klute, A. (ed.), Methods of Soil Analysis, Part 1. American Society of Agronomy, Madison, pp. 383-412.
GRATANI, L., TAGLIONI, S., and CRESCENTE, M.F. (1992): The accumulation of lead in agriculture soil and vegetation along a highway. Chemosphere 24:941-949.
KAISER, H.F., and RICE,J. (1974): Little jiffy, mark IV Educ. Psychological Measurement, 34, 111-117.
HAMILTON, R.S., REVITT, D.M., and WARREN, R.S. (1984): Levels and physicochemical associations of Cd, Cu, Pb and Zn in road sediments. Science of the Total Environment, 33, 59-74.
HARRISON, R.M., LAXEN, D.P.H., and WILSON, S.J. (1981): Chemical association of lead and zinc in street dust and road side soils. Environ. Sci. Technol., 15, 1378-1381.
HOWARI, F.M., and BANAT, K.M. (2001): Assessment of Fe, Zn, Cd, Hg, and Pb in the Jordan and Yarmouk River sediments in relation to their physicochemical properties and sequential extraction characterization. Water, Air, and Soil Pollution, 132, 43-59.
HOWARI, F.M., ABU-RUKAH, Y., and GOODELL, O.C. (2004): Heavy metal pollution of soils along North Shauna-Aqaba Highway, Jordan. Int. J. Environment and Pollution, 22, 597-607.
GHREFAT, H.A., ABU-RUKAH, Y., and ROSEN, M.A. (2011): Application of geoaccumulation index and enrichment factor for assessing metal contamination in the sediments of Kafrain Dam, Jordan. Environmental Monitoring and Assessment, Vol. 178, pp. 95-109.
LI, J.L., HE, M., HAN, W., and GU, Y.F. (2009b): Analysis and assessment on heavy metal sources in the coastal soils developed from alluvial deposits using multivariate statistical methods. Journal of Hazardous Materials, 164, 976-981.
LU, X.W., WANG, L.J., LEI, K., HUANG, J.M, and ZHAI, Y.X. (2009): Contamination assessment of copper, lead, zinc, manganese and nickel in street dust of Baoji, NW China. Journal of Hazardous Materials, 161, 1058-1062.
JIRIES, A.G., HUSSEIN, H.H., and HALASH, Z. (2001): The quality of water and sediments of street runoff in Amman, Jordan. Hydrological Processes, 15, 815-824.
JOHNSTON, R.W., RALPH, J., and WISEN, S. (1985): The budget of Pb, Cu and Cd for a major highway. Science of the Total Environment, 46, 137-145.
MORTON-BERMEA, O., ALVAREZl, E., GONZALEZ-HERNANDEZ, G., ROMERO, F., LONZANO, R., and BERAMENDI-OROSCO, L. E. (2009): Assessment of heavy metal pollution in urban topsoils from three metropolitan areas of Mexico City. Journal of Geochemical Exploration, 101, 218-224.
MULLER, G. (1979): Schwermetalle in den Sedimenten des Rheins - Veränderungen seit 1971. Umschau, 24, 778-78.
NAZZAL, Y., ROSEN, M.A., AL-RAWABDEH, AM. (2012): Assessment of metals pollution in urban road dusts from selected highways of the Greater Toronto Area in Canada. Environ Monit Assess J, Springer. Doi: 10.1007/s10661-012-2672-3.
Nazzal, Y., HABES GHREFAT., and ROSEN, M.A. (2014): Application of multuivariate geostatistics in the investigation of heavy metal contamination of road side dusts from selected highways of the Greater Toronto, Canada. 71, 1409-1419.
NRIAGU, J.O., and PANCYNA, J.M. (1988): Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature, 133, 134-139.
POPULATION OF CENSUS METROPOLITAN AREAS. (2006): Census boundaries. Statistics Canada. http://www40.statcan.ca/l01/cst01/ demo05a-eng.htm. Retrieved 2010-03-02.
RAY, A.K., TRIPATHI, S.C., PATRA, S., and SARMA, V.V. (2006): Assessment of Godavary estuarine mangrove ecosystem through trace metal studies. Environmental International, 32, 2190-223.
SELVAM, A.P., PRIYA, L.S., BANERJEE, K.G.; HARIHARAN, G., PURVAJA, R., and RAMESH, R. (2012): Heavy metal assessment using geochemical and statistical tools in the surface sediments of Vembanad Lake, Southwest Coast of India. Environmental Monitoring and Assessment, 184, 5899-5915.
SOLLITTO, D., ROMIC, M., CASTRIGNANO, A., ROMIC, D., and BAKIC, H. (2010): Assessing heavy metal contamination in soils of Zagreb region (Northwest Croatia) using multivariate geostatistics. Catena, 80,182-194.
SOUMYA, HAJJI.KOLSI., SALEM, BOURI., WAFIK, HaACHICHA., and HAMED, BEN DHIA. (2013): Implementation and evaluation of multivariate analysis for groundwater hydrochemistry assessment in arid environmenr: a case study of Hajeb Elyoun-Jelma, Central Tunisia. Environmental Earth Sciences, 70; 2215-2224.
SUN, L.V., YANG, X.B., WANG, N.Q., and CHEN, S. (2008): Spatial distribution of Cd, and Cu, in soils in Shenyang Zhangshi irrigation area (SZIA), China Journal of Zhejiang University, Science, B, 9, 271-278.
TOMLINSON, D.L., WILSON, J.G., HARRIS, C.R., and JEFFREY, D.W. (1980): Problems in the assessment of heavy metal levels in estuaries and the formation of a pollution index. Helgolander Meeresuntersuchungen Helgolander Meeresunters, 33, 566-575.
THURSTON, P.C. (1991): Geology of Ontario: introduction. In P.C. Thurston, H.R. Williams, R.H. Sutcliffe, and G.M. Scott (Eds.), Geology of Ontario, special volume no. 4 (pp. 3–26). Toronto: Ontario Geological Survey.
TUREKIAN, K.K., and WEDEPOHL, K.H. (1961): Distribution of the elements in some major units of the earth's crust. Geological Society of America, 72, 175-192.
WEBSTER., ATTEIA, O., and DUBOIS, J.P. (1994): Coregionalization of trace metals in the soil in the Swiss Jura. Eur. J. Soil Sci., 45, 205-218.
WEDEPOHL, K.H. (1969): Composition and abundance of common igneous rocks. In: Handbook of geochemistry, K.H. Wedepohl, ed., vol. I., pp. 227-249. Berlin-Heidelberg-New York: Springer 1969.
WEI, B., and YANG, L. (2010): A review of heavy metal contamination in urban soils, urban roadside and agricultural soils from China. Microchemical Journal, 94, 99-107.
WEI, B., JIANG, F., LI, X., and MU, S. (2009): Spatial distribution and contamination assessment of heavy metals in urban road dusts from Urumqi, NW China. Microchemical Journal, 93, 147-152.
WONG, J.W.C., and MAK, N.K. (1997): Heavy metal pollution in children playgrounds in Hong Kong and its health implications. Environmental Technology, 18, 109-115.
XIA, X., CHEN, X, LIU, R., and LIU, H. (2011): Heavy metals in urban soils with various types of land use in Beijing, China. Journal Hazardous Materials, 186, 2043-2050.
XIAUYU, Li., LIJUAN, LIU., YUGANG, WANG., GEPING, LUO., XI, CHEN., XIAOLIANG, YANG., MYRNA, H. P. H., RUICHAO, GUO., HOUJUN, WANG., JIEHUA, CUI., and XINGYUAN, HE. (2013): Heavy metal contamination of urban soil in an old industry city (Shenyang) in Northeast China. Geoderma, 192, 50-58.