Assessing heavy metal contamination in soils of the Zagreb region (Northwest Croatia) using multivariate geostatistics Donato Sollitto a, ⁎, Marija Romic b , Annamaria Castrignanò a , Davor Romic b , Helena Bakic b a CRA – SCA, Via C. Ulpiani 5, 70125 Bari, Italy b University of Zagreb, Faculty of Agriculture, Svetošimunska 25, 10000 Zagreb, Croatia abstract article info Article history: Received 17 April 2009 Received in revised form 27 October 2009 Accepted 23 November 2009 Keywords: Heavy metals Factor kriging analysis Multivariate geostatistics Soil pollution The assessment of soil contamination and location of pollution sources represent a crucial issue in soil remediation. Topsoil samples were collected in the Zagreb area (Northwest Croatia) and the total contents of trace and major elements were determined. A multivariate geostatistical analysis was used to estimate soil chemical composition variability. Factorial Kriging Analysis (FKA) was used to investigate the scale- dependent correlation structure of some variables by modelling co-regionalization of ten chemical variables, co-kriging specific factors and mapping them. The FKA provided two regionalized factors at different spatial scales of variability: the first factor at shorter range for Zn, Pb, Cd, Cu and Ni indicated different sources of anthropogenic contamination, whereas Ca (mainly loading on the longer range factor) was related to the lithology and parent material composition. The methodology used has proved to be a useful tool to separate geological and anthropogenic causes of variation in soil heavy metal content and to identify common pollution sources. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Physical and chemical soil properties may depend on several factors, both natural and anthropogenic ones, jointly acting over different spatial and temporal scales: natural pedological processes (e.g. rock weathering and organic matter decomposition) are related to parent material, geomorphology of the area, presence of vegetation, the climate conditions and other interactions with the environment. The effects of these processes are strictly time-dependent and revealed in a quite complex structure of soils. On the other hand, soil management practices may also significantly affect pedological properties by altering soil structure mechanically due to agricultural and urban activities, and by changing chemical composition via pollution loading. The presence of some elements in a toxical concentration in the soil may be due to both natural and anthropogenic factors, therefore it often may be quite difficult to discriminate among the different causes. The parent material largely influences heavy metal content in many soil types, with concentration sometimes exceeding the critical values (Palumbo et al., 2000; Salonen and Korkka-Niemi, 2007). Some heavy metals, such as Ni, Cr and Mn, may be contained as trace elements in some rock types of volcanic and metamorphic origin (Alloway, 1995). During weathering processes the primary crystalline structures of some rock minerals are completely broken, relevant chemical elements may be thus either adsorbed in the topsoil or transported towards surface water or ground water targets. Anthropogenic sources of heavy metal contamination are mainly combustion processes in industry and transportation. Lead and cadmium are the main heavy metals arising from combustion and are often associated with zinc owing to tyre wear on the roads. Waste water from industrial processes may contain an important load of zinc, copper, chromium and nickel. Moreover, mining activities for extraction and manufacturing of metal products may result in a large amount of pollutants to be released into the atmosphere and, secondly, in the adjoining soils and waters. Long-term and extensive use of agricultural land with frequent application of pesticides (Nicholson et al., 2003) may cause heavy metals such as copper, nickel, zinc and cadmium to accumulate in the topsoil. A soil pollution assessment becomes very difficult when different sources of contamination are present and their products are variably distributed. In these cases the spatial variability of the heavy metal concentrations in soils is basic information for identifying the possible sources of contamination and to delineate the strategies of site remediation. Classic geostatistics methods based on univariate analysis can provide distribution maps for each pollutant and delineate the areas where its concentration exceeds the threshold values. Although the Catena 80 (2010) 182–194 ⁎ Corresponding author. Tel.: +39 080 5475024 E-mail address: donato.sollitto@entecra.it (D. Sollitto). 0341-8162/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2009.11.005 Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena