ORIGINAL PAPER Scale-dependent correlations between soil heavy metals and As around four coal-fired power plants of northern Greece Nikos Nanos • Theodoros Grigoratos • Jose ´ Antonio Rodrı ´guez Martı ´n • Constantini Samara Ó Springer-Verlag Berlin Heidelberg 2014 Abstract We analyse the concentration of five trace elements (As, Cu, Ni, Pb and Zn) in the topsoil of the Kozani-Ptolemais basin where four coal-fired power plants run to provide almost 47.8 % of electricity requirements in Greece. We assume that if the power plants have altered the spatial (co)variation of the analysed elements through their toxic by-products, their effect would be observable only on a small spatial scale, since deposition of airborne pollutants is more evident if it is near the emission source. We used Factorial Cokriging to estimate the small-scale correlations among soil elements and to compare them to large spatial-scale correlations. Soil samples were collected from 92 sites. Given the low concentrations in soil heavy metals and As, we observed no serious soil contamination risk. We estimated correlations among the analysed ele- ments on two spatial scales. On the larger scale, Ni and As exhibited higher correlation and received higher weights for the first regionalized factor, contrary to Cu, Pb and Zn which weighted more for the second regionalized factor. On the small spatial scale As associated with neither Ni nor other heavy metals. We conclude that soil arsenic has been altered by enrichment caused by some power plants through fly ash deposition and/or disposal. However, enrichment of soil elements was detectable only on the smaller spatial scale because anthropogenic inputs in soil through airborne emissions and subsequent deposition are evident only in the vicinity of the emission source. Keywords Factorial Cokriging  Fly ash  Geostatistics  Heavy metals  Multiscale variation  Soil pollution 1 Introduction The natural concentration of metals and metalloids in soils, known as heavy metals (HMs), depends primarily on geological parent material composition (Alloway 1995; Ramos-Miras et al. 2011; Roca-Perez et al. 2010; Wang et al. 2011). However, in recent centuries, the concentra- tion of HMs in soil has increased due to human inputs stemming from several activities such as industry, power generation or smelting (Colgan et al. 2003; Gao et al. 2013). More specifically, coal-fired power plants are among the most relevant HMs sources in soil (Quick et al. 2003). The coal-fired power generating industry is likely to emit not only fly ash, but also fugitive dust originating from lignite transportation and ash disposal (Arditsoglou et al. 2004; Samara 2005). As a result, several power plants have enriched nearby soils with one or more heavy metals or other potentially toxic elements; i.e., As, Cd, Pb and Ni (Agrawal et al. 2010), Hg in China and Spain (Yang and Wang 2008; Rodrı ´guez Martı ´n et al. 2013) or As in Slo- vakia (Keegan et al. 2006). Heavy metals emitted in a gaseous form, or attached to fly ash, can travel thousands of kilometres in the atmosphere before being deposited. Electronic supplementary material The online version of this article (doi:10.1007/s00477-014-0991-3) contains supplementary material, which is available to authorized users. N. Nanos (&) Madrid Technical University, Ciudad Universitaria s/n, 28040 Madrid, Spain e-mail: nikolaos.nanos@upm.es T. Grigoratos  C. Samara Environmental Pollution Control Laboratory, Department of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece J. A. Rodrı ´guez Martı ´n Departamento de Medio Ambiente, Instituto Nacional de Investigacio ´n y Tecnologı ´a Agraria, 28040 Madrid, Spain 123 Stoch Environ Res Risk Assess DOI 10.1007/s00477-014-0991-3 Author's personal copy