Heavy metal concentrations in soils and irrigation waters in Thessaly region, Central Greece

The purpose of this work was to provide information on heavy metals concentrations in soils and in irrigation water in Thessaly, Central Greece, where tobacco (Nicotiana tabacum) is cultivated. Tobacco tends to accumulate high levels of heavy metals, especially Cadmium. During the years 1998, 1999, and 2000, 795 surface soil samples (0 to 30 cm depth) and 200 water samples were collected from Karditsa, Larissa, and Trikala areas. Soil samples were analyzed for pH, organic matter, electrical conductivity, and clay content. Total (extraction with Aqua Regia) and available (DTPA-extractable) heavy metal (Zn, Cu, Mn, Cd, and Pb) concentrations were determined by FAAS and GF-AAS technique. The same technique was also used for the determination of the dissolved heavy metals in acidified (HNO3) water samples (pH < 2). The values of soil pH ranged between 4.3 and 8.4, organic matter content between 0.2 and 2.6%, electrical conductivity between 108 and 1100 mu S cm(-1), and clay content between 12 and 39%. Total concentration of extractable Zn, Cu, Mn, Cd, and Pb (Aqua Regia method) ranged between 12 and 57, 5 and 61, 156 and 2231, 0.03 and 0.93, and 3 and 47 mg kg(-1) dry soil, respectively and were all below European Community recommended limits. The concentration of heavy metals (DTPA method) in relation to total concentration (Aqua Regia method) was as follows: Cd: 17.8%; Pb: 6.7%; Cu: 3.8%; Mn: 1.9%; and Zn: 1.6%, indicating that Cd had the highest relative availability of the five metals tested. Significant negative correlation was found between soil pH and DTPA-extractable Zn (0.48**) and Mn (0.78**). Total soil metals were significantly correlated with organic matter content Zn (0.33**), Cu (0.48**), Pb (0.39**), soil clay Zn (0.32**), and Cu (0.35**). In irrigation waters dissolved heavy metals in most cases were not detectable.