Heavy Metal Mobile Forms as an Indicator of Soil Pollution: A Case Study in South Central Bulgaria

I. ANGUELOVA1, I. ATANASSOV2 and G. ANGUELOV1
1 College of Engineering Sciences, Technology, and Agriculture, Florida A&M University, Tallahassee, Florida, USA 32307
2 Institute for Sustainable Development, BG-1408 Sofia, Bulgaria

Abstract

ANGUELOVA, I., I. ATANASSOV and G. ANGUELOV, 2003. Heavy metal mobile forms as an indicator of soil pollution: a case study in South Central Bulgaria. Bulg. J. Agric. Sci., 9: 425–434

Heavy metal Environmental Quality Objectives are based on the total contents of the elements, which is not sufficient to evaluate their mobility and potential bioavailability. As of yet there is no quality guidelines for estimating soil pollution based on the mobile heavy metal content. The need for information on the suitability of soil extractant that could give a reliable prediction of total metals in soils and their mobility has been growing. In the present paper possibilities for assessing contamination by using the mobile forms of Pb, Zn, Cd, and Cu are discussed.
The study is based on the monitoring of distributions of metals in the impact area of a large non-iron smelter. The soils are Calceric Alluvial-Meadow (Calceric Fluvisols). The soil samples were taken at a distance of 250 to 4000 m from the smelter. Heavy metals were found to be concentrated in the upper layer of the soil profiles up to 25 cm and no metal migration into the deeper horizons was observed. The content of the mobile forms of Pb, Zn, Cd and Cu, determined by an extract of ammonium acetate varies between 70–92 % for Cd, 30–55 % for Pb, 5–26 % for Cu, and 4–21 % for Zn in relation to the total elements' content. The mobile forms tend to diminish when the total content of the elements in the soil decreases and when the distance from the source of contamination increases. The heavy metals in the investigated soils are represented by compounds with insignificant solubility in water (Pb, 0.1–0.4 %; Zn, 0.4 %; Cd, 1–5 %; Cu, 0.2–0.4 %) in comparison with their total contents. A significant correlation between the content of the total and mobile forms of Pb, Cd and Cu in the soil studied is established.

Key words: heavy metals, heavy metal mobile forms, heavy metal water soluble fraction, soil pollution
Abbreviations: HM – heavy metal; HMs – heavy metals