Distribution of Heavy Metals and Minerals in the Various Size Fractions of Soil from Copșa Mică, România

Abstract

The Copsa Mică area is one of the most polluted anthropic sites in Romania. Because higher heavy metal concentrations occur in finer fractions, this research focuses on the size fraction < 500 μm. Two kilograms soil sample was sieved on the 500-μm sieve and was air classified into size fractions down to the low micrometer range. The size fraction’s composition was investigated by ICP-OES IC, XRD, and FTIR spectrometry. Approximately 80 and 62% of the material was smaller than 2 mm and < 500 μm, respectively. The predominant size fraction had a mass median diameter (MMD) of approximately 75 μm. The smallest size fraction with a MMD of 2.2 μm had a share of 3.6% and contained the highest amount of heavy metals. The concentrations of Pb, Zn, Cd, Cu, Sb, and As exceeded the legally regulated values for soils according to Romanian legislation. The respective concentrations were 26,900, 27,600, 415, 2130, 466, and 915 mg·kg−1. In the coarser size fractions 5, 4, and 3, the predominant minerals were quartz and alkaline feldspar, while in the finer size fractions 1 and 2, the clay minerals and total carbon (TC) were predominant. Illites and montmorillonites in the fine fraction composition retain heavy metals due to the high levels of cation exchange capacity. Black carbon accumulated in soil acts as a heavy metal adsorbent due to its porosity and high specific surface area. The good correlation between heavy metals and TC in the top soil can be an indicator of the level of heavy metal pollution.