Contamination of Riverside Sediments and Soil in the Alluvium of Nitra River by Cadmium, Mercury and Lead as a Result of Previous Intense Industrial Activity

The Nitra river belongs to the most contaminated rivers in the Slovakia due the previous intensive industrial activity of several enterprises located in its neighborhood. The aim of the study was to estimate the risk of contamination of riverside sediments as well as alluvial soil in vicinity of Nitra river by dangerous heavy metals. Pseudototal content of risk metals (Pb and Cd) including all the forms besides residual metal fraction was assessed in soil extract by aqua regia and content of mobile forms of selected heavy metals in soil extract by NH4NO3 (c=1mol/L). Used analytical method was flame AAS (AAs Varian AA Spectr DUO 240 FS/240Z/UltrAA). The Hg content was determined using AMA 254 Advanced Mercury Analyzer. Gained results were evaluated according Law No. 220/2004 (valid in the Slovak Republic).The samples of riverside sediments were collected from 28 exactly defined sample points along the Nitra river. The Pollution load index (PLI) has been increasing downstream of Nitra river due to contamination by Cd and Hg. The determined values of total Cd and Hg contents in riverside sediments were in interval 0.74 – 1.88 mg/kg and 0.06 – 5.44 mg/kg, respectively. With exception of two sample points the hygienic limits (0.4 mg Cd/kg and 0.15 mg Hg/kg) were exceeded in all sediment samples. Based on the recommendations of local residents three localities (Male Krstenany, Vycapy–Opatovce and Cernik) along the river Nitra were selected for the research with the requirement that examined site was located in the flood territory and was flooded during the year. In each of the localities the sample points using GPS were assessed. In all studied localities the soil content of mobile Pb forms determined in extract of NH4NO3 (c=1mol/L) was higher than the limit value (0.1 mg/kg) given by the legislation. The intervals were 0.10 – 0.24, 0.17 – 0.32 and 0.11 – 0.25 mg Pb/kg of soil in Male Krstenany, Vycapy–Opatovce and Cernik, respectively. The values of total Cd content determined in soil extracts by aqua regia were in intervals 0.25 – 0.95, 2.04 – 2.52 and 0.63 – 1.35 and total content of Hg in intervals 0.06 – 1.6, 0.04 – 0.07 and 0.03 – 0.36 mg/kg respectively. The hygienic limits given by the legislation are 0.7 mg Cd/kg and 0.5 mg Hg/kg of soil. It means that cadmium and mercury are the most dangerous metals present in the enhanced amounts in soil of investigated localities. The isoline maps were created for each of determined heavy metal in each locality. The obtained results confirmed the risk of alluvial soils as well as riverside sediment contamination by the Nitra river.