Natural and anthropogenic origins of selected trace elements in the surface waters of Tabriz area, Iran

This research determined potential sources of certain trace elements in the surface waters of the Tabriz area in northwestern Iran. In total, 19 samples from surface waters in the Tabriz area, including the Aji-Chay, Ansa-Rood, Basmenj-Chay, Gomanab-Chay, Mehran-Rood and Sinikh-Chay Rivers, and their branches, were collected in December 2016. Samples were measured/analyzed with respect to electrical conductivity (EC), pH, major (Ca2+, Mg2+, Na+, K+, HCO3−, SO42−, Cl−) and minor (NO3−, F−, SiO2) elements, and certain trace elements (Fe, Mn, Al, Zn, Cd, Pb, Cr, Al and As). The order of abundance for trace elements was Mn > Fe > Al > Zn > Cr > As > Cd > Pb. Cluster analysis divided the samples into two clusters, and the accuracy of the clustering was determined to be 100% by discriminant analysis. The discriminant analysis introduced Cd and Cr as the best parameters to predict sample grouping. Values of EC and concentrations of the major ions and trace elements such as Cd, Pb, Cr and Al, were greater in cluster 2 than in cluster 1. The high EC and its dependent anions (e.g. SO42− and Cl−) in cluster 2 can be considered as one of the driving factors for their release into surface water by forming SO42− and Cl− complexes with metals. The concentrations of SiO2 and As were greater in cluster 1 than in cluster 2 due to the impact of the volcanic formations of Sahand Mountain. Factor analysis identified four factors, which cumulatively explained 80.1% of the variance of the hydrochemistry of the surface water, and which were related to both natural and anthropogenic processes.