Abstract
Heavy metal pollution of river freshwater environments currently raises significant concerns due to the toxic effects and the fact that heavy metal behavior is not fully understood. This study assessed the contamination level of eight heavy metals and trace elements (Cr, Ni, Cu, Zn, As, Pb, Cd, and Hg) in the surface sediments of 19 sites in 2018 during four periods (March, May, June, and October) in Olt River sediments. Multivariate statistical techniques were used, namely, one-way ANOVA, person product-moment correlation analysis, principal component analysis, hierarchical cluster analysis, and sediment quality indicators such as the contamination factor and pollution load index. The results demonstrated higher contents of Ni, Cu, Zn, As, Pb, Cd, and Hg, with values that were over 2.46, 4.40, 1.15, 8.28, 1.10, 1.53, and 3.71 times more, respectively, compared with the national quality standards for sediments. We observed a positive significant statistical correlation (p < 0.001) in March between elevation and Pb, Ni, Cu, Cr, and Zn and a negative correlation between Pb and elevation (p = 0.08). Intermetal associations were observed only in March, indicating a relationship with river discharge from spring. The PCA sustained mainly anthropogenic sources of heavy metals, which were also identified through correlation and cluster analyses. We noted significant differences between the Cr and Pb population means and variances (p < 0.001) for the data measured in March, May, June, and October. The contamination factor indicated that the pollution level of heavy metals was high and significant for As at 15 of the 19 sites. The pollution load index showed that over 89% of the sites were polluted by metals to various degrees during the four periods investigated. Our results improve the knowledge of anthropogenic versus natural origins of heavy metals in river surface sediments, which is extremely important in assessing environmental and human health risks and beneficial for decision-maker outcomes for national freshwater management plans.
Highlights
Heavy metal (HM) contents and fluctuations threaten aquatic environments due to their availability, toxicity and persistence[1]
Increases in industrial development, urbanization, and human activity have led to large amounts of wastewaters and solid wastes containing HMs being discharged in Romanian r ivers[19]
We found the pollution load index (PLI) values to have ranges of 0.06‒5.73 in March, 0.49‒6.04 in May, 0.33‒5.7 in June, and 0.35‒5.8 in October, indicating that over 89% of the sites were polluted by HMs to various degrees (Fig. 5)
Summary
Heavy metal (HM) contents and fluctuations threaten aquatic environments due to their availability, toxicity and persistence[1]. Human activities repeatedly increase contamination in aquatic ecosystems, and various amounts of metals are assimilated and deposited in water, sediment, and b iota[3]. HMs discharged into the environment can be deposited in sediments, allowing the prediction of future environmental change based on past and present monitoring[6]. They are considered complex associations of gases, dissolved compounds, and organic materials, resulting from various sources controlled by physicochemical and biological processes and factors[16]. Even the Nemerow Pollution Index showed the same level of sediment contamination of HMs. Past studies have attributed severe ecological risk to sites located downstream by the municipality of Râmnicu Vâlcea, which is associated with contamination sources from wastewaters and industrial discharges from the Oltchim chlor-alkali plant[23,26]. The outcom es of this study will serve as a reference for Romania, enhance understanding internationally, and help inform governmental strategies for addressing environmental pollution
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