Distinguishing between natural and anthropogenic sources of trace elements in the sediments using the methods of geochemical normalization and statistical analysis

Abstract

The contamination of sediments by potentially harmful trace elements is of major concern, because of their toxicity, persistence and bioaccumulative nature. In many industrial and urban areas, sediments are the largest repository for, and potential source of these elements. Assessing trace element contamination of sediment is complicated since these elements are a ubiquitous, naturally occurring component of sediment, their concentrations in un-contaminated sediment can vary by orders of magnitude over relatively small spatial scales, and naturally occurring and anthropogenically introduced metals tend to accumulate in the same areas. Due to their particle reactivity, trace elements tend to accumulate in sediments and may persist in the environment long after their primary source has been removed. Element adsorption increases with decreasing grain size of the sediment. Thus, the metal concentrations significantly enriched in fine-grained sediment rich in clay minerals. Because of that, in geochemical and ecochemical studies, the normalization of elemental content using an immobile element is common practice for correcting grain-size effects and dilution by sedimentary phases such as carbonates and silica. The aims of the presented study were: (1) to assess the geochemistry of trace elements (Cr, Zn, Cd, Ni, Pb, and Cu) in canal sediments (Danube alluvial formation) and Tisa River sediments and its tributaries, after normalization of the elements data to a conservative element; (2) to discriminate natural and anthropogenic contributions; and (3) to identify possible sources of pollution. As the element for sediment normalization was used Al, since it represents aluminosilicates, the main group of minerals generally found in the fine sediment fractions. Flame atomic absorption spectrometry (FAAS) was used to determine the levels of the investigated elements. Multivariate statistical methods have been applied in this research to identify similarities in the sampling stations and to assess the relationship between the elements. The results from this study show that investigated sediments are affected by combined trace elements contamination. Also, there was shown a significance of applying geochemical normalization and statistical analysis for assessing trace element contamination and for distinguishing between natural and anthropogenic sources of trace elements in the sediments