Pollution assessment using local enrichment factors: the Berounka River (Czech Republic)

Abstract

The Berounka River is considered a relatively clean river, but recent studies have reported various levels of pollution. The purpose of this work is to identify anthropogenic pollution by metals (i.e. Pb, Zn, Cu) and magnetic particles in the sediments of that river and its tributaries. Samples were obtained from hand-drilled cores taken from representative areas within the fluvial system; in distal floodplains (overbank fines) and closer to the channel (laterally deposited sediments). Samples were subjected to analysis using mass magnetic susceptibility (MS), X-ray fluorescence spectrometry (XRF) and also by inductively coupled plasma mass spectrometer (ICP MS) which allowed for a determination of 206Pb/207Pb isotope ratios. Macroelement ratios (K/Ti and Ti/Al) were used to distinguish variegated sediment provenance in the Berounka system. Normalization of trace elements by Ti (in the case of trace elements) and by Fe (magnetic susceptibility) allowed us to establish lithogenic background functions of trace elements and magnetic susceptibility within these two geologically different areas. A pollution assessment of the study area was performed using magnetic susceptibility and local enrichment factors (LEFs) for the risk elements. By comparing 1/(LEF Pb) and Pb isotopic composition, the origins of Pb within the catchment were determined. This unique method was able to distinguish Pb from various origins. The upper parts of the floodplain cores contained higher levels of trace elements and magnetic particles (anthropogenically polluted), but samples taken from the cores in the active channel belt exhibited considerably higher concentrations of trace elements and magnetic particles than the upper parts of the floodplain cores and to much greater depths. We interpreted the deeper parts of the floodplain cores as a local lithogenic background. The upper parts of floodplain sediments hence showed moderate pollution (LEF of Pb and Zn ∼2, MS ∼2.5); whereas laterally deposited sediments showed significantly higher LEF values (LEF of Pb ∼6, Zn ∼9, MS ∼8). The analysis of the sediments confirmed that the Berounka River system contains higher concentrations of trace elements and magnetic particles than can be accounted for by natural geological processes. Our pollution assessment of the Berounka River and its tributaries demonstrated that their sediments are moderately polluted from sources situated on its tributaries: Ag–Pb mining near the city of Střibro in the Mže catchment; Pb–Zn mining in the Přibram ore district in the Litavka catchment and Fe ore processing and smelting in the Klabava catchment.