Determination of background levels and pollution assessment for seven metals (Cd, Cu, Ni, Pb, Zn, Fe, Mn) in sediments of a Mediterranean coastal lagoon

Abstract

The determination of background levels of trace metals in soils and sediments is a key point for the proper assessment of pollution degree. This study demonstrates the suitability of integrating geological and statistical methods for the reliable determination of background levels, applying it to the sediments of Lake Albufera, a wetland of international importance that is highly eutrophic. The procedure followed includes sampling of sediment cores at different points of the lake, including reference sites, and the subsequent statistical analysis of the data, comprising descriptive statistics, probabilistic plots and modal analysis. The final proposal of background levels considers the data subset separated by the statistical analysis and the spatial and age characteristics of sediments, proving the usefulness of jointly using geological and statistical methods. The upper limits of the background populations, defined as the mean+2σ and expressed in mg/kg, are Cd (0.38), Cu (28.8), Ni (25.9), Pb (25.5), Zn (88.6), Fe (2.2%) and Mn (345.7). Background levels proposed for different parts of Spain, found in an extensive literature review, are also provided in this article. Once determined the background levels, the assessment of pollution degree of sediments using pollution indexes indicates that the top 25 to 30cm of sediments has a pollution level between moderate and severe in the peripheral sites, which are nearest to the pathways of contamination, and that the north zone of the lake is the most polluted by the group of the five metals, including Cd, Cu, Ni, Pb and Zn.