Unravelling metal mobility under complex contaminant signatures

Anderson Abel de Souza Machado; Kate L Spencer; Christiane Zarfl; Francis T O'Shea

doi:10.1016/j.scitotenv.2017.11.239

Unravelling metal mobility under complex contaminant signatures

Sci Total Environ. 2018 May 1:622-623:373-384. doi: 10.1016/j.scitotenv.2017.11.239. Epub 2017 Dec 13.

Authors

Anderson Abel de Souza Machado¹, Kate L Spencer², Christiane Zarfl³, Francis T O'Shea⁴

Affiliations

¹ Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany; Department of Biology, Chemistry and Pharmacy, Freie Universität Berlin, Altensteinstr 6, 14195 Berlin, Germany; School of Geography, Queen Mary University of London, Mile End Road, London E1 4NS, UK. Electronic address: machado@igb-berlin.de.
² School of Geography, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
³ Center for Applied Geosciences, Eberhard Karls Universität Tübingen, Hölderlinstr 12, 72074 Tübingen, Germany.
⁴ School of Geography, Queen Mary University of London, Mile End Road, London E1 4NS, UK; Geography Department, Kings College London, Strand, London, WC2R 2LS, UK.

PMID: 29216472
DOI: 10.1016/j.scitotenv.2017.11.239

Abstract

Metals are concerning pollutants in estuaries, where contamination can undergo significant remobilisation driven by physico-chemical forcing. Environmental concentrations of metals in estuarine sediments are often higher than natural backgrounds, but show no contiguity to potential sources. Thus, better understanding the metal mobility in estuaries is essential to improve identification of pollution sources and their accountability for environmental effects. This study aims to identify the key biogeochemical drivers of metal mobilisation on contaminated estuarine sediments through (1) evaluation of the potential mobilisation under controlled conditions, and (2) investigation of the relevance of metal mobilisation for in situ pollution levels in an area with multiple contaminant sources. Sediments from a saltmarsh adjacent to a coastal landfill, a marina, and a shipyard on the Thames Estuary (Essex, UK) were exposed in the laboratory (24h, N=96, 20°C) to water under various salinity, pH, and redox potential. Major cations, Fe(II), and trace metal concentrations were analysed in the leachate and sediment. Salinity, pH and redox had a significant effect on metal mobilisation (p<0.001), e.g. under certain conditions Fe(II) leaching was increased ~1000-fold. Measurements in situ of surface and subsurface sediment cores revealed that landfill proximity poorly explained metal spatial distribution. However, physicochemical parameters explained up to 97% of geochemically normalized metal concentrations in sediments. Organic matter and pH were dominant factors for most of the metal concentrations at the sediment surface. At subsurface, major cations (Ca, Na, Mg and K) were determinant predictors of metal concentrations. Applying the empirical model obtained in the laboratory to geochemical conditions of the studied saltmarsh it was possible to demonstrate that Fe mobilisation regulates the fate of this (and other) metal in that area. Thus, present results highlight the importance of metal mobility to control sediment pollution and estuarine fate of metals.

Keywords: Coastal landfill; Contaminant mixtures; Estuaries; Pollution assessment; Sediment geochemistry.