Assessment of metal contamination in a small mining- and smelting-affected watershed: high resolution monitoring coupled with spatial analysis by GIS

Abstract

The Riou Mort River watershed (SW France), representative of a heavily polluted, small, heterogeneous watershed, represents a major source for the polymetallic pollution of the Lot-Garonne-Gironde fluvial-estuarine system due to former mining and ore-treatment activities. In order to assess spatial distribution of the metal/metalloid contamination in the watershed, a high resolution hydrological and geochemical monitoring were performed during one year at four permanent observation stations. Additionally, thirty-five stream sediment samples were collected at representative key sites and analyzed for metal/metalloid (Cd, Zn, Cu, Pb, As, Sb, Mo, V, Cr, Co, Ni, Th, U and Hg) concentrations. The particulate concentrations in water and stream sediments show high spatial differences for most of the studied elements suggesting strong anthropogenic and/or lithogenic influences; for stream sediments, the sequence of the highest variability, ranging from 100% to 300%, is the following: Mo< Cu < Hg < As < Sb < Cd < Zn < Pb. Multidimensional statistical analyses combined with metal/metalloid maps generated by GIS tool were used to establish relationships between elements, to identify metal/metalloid sources and localize geochemical anomalies attributed to local geochemical background, urban and industrial activities. Finally, this study presents an approach to assess anthropogenic trace metal inputs within this watershed by combining lithology-dependent geochemical background values, metal/metalloid concentrations in stream sediments and mass balances of element fluxes at four key sites. The strongest anthropogenic contributions to particulate element fluxes are 90-95% for Cd, Zn and Hg in downstream sub-catchments. The localisation of anthropogenic metal/metalloid sources in restricted areas offers a great opportunity to further significantly reduce metal emissions and restore the Lot-Garonne-Gironde fluvial-estuarine ecosystem.

Experimental Study of Mobility and Kinetic Characterization of Trace Elements in Contaminated Sediments from a River Basin in Northern Peru

“…Compared with trace metal contents from mine sites in France, Chile, and Bolivia, Cu concentrations in all points are high (Coynel et al 2009;Higueras et al 2004;SalvarredyAranguren et al 2008, Yacoub et al 2014. Minimal variations between samples were obtained for Ni concentrations.…”

Spatial Cadmium Distribution in the Charente Watershed and Potential Risk Assessment for the Marennes Oleron Bay (Southwest France)

“…Note that this Riou Mort River in the Charente watershed is not identical with the well-studied Riou Mort River draining the polluted Decazeville basin, responsible for important historical polymetallic (mainly Cd, Zn, Cu, Pb, Hg, Ag) pollution in the Lot-Garonne river continuum (e.g. Blanc et al, 1999;Audry et al, 2004;Coynel et al, 2009 …”

“…Collected just after a strong hydrological event, the geochemical composition of these samples corresponds to the maximum particulate transfer to the estuary and coastal zone. Unlike SPM, whose composition can rapidly fluctuate, stream sediments integrate metal contamination (Coynel et al, 2009). …”

“…The preferential accumulation of metals, either of natural or anthropogenic origin, in the fine-grained sediment fractions may induce grain size effects and reduced sample representativeness (Förstner & Wittmann, 1981;Horowitz, 1991;Benoit & Rozan, 1998). Therefore, stream sediment samples were sieved (<63 µm; nylon sieves) to remove coarse material which was obviously not representative of typical grain size of suspended sediment (Coynel et al, 2009). …”

“…Cd, Zn, Hg, Ag; Blanc et al, 1999;Schäfer et al, 2006;Castelle et al, 2009;Larrose et al, 2010;Lanceleur et al, 2011) contamination due to former Zn ore treatment in the industrial Decazeville basin, that was stopped after a major pollution accident in 1986. In this watershed drained by the Riou Mort River, anthropogenic contributions to particulate element fluxes were estimated to ~90-95% for Cd, Zn and Hg (Coynel et al, 2009). Despite decreasing Cd emissions in the Decazeville area due to ongoing remediation efforts since the early 1990s, the Lot-Garonne River system still contributes up to 80% to the annual Cd gross fluxes into the Gironde Estuary Audry et al, 2004).…”