Abstract
The impact of discharges from abandoned metal and ironstone mines has been a much studied form of aquatic pollution in recent decades. Few attempts however, have been made to accurately determine the overall contaminant mass flux arising from abandoned mine sites at scales above catchment level. Such assessments are critical to determine the significance of former mining to national, regional and ultimately global trace metal flux. This paper presents the most comprehensive national survey to date across England and Wales of the total pollution burden discharged at source from abandoned non-coal mine sites. 338 discharges have been identified (from 4923 known abandoned metal mines) and while concurrent flow and contaminant concentration records are only available for around 30% of these, significant quantities of metals (and As) have been quantified to be discharged. A minimum of 193 tonnes of Zn, 18.5 tonnes of Pb, 0.64 tonnes Cd, 19.1 tonnes of Cu, 551 tonnes Fe, 72 tonnes Mn and 5.1 tonnes As are released in water discharges from abandoned non-coal mines to the surface water environment of England and Wales each year. Precautionary extrapolation of mass fluxes based on the frequency distribution of measured concentration and flow data, for discharges with absent data, suggests that the actual total mass flux for these contaminants could be up to 41% higher. The mass flux of Pb released from mines exceeds that of all currently permitted discharges (e.g. active industrial sites and wastewater treatment works) to surface waters across England and Wales, while those of As, Cd and Zn are of a similar magnitude. These data put into context the enduring legacy of historic mining on the water environment, highlighting its significance relative to more highly regulated polluting sites. Comparison of the figures with estimates of global trace metal flux suggests that the national total identified here is significant on a global scale.
Highlights
Anthropogenic perturbation to global trace metal cycles has long been identified since the pioneering atmospheric trace metal inventories of Nriagu (1978) and Lantzy and Mackenzie (1979)
Data have been collated from national environmental archives, published and grey literature and manually collected from abandoned metal mines to detail the mass flux of a suite of trace elements from polluting mine sites into the water environment of England and Wales
67% of the Zn flux reported arises from the ten most polluting discharges. Extrapolation of these data using a series of sub-median centile data derived from frequency distributions of some of the most commonly monitored metals (Cd, Pb and Zn) and flow suggest their total fluxes could be in the region of 27-41% higher when datasets for flow and water quality become more complete
Summary
Anthropogenic perturbation to global trace metal cycles has long been identified since the pioneering atmospheric trace metal inventories of Nriagu (1978) and Lantzy and Mackenzie (1979). Few attempts have been made since to provide a detailed regional or global flux estimate for the mining sector on emissions to the water environment due to (a) the lack of suitably comprehensive datasets of source discharge flow and quality on which to base such assessments and (b) the short half lives of trace metal contaminants in the aqueous phase as they rapidly transfer from water column to fluvial sediments (Nriagu and Pacyna, 1988). The latter point renders assessments of metal discharge flux at source from ambient water quality monitoring stations problematic since they usually lie some distance downstream from polluting sources. Assessments of trace contaminant release at source are essential for fully appreciating the ongoing pollution inputs from abandoned mines into the surface water environment which contribute to the secondary sources of contaminated sediments in mining-affected river systems
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