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Title: Determination of Metal Background Reference Concentrations: Feasibility Study
Author: E.L. Ander
Author: S.T. Casper
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1582, Representation ID: 556, Object ID: 2726
New water quality standards proposed by the EU Water Framework Directive (WFD) for metals that are ‘specific or other polluting’ substances form the background to this project, whose purposes are two-fold: to compare natural concentrations of metals in UK waters with the proposed standards; and to establish what this entails for the ‘added risk’ approach to water quality assessment advocated by the WFD. The study compared natural background concentrations of nine metals (aluminium, arsenic, chromium, copper, iron, manganese, nickel, lead, zinc) in stream water in England and Wales with the proposed WFD standards. We found a range of natural background concentrations for these metals, highlighting the difficulty of using a single value for a background concentration. Analysis of the large dataset of stream water metal concentrations held by the British Geological Survey (BGS) (G-BASE project) showed that, for some metals, there would be widespread failure to meet the proposed WFD standards. In terms of the magnitude of failure for the different metals studied, we determined that there would be: - more than 75 percent failure for iron, arsenic and manganese; - more than 20 percent failure for aluminium, zinc and nickel (depending on the value of the standard used); - less than five percent failure for copper, chromium and lead. The data suggest that the proposed standards for iron, manganese and arsenic might be over-protective, and could be expected to generate additional work arising from compliance failure simply because of high natural background concentrations. However, existing standards for iron and arsenic are probably not protective enough, as they are rarely exceeded by natural background concentrations. This study also looked at the relationship between stream water metal concentrations and geological units, stream water pH, conductivity and organic carbon concentrations to help explain regions with high background concentrations. Such relationships can help to understand where failure to meet a given standard might be attributable to prevailing natural conditions, and could indicate where a locally derived MBRC might be more appropriate. This approach could also be used as part of a further assessment in response to compliance failure. The results of this project provide a strong case for amending proposed WFD standards for arsenic, iron, and manganese, and for implementing a compliance regime that will allow background concentrations of metals to be taken into account. Without these, there is a substantial risk of widespread failure to meet some standards, in some cases simply because of natural background levels. It is also unlikely to be cost-effective or even appropriate to try to reduce metal concentrations in water bodies failing WFD standards, where a substantial part of the metal comes from a natural rather than anthropogenic source.
Publisher: Environment Agency
Subject Keywords: GeochemistryMetalsWater qualityWater pollutionSurface waterArsenicChromiumIronManganeseLeadZincAluminiumRegulations
Extent: 163
Total file downloads: 336

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