Estimation of background reference concentrations for metals in UK freshwaters

This report provides estimates of ambient background concentrations (ABCs) for several metals and one metalloid in UK freshwaters. ABCs are defined as concentrations representing low anthropogenic inputs, rather than natural backgrounds.  Specifically, this report aims to: 

• Establish a practical methodology for the use of freshwater monitoring data to estimate ABCs for UK hydrometric areas and water bodies, as defined under the Water Framework Directive. 
• Collate freshwater monitoring data from England, Wales, Scotland and Northern Ireland for dissolved concentrations of copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), zinc (Zn) and arsenic (As). 
• Where possible, estimate ABCs from these data for individual hydrometric areas. 
• Outline uncertainties in the methodology and discuss options for how ABCs may be used in a compliance assessment framework and what may done when too few quality data are available for the derivation of hydrometric area-specific ABCs. 
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