Flood-related contamination in catchments affected by historical metal mining: An unexpected and emerging hazard of climate change

• Pb concentrations in flood sediments exceed threshold values, in some samples by a factor of 82.
• Contamination of animal feed caused blood Pb poisoning and mortality in cattle.
• Climate change means that the events of summer 2012 are likely to continue and intensify.
• A geomorphological approach is needed to understand metal flux in fluvial systems.

Floods in catchments affected by historical metal mining result in the remobilisation of large quantities of contaminated sediment from floodplain soils and old mine workings. This poses a significant threat to agricultural production and is preventing many European river catchments achieving a ‘good chemical and ecological status’, as demanded by the Water Framework Directive. Analysis of overbank sediment following widespread flooding in west Wales in June 2012 showed that flood sediments were contaminated above guideline pollution thresholds, in some samples by a factor of 82. Most significantly, silage produced from flood affected fields was found to contain up to 1900 mg kg− 1 of sediment associated Pb, which caused cattle poisoning and mortality. As a consequence of climate related increases in flooding this problem is likely to continue and intensify. Management of contaminated catchments requires a geomorphological approach to understand the spatial and temporal cycling of metals through the fluvial system.