Zinc : the invisible threat

Between 2007 and 2009 a BGS team undertook a comprehensive monitoring programme — using flow measurements, synoptic sampling, and zinc isotopes — of the Rookhope Burn catchment in the Weardale valley, North Pennines. This area has been subject to historical mining of lead and zinc for over two centuries. Zinc is the major contaminant; exceeding the environmental quality standards (EQS) value for salmonid fish where three adits discharge significant quantities of mine water with a Ca-HCO3-SO4 composition enriched with calcium sulphate and bicarbonate to the Rookhope Burn. Areas of contaminated land, spoil heaps, tailings dams and stream sediments also act as potential sources of contamination. Distinctive increases in zinc load in the Rookhope Burn occur as a result of major visible point sources of mining-related contamination (mine adits) and subsurface diffuse contributions of mine water through the river bed.