Mercury contamination associated with artisanal gold mining on the island of Mindanao, the Philippines

The Agusan River basin of eastern Mindanao, the Philippines, hosts several centres of artisanal gold mining, the most important of which, Diwalwal, is a significant gold producer in global terms. An investigation of the envir onmental impacts of artisanal mining in the Agusan system, with particular reference to mercury contamination, was initiated in 1995 following reports of several incidents of human Hg poisoning in the province of Davao del No rte. Results show drainage downstream of Diwalwal is characterised by extre mely high levels of Hg both in solution (maximum 2906 mu g/l) and in bottom sediments (> 20 mg/kg). Filtered surface water Hg levels exceed the WHO Dr inking Water guideline and the US-EPA Water Quality Criteria for the Protec tion of Aquatic Life for a downstream distance of more than 14 km, includin g channel sections utilised for fishing and potable water supply. The Envir onment Canada sediment quality Hg Toxic Effect Threshold for the Protection of Aquatic Life is exceeded for a downstream distance of 20 km. Hair Hg da ta indicate that ballmill and CIP plant operators processing Hg contaminate d tailings at eastern Mindanao's principal gold beneficiation centre, Apoko n, may be subject to enhanced occupational Hg exposure. It appears that the wider population of this area has not been affected. (C) 1999 NERC. Publis hed by Elsevier Science B.V. All rights reserved.