Fluvial contamination associated with artisanal gold mining in the Ponce Enriquez, Portovelo-Zaruma and Nambija areas, Ecuador

Artisanal gold mining in the Ponce Enriquez, Portovelo-Zaruma and Nambija areas of Ecuador has resulted in extensive contamination of the fluvial environment by mercury (Hg) and potentially toxic ore-related elements including arsenic (As), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn). This occurs principally through the fluvial dispersion of contaminated mineral processing wastes and recycling of Hg sublimated during the burning of amalgam. Mercury concentrations in filtered (<0.45 mum) surface waters do not exceed the WHO Drinking Water Guideline value and the USEPA Water Quality Criteria for the Protection of Aquatic Life. Criteria for other potentially harmful elements are, however, exceeded by a wide margin in the Ponce Enriquez (As, Cu, Zn) and Portovelo-Zaruma (Cd, Cu, Zn) districts, but not in the Nambija area. The Environment Canada sediment quality Hg Toxic Effect Threshold for the Protection of Aquatic Life is exceeded in all three mining areas. As, Cd and Cu in many sediment samples from the Ponce Enriquez and Portovelo-Zaruma districts exceed Sediment Toxic Effects Thresholds by factors of 10 to > 1000. The results highlight the need to ensure that contaminated sediment and water do not enter commercial banana plantations and shrimp ponds downstream of the Ponce Enriquez mining district.