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 a reas of Ecuador has resulted in extensive contamination of the fluvial envi ronment by mercury (Hg) and potentially toxic ore-related elements includin g arsenic (As), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn). This oc curs principally through the fluvial dispersion of contaminated mineral pro cessing wastes and recycling of Hg sublimated during the burning of amalgam . Mercury concentrations in filtered (<0.45 mum) surface waters do not exce ed the WHO Drinking Water Guideline value and the USEPA Water Quality Crite ria for the Protection of Aquatic Life. Criteria for other potentially harm ful 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 Na mbija area. The Environment Canada sediment quality Hg Toxic Effect Thresho ld 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 Portov elo-Zaruma districts exceed Sediment Toxic Effects Thresholds by factors of 10 to > 1000. The results highlight the need to ensure that contaminated s ediment and water do not enter commercial banana plantations and shrimp pon ds downstream of the Ponce Enriquez mining district.