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

Artisanal gold mining in the Ponce Enríquez, Portovelo-Zaruma and Nambija areas of Ecuador has resulted in extensive contamination of the fluvial environment by mercury (Hg) andpotentially toxic ore-related elements including arsenic (As),cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn). Thisoccurs principally through the fluvial dispersion ofcontaminated mineral processing wastes and recycling of Hgsublimated during the burning of amalgam. Mercuryconcentrations in filtered (<0.45 μm) surface waters do notexceed the WHO Drinking Water Guideline value and the USEPAWater Quality Criteria for the Protection of Aquatic Life.Criteria for other potentially harmful elements are, however,exceeded by a wide margin in the Ponce Enríquez (As, Cu,Zn) and Portovelo-Zaruma (Cd, Cu, Zn) districts, but not inthe Nambija area. The Environment Canada sediment quality HgToxic Effect Threshold for the Protection of Aquatic Life isexceeded in all three mining areas. As, Cd and Cu in manysediment samples from the Ponce Enríquez and Portovelo-Zaruma districts exceed Sediment Toxic Effects Thresholds byfactors of 10 to >1000. The results highlight the need toensure that contaminated sediment and water do not entercommercial banana plantations and shrimp ponds downstream ofthe Ponce Enríquez mining district.