Notable case, Portovelo e Zaruma, El Oro, Ecuador
Portovelo-Zaruma gold district and the Puyango-Tumbes River
Portovelo-Zaruma, río Puyango-Tumbes
In southern Ecuador 87 gold-processing centres at Portovelo and Zaruma use mercury amalgamation and cyanidation on polymetallic ores and discharge into the Puyango-Tumbes River. Mercury, cyanide and metals travel tens of kilometres downstream and reach Peru.
At a glance
- Status
- Not addressed
- Media
- surface water, sediment, living organisms
- Kind of site
- mining
- Area. No area in the sources consulted. Free cyanide is high in the river water for 50 km below the plants; mercury in sediment peaks in the first 40 km. The coordinates are those of Zaruma.
Contaminants
Status
Not addressed
The plants are working. A communal tailings facility has been built at Portovelo, but the need to truck tailings up to it makes poor compliance with weakly enforced rules likely (Marshall et al. 2020). The pollution crosses the border: in Peru, in the Puyango-Tumbes watershed, pregnant women have more mercury in their hair than in neighbouring areas (Chapela-Lara et al. 2025).
Story
Zaruma is a mining town of Spanish foundation (the first settlements in the region date from 1549, according to Wikipedia). Today the district consists of small mines and the processing centres that serve them: 87 plants along the river, producing about 6 tonnes of gold a year (Marshall et al. 2018). The ore is first amalgamated with mercury; the tailings, still rich in gold and by then contaminated with mercury, are then leached with cyanide.
Between 2012 and 2014 total mercury in sediment over the 40 km below the plants ranged from 0.78 to 30.8 mg/kg in the dry season and from 1.80 to 70.7 mg/kg in the wet season, almost always above the Canadian probable effect level of 0.5 mg/kg; arsenic, cadmium, copper, lead and zinc were measured alongside it (Marshall et al. 2018). Mercury isotopes made it possible to follow the plants' signature in downstream sediment, across the border with Peru (Schudel et al. 2018).
Free cyanide in surface water is high for 50 km, peaking at 9,088 times the Canadian standard of 5 µg/L. Cyanidation of contaminated tailings forms mercury-cyanide complexes, which are highly bioavailable: in laboratory tests fish accumulate mercury in muscle and kidney, almost all of it inorganic (Marshall et al. 2020).
Timeline
- 1549First Spanish settlements in the Zaruma region (Wikipedia).
- 20142012–2014 measurement campaigns of mercury and metals in Puyango water and sediment.
- 2018Mercury isotopes demonstrate the transboundary pollution towards Peru.
- 2020Data on cyanide in the river, high for 50 km below the plants, are published.
Health
At Portovelo and Zaruma, 865 urine samples from miners were analysed to estimate the prevalence of mercury values above 25 µg/L (Schutzmeier et al. 2016). Downstream, in Peru's Tumbes region, 148 pregnant women had on average 2.08 µg/g total mercury in hair and 45% exceeded 2.0 µg/g; the median was higher in the Puyango-Tumbes watershed (2.72 µg/g) than in the other zones (Chapela-Lara et al. 2025).
Remediation
- —tailings containmentCommunal tailings facility at Portovelo, to reduce discharge to the river; tailings must be trucked there and compliance is uncertain (Marshall et al. 2020).
Plants and fungi at this site
Microbial bioremediationLaboratory, with soil from the site
Bacillus safensis
Laboratory test on mine tailings from Zaruma: a strain of the Bacillus safensis group mobilises lead, in an experimental design varying initial pH, temperature, incubation time and solids concentration. The study assesses bacteria-mediated environmental mobility of lead rather than a ready remediation technique.
Outcome Maximum lead mobilisation of 1,278.76 mg/kg, a 96.51% release, at pH 5.75 and 31 °C.
From the literature
Species that acted on one of this site's contaminants in at least one study. The list is automatic and takes no account of this site's soil, concentrations or climate.
Plants
- Agrostis capillarisCommon bentEvidence: field
- Arabidopsis halleriHaller's rockcressEvidence: field
- Cannabis sativaIndustrial hempEvidence: field
- Eichhornia crassipesWater hyacinthEvidence: field
- Festuca rubraRed fescueEvidence: field
- Noccaea caerulescensAlpine pennycressEvidence: field
Fungi
- Funneliformis mosseaeEvidence: greenhouse
- Rhizophagus irregularisEvidence: greenhouse
- Paxillus involutusBrown roll-rimEvidence: greenhouse
- Aspergillus nigerBlack mouldEvidence: laboratory
- Mucor circinelloidesEvidence: laboratory
- Suillus luteusSlippery jackEvidence: laboratory
The rest are on the contaminant pages.
Sources
- Marshall B.G. et al. Evidence of transboundary mercury and other pollutants in the Puyango-Tumbes River basin, Ecuador-Peru. Environmental Science: Processes & Impacts, Royal Society of Chemistry, 2018
- Marshall B.G. et al. Cyanide Contamination of the Puyango-Tumbes River Caused by Artisanal Gold Mining in Portovelo-Zaruma, Ecuador. Current Environmental Health Reports, Springer, 2020
- Schudel G. et al. An investigation of mercury sources in the Puyango-Tumbes River: Using stable Hg isotopes to characterize transboundary Hg pollution. Chemosphere, Elsevier, 2018
- Schutzmeier P., Berger U., Bose-O'Reilly S. Gold Mining in Ecuador: A Cross-Sectional Assessment of Mercury in Urine and Medical Symptoms in Miners from Portovelo/Zaruma. IJERPH, MDPI, 2016
- Chapela-Lara S. et al. Mercury Levels in Hair of Pregnant Women in Tumbes, Peru: A Cross-Sectional Study. American Journal of Tropical Medicine and Hygiene, ASTMH, 2025
- Zaruma, Wikipedia (en), 2026
Draft compiled from public sources, not yet reviewed.