Romero-Crespo et al. 2023 — Trace elements in crops and soils near Ecuador gold mining
Crops grown in agricultural orchards adjacent to the Ponce Enriquez gold mining field in southern Ecuador contained arsenic and cadmium concentrations that exceeded FAO/WHO maximum permissible levels in the majority of samples. Arsenic exceeded the FAO/WHO limit of 0.10 mg/kg fresh weight in 67% of crop samples; cadmium exceeded 0.05 mg/kg in 78% of samples. Lead was below the analytical detection limit (0.10 mg/kg) in all food samples despite elevated concentrations in some soils. Probabilistic health risk assessment using Monte Carlo simulation indicated that both children and adults face carcinogenic and non-carcinogenic risks through consumption of locally grown food that exceed acceptable thresholds, primarily driven by arsenic and chromium.
Key numbers
Crop concentrations (mg/kg fresh weight, n = 9 crop types): arsenic ranged not detected to 12.50 (lettuce), 8.42 (chives), 2.55 (turnips), 1.94 (carrots), 1.25 (herbs); cadmium ranged not detected to 1.64 (turnips), 1.01 (chives), 0.81 (lettuce), 0.72 (celery), 0.55 (herbs), 0.33 (carrots), 0.06 (cassava); chromium up to 3.04 mg/kg in lettuce (only sample exceeding FAO MPL of 2.30 mg/kg); nickel up to 9.10 mg/kg (herbs); lead below LOD (0.10 mg/kg) in all food samples; zinc ranged 12.91 (cassava) to 74.01 (celery) mg/kg.
Soil concentrations (mg/kg, n = 8 samples): arsenic 23.54–421.74; cadmium 1.06–1.94; chromium 77.24–101.04; nickel 50.21–67.58; lead 8.69–15.16; zinc 150.52–220.06. As, Cr, Cu, and Ni exceeded Ecuadorian quality guidelines for agricultural soils in all samples.
Hazard Index (HI) from total noncarcinogenic risk of dietary ingestion was above 1 for both adults and children. Total carcinogenic risk was 9.98 × 10⁻⁴ (above the acceptable 10⁻⁴ threshold). Sensitivity analysis identified arsenic in lettuce and chives as the dominant contributors to carcinogenic risk.
Methods: ICP-MS (Agilent 7700x) for Cd, Ni, Pb in soils; ICP-OES (Perkin-Elmer OPTIMA 5300DV) for food samples; certified reference material NIST Standard Tomato Leaves 1573a used for food QC; recovery 76–97%. Crop samples were washed with distilled water, lyophilised, and digested with concentrated HNO3/H2O2. Analysis is total arsenic (tAs); speciation into iAs/organoarsenic not performed.
Methods (brief)
Soil samples (5–20 cm depth, composite) and edible portions of nine crop types (celery, chives, corn, coriander herbs, lettuce, turnips, green beans, cassava, carrots) collected from orchards managed by the Association of Jancheras (women mine-rock waste collectors) in Ponce Enriquez, June 2021. Probabilistic health risk assessment used Monte Carlo simulation (Oracle Crystal Ball, 10,000 iterations) with triangular/lognormal/uniform distributions for exposure frequency, duration, and body weight. Analysis limited to total arsenic; no iAs speciation performed.
Implications
Certification: Highlights that mining-adjacent agricultural soils can produce crops with As and Cd far above international food safety limits even when soil Pb and Cd remain below regulatory soil thresholds. Relevant to supply-chain auditing for cocoa, coffee, and produce sourced from Ecuador’s mining regions.
Courses: Illustrates how artisanal gold mining (ASGM) with mercury-amalgamation and cyanidation generates soil As contamination that transfers to leafy vegetables and root crops at concentrations posing carcinogenic risk.
App: As and Cd data for lettuce, chives, carrots, turnips, cassava, corn, celery, herbs, green beans in a mining-influenced context; tAs, not iAs speciated.