Román-Ochoa et al. 2021 — Heavy metal contamination in Arequipa region grains and processed foods
This is the first published report of heavy metals in grains and processed grain products from Arequipa, Peru’s major southern agricultural region. The study measured As, Cd, Sn, Pb, and Hg in 18 districts across Arequipa, plus processed foods from Arequipa city markets, using ICP-MS and CVAAS. The most concerning finding is that Pb concentrations in extruded, toasted, and flour-based processed products were dramatically elevated (mean 2.12 mg/kg) compared to raw grain averages (mean 0.03 mg/kg), with the elevation attributed to processing conditions. Polished and paddy rice As concentrations were within CAC general standards (0.2 mg/kg for cereals), but health risk assessment using uncertainty analysis found unacceptable cancer risk (above 10⁻⁴) for the P₉₀ₜₕ of polished rice and quinoa products.
Key numbers
Mean concentrations in raw grains (mg/kg, Table 1):
- Quinoa: As 0.06, Cd 0.02, Sn 0.00, Pb 0.04, Hg 0.003
- Maize: As 0.03, Cd 0.02, Sn 0.00, Pb 0.01, Hg 0.003
- Rice (paddy + polished): As 0.17, Cd 0.11, Sn 0.02, Pb 0.04, Hg 0.004
- Bean: As 0.02, Cd 0.01, Sn 0.00, Pb 0.01, Hg 0.003
- Total average grains: As 0.02, Cd 0.01, Sn 0.00, Pb 0.03, Hg 0.01
Mean concentrations in processed products (mg/kg, Table 1):
- Quinoa products: As 0.05, Cd 0.04, Sn 0.00, Pb 0.55, Hg 0.004
- Maize products: As 0.01, Cd 0.00, Sn 0.00, Pb 0.75, Hg 0.004
- Rice products: As 0.05, Cd 0.01, Sn 0.03, Pb 5.08, Hg 0.003
- Total average processed: As 0.04, Cd 0.02, Sn 0.02, Pb 2.12, Hg 0.002
CAC maximum levels for cereal grains: As 0.2, Cd 0.1, Pb 0.2 mg/kg Rice As (0.17 mg/kg) within standard; rice Cd (0.11 mg/kg) above standard; processed rice Pb (5.08 mg/kg) dramatically above standard.
LOD values: As 0.95, Cd 33.10, Sn 18.19, Pb 1.30 ppt LOQ values: As 3.13, Cd 109.23, Sn 60.04, Pb 4.29 ppt
Methods (brief)
ICP-MS (ELEMENT2, Thermo Fisher Scientific) and CVAAS (EPA SW 846 Method 7471B). Microwave-assisted digestion (MARS6, CEM). Grain and processed food samples (250 g) collected from 18 Arequipa districts and 3 Arequipa city markets, April–December 2019. All samples triplicated. Uncertainty analysis (5th, 50th, 90th percentiles) for EDI, HI, and TR via Monte Carlo approach.
Limitations
As values for rice are reported as total arsenic, not speciated; iAs fraction unknown for this region. Grain collection was cross-sectional (single period), preventing seasonal assessment. Processing Pb elevation is reported but specific processing steps (extrusion, toasting) responsible are not isolated. The n=53 total food types across broad categories is modest.
Implications
- Certification: Processing-associated Pb spike in rice and quinoa products is a certification-relevant finding. Raw grain Pb may be compliant while processed-product Pb is not — relevant for product-category distinctions. Flags need for finished-product testing, not just ingredient testing.
- Courses: Illustrates processing as a Pb amplification pathway (contact with equipment). First-mover paper for Arequipa — geographic gap filling.
- App: Total As 0.17 mg/kg (170 µg/kg) for Peruvian rice aligns with global south-central South American rice being high-risk for arsenic. No iAs speciation available.