Afonne and Ifediba 2020 — Heavy metals risks in plant foods (Current Opinion in Toxicology)
This review in Current Opinion in Toxicology synthesizes research on heavy metal contamination in plant foods — cereals, root and tubers, fruits and vegetables — with emphasis on the health risks from consuming contaminated crops grown in industrially and agriculturally polluted soils. The authors argue that agricultural wastewater irrigation, fertilizer use, mining, and urban pollution in densely populated developing countries have created a dietary heavy metal exposure burden that demands precautionary regulatory response. Codex CXS 193-1995 FAO/WHO maximum levels in plant foods are tabulated: Pb in cereal grains 0.2 mg/kg, root/tubers 0.1 mg/kg, fruity vegetables 0.05 mg/kg, leafy vegetables 0.3 mg/kg; Cd in cereal grains 0.1 mg/kg, rice 0.4 mg/kg. The review covers rice arsenic contamination comprehensively, notes that rice near mining areas in central China exceeded regulatory limits, and discusses maize, potato, wheat, cassava, and leafy vegetable contamination studies from Nigeria, Tanzania, Slovakia, Kosovo, and China.
Key numbers
Regulatory limits cited (Codex FAO/WHO, Table 1):
- Pb: cereal grains 0.2 mg/kg, pulses 0.2 mg/kg, root/tubers 0.1 mg/kg, fruits 0.1 mg/kg, fruity vegetables 0.05 mg/kg, leafy vegetables 0.3 mg/kg, legume vegetable 0.1 mg/kg, vegetable oil 0.1 mg/kg
- Cd: cereal grains 0.1 mg/kg, rice 0.4 mg/kg, pulses 0.1 mg/kg, root/tubers 0.1 mg/kg, bulb vegetables 0.05 mg/kg, leafy vegetables 0.2 mg/kg, legume vegetable 0.1 mg/kg, rice 0.2 mg/kg, vegetable oils 0.1 mg/kg
- As: no Codex ML specified in this review (cited as unspecified)
- tHg: no Codex ML specified for plant foods (cited as unspecified)
Key findings cited from primary studies:
- Rice near three mines in central China (Fan et al. 2017): arsenic and Cd exceeded regulatory limits in brown rice; Hazard Index 22.6 for Pb, Cd, As, Mn, Sb combined; 99.77% of cancer risk from Cd
- Maize at a Tanzania gold mine: Hg above maximum tolerable limits (Koleleni and Mbike 2018)
- Wheat (16 cultivars, China): As, Cd, Pb decrease in order root > leaf > stem > grain; Cd accumulated more than As or Pb; child THQ for As > 1
- Nigeria food crops (Iruekpen, 15 crops): Cr and Pb exceeded HRI > 1 in 7 crops (Afonne et al. 2017, the authors’ own prior work)
- Water spinach near Dutch municipal solid waste landfill: Cd and Pb 5–86 times above WHO permissible limit in edible parts
- Potatoes from Slovak region post-mining: Pb, Cd below regulatory standards; low risk from potato consumption
- Cassava from industrial sites: heavy metals above FAO/WHO permissible limit
Methods (brief)
Narrative review, Current Opinion in Toxicology themed issue on Risk Assessment in Toxicology, edited by Orisakwe and Simmons. Published January 2020 (available online). Evidence tier A: peer-reviewed in a respected toxicology journal; the review draws on a wide geographic evidence base and covers all major plant food classes. Key limitation: narrative (not systematic), no pooled quantitative estimates, and all concentration data are secondary, requiring trace-back to cited primary studies for HMT&C use.
Implications
Certification: The Codex limit table is a useful secondary summary cross-checking against primary Codex CXS 193-1995. The central-China mining-area rice findings (Fan et al. 2017, cited) are relevant for iAs/Cd in rice ingredient sourcing. Geographic origin is a key risk discriminant for plant foods.
Courses: Covers the main plant food classes systematically — good for the ingredient contamination module. The Nigeria food crop health risk study (Afonne et al. 2017) is a concrete developing-country case study. The precautionary measures section (good agricultural practices, organic planting, soilless agriculture, washing) is directly applicable to the mitigation module.
App: Regulatory limits table provides Codex caps for app risk flagging: rice Cd 0.4 mg/kg, cereal grain Pb 0.2 mg/kg.