Stasinos et al. (2014) published in the Journal of Food Science review the literature on heavy metal bioaccumulation in three common food tubers — carrots, onions, and potatoes — emphasizing the pathway from polluted irrigation water to food chain contamination, with particular focus on dietary implications for Cr and Ni. The paper spans studies from Latvia, Greece (Asopos River and Thiva basin), the United States, Spain, Morocco, and Poland. A key policy argument is that EU and US legislation set strict limits for heavy metals in water but lack correspondingly strict limits for food tubers, creating a regulatory gap that the authors urge EFSA to address. Children and pregnant women are identified as the highest-risk consumers.
Key numbers
Carrots (selected key values from compiled studies; units dry weight unless noted):
- Latvia farmlands: Ni 0.28 mg/kg, Cr 0.16 mg/kg, Pb 0.05 mg/kg, Cd 0.12 mg/kg (mean DW)
- Asopos River, Greece (polluted vs. control, wet weight): Ni 474 vs. 93 µg/kg (410% relative difference), Cr 43 vs. 20 µg/kg, Cd 11 vs. 4 µg/kg
- Thiva basin, Greece: Cr 1.9–4.1 mg/kg DW (mean 2.2), Ni 3.0–4.0 mg/kg DW (mean 3.5)
- Slag-contaminated soil (Germany): Pb up to 9.1 mg/kg DW in carrot roots (vs. 0.27 mg/kg control)
- Morocco/Spain: carrot Co 15.1–25.0 µg/kg (Morocco), carrot Ni 31.0–42.0 µg/kg (Spain)
- Treated sewage water irrigation: Cd ~0.15 mg/kg DW, Cr ~0.15 mg/kg DW, Ni ~0.3 mg/kg DW in irrigated carrots
Potatoes: Cd, Cr, Ni concentrations reviewed from multiple sites. Al tissue uptake in potato root inhibited cell elongation at pH 4.5. Cr tissue distribution: roots > shoots >> tubers, so edible tuber part contains less Cr than internal tissues.
Onions: soil Cr contamination >93% frequency in review areas; half of onions taking up >0.1 mg/kg Cd from contaminated soils.
Methods (brief)
This is a narrative review compiling data from ICP-MS, AAS (graphite furnace and flame), and ICP-OES studies. No original primary measurements. Studies reviewed used a variety of soil preparation methods; some use dry weight, some use wet weight, and the review does not always distinguish. Dietary implications section discusses Cr and Ni intake from these vegetables against EU tolerable daily intake (TDI) values. Limitation: no systematic meta-analysis or statistical pooling; heterogeneous units and bases across cited studies make direct comparisons difficult.
Implications
Certification: The carrot, onion, and potato concentration data (especially from irrigation-water-contaminated sites) is directly relevant to any certification scope that covers root vegetables. The Ni and Cr values in carrots from the Greek Asopos region (474 µg/kg Ni, 43 µg/kg Cr wet weight) represent polluted-site extremes; clean-background values from Latvia (0.28 mg/kg Ni DW, 0.16 mg/kg Cr DW) are more representative of commercial supply chains without industrial contamination.
Courses: Strong reference for the pathway from irrigation water quality to root vegetable contamination. The regulatory gap argument (water regulated, food tubers not) is useful for regulatory context modules.
App: Supports risk-flagging for carrots, onions, and potatoes as Ni and Cr accumulating root vegetables, particularly when irrigation source is unknown or from industrial areas.