Zhao et al. 2024 — Toxic metals and metalloids in food: global occurrence, dietary intake, and mitigation
This peer-reviewed narrative review from Nanjing Agricultural University synthesises the contamination status of arsenic (As), cadmium (Cd), and lead (Pb) across 25+ food categories, drawing on Total Diet Study data from Australia, Brazil, France, Japan, New Zealand, Singapore, and 19 European countries, and assesses dietary intake relative to health-based guidance values. The central finding is that for the general population dietary intake remains generally below JECFA/EFSA guidance values, but vulnerable populations — infants, children, and pregnant women — are at or above those values for iAs and Cd. Mitigation strategies at the agronomic, processing, and supply-chain level are catalogued.
Key numbers
Arsenic — total As in food (Table 1, TDS-aggregated national means):
- Seafood: dried seaweeds 0.114–236 mg/kg tAs (n=953); fish 0.10–62 mg/kg (n=1,409); shellfish/molluscs 0.09–66 mg/kg (n=171)
- Rice 0.002–1.83 mg/kg tAs (n=1,693)
- Cereals (excluding rice) 0.007–0.43 mg/kg (n=410)
- Vegetables 0.001–1.27 mg/kg (n=2,503)
- Mushrooms 0.011–5.79 mg/kg (n=302)
Arsenic — iAs in rice (29-country global survey, 1,180 polished rice samples):
- iAs range: <0.002–0.39 mg/kg
- 0.4% of samples exceeded the EU/Codex maximum level for iAs in polished rice (0.2 mg/kg)
- For infant rice products: 17.6% of the same global survey exceeded the 0.1 mg/kg limit for infants
- South American rice showed relatively high iAs; North American and European rice showed higher DMA proportions than Asian rice
- US rice median tAs 0.25 mg/kg; France 0.28 mg/kg; Egypt 0.04 mg/kg (901 polished samples, 10 countries)
- Hijiki seaweed (Hizikia fusiforme): tAs mean 110 mg/kg, iAs mean 77 mg/kg — a notable iAs outlier in seafood
Cadmium (Table 1, national mean ranges across 19+ countries):
- Shellfish/molluscs: 0.01–4.8 mg/kg (n=7,403) — highest Cd food category
- Cocoa, tea, coffee: 0.0001–1.8 mg/kg (n=3,505)
- Offal (liver/kidney): 0.03–0.5 mg/kg (n=1,406); poultry offal 0.006–0.5 mg/kg (n=1,224)
- Nuts/oilseeds: 0.02–0.1 mg/kg (n=350)
- Vegetables: 0.006–0.1 mg/kg (n=18,183); leafy vegetables accumulate more than root/legume types
- Rice: national means 0.004–0.02 mg/kg (n=2,295); below EU (0.15 mg/kg) and FAO/WHO (0.4 mg/kg) limits at the national mean level, but wide within-country variance (India: 0.005–1.005 mg/kg; China: <0.001–0.74 mg/kg with 2.2% above 0.2 mg/kg)
- Cereals (excluding rice): ND–0.02 mg/kg (n=12,637); wheat 0.009–0.04 mg/kg (n=1,503)
Lead (Table 1, national mean ranges):
- Coffee/tea/cocoa: ND–1.03 mg/kg (n=764) — highest Pb category reported
- Vegetables: ND–0.4 mg/kg (n=13,402)
- Alcoholic beverages: ND–0.38 mg/kg (n=2,304)
- Rice: ND–0.004 mg/kg (n=85) at national means; global survey of 782 market rice (13 countries) found Pb 0.001–0.33 mg/kg; Chinese survey (712 milled rice) found Pb <0.005–0.4 mg/kg with 0.84% above 0.2 mg/kg
- Cereals: ND–0.029 mg/kg (n=5,027)
- Mining-impacted areas of Hunan, China: rice grain median Pb 0.05–0.78 mg/kg (11 sites); e-waste recycling area southeast China: mean rice Pb up to 2.04 mg/kg
Dietary intake (Fig. 2, cross-country summaries):
- Total As dietary intake: 9 µg/day (US) to 258.4 µg/day (Norway); grain-based products contribute 23% of iAs intake in Europe
- Dietary Cd intake: 4.6 µg/day (US) to 34.6 µg/day (Bangladesh); Bangladesh exceeds EFSA TWI of 21.4 µg/day; cereals contribute 26.6–65.4% of Cd intake in Asia vs Europe
- Dietary Pb intake: varies from 1.8 to 35.4 µg/day across countries
Health-based guidance values (Table 2):
- iAs: JECFA BMDL05 3 µg/kg bw/day; EFSA BMDL01 0.3–8 µg/kg bw/day
- Cd: JECFA PTMI 25 µg/kg bw/month; EFSA TWI 2.5 µg/kg bw/week
- Pb: JECFA PTWI withdrawn (no threshold); EFSA BMDL01 0.50 µg/kg bw/day (neurotoxicity); BMDL10 0.63 µg/kg bw/day (chronic kidney disease)
Methods (brief)
Narrative review. Occurrence data in Table 1 are sourced from two large cross-national datasets (references 143 and 144 in the paper, identified as EFSA SCENIHR / GEMS Food databases). iAs data for the 29-country rice survey sourced from Meharg et al. (ref. 36). Dietary intake estimates compiled from national Total Diet Study publications. No primary analytical work; all values are re-analysed secondary data.
Implications
Certification: The review’s Table 1 provides a defensible multinational baseline for As, Cd, and Pb in 25+ food matrices against which HMT&C threshold-setting can be anchored. Key reference points: cocoa Cd to 1.8 mg/kg (raw cocoa bean end); shellfish Cd to 4.8 mg/kg; offal Cd 0.03–0.5 mg/kg; rice iAs 17.6% of global samples exceed the 0.1 mg/kg infant limit. These are literature-reported maximums/ranges, not distributions; they establish ceiling context rather than percentile distributions.
Courses: The iAs/tAs distinction is illustrated concretely: despite seafood having the highest tAs of any category (up to 236 mg/kg in seaweed), it poses lower iAs risk than rice because organoarsenicals dominate. DMMTA emergence in rice (converted to DMA by standard acid extraction, masking its greater cytotoxicity) is flagged as a future analytical concern. Hijiki seaweed is named as an iAs outlier (mean 77 mg/kg iAs) warranting category-specific risk assessment rather than reliance on total As alone.
App: The occurrence table supports per-ingredient risk tier assignments. Cocoa, offal, and shellfish rank highest for Cd; rice and seaweed rank highest for iAs; tea and cocoa contribute the highest Pb among commonly consumed ingredients. The global iAs exceedance rates for rice (0.4% of polished rice above 0.2 mg/kg; 17.6% above 0.1 mg/kg infant threshold) provide app-level probability anchors for rice-derived ingredients in infant products.