Yoshinaga and Ogawa 2025 — Duplicate diet study: dietary metal exposure in Japanese adults
This duplicate diet study measured 12 metals (V, Co, Ni, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, and Pb) in 150 complete 24-hour dietary samples from adult Japanese, collected 2017–2019. This is the gold-standard approach for dietary exposure assessment: participants consumed their normal diet and contributed a duplicate portion, which was then measured directly rather than estimated from food composition tables. The study confirms that diet is the predominant oral route of exposure for most metals, with soil and dust contributing 20–34% only for V, Sb, and Pb. All metals were below US EPA Reference Dose (RfD) thresholds, indicating low health risk in this population — consistent with Japan’s generally strong food safety regulation and low soil-metal contamination.
Key numbers
Median daily intake (µg/person/day, N=150):
- V: 7.20
- Co: 7.09
- Ni: 86.4
- Rb: 1,490 (1.49 × 10³)
- Sr: 1,210 (1.21 × 10³)
- Mo: 169
- Ag: < 0.71 (below LLD in many samples; n=83 non-detectable)
- Cd: 12.0
- Sb: 0.712 (n=49 non-detectable)
- Cs: 5.57
- Ba: 334
- Pb: 2.24 (n=65 non-detectable; susceptible to laboratory contamination)
Diet as fraction of total oral intake:
- Diet = ~100% for most metals
- V: diet ~66–80% (soil/dust 20–34%)
- Sb: diet ~66–80%
- Pb: diet ~66–80%
All values below EPA RfD (where RfD exists; Co, Rb, Cs, and Pb lack EPA RfD).
Cd context: Median 12.0 µg/person/day (approximately 0.17 µg/kg BW/day for 70 kg adult) — below EFSA TWI of 2.5 µg/kg BW/week (≈ 0.357 µg/kg/day). Consistent with prior Japanese duplicate diet data showing modest Cd intake reflecting rice consumption in the Japanese diet.
Pb note: 65 of 150 samples below LLD; susceptibility to lab contamination with trace Pb noted by authors. Median 2.24 µg/person/day is below prior NIHS market-basket estimates, which were consistently higher. Downward trend in Pb intake consistent with Japanese historical time-series data.
Method validation: CRM NIES No. 27 (Typical Japanese Diet) used; measured means agreed well with certified/reference values.
LLD (lower limit of detection) in dried diet samples: Metal-specific; values in Table 2 of original. ICP-MS detection with helium collision gas and on-line In-115 internal standardization.
Methods (brief)
24-hr duplicate diet collection from 150 adult volunteers. Samples freeze-dried and pulverised. Aliquot (50 mg) digested with ultrapure HNO3 in closed Teflon vessel (double-digestion method). ICP-MS (Agilent 8800), helium collision gas, In-115 internal standard, at National Institute for Environmental Studies (NIES), Japan. 3-σ LLD from procedural blanks (n=16). CRM NIES No. 27 for QA. Cd data recapitulated from previous study by same group (Yoshinaga and Ogawa, 2024).
Implications
Certification: Total diet study data from Japan is a relevant comparator for HMT&C exposure context. The Cd median intake (12.0 µg/day) reflects the Japanese dietary pattern (heavy rice reliance); diets in other markets may differ. Pb at 2.24 µg/day median from diet provides a baseline for how tightly the food supply needs to be controlled to achieve ongoing reductions.
Courses: This is a methodologically exemplary total diet study using the duplicate diet approach (most accurate method). The comparison between market basket (consistently higher Pb estimates) and duplicate diet (lower) illustrates how different dietary exposure methodologies yield different estimates; important for any audience evaluating exposure claims.
App: The metals measured here (V, Co, Ni, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, Pb) across the full Japanese diet provide population-level intake benchmarks. Ni intake of 86.4 µg/day is a relevant cross-check for ingredient-level Ni accumulation models. Note: this measures total dietary exposure, not individual food items, so it cannot be decomposed into per-ingredient contributions without additional data.