Tatsuta et al. 2024 — Dietary methylmercury intake by 0–5 year-old children, Japan (duplicate diet)
This is the first study to apply the 24-hour duplicate-diet method to estimate methylmercury (MeHg) intake by Japanese infants and children aged 0–5 years across the formula-milk, baby-food, and toddler-meal stages. Across 276 three-day dietary duplicate samples, median estimated MeHg intake was 18.3 ng/kg bw/day (5–95th percentile 0.65–209.2 ng/kg bw/day) — highest at baby food stages 3 and 4 (9–17 m) and toddler meal stages 1–2 (18–47 m). Hair total mercury (THg) median was 1.05 ppm; 51.8% of children had hair THg above the EPA-equivalent 1.0 ppm RfD threshold and 15.6% above the 2.2 ppm PTWI threshold. Authors conclude MeHg intakes in some Japanese children exceed reference and PTWI levels because Japanese cuisine commonly uses lean fish (tuna, bonito, yellowtail, horse mackerel, sardines) in baby and toddler meals.
Key numbers
Sample structure (n=276 dietary samples, 260 children): Formula milk 0–4 m, n=32; Baby food Stage 1 (5–6 m), n=30; Stage 2 (7–8 m), n=38; Stage 3 (9–11 m), n=38; Stage 4 (12–17 m), n=35; Toddler meal Stage 1 (18–35 m), n=33; Stage 2 (36–47 m), n=33; Stage 3 (48–71 m), n=37. (Table 1)
Method detection limits: THg MDL 0.03 ng/g, MQL 0.08 ng/g (CVAAS, MA-3000); MeHg MDL 0.18 ng/g, MQL 0.45 ng/g (GC-ECD with dithizone-toluene extraction). Concentrations <MDL substituted by half MDL.
THg in diet samples (median, ng/g wet basis, with 5–95th percentile; Table 2):
- Formula milk: 0.020 (0.015–0.099); samples <MDL 62.5%, <MQL 31.3%
- Baby food Stage 1: 0.085 (0.017–0.974); <MDL 13.3%, <MQL 40.0%
- Stage 2: 0.150 (0.020–2.905); <MDL 13.2%, <MQL 26.3%
- Stage 3: 0.445 (0.181–5.500); <MDL 0%, <MQL 0%
- Stage 4: 0.500 (0.134–3.620); <MDL 0%, <MQL 8.6%
- Toddler meal Stage 1: 0.510 (0.184–3.630); <MDL 0%, <MQL 3.0%
- Stage 2: 0.490 (0.204–4.260); <MDL 0%, <MQL 3.0%
- Stage 3: 0.450 (0.192–1.900); <MDL 0%, <MQL 5.4%
Estimated daily THg intake (median, ng/kg bw/day; Table 2): Formula milk 2.4 (0.5–6.9); Baby Stage 1 4.2 (0.5–14.0); Stage 2 7.0 (0.6–103.3); Stage 3 25.0 (8.5–492.8); Stage 4 41.0 (7.9–329.6); Toddler Stage 1 32.4 (11.0–259.9); Stage 2 36.0 (9.5–252.9); Stage 3 25.2 (8.4–125.6).
MeHg measured directly only in samples with THg ≥1 ng/g (n=63; 22.8%). Median MeHg/THg fraction across positive samples 90.0% (Table 3). MeHg in positive baby foods: Stage 1 (n=2) median 2.60 ng/g (1.16–4.04); Stage 2 (n=6) 2.55 (0.95–3.68); Stage 3 (n=12) 2.05 (0.97–6.75); Stage 4 (n=16) 1.55 (0.96–3.63). Toddler meals: Stage 1 (n=11) 1.40 (0.92–6.25); Stage 2 (n=10) 1.65 (0.94–6.52); Stage 3 (n=6) 1.60 (0.84–2.50).
Estimated MeHg intake across all participants (THg × 0.90 method-of-construction; Table 4, n=276): Formula milk median 2.2 ng/kg bw/day (0.5–6.2); Baby Stage 1 3.8 (0.4–12.6); Stage 2 6.3 (0.5–93.0); Stage 3 22.5 (7.6–443.5); Stage 4 36.9 (7.1–296.6); Toddler Stage 1 29.2 (9.9–233.9); Stage 2 32.4 (8.5–227.6); Stage 3 22.7 (7.5–113.0). Median MeHg intake across all stages 18.3 ng/kg bw/day (5–95th 0.65–209.2).
Hair THg (median ppm, 5–95th, % over EPA RfD 1.0 ppm equivalent, % over PTWI 2.2 ppm equivalent; Table 5): Formula milk 1.2 ppm (0.4–3.9); 59.4% over 1.0 ppm and 15.6% over 2.2 ppm. Baby Stage 1 1.0 (0.3–2.5), 46.7% / 6.7%; Stage 2 0.6 (0.2–1.4), 23.7% / 2.6%; Stage 3 0.7 (0.3–1.9), 34.2% / 0%; Stage 4 1.0 (0.3–4.4), 51.4% / 20.0%. Toddler Stage 1 1.4 (0.6–2.8), 78.8% / 21.2%; Stage 2 1.3 (0.3–6.0), 63.6% / 30.3%; Stage 3 1.3 (0.4–4.5), 62.2% / 29.7%. Overall n=276 (143 children stratified): hair THg median 1.1 ppm (0.3–4.0); 51.8% above 1.0 ppm; 15.6% above 2.2 ppm.
Correlations between dietary MeHg intake and hair THg (Table 6): Formula milk r = −0.403 (p=0.030); Baby Stage 4 r = 0.493 (p=0.002); Toddler Stage 1 r = 0.343 (p=0.044); Toddler Stage 2 r = 0.401 (p=0.021); other stages non-significant.
QA: CRMs ERM BD-150 (skimmed milk powder, n=9) recovery 88–92% for THg; SRM1567b (wheat flour, n=9) 96–130%; DORM-4 (fish protein powder, n=3) 98–102% for MeHg. Hair reference materials NIES No.13 and IAEA-086: mean inter-day RSDs 1.8% and 2.3% respectively.
Methods (brief)
24-hour duplicate diet method per WHO Guidelines: all consumed foods (including water, supplements, beverages) collected in clean polypropylene containers over 3 consecutive days; samples refrigerated and shipped to laboratory; homogenized, lyophilized, and powdered. THg measured by cold vapor atomic absorption spectrometry (CVAAS, Hg-201, Sanso Inc., Tokyo) following acid digestion per Mercury Analysis Manual; MeHg measured by GC-ECD (G2700, Yanaco Analytical Systems, Kyoto) after alkaline decomposition and dithizone-toluene extraction. Hair THg measured on first day of dietary sample collection from 3 cm from occiput root using direct thermal decomposition-gold amalgamation CVAAS (MA-3000, Nippon Instruments). MDL for THg in diet 0.03 ng/g, MQL 0.08 ng/g; MeHg MDL 0.18 ng/g, MQL 0.45 ng/g. <MDL values substituted by half MDL. Recovery for ERM BD-150 88–92%, SRM1567b 96–130%, DORM-4 98–102%. Authors note MeHg measurement was only feasible in samples with THg ≥1 ng/g; for the remaining 213 samples, MeHg intake was estimated by multiplying THg by 90% (the median MeHg/THg ratio observed in measurable samples). Authors note residence near coastal areas was associated with higher hair THg.
Implications
- Certification (HMTc): Provides Japanese baby- and toddler-stage MeHg dietary intake distribution, directly relevant to MeHg-bearing infant and toddler matrices (fish-containing baby foods, fish-containing mixed meals). Shows that dietary MeHg intake escalates dramatically from formula stage (median 2.2 ng/kg bw/day) to baby-food stage 4 and toddler-meal stages 1–2 (median 29–37 ng/kg bw/day), consistent with the entry of fish into the diet.
- Courses: Strong regulatory-affairs and supply-chain case study on how the 24-hour duplicate-diet method captures total dietary exposure that food-only occurrence studies miss, and on the wide range of MeHg intake driven by the fish content of national cuisines. Useful for QA teams analyzing fish-containing baby and toddler products.
- App: Adds Japanese baby-food and toddler-meal stage-specific MeHg dietary intake distribution. Reinforces the case for tracking MeHg separately from total Hg in infant/toddler product profiles and for treating MeHg as the matrix-driven analyte on the product layer rather than the ingredient layer.
Wiki pages this source may touch
- mercury-methyl
- mercury-total
- fish
- infant-formula-powder
- meat-and-poultry-purees
- fish-containing-baby-foods
- infant-formula-powder
- efsa-methylmercury-twi
- epa-iris-methylmercury-rfd
- jecfa-methylmercury-ptwi
Page history
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