This modeling study took fresh-weight cerium concentrations from carrots grown in sand culture with cerium oxide nanoparticles or ionic cerium and projected dietary intake from one serving for seven age and body-mass classes. Because no oral reference dose exists for cerium, the authors compared intake with the mean and median oral reference doses of nine other rare earth elements. Peeling cut projected intake sharply, and conclusions about risk depended on which surrogate reference value was used.
Key numbers
- No oral reference dose for cerium was available; the median oral reference dose of nine other rare earth elements, 5 µg/kg body weight per day, was used as one surrogate (p. 3). The mean surrogate is printed as “171.9 mg kg-1 d-1” while the nine source values are given in µg/kg per day, so that unit appears to be a typographical error (p. 3).
- Maximum observed fresh-weight cerium in carrot: 65.8 mg/kg from the cerium oxide nanoparticle treatments and 126.9 mg/kg from the ionic cerium treatments (Table 1, p. 6).
- Fresh-weight cerium needed to reach the median surrogate reference dose in one serving: 1.0 mg/kg for children aged 1 to 3 years (13 kg) up to 6.1 mg/kg for males aged 19 to 30 years (76 kg); against the mean surrogate the range was 36.0 to 210.2 mg/kg (Table 1, p. 6).
- Projected intake from ionic cerium carrots was generally about double that from nanoparticle-treated carrots at the same treatment concentration (p. 4).
- Peeling reduced projected dietary intake by roughly 10-fold to 100-fold for both nanoparticle and ionic treatments (abstract, p. 1).
Methods (brief)
Carrots (cv. Danvers Half Long) were grown in sand culture with cerium oxide nanoparticles or ionic cerium(IV) at 0.5, 5, 50 or 500 mg/kg dry weight, alongside zinc and copper treatments (growth details in an earlier paper by the same group). Dry-weight peel and peeled-taproot concentrations were converted to fresh weight using water content, then combined with a standard serving mass and standard body masses to project intake for one serving on one day; reverse calculations estimated the tissue concentration that would reach the reference dose.
Evidence fitness
Useful as a screening scenario showing how cerium taken up by a root vegetable could translate into intake, and that peeling removes most of it. It does not describe cerium in carrots on the market, the treatment concentrations were deliberately wide, and the cerium reference values are surrogates borrowed from other rare earth elements rather than an established cerium value.
Limitations
Sand culture rather than soil; single cultivar; intake projected for a single serving; the surrogate reference dose spans two very different values (median versus mean) and the printed unit for the mean appears to be wrong. The source does not report the cerium chemical form inside carrot tissue.
Related evidence
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