Twenty adults used two sunscreens made with zinc oxide enriched above 99% in 68Zn, one with about 19 nm particles and one with larger particles averaging 110 nm, for five outdoor days. Blood and urine were collected before, during, and six days after exposure. Small increases in tracer 68Zn appeared in blood and urine. The nanoparticle group in women showed the largest blood signal. The authors state that the chemical form crossing the skin, particles or dissolved zinc, was not determined.
Key numbers
Figures below are copied as printed. Units are not converted. Species are not merged.
| Analyte | What was reported | Value | Unit | Basis | Where |
|---|---|---|---|---|---|
| ZnO | Av dose (mg/cm2) | 5.1 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 5.3 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 3.7 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 4.7 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 5.1 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 3.8 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 4.0 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 3.9 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 3.7 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 4.6 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 4.6 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 3.8 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 3.7 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
| ZnO | Av dose (mg/cm2) | 4.3 | mg/cm2 | topical application rate of sunscreen formulation | Table 1, p. 32 |
The structured evidence record for this source holds 84 copied values. The table above is the short set.
Methods (brief)
Sunscreens contained about 20% weight/weight enriched ZnO. Mean application was 4.3 mg/cm2 (range 2.8 to 5.8), twice daily for five days on a cut-out area of the back. Isotopic change was expressed as delta68Zn%, the percentage difference in the 68Zn/64Zn ratio versus each person’s pre-exposure ratio. Total zinc was measured by ICP-MS. A separate tape-strip check used 2 mg/cm2.
Evidence fitness
These data support Outdoor application of sunscreens containing about 20% w/w 68Zn-enriched ZnO produced small increases in tracer 68Zn in blood and urine of every exposed subject; After 5 days, tracer in blood was about 1/1000 of total Zn in the blood compartment, and for the nanoparticle-female group the post-exposure blood tracer mass was 8.6 to 26.0 µg (mean 15.8 µg) against about 12 mg total Zn in whole blood; Mean whole-blood total Zn was 3.55 mg/L (range 2.36 to 4.62 mg/L).
They do not support Does not establish whether absorbed zinc was ZnO particles or soluble zinc; Does not report ZnO or Zn concentrations remaining in skin layers; Does not support a large fraction of the applied dose reaching blood: the printed blood tracer is less than 0.001% of the applied dose; High urine delta68Zn% peaks are not all interpretable as absorbed zinc; the authors separate a cluster consistent with sunscreen contamination of beach urine.
Limitations
Seventeen of 20 subjects finished all five days. Isotope ratios were complete only for pre-exposure, end of day 5, and post-exposure, with fuller time series for four subjects. Some beach urine samples are treated by the authors as contaminated. The trial lasted five days. No detection limit is printed for blood or urine zinc concentration. The study population is adults, so the mineral-sunscreen product suggestion is a category match only.
Related evidence
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