92 SUN CARE
69.6% O) samples. The dissolution of the filters in the marine environment can influence their toxicological effect. Therefore, inductively coupled plasma mass spectrometry (ICP-MS) was used to assess particle’s dissolution in seawater. Ti and Fe solubility was found to be negligible. Zn dissolution was observed, which increased over time and was related particle size: the higher concentration, after 72 hours, was 590µg/L of nano-ZnO, followed by 338µg/L of ZnO and 326µg/L of US (Table 1). Note that the US sample shows a larger
particle size and its composition includes not only zinc oxide but also titanium dioxide and silica. Therefore, the lower zinc solubility and lower potential release to the marine environment.
Ecotoxicity The environmental hazard was evaluated by means of acute ecotoxicological tests by using species at different levels of organization. First, the luminescent bacteria test (ISO 11348- 3:2007) was used to evaluate the toxicity (up to 30 minutes). Light production is directly proportional to the metabolic activity of the bioluminescent bacteria Vibrio fischeri population, the inhibition of enzymatic activity due to toxicity or cell death causes a decrease in the bioluminescence that is compared to a negative control (to measure the lethality). EHMC was the most toxic UV filter for Vibrio
fischeri: the effective concentration (EC) causing 50% inhibition was EC50 = 0.98 mg/L. Mineral filters containing zinc oxide showed lower toxicity compared to that of the chemical filter. Ordered from highest to lowest effect: nano-
ZnO (EC50 = 1.936 mg/L), ZnO (EC50 = 2.268 mg/L) and US (EC50=4.426 mg/L). Titanium based mineral filters showed no toxicity: TiO2 (Titanium Dioxide), UT (Titanium Dioxide, Silica), UTM (Titanium Dioxide, CI-77492, Silica,
6 5 4 3 2 1
0 0
6 5 4 3 2 1
0 0 0.01 0.1 1 10 100 0.01 0.1 US 1 10 100 Nano ZnO Figure 1: Ecotoxicity increase on Vibrio fischeri dependent on filter characteristics
TABLE 1: ZINC SOLUBILITY IN SEAWATER Sample
Nano Zinc oxide
Time 0.25h 24h 48h µg/L
470 525 Zinc oxide (>100nm) 72h 0.25h 24h 48h 565 590 297 300 326
CI-77491, CI-77499) filters (Figure 1). Among the mineral UV filters, the toxicity
to Vibrio fischeri depends on several characteristics. Zinc oxide filters show half the toxicity (or lower) of the chemical filter, calculated from the ratio between EC50 values. This toxicity decreases with increasing
particle size to values above 100nm (nano ZnO NPs showed EC50 = 1.936 mg/L while ZnO showed EC50 = 2.268 mg/L) and with increasing zinc solubility (ICP-MS showed 470 µg/L for nano ZnO, the highest Zn release, while 297 µg/L for ZnO after 0.25 hours). The US filter, with a high zinc oxide content
in its composition, showed lower toxicity, 4.5 times lower than the chemical filter, calculated from the ratio between the EC50 values. This
6 5 4 3 2 1
mg/L 0 0
6 5 4 3 2 1
mg/L 0 0 0.01 0.1 1 10 100 0.01 0.1 1 UT 10 100 ZnO
6 5 4 3 2 1
mg/L 0 0
6 5 4 3 2 1
mg/L 0 0 0.01 0.1 1 10 Figure 2: Results of Artemia test after 24 hours (green continuous line) and 48 hours (yellow dashed line) exposition to mineral filters PERSONAL CARE August 2025
www.personalcaremagazine.com 100 0.01 0.1 UTM 1 10 100 222 US (>100)
72h 0.25h 24h 48h 338
286 292
72h 326
can be explained by a combination of lower Zn solubility (222µg/L after 0.25 hours), larger particle size (higher than 100nm) and the combination (interaction) with titanium dioxide (shown by SEM-EDX). In addition, the US filter has been shown to
achieve SPF50 and broad-spectrum protection with 15wt% concentration in formula, while a chemical filter needs to be combined with others. Furthermore, if the maximum permitted
concentrations are compared (25wt% vs. 10wt%) and a corrections factor is applied, the US filter becomes 11 times less toxic. The influence of the chemical composition is evident because titanium oxide-based filters are inert: TiO2 (Titanium Dioxide), UT (Titanium Dioxide, Silica) and UTM (Titanium Dioxide, CI-77492, Silica,
TiO2
24h ■ 48h ■
mg/L
mg/L
nº mobile nauplii (total=5)
nº mobile nauplii (total=5)
nº mobile nauplii (total=5)
nº mobile nauplii (total=5)
nº mobile nauplii (total=5)
nº mobile nauplii (total=5)
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