Sunscreens are used to prevent UV rays from producing hydroxyl radicals, which can travel through the body, causing mutations and cancer. Zinc Oxide (ZnO) is used as a UV blocking pigment. However, ZnO is a photocatalytic particle, and it can potentially produce dangerous hydroxyl radicals outside of the body. Coatings on ZnO are sometimes used to minimize photocatalytic risks.

The purpose of this research is to study uncoated and coated Zno, its ability to produce hydroxyl radicals at levels found in sunscreens and at levels found in pools, and the effect of these particles on chlorination. My hypothesis is that uncoated Zno will produce hydroxyl radicals in water and pools. Coated ZnO will only produce hydroxyl radicals in pool water, because chlorine will degrade the coating. These radicals will in turn react with chlorine and hinder chlorination efficacy.

Water & Model Pool Water, undiluted ZnO Solutions (10% uncoated and coated Zno solutions in water and model pool water), and ZnO Solutions & Coppertone sunscreen diluted to pool usage level were tested for the production of hydroxyl radicals and effects on chlorination. Coated ZnO had a silicone coating.

The Methylene Blue Dve Test was used to qualitatively test for hydroxyl radicals through bleaching. Controls and Sunscreens diluted to pool usage levels tested negative for radicals. Undiluted Zno Solutions tested positive for radicals. Coated Zno in pool water had a stronger bleaching than coated ZnO in water, likely because chlorine reacted with the silicone coating.

To test effects on chlorination, sunscreen solutions were inoculated with I type of bacteria (M. Luteus, R. Rubrum, or B. Subtilis), representing the common bacterial shapes of spheres, spirals, and rods. I mL of sunscreen and bacteria was transferred to nutrient broth. Samples were incubated for 3 days at 37 degrees Celsius, and absorbance was measured before and after incubation. Change in absorbance was converted to bacterial growth ( of a petri dish) with a linear regression standard curve. Negative change in absorbance was equated to zero bacterial growth.

In water, 5.250% of a petri dish of M. Luteus, 62.64006 of a petri dish of B. Subtilis, 26.333% of a petri dish of R. Rubrum grew. In model pool water. M. Luteus and R. Rubrum did not grow, and 18.611% of a petri dish of B. Subtilis grew. No bacteria grew in uncoated ZnO solutions (lindiluted). In coated ZnO solutions, M. Luteus and R. Rubrum did not grow, while 27.173% of a petri dish of B. Subtilis grew in water, and 10.356% of a petri dish of B. Subtilis grew in model pool water. For sunscreen solutions diluted to pool water, there was bacterial growth similar to the controls.

AD ANOVA test found statistically significant differences between group means for bacterial growth in water compared with bacterial growth in Z10 solutions. Change in absorbance data was used for ANOVA statistical analysis, Paired T-Tests between absorbance data before and after incubation found insignificant bacterial growth in Zno solutions,

My results partially supported my hypothesis. Uncoated and coated ZnO solutions produced hydroxyl radicals in water and pool water. The silicone coating around Zno was ineffective in preventing hydroxyl radical production, especially in pool water. ZnO solutions inhibited bacterial growth, and Zno may have antibacterial properties.

Further research is necessary to determine the human health effect from exposure to free radicals outside the body, whether coatings around ZnO are ineffective (this study only tested silicone coatings), and if the antibacterial effects of ZnO are beneficial to humans.