Samm, UR - We're at the End of the Line.

Well, we've finally reached the end of the semester. My research project has been challenging to say the least, between changing methods and trying to figure out how to use those rascally little test strips. But it's been a real learning experience, and I'm anxious to share my results!

A Look Back in Time

For those of you who are now just joining in, I have based my project on a study done this past summer in Spain, where two researchers found that zinc oxide and titanium dioxide (both ingredients found in a variety of sunscreens) were reacting with ultraviolet light from the sun to create new compounds, such as hydrogen peroxide.

These ingredients mix react with UV lights and create excited electrons. Excitation is the process when an electron gains energy and cannot remain in it's particular orbit, so it goes to another orbit with a higher energy. As it leaves, a hole is created. The hole causes water to break up and become a free radical and hydrogen. The excited electron reacts with the oxygen already present in the water, which then reacts with the hydrogen created from the hole, and finally creates hydrogen peroxide.High levels of hydrogen peroxide can be toxic, especially to phytoplankon, which the two researchers found can inhibit their growth and development. This is primarily bad because phytoplankton are at the very bottom of the food chain. From small zooplankton, to large whales, phytoplankton help feed the entire ocean, making them extremely crucial in the food chain. 

With this knowledge, I wanted to learn more about how zinc oxide levels change over time in water from sunscreen. So, my scientific question became:

When under ultraviolet light, how will sunscreens containing zinc oxide concentrations change over time in fresh water?

I used Babo Botanicals Clear Zinc Sunscreen, and pure zinc oxide as sunscreen test subjects. I decided to make pure zinc oxide as one of my sunscreens so that I could tell if any other ingredients in sunscreen would affect the readings. In order to make the pure zinc oxide into a paste, I had to mix the flour-like substance with deionized water (DI H2O). I used seven glass beakers, 250mL in size. Three beakers were smeared with roughly 20g of Babo Botanicals sunscreen, three beakers were smeared with roughly 20g of the pure zinc oxide paste, and one beaker was kept unsmeared, as a control. All the beakers were filled with 250mL of DI water. All of the beakers were put into a UV Box. Once a day, for five days I tested each beaker with Sensafe's Water Metals Check Test Strips. I dipped the test strip into the beaker and gently swirled it around for 20 seconds, then let it sit for another 2 minutes. After that time, I had a 30-second window to match the colour on the strip with the colour chart on the bottle of test strips. Once that was done, I lined all the test strips for that day into a tupperware lined with paper towel so that the test strips could dry without contaminating each other.

The images above are the results from my test strips. The first image is organized by Day (Control, Babo 1, Babo 2, Babo 3, Pure Zn 1, Pure Zn 2, and Pure Zn 3), while the bottom image is organized by test subject, Day 1-5. Unfortunately, the colour on my test strips does not match the colours on the bottle (which I will attend to in a minute), so in order to create a graph of my data, I used a simple scale of 1-5 as my concentration of metals present in the water (1 being the lightest, 5 being the darkest and present of the most metals).

My graph was made by averaging the three Babo Botanicals beakers and then averaging the three pure zinc paste beakers for each day, and using those points on my line graph. The control test strips were the only ones to get a reading of 1, seeing as they showed no signs of metal leeching. All Babo Botanical and pure zinc oxide test strips were given a reading of  2-5.

I have found that the Babo Botanicals Clear Zinc Sunscreen had higher concentrations of metals in the water, even though I used slightly more pure zinc paste to line the beakers. This could be because there are many more inactive ingredients in retail sunscreen that give it texture and scent, which could be reacting with water and UV light along with the zinc oxide. If I had to do this experiment again (which I definitely want to!), I would most definitely NOT use those test strips. A huge problem was that the colour of my test strips did not match up at all with the colour chart provided to me on the bottle.

While the chart colours are tan going to dark brown at best, all of my test strips were red/purple! And even though after they dried I was able to detect a difference in shade, trying to compare the tan/brown to my reds was like trying to compare apples to oranges!