The experiment

Grab your coffee and enjoy the second installment of a two-part series written by guest writer, Madison Toonder. She continues with her investigation into the effects of sunscreen on oysters. If you missed her first post (or it has been awhile since you read it) in which she discusses how she got started on her project, check it out here!



“For two consecutive years, I researched the effects of chemical active ingredients in micronized chemical (spray) sunscreen, nanosized zinc sunblock and non-nanosized zinc oxide sunblock on the oyster and discovered how harmful micronized products are on these bivalves …”

Researchers theorize that some types of nanoparticles may build up in the bivalve mollusk’s system over time and linger in their bodies up to three days longer than any nutritive material because of their small size. Based on studies regarding the negative impact of chemical sunscreen used by humans, I also hypothesized that micronized chemical sunscreen would lead to rapid deterioration of oyster health. Because oysters are so small, mortality after introduction of chemical sunscreen was also likely.

My experimentation process consisted of introducing oyster clumps to micronized chemical sunscreen and nanosized zinc oxide sunblock in separate controlled environments. I tested outside temperature, water temperature, pH (acidity), nitrate, nitrite, ammonia, and turbidity (cloudiness) every 12 hours to analyze tank conditions and repeated this for 21 days. I took pictures and noted my observations of oyster behavior and filtration capacity throughout testing.


One of the most challenging aspects of designing my research plan was determining an accurate concentration formula of how much sun protection to add to the tanks. After numerous discussions with mentors, I discovered a formula based on the percentage of sun protection in sewage water. In order to determine the amount of sun protection to best replicate the quantity of pollutants in estuaries and bays, a simple mathematical formula was developed: based on the concentration of active ingredients in the sun protection and the amount of water in my trial tanks:

C1V1 = C2V2

The mathematical formula (initial concentration x initial volume = final concentration x final volume) was used to calculate the amount of sunscreen to add to the tanks based on the percent of active ingredients in the sun protection as well as the amount of water in the tanks to best replicate ‘natural’ quantities.  The target concentration of 2µg of active ingredients per 1L of bay water was used.

My data supported my hypothesis.


As predicted, the introduction of zinc oxide nanoparticles led to a gradual decline in the filtration ability of the oysters. This is attributed to the theory that nanoparticles of non-nutritive materials can remain in the bivalve mollusks system for three days longer than nutritive particles (algae), potentially affecting their filtration capacity. Additionally, both trials confirmed that bivalve mollusks exposed to micronized chemical sunscreen died after five days of exposure. The chemicals in the sunscreen infiltrated their system and caused irreparable damage, which led to their death. Micronized chemical sunscreen also contains oxybenzone, a fast-acting hormone disruptor; this potentially affected oyster cellular activity and minimized essential bodily function.


Therefore, chemical sunscreen seems to have an immediate effect on the bivalve mollusk whereas zinc oxide nanoparticles have a more gradual negative impact. Finally, in support of sustainable procedural design and proper care of organisms, the oysters in the control tank filtered consistently throughout experimentation, as expected.

Oysters in the GTM Research Reserve

Because my research demonstrated that sun protection containing nanoparticles of zinc oxide and micronized chemicals negatively affects oysters, consumers can be better educated about how their sun protection choices affect the environment around them. This newfound knowledge can specifically apply to promoting more efficient conservation techniques for the oyster population and overall estuary health.

What can you do to help?

An easy way for you to make a difference is to use natural alternative, non-nanosized zinc oxide sunblock rather than micronized chemical spray sunscreen or nanosized sunblock. I would recommend This woman makes her own products with all natural ingredients!  You can find the recipe and make it yourself at home (like I did in my research) or purchase it from her.

In summary, as researchers continue to better understand the role pollutants, like sunscreen, play on the population and health of the shellfish, the human impact on the ecosystem can be made more efficient.

Madison Toonder, High School Student

Madison is an 11th grader from FL who attends Stanford University Online High School. She aspires to be an exotic/marine animal veterinarian with a focus on conservation of endangered species. In the pursuit of this career, she conducts scientific research on the oyster, sea turtle, alligator and pangolin with scientists across the world and competes in science fairs up to the national level. Two years ago, she was named second in the nation in STEM mathematics by Broadcom Foundation for her environmental oyster data. She has been recognized by NOAA for “Taking the Pulse of the Planet” and was a recipient of the 2016 Sea World Busch Gardens Environmental Excellence Award. At Stanford OHS, Madison is leading a social media conservation initiative with SeaWorld MyActions as a part of Student Service Board. Last year she founded the Pre-Veterinary Club in order to connect aspiring veterinarians and encourage conservation. She currently is the elected vice president of National Beta Club and co-founder and leader of UNICEF club.  In her free time, she regularly volunteers at a veterinary hospital where she assists in patient diagnosis, care and surgery. In addition, Madison interns at the Brevard Zoo as a zoo teen and conservation representative; she routinely handles exotic animals such as the Ball Python, Red Rat Snake and Northern Blue-Tongued Skink. Madison is constantly expanding the reach of her conservation message by speaking at numerous environmental events and writing conservation blogs. She has served as a panelist at Brevard Zoo’s Youth Environmental Summit and been writing about her conservation message for the past 3 years. Last winter, she was selected as key note speaker for GTMNERR’s “Friends of the Reserve” event.

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