Model Sunscreen UV Filter Breakdown in Water

ISEF Category: Chemistry

Subcategory: Environmental Chemistry  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

Sunscreen does not just sit still in water. Sunlight can change its molecules, and that can change how long they last and what they turn into. If you like chemistry that links to oceans, pools, and public health, this topic gives you a real problem to model and test.

What Is It?

This project looks at what happens to common sunscreen UV filters, like oxybenzone and avobenzone, after they hit sunlight in water. Think of each molecule like a tiny solar shield. When UV light hits it, the molecule can absorb energy, change shape, or break apart. Those changes affect how much UV protection stays in the water and what new compounds form.

You can study this in two layers. First, DFT, which stands for density functional theory, helps you predict how a molecule absorbs light and how stable it is in different forms. Second, reaction kinetics tracks how fast the molecule changes over time. Put together, those tools let you connect molecular structure with real-world breakdown in pool or seawater.

Why This Is a Good Topic

This makes a strong science fair project because you can ask a focused question, gather measurable data, and connect chemistry to a real environmental issue. You can compare different water conditions, different UV filters, or different light exposures. The project also teaches you modeling, calibration, and data analysis, which matter in real research. A student can make real progress without inventing a new instrument.

Research Questions

• How does water type, such as pool water versus artificial seawater, change the rate of UV filter breakdown under sunlight?
• What is the effect of pH on the photochemical fate of oxybenzone in water?
• Does avobenzone degrade faster than oxybenzone under the same light exposure conditions?
• To what extent do dissolved salts change the colorimetric signal used to track sunscreen breakdown products?
• Which exposure condition, direct sunlight, shaded sunlight, or indoor UV lamp, produces the fastest loss of UV filter signal?
• How does temperature affect the apparent reaction rate of a sunscreen UV filter in water?

Basic Materials

• UV filter standards or consumer sunscreen products with labeled active ingredients.
• Clear quartz or UV-transmitting glass containers.
• Artificial seawater mix or salt, and deionized water.
• Pool water samples or pool chemistry simulator reagents.
• pH strips or a digital pH meter.
• Smartphone camera with manual exposure control.
• White background and fixed photo box for consistent imaging.
• Colorimetric reagent chosen from published methods for the target UV filter or degradation marker.
• Digital kitchen scale with 0.1 g accuracy.
• Notebook or spreadsheet for tracking sample IDs and exposure times.

Advanced Materials

• UV-Vis spectrophotometer.
• Fluorescence spectrometer, if the method uses a fluorescent marker or product.
• HPLC or LC-MS access for product confirmation.
• Computational chemistry software for DFT calculations.
• Access to a workstation or cluster for quantum chemistry runs.
• Quartz cuvettes.
• pH meter and conductivity meter.
• Controlled light source with known spectrum.
• Analytical balance.
• Filtration supplies and solvent-grade reagents for sample cleanup.

Software & Tools

• Python: Organizes data, fits kinetic models, and graphs rate comparisons.
• ImageJ: Measures color intensity from photos of exposed samples.
• Excel or Google Sheets: Stores data, builds charts, and checks trends.
• Avogadro: Builds molecular structures before DFT calculations.
• ORCA: Runs DFT calculations for absorption and electronic structure if you have access to a suitable computer.

Experiment Steps

1. Define the exact sunscreen filter, water matrix, and light condition you will compare first.
2. Choose a measurable signal, such as absorbance, color shift, or product formation, and match it to a published method.
3. Set up control samples that separate light effects from dark storage and water chemistry effects.
4. Build a calibration plan so your signal can be converted into concentration or relative loss.
5. Plan your DFT targets, such as ground-state structure, excited-state proxy, or relative absorption trend, before running calculations.
6. Decide how you will compare kinetics across conditions using the same statistical test and graph format.

Common Pitfalls

• Using consumer sunscreen lotions with unknown additives, which hides the behavior of the UV filters you meant to study.
• Photographing samples under changing room light, which makes color measurements drift between sessions.
• Skipping dark controls, which makes you mistake storage loss for sunlight-driven photochemistry.
• Comparing pool water and seawater without matching pH or salt strength, which confounds the role of ions.
• Treating a single absorbance drop as proof of degradation, which can confuse photobleaching with true chemical breakdown.

What Makes This Competitive

A stronger project goes beyond a simple before-and-after test. You can compare multiple water chemistries, link measured rates to DFT-predicted absorption trends, and test whether your experimental ranking matches the model. Good controls, clean calibration, and a kinetic model with uncertainty analysis will make your work much stronger. A novel comparison, like real pool water versus artificial seawater versus freshwater, can also raise the project.

Project Variations

• Compare sunscreen filter breakdown in freshwater, pool water, and seawater to separate salt effects from light effects.
• Test whether mixed UV filters degrade differently than single-filter samples under the same sunlight exposure.
• Use a different analysis angle by modeling how pH changes the predicted absorption and observed reaction rate.

Learn More

• PubMed: Search for review articles on sunscreen photodegradation, oxybenzone, and avobenzone to find background chemistry and measurement methods.
• NOAA Ocean Service: Look for articles on sunscreen ingredients, coral exposure, and marine water chemistry context.
• NASA Earthdata: Use sunlight and UV-related datasets to connect exposure conditions to real outdoor measurements.
• PubChem: Check compound properties, structure files, and identifiers for oxybenzone and avobenzone.
• MIT OpenCourseWare Chemistry courses: Review lectures on molecular structure, spectroscopy, and kinetics to support your modeling work.