Sunlight and Plastic: What Your Bottled Water Might Be Emitting

Redacción HC
02/06/2024

We've long been told to avoid leaving bottled water in the sun—but new scientific evidence reveals it's not just about taste or temperature. A recent study published in Eco-Environment & Health reveals that exposure to UV-A or sunlight can cause plastic water bottles to emit dozens of volatile organic compounds (VOCs), some of which have potential toxic effects.

While the absolute concentrations are low, repeated exposure—especially in sunny environments or through habitual use—raises new questions about the chemical safety of bottled water packaging, particularly under common storage conditions.

Bottled Water Under the Microscope

Plastic bottles made of polyethylene terephthalate (PET) are prized for being lightweight and durable. But their chemical stability is challenged under light exposure. Researchers from Jinan University and the South China Institute of Environmental Sciences set out to systematically identify and assess VOC emissions from PET bottles when exposed to UV-A and sunlight over time.

Six commercially available water bottles sourced from different continents were exposed for 1 and 7 days to either UV-A light or natural sunlight—conditions that mimic typical consumer behavior such as leaving water in a car or on a sunny beach.

What the Study Found: Dozens of Emitted Chemicals

Using solid-phase microextraction (SPME) and gas chromatography–mass spectrometry (GC-MS), the researchers identified between 19 and 37 VOCs per bottle, depending on the exposure type and duration. Among them:

• Alkanes and alkenes (hydrocarbons)
• Alcohols
• Aldehydes
• Carboxylic acids
• Aromatic compounds

One standout compound, n-hexadecanoic acid, was flagged as the most toxic based on in silico (computer-based) toxicological predictions. Concentrations ranged from 0.11 to 0.79 nanograms per gram (ng/g) after 7 days of exposure—extremely small amounts, yet still noteworthy.

"Even low-level emissions may pose concern if repeated regularly or under high-heat conditions," the authors note.

Not All Bottles Behaved the Same

Interestingly, bottle composition mattered. For example, one bottle emitted 28 VOCs after just one day under UV-A light, increasing to 32 by day seven. Under sunlight, the same bottle released up to 30 VOCs. Another bottle peaked at 37 compounds, underscoring the variability between different plastic formulations and manufacturing processes.

In nearly all cases, over 50% of the VOCs were oxidized compounds or short-chain hydrocarbons—substances known to interact with indoor air chemistry and human respiratory systems.

"This isn't just about water quality; it's about the indoor and immediate air environment surrounding these bottles," explained Dr. Ruijuan Liu, lead researcher.

Should You Be Worried? Understanding the Real Risk

The individual exposure from a single opened bottle is minimal. The researchers estimate that even the most toxic compounds are present in quantities far below established health risk thresholds. However, the cumulative effect of repeated exposures, especially in hot climates, is less well understood.

Additionally, this study analyzed compounds released into the air, not directly into the water itself. Still, the potential for airborne inhalation exposure during bottle opening or prolonged storage in confined spaces (e.g., cars) should not be overlooked.

Implications for Public Health and Policy

For Consumers:

• Avoid leaving bottles in direct sunlight or hot environments for extended periods.
• Consume bottled water promptly after opening.
• Store water in shaded, cool places whenever possible.

For Manufacturers:

• Consider using UV-resistant packaging or antioxidant additives that mitigate VOC formation.
• Design clearer consumer labeling to discourage unsafe storage practices.

For Regulators:

• Develop updated safety standards that include VOC emission assessments from plastic food and beverage containers.
• Support long-term studies on the interaction between plastic packaging, sunlight exposure, and chemical safety.

"Regulatory frameworks must evolve to consider these low-level but widespread exposures," urges co-author Zongyi Tan.

A Global Perspective on a Local Habit

These findings are especially relevant for sunny regions like Latin America, where outdoor work, commuting, and recreation often mean bottled water is carried and stored in high-heat conditions. Public health campaigns could promote simple behavior changes—like carrying water in insulated bags or avoiding trunk storage—to help reduce unnecessary exposure.

As heatwaves become more frequent under climate change, these micro-level risks may take on greater public health significance, particularly for vulnerable populations such as children and the elderly.

Final Thoughts: When Plastics "Sweat" Chemicals

This study underscores that photodegradation of plastics isn't just an environmental issue—it's also a chemical exposure issue. The good news is that most of the VOC concentrations observed were well within safe limits. The challenge is in raising awareness, promoting responsible design, and building safeguards into everyday behavior.

"The risk isn't high—but it's persistent and invisible. Prevention is easy and costs nothing," conclude the authors.

Topics of interest

Pollution Health