Leaving plastic in sunlight
Severe impactEarth Action found UV can raise particle release up to 100×.
The short answer
The largest single multiplier in the published packaging work, and the most invisible. UV breaks polymer chains, which makes the surface chalky and brittle and dramatically increases how readily it sheds. A water bottle on a sunny windowsill, a case on a patio, or a bottle strapped to the outside of a rucksack all qualify.
Why it happens
- UV photons break carbon-carbon bonds in the polymer backbone
- The degraded surface becomes brittle and micro-cracked, so it releases particles readily
- The effect is cumulative and irreversible — the damage does not heal in the dark
- Clear plastic offers no protection; it transmits the UV doing the damage
The fix, easiest first
- Store water and oil in a cupboard, not on a windowsill or worktop
- Choose dark glass or opaque tins for anything light-sensitive
- Do not leave cases of bottled water outdoors or in a conservatory
- Replace any plastic that has gone chalky, faded or brittle
Packaging this applies to
PET plastic bottle
Polyethylene terephthalate, PET (#1)
Plastic squeeze bottle
LDPE or PET, flexible wall
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Get my exposure scoreFrequently Asked Questions
Does sunlight make plastic release microplastics?
The largest single multiplier in the published packaging work, and the most invisible. UV breaks polymer chains, which makes the surface chalky and brittle and dramatically increases how readily it sheds. A water bottle on a sunny windowsill, a case on a patio, or a bottle strapped to the outside of a rucksack all qualify.
Why does this happen?
UV photons break carbon-carbon bonds in the polymer backbone. The degraded surface becomes brittle and micro-cracked, so it releases particles readily. The effect is cumulative and irreversible — the damage does not heal in the dark. Clear plastic offers no protection; it transmits the UV doing the damage.
What should I do instead?
Store water and oil in a cupboard, not on a windowsill or worktop. Choose dark glass or opaque tins for anything light-sensitive. Do not leave cases of bottled water outdoors or in a conservatory. Replace any plastic that has gone chalky, faded or brittle.
Sources
- Earth Action with rePurpose Global (2026). Microplastic migration from food and beverage packaging (reported May 2026). Forbes.
- Qian N, Gao X, Lang X, et al. (2024). Rapid single-particle chemical imaging of nanoplastics by SRS microscopy. Proceedings of the National Academy of Sciences (PNAS).
- Winkler A, Santo N, Ortenzi MA, et al. (2022). Does mechanical stress cause microplastic release from plastic water bottles?. Water Research.
- Hernandez LM, Xu EG, Larsson HCE, et al. (2019). Plastic teabags release billions of microparticles and nanoparticles into tea. Environmental Science & Technology.