Plastics Common in Food Containers and Bottle Caps Did the Most Damage<\/p>\n
All six plastics produced free radicals when exposed to water, but some produced far more than others. The most water-repelling plastics, polyethylene and polypropylene, were the most reactive, and PET and acrylic were the least reactive.<\/p>\n
When the researchers tested what the hydroxyl radicals could do, a common protein clumped together at the plastic surfaces \u2014 a sign that its structure had been damaged.<\/p>\n
Adding a substance that neutralizes free radicals reduced clumping, suggesting that the radicals caused the damage.<\/p>\n
In later experiments, red blood cells from mice broke into fragments after direct contact with the plastic particles. \u201cThe plastics that were most reactive at the surface did the most damage. That included polypropylene and polyethylene, the plastics used in a lot of food containers, packaging, and bottle caps,\u201d says Patel.<\/p>\n
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Water Molecules Behave Differently at the Surface of Plastic<\/p>\n
\u201cThe surprising part is that neither the plastic nor the water needs to be chemically unusual. What matters is the boundary where they meet,\u201d says Min.<\/p>\n
Water molecules behave differently when they\u2019re in contact with the surface of plastic, and that shift creates conditions where reactive molecules can form, he says. \u201cYou can think of this as a special chemical environment that emerges when two otherwise familiar materials come into contact,\u201d says Min.<\/p>\n
Over time, plastic breaks into smaller pieces. That process can accelerate with exposure to heat, sunlight, and wear and tear, such as squeezing a bottle or opening and closing its cap.<\/p>\n
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\u00a0The smaller the pieces get, the more surface area they have relative to their mass, which means more of the plastic is in contact with water and may make these reactions more important, says Min.Findings Suggest Not All Plastics Are Equal<\/p>\n
Researchers already know microplastics are everywhere, says Patel. \u201cWhat we\u2019re still figuring out is how they might cause harm. This study offers one explanation: The particle\u2019s surface may generate damaging molecules directly,\u201d she says.<\/p>\n
\u201cIt also suggests that not all plastics are equal. The more reactive types caused more damage. That could eventually help us prioritize which plastics to phase out of food contact and products used by children,\u201d she says.<\/p>\n
Strengths and Limitations of the Study<\/p>\n
The findings of the study were consistent: The lab experiments and computer simulations pointed to the same explanation, and the effect showed up in all six common plastics tested.<\/p>\n
But it\u2019s also important to be clear about what the study is and isn\u2019t, says Patel. \u201cThese are lab experiments. They don\u2019t show this is happening in people\u2019s bodies, or at what doses,\u201d says Patel.<\/p>\n
\u201cIt is also important to emphasize that science has not yet established exactly what levels of microplastic exposure cause harm in humans,\u201d says Min.<\/p>\n
Next, researchers want to learn whether these reactions cause damage in living cells and tissues, and if the effects depend on the type of plastic and the size of the particles, he says.<\/p>\n
Simple Ways to Reduce Microplastic Exposure<\/p>\n
Microplastics are so widespread that avoiding them completely probably isn\u2019t realistic, says Min. \u201cI would encourage people to take reasonable precautions without becoming unnecessarily alarmed,\u201d he says.<\/p>\n
\u201cThis study doesn\u2019t change what I do so much as reinforce it. If anything, it suggests that even \u2018clean\u2019 plastic without BPA or other additives may not be harmless, so \u2018BPA-free\u2019 shouldn\u2019t be the end of the conversation,\u201d she says. BPA, or bisphenol A<\/a>, is a chemical used in some plastics that has been linked to fertility issues.<\/p>\n