Exposing single-use plastic water bottles to high temperatures and direct sunlight can cause chemicals to migrate from the plastic into the water, according to research and experts. This migration can occur even at room temperature and is exacerbated by heat.
Many disposable water bottles are made from polyethylene terephthalate (PET). While PET is recyclable and widely used for beverages, chemists have found that these bottles are not inert when exposed to heat and sunlight. Substances used in the manufacturing of plastic, such as the metal antimony, can leach into liquids stored inside.
Research indicates a direct correlation between temperature and the rate of chemical migration. Studies have detected various chemicals, including bisphenol A (BPA) and phthalate esters, seeping into bottled water as temperatures rise. Some of these compounds, like certain phthalates, are known endocrine disruptors, while the long-term health effects of others remain unclear due to a lack of comprehensive studies on cumulative exposure and synergistic effects with other environmental chemicals.
"We lack evidence on the cumulative effect of these chemicals in human bodies," said Olwenn Martin, an associate professor in health and environment at University College London. "There is also the synergistic relationship of this with other chemicals that we are exposed to, so linking it to specific health implications—we're not there yet."
Experts advise storing bottled water in cool, dark places. Even indoor storage can lead to migration if temperatures consistently climb. The International Bottled Water Association recommends storing bottled water at room temperature or cooler, away from direct sunlight.
Chemicals can begin to migrate around 68°F (20°C), with greater mobility observed at temperatures above 86-104°F (30-40°C). The stability of PET bottles decreases under these conditions, increasing the likelihood of leaching.
Different types of liquids can also affect the rate of chemical migration. Juices and acidic beverages may encourage the leaching of certain compounds, while fatty contents can increase the migration of others. Heat universally accelerates this process.
In light of these findings, some experts, including Martin and her colleague Iacovidou, recommend using reusable metal bottles for carrying water as an alternative to single-use plastics, particularly when the potential for exposure to heat and sun exists.