Polyethylene terephthalate (PET) bottles are among the most common containers globally, used for single-serving water, soft drinks, and various other products. Widespread use and growing public awareness of plastic-related health issues have naturally raised questions about their safety. Concerns often center on the potential for the plastic material, typically identified by recycling code #1, to transfer chemical compounds into the contents we consume. To understand if these bottles are safe, it is necessary to examine the scientific evidence regarding their chemical composition, the factors influencing chemical transfer, and the risks associated with their intended use.
Defining Polyethylene Terephthalate
Polyethylene terephthalate, or PET, is a thermoplastic polymer resin that belongs to the polyester family. This plastic is created through a chemical reaction involving terephthalic acid and ethylene glycol, resulting in a stable macromolecule composed of repeating units. PET is highly valued for its combination of properties, including being lightweight, shatterproof, and possessing a high strength-to-weight ratio.
Its durability and natural transparency make it an ideal material for packaging beverages, as it provides an effective barrier against moisture and oxygen. The plastic’s molecular structure provides chemical inertness, meaning it generally does not react with the food or liquid it contains. The use of PET in food and beverage containers is so prevalent that it accounts for the vast majority of plastic bottles sold in the United States.
Chemical Compounds and Regulatory Oversight
Concerns about PET’s safety frequently revolve around the potential migration of trace chemicals used in its production. The primary regulatory focus is on compounds that might leach from the plastic into the packaged contents, even in minute amounts. Regulatory bodies worldwide, including the U.S. Food and Drug Administration (FDA) and the World Health Organization (WHO), have established strict standards for food contact materials.
One such compound is antimony trioxide, which is used as a catalyst to speed up the manufacturing process of PET resin. Small amounts of this antimony residue remain trapped within the finished plastic, and studies confirm that a trace amount can migrate into bottled water over time. However, the measured concentrations in commercial bottled water are typically well below the maximum contaminant levels set by major regulatory agencies. For instance, the U.S. Environmental Protection Agency (EPA) maximum contaminant level for antimony in drinking water is 6 parts per billion (ppb).
Another trace compound that can be detected is acetaldehyde, which is an unintended byproduct formed during the high-temperature processing of PET. Acetaldehyde is considered a sensory issue rather than a health risk at the typical levels found in bottles. It possesses a low sensory detection threshold and can impart a slightly sweet or fruity off-taste to non-carbonated mineral water, prompting manufacturers to optimize production processes to minimize its presence.
A common public misconception is that PET bottles contain Bisphenol A (BPA), an endocrine-disrupting chemical found in some other plastics, like polycarbonate (#7). PET plastic is fundamentally different, as its production process does not involve BPA, making it a BPA-free material. While trace amounts of BPA have occasionally been detected, possibly due to cross-contamination, the levels are consistently found to be far below the established tolerable daily intake thresholds.
How Temperature and Storage Affect Safety
While PET bottles are deemed safe for their intended single-use purpose, external conditions like high temperature and prolonged storage can influence the rate of chemical migration. Scientific studies have consistently shown that exposure to elevated temperatures can increase the leaching of trace compounds like antimony and acetaldehyde. When bottles are stored above normal room temperature, such as in a hot car or a sunlit warehouse, the migration rate accelerates.
At temperatures exceeding 45–50°C (113–122°F), the levels of antimony in the water can rise significantly, and in extreme or prolonged cases, may approach or even temporarily exceed drinking water guidelines. For example, one study found that at 65°C (149°F), the exposure duration necessary to exceed the EPA’s maximum contaminant level for antimony was 38 days. This is why proper storage conditions are important, particularly in hot climates.
Conversely, the practice of freezing bottled water does not increase chemical leaching, and it is a safe method of storage. The widely circulated myth that freezing causes PET bottles to release dioxins is scientifically unfounded. Dioxins are environmental pollutants created by combustion at extremely high temperatures, and they are not present in PET plastic.
Storage time also plays a role, as the concentration of antimony and other chemicals can increase the longer the liquid remains in contact with the plastic. This rise in concentration is typically gradual at ambient temperatures, and the levels generally remain within regulatory limits for the commercial shelf life of the product.
Risks Associated with Repeated Use
The safety discussion shifts when consumers choose to reuse a single-use PET bottle repeatedly. These bottles are engineered for a one-time application and are not designed to withstand the physical demands of repeated washing and refilling. The most significant health risk associated with reusing these containers is microbial contamination, not chemical leaching.
Repeated use and cleaning can cause microscopic scratches and abrasions on the plastic surface. These tiny imperfections create ideal environments for bacteria and fungi to adhere and multiply. Bacteria, often originating from the mouth and hands, can form complex colonies, or biofilms, within the bottle.
Studies comparing the microbial load in reused plastic bottles have sometimes found high levels of bacteria, which can pose a risk of gastrointestinal infection. The narrow necks of PET bottles also make thorough cleaning difficult, further contributing to bacterial growth. Consumers should discard single-use PET bottles showing signs of wear or degradation and consider using reusable bottles made from materials specifically designed for long-term, repeated cleaning, such as stainless steel or glass.