Plastic Water: The Dark Effects of Sunlight on Plastic Water Bottles

article top

This may be hard to swallow, but the drinking bottle that you are dutifully carrying around with you all day to stay properly hydrated may be delivering more than water into your body. 

The most commonly used plastic water bottle is made of polyethylene terephthalate, or PET, which is indicated on the bottle with a stamp of the number 1 surrounded by arrows. This plastic is considered safe to use for water. But is it?  


While some chemical residues from the production process contaminate all plastic containers and can be released into the contained food or drink, PET plastic water bottles are relatively low in these chemical residues, making them relatively safe to use for water, if the bottle is used as intended.  

Most people don’t know the environmental conditions for which their plastic bottle was made. Actually, these bottles are not intended to be exposed to sunlight, or be stored in a hot car. 

UV radiation from sunlight has the ability to break chemical bonds in plastics, including PET, and this causes the plastic to quickly decompose. According to an article in Plastics Today, “PET is sensitive to UV light especially at elevated temperatures, under high humidity, and in the presence of oxygen—all of which are present when PET bottles are exposed to the weather.”  This also happens when people keep their water bottle in their car, or beside them at the beach. 

According to an article in Recycle Magazine, “The data clearly shows that exposure to ultraviolet radiation was very damaging to the PET material…Exposure to UV radiation, whether it is from outside storage or possibly even exposure to fluorescent lighting in retail stores, should be considered as another contributor to PET quality degradation.”  In other words, sunlight and heat breakdown the plastic, producing a slew of chemicals.

What’s wrong with the chemicals from plastics breaking down? According to the Endocrine Society, “Plastics contain and leach hazardous chemicals, including endocrine-disrupting chemicals (EDCs) that threaten human health…EDCs are chemicals that disturb the body’s hormone systems and can cause cancer, diabetes, reproductive disorders, and neurological impairments of developing fetuses and children. The report describes a wealth of evidence supporting direct cause-and-effect links between the toxic chemical additives in plastics and specific health impacts to the endocrine system.” 

A public health discussion of PET water bottles was published by the Hong Kong Centre for Food Safety, in an article on Reusing Disposable PET Bottles. (Emphasis added.)

1. Chemicals such as chemical monomers and additives that are used in the manufacture of plastic may migrate into water or beverages no matter if they were being used only once or repeatedly.

2. The amount of chemical migration from plastic will depend on the nature of the substance it comes into contact, the contact temperature and the contact time. However, proper usage of the plastics will have insignificant chemical migration, which does not pose any health risk to consumers.

3. For PET bottles, trace amount of antimony, a heavy metal which is used in the production of PET, can migrate into water upon storage. A previous study conducted by Centre for Food Safety, however, showed that concentrations of antimony in PET bottled beverages were very low (well below the WHO’s guideline value for drinking-water quality) and would not pose any health risk.

4. Manufacturers have to ensure that plastic bottles are safe to use for its immediate intended purpose (e.g. water bottle should be suitable for containing water and will not transfer its chemical constituents into water in an unacceptable amount). Yet, they may not be able to ensure the safety of their bottles for uses beyond which they are designed for (e.g. the use of a water bottle for storing vinegar or oil).

5. It is important that consumers do not misuse plastic bottles as this may result in greater amount of chemical migration than would otherwise be expected.

6. With all plastic types, migration increases with temperature and time of contact. Although increased migration of chemicals from plastic bottles does not necessarilypose health risk, it could change the organoleptic properties such as taste, colour and odour of water they contain. Therefore, it is better not to expose PET-bottled water to sunlight directly.

Note that these PET water bottles are not meant for use in the sunlight or heat. Analysis of the health impacts of these plastic bottles was performed assuming the bottles were not going to be in direct sunlight or heat. This means that scientific studies about their safety and low level of chemical leaching is only applicable to bottles kept out of the heat and sunlight. Having a plastic bottle of water with you at the beach sitting in the sunshine, or sitting in your hot car, are considered a misuse of the bottle, and essentially voids health assurances by releasing more chemicals than expected from test without heat or sunshine. 

Unfortunately, the current discussion of the safety of PET plastics for water bottles fails to mention the UV and heat problem, and assumes, without any scientific evidence, that the chemicals leaching out from the plastic in the sunlight and heat, and which make the water smell and taste bad, are not a health risk. For example, the website references the Hong Kong article above, but reaches a different conclusion in its article, Can Cases of Water Bottles Sit in the Sun.  According to Livestrong, “However, while leaving the bottle in the sun may change the color, taste or smell of the water, it won’t cause dangerous chemicals to leach into the water, the Centre for Food Safety in Hong Kong states.

Actually, the Hong Kong Food Safety article, quoted above, states, “Although increased migration of chemicals from plastic bottles does not necessarilypose health risk, it could change the organoleptic properties such as taste, colour and odour of water they contain.” Of course, the term “not necessarily pose a health risk” means it likely does pose a health risk, but not absolutely so.  

Livestrong is not alone in ignoring or downplaying the UV impact on plastic water bottles. So does the CDC. To purify water for consumption, the CDC recommends soda bottle disinfection, or SODIS. While mostly for poor countries where plastic bottles are more available than clean water, the CDC recommends, “Users of SODIS fill 0.3-2.0 liter plastic soda bottles with low turbidity water, shake them to oxygenate, and place the bottles on a roof or rack for 6 hours (if sunny) or 2 days (if cloudy). The combined effects of UV-induced DNA alteration, thermal inactivation, and photo-oxidative destruction inactivate disease causing organisms.” Nowhere is it mentioned that the PET soda bottles used release toxic chemicals into the water while it is “disinfecting” and deteriorating in the sunshine. 

What are these chemicals? Marine biologists concerned about the effect of plastics polluting the oceans have studied the impact of UV degradation of plastics, and found a soup of chemicals produced. According to the article entitled, UV degradation of natural and synthetic microfibers causes fragmentation and release of polymer degradation products and chemical additives , “In the current study, non-target analysis revealed the presence of several tentatively identified degradation products of PET… In the order of relative abundance, these included: 1,2-ethanediol monobenzoate, terephthalic acid, 4-acetylbenzoic acid, benzoic acid, 4-methylbenzoic acid, phenacyl formate, vinyl benzoate, diethylene glycol dibenzoate and 4-ethylbenzoic acid…All compounds showed an exponential increase in formation over the course of the experiment, suggesting a continued production as the UV degradation process proceeded…This shows that the original constituent chemicals used in the production of PET are also formed during UV degradation, together with a suite of other products.”

Should we ignore these chemicals leaching out of the plastic that we smell and taste? If they are detectable to the senses, aren’t they affecting us, even if the science is not looking into the impacts of these chemicals?

One chemical we haven’t discussed is antimony, a heavy metal that causes cancer. According to the Ecology Center in their PET plastic report 2022, “Our partners at Defend Our Health tested 20 popular beverages packaged in plastic bottles and found antimony, a cancer-causing plastic chemical, in every bottle. 40% of beverages tested, including Pepsico and Coca-Cola brands, had antimony levels higher than California’s public health goal for drinking water. Antimony, known to be toxic to the liver and heart, is used to speed up the final reaction in the process of making PET (#1) plastic. This same polymer is the common “polyester” used in apparel and other textiles. This means the problem doesn’t end with plastic bottles. Antimony is also found in food packaging and other packaging made from PET, as well as clothing, stuffed animals, and other polyester items.

Of course, the Hong Kong experts say the antimony is below the WHO guidelines in the PET bottles they tested. However, California guidelines have recently been changed, with drinking water limits of antimony lowering from 20 parts per billion to 1 part per billion, reflecting a growing awareness of the health impacts of antimony.

Chemical contaminants from PET water bottles can act as a hormone disruptor, a carcinogen, and an irritant to the skin, kidneys, nervous system, intestines, and liver. If you can smell it, it goes from your nose to your lungs into your bloodstream. If you can taste it, you are going to swallow and absorb it.  

You would expect that there would be lots of studies on plastic chemical toxicity in humans, given the vast daily exposure we all have to food and drink contaminated with plastic residue and breakdown products. On the other hand, 390.7 million metric tons of plastic was produced in 2021, and the amount is growing. That’s a lot of economic incentive to keep things going plastic. Why bother with the science of plastic-caused disease when we all love plastic so much?

According to the Cleveland Clinic, “The science of plastics and health is a little fuzzy. Many ingredients in plastic haven’t been thoroughly tested in people. Much of what we know comes from studies in animals. We don’t know exactly how all these compounds affect human health. But there are hints that compounds in plastics may be linked to problems.”

If you want to take the hint and avoid plastic poisons in your water, here are some suggestions:

1. Use alternatives to plastics, especially glass, whenever possible.  

2. If you use plastic PET bottles, keep them out of the sunlight. If outdoors, keep the plastic bottle covered and cool. 

3. Don’t keep bottled water sitting in the hot car.

4. Keep in mind that you don’t know the history of that plastic bottle, and whether anyone, including the store where you purchased it, kept the plastic water bottles in the sun and heat. You might want to first try a bottle before buying a case to make sure it doesn’t smell or taste bad.

5. If the contents on any bottle look, smell, or taste bad, do not consume and discard the bottle.

6. Be aware than flavored drinks may mask the plastic smell and taste.  

7. Store PET water bottles in a cool, dark place.  

8. If you are storing water for emergencies in plastic containers, regularly check the water for smell and taste, which can indicate a need to replace the water and the container.

9. Keep all plastic containers of food and drink out of the sun and heat and away from florescent lighting, which also emits UV.

The convenience of using PET for water bottles will keep it popular with industry and the public over the foreseeable future, despite the increasing evidence showing health risks from plastics exposed to UV. Hopefully, the plastics industry will continue to improve on water bottle chemistry, so all you drink in a plastic bottle of water is water.  




Leave a Reply