This is a guest post by Laura of Waste-Free PhD. Thank you, Laura!
Bags, bottles, buckets, and bumpers… seemingly unrelated materials that all have one thing in common: plastic. Plastics are a flexible, durable, cheap, and lightweight technology that have revolutionized the way we live. Since the 1950s, plastic production and usage has taken off. Most of the plastic produced for packaging, where it is used for the least amount of time.
Plastics aren’t inherently bad. Plastic packaging helps prevent food waste and, in some cases, has a smaller environmental footprint than other materials because of their energy efficient production and light weight. Their harm comes from their persistence in the environment, short usage time, such as with single-use plastic utensils, and leaching of harmful compounds from food and water contact materials, like Tupperware and Styrofoam containers.
Overall, plastics can be difficult to navigate. Hopefully this summary on plastics will help you determine which types to avoid or how to use plastics more mindfully in your everyday life.
So what exactly is plastic?
‘Plastic’ is a broad term referring to a range of synthetic or semi-synthetic organic polymers, or rather man-made, carbon-based, long-chained molecules. Plastics can be manufactured in a variety of ways with various additives, like plasticizers, that prevent degradation and provide other characteristics, such as a “glassy” or transparent texture, depending on the type of plastic. Synthetic plastics are made from petrochemicals, like petroleum.
How plastics can potentially alter our hormones
Plastics can leach potentially harmful compounds depending on the type of plastic used, the type of compound, and the type of conditions plastics are exposed to (heat or microwaving). Bisphenol-A (BPA), for example, is a potent estrogen-mimicking chemical that can potentially lead to endocrine disruption. It can act as estrogen (female hormone) in the body or act against androgen (male hormone).
Endocrine disruption is an imbalance in our body’s natural hormones brought about by external compounds that can mimic, block, or otherwise ‘disrupt’ natural hormone functioning. Endocrine disruptors have been associated with a wide variety of health impacts, including: insulin resistance, altered metabolism, obesity, various types of cancer, neurological issues, and reproductive issues (Endocrine Society, 2018).
BPA is not the only endocrine disrupting compound that originates from plastic. There are many diverse types of these compounds that are still being studied. Tea tree oil, for example, is an estrogenic substance.
Which of these compounds should we be worried about and which plastics do they come from?
How do we limit our exposure to them and navigate the wild and confusing world of endocrine disruption?
Hopefully these brief summaries on plastic type, characteristics, and compounds associated with them will help to inform your decisions.
#1: Polyethylene Terephthalate (PET)
Characteristics: PET is a clear, tough, and smooth plastic commonly used in beverage bottles and injection-molded containers.
Uses: PET is used in bottles for: soft drinks, water, juice, sports drinks, beer, mouthwash, ketchup, and salad dressing; for jars of: peanut butter, jelly, jam, and pickles, as well as ovenable plastic film and microwavable food trays (American Chemistry Council, 2018).
Potentially Harmful Compounds?: Yes. PET water bottles have been found to contain estrogenic compounds, such as antimony, BPA, 4-Nonylphenol, and Triclosan, with concentrations of some compounds increasing with exposure to higher temperatures and UV exposure from sunlight (Fan et al. 2014; Shotyk and Krachler, 2007; Choe et al. 2003; Rowell et al. 2016; Li et al. 2010).
Recommended Use: PET is not recommended for prolonged or repeated usage. If you use PET water bottles, minimize their exposure to UV light by storing them in the dark or in the fridge and make sure you don’t leave them in your vehicle for a prolonged period of time in the heat. If you store food using PET, transfer it onto a plate before microwaving or onto a baking sheet before heating it in the oven.
#2: High-Density Polyethylene (HDPE)
Characteristics: The most widely used type of plastic, HDPE is used in many bottles and containers because of their chemical resistance and stiffness.
Uses: HDPE is used to make bottles for milk, water, juice, cosmetics, shampoo, dish and laundry detergents, household cleaners, grocery bags, and for cereal box liners (American Chemistry Council, 2018).
Potentially Harmful Compounds?: Maybe. HDPE is a relatively stable and safe material. Studies have found BPA and nonylphenol to migrate from HDPE in low concentrations (Guart et al. 2011; Le et al. 2008). Other studies have found endocrine-disrupting compounds in low concentrations in milk stored in HDPE, which could originate from various sources (Casajuana and Lacorte 2004).
Recommended Use: HDPE is a pretty safe material, but there is a risk of being exposed to low levels of endocrine disruptors into food and drink. Similar to PET, exposure to UV light, high temperatures, and repeated use may cause more compounds to be released from HDPE.
#3: Polyvinyl Chloride (PVC, Vinyl)
Characteristics: PVC is resistant to grease, oil, and chemicals and has stable electrical properties. PVC is an organochlorine chemical.
Uses: PVC is used in both rigid and flexible packaging. Rigid packaging include blister packs and clamshells, while flexible packaging includes bags for bedding and medical, shrink wrap, deli and meat wraps (American Chemistry Council, 2018). PVC is also used in the construction industry for pipes, fittings and gutters, window profiles, and many other applications, as well as for clothing, synthetic leather, car seat covers, and other uses (Pacheco-Torgal et al. 2012).
Potentially Harmful Compounds?: Yes, avoid when possible. Organochlorines are highly persistent in the environment, soluble in fat (so they can accumulate in fatty tissue), and tend to be more toxic than non-chlorinated analogs.
There are many additives, like residual vinyl chloride monomer (VCM), used in the manufacturing of PVC that may be released during use. VCM is a toxic chemical that can cause rare liver cancer, angiosarcoma, and blood tumors. Its toxicity was discovered in the 1970s when PVC factory workers were presenting symptoms.
Phthalate plasticizers, including DEHP, are used in PVC manufacturing. DEHP is considered as “not carcinogenic to humans” by the World Health Organization (WHO). However, DEHP and other phthalates are known endocrine disruptors.
Recommended Use: Avoid whenever possible.
#4: Low Density Polyethylene (LDPE)
Characteristics: LDPE is a tough, flexible, and relatively transparent material.
Uses: LDPE is used in bags for dry cleaning, newspapers, bread, frozen foods, fresh produce, garbage bags, shrink wrap and stretch film, coating for paper milk cartons, hot and cold beverage cups, container lids, and some squeezable bottles (American Chemistry Council, 2018).
Potentially Harmful Compounds?: There is no scientific evidence to support that LDPE is a source of potentially harmful compounds.
Recommended Use: Like with all plastics, avoid microwaving and exposing plastic to high temperatures and UV light.
#5: Polypropylene (PP)
Characteristics: PP is strong, has a high melting point, and good chemical resistance. The structure of polycarbonate includes BPA and a carbonate group.
Uses: PP is used for containers for yogurt, margarine, takeout meals, deli foods, medicine bottles, bottle caps and closures, and bottles for ketchup and syrup (American Chemistry Council, 2018).
Potentially Harmful Compounds?: Maybe. A study found detectable estrogenic activity from PP, but other evidence is lacking (Yang et al. 2011).
Recommended Use: The evidence of estrogenic activity from PP is lacking. Like with all plastics, avoid microwaving and exposing plastic to reduce the risk of release of estrogenic compounds. Limit reuse of PP plastic.
#6: Polystyrene (PS)
Characteristics: PS can be rigid or foamed. Usually it’s hard and brittle with a low melting point.
Uses: PS is use for food service items, such as cups, plates, bowls, cutlery, hinged takeout containers, meat and poultry trays, and yogurt containers (American Chemistry Council, 2018).
Potentially Harmful Compounds?: PS is made of cross-linked styrene, which has been found to readily leach from PS material, especially with longer storage times and higher temperatures (Ahmad and Bajahlan, 2007). Styrene has been found to have anti-estrogenic activity (Yang et al. 2011). Styrene exposure has been shown to cause a variety of health impacts, including neurotoxic and carcinogenic effects.
Polystyrene lab tubes were found to release nonylphenol, an endocrine disruptor (Soto et al. 1991).
Recommended Use: Avoid using PS for any hot liquids or foods. When possible, avoid for any food or drink.
#7: Polycarbonates (PC)
This code indicates that the packaging is made from a resin type other than the 6 listed above or is made of more than one type of resin. I’ll focus on info for the most common #7 types: polycarbonate.
Characteristics: PC is a lightweight, tough, and clear plastic with high heat resistance and electrical resistance.
Uses: PC is used for CDs, DVDs, and Blu-ray discs, water bottles, baby bottles, construction materials, as well as other applications.
Potentially Harmful Compounds?: Yes. Studies have found BPA to leach from PC bottles, especially at high temperatures (Le et al. 2008). BPA has also been shown to leach from PC baby bottles with higher temperatures and detergent use, though it decreases down to control levels after rinsing (Maia et al. 2009).
Recommended Use: Avoid using for food or drink. If necessary, only use for low-temperature food or drink.
Limitations in Giving Recommendations
As a scientist, I would be remiss in not addressing the limitations of the data presented for each plastic type. Though plastics have been found to release endocrine disruptors, concentrations and potency vary. It is difficult to determine toxic effects in humans, especially with low concentrations over long periods of time and in mixtures.
Endocrine disruptors may also accumulate in fatty tissue over time and be released during periods of rapid weight loss. And, certainly, exposure to endocrine disruptors during periods of development (pregnancy, pre-puberty) are far more likely to cause health issues. This is an area of ongoing research.
Answers aren’t black and white.
Overall Recommendations for plastic use
- When in doubt, don’t use plastic for food or drink. Do reuse your plastic for non-food and drink items, especially if your plastic exhibits any visible damage.
- Limit the use of plastics for storing hot foods, but don’t ruin your life over it.
- Storing plastic water bottles in a hot car on a summer day is a big no-no!
Laura Markley is a scientist and founder of Waste-Free PhD, where she focuses on low-waste living and scientific misinformation in the zero-waste movement. She has presented her work at 9 conferences, including the New York State Association for Reduction, Reuse, and Recycling. She’s currently pursuing her PhD in Environmental Engineering at Syracuse University, where she researches the release of compounds from plastics. When she’s not buried in research, Laura can be found at a local coffee shop downing a 32-ounce mason jar full of cold brew to feel alive.