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PlasticsPlastics are everywhere and part of almost everything we do. They've transformed our lives. Yet you should know that plastics contain chemicals that, especially when heated, may leach out. When consumed or absorbed, these chemicals may mimic estrogens and increase the risk of breast cancer.
What are the chemicals that are causing concern and where are they found?
In a now-classic report published in 1991, Soto and colleagues reported that that a substance that had been added to plastic (polystyrene) laboratory tubes had led to the growth and proliferation of cultured human breast tumor cells (MCF-7 cells) in a pattern similar to what is seen when estrogen is added to the cultures [Soto et al., 1991]. This substance was identified as nonlyphenol, a member of the chemical class of compounds called alkyphenols. These alkylphenols are commonly added to plastics, for use as antioxidants, and they (along with a number of other plastic additives) have been shown to leach from plastic wraps and containers into food products [Junk et al., 1975].
In the 15 years since the Soto et al. study has been published, several other plastic additives have been demonstrated to leach from the plastic structure under situations in which they are commonly used, and several of these substances have been implicated in increased cancer risk when people or animals are exposed to them in high doses or over extended periods of time.
Plastic additives that have been linked to possible increased breast cancer risk include:
- Bisphenol-A is a chemical that is used to make polycarbonate plastic and epoxy resins. It is found in eyeglass lenses, medical equipment, water bottles, baby bottles, CDs, DVDs, cell phones, consumer electronics, computers, plastic food containers, lining of metal food cans, and dental sealants.
In addition to leaching from plastics during their use, substantial amount of bisphenol-A are released into the environment during manufacturing processes.
- Alkylphenols (including nonylphenol) and the ‘parent chemicals’ (those that are broken down to alkylphenols) alkylphenol epoxylates are substances that are added to many different kinds of plastics to make them more stable and usable. In addition to being released from the plastic products they comprise, alkylphenols are often released into the environment through biodegradation processes common in many sewage treatment plants over the past several decades [Giger et al., 1984].
- Phthalates are chemicals that are found in plastic wrap, soft plastic “chew” toys for babies, medical equipment and many personal care products. Phthalates are mainly added to soften otherwise brittle plastic polymers, but they are also found in perfumes, cosmetics and other personal care products.
- Polyvinylchlorine (PVC) plastics are found in food packaging, medical products, appliances, cars, toys, credit cards, and rainwear. In addition to containing phthalates and other common plastic additives, the manufacture and disposal of PVCs result in the creation and release into the environment of other substances that have been linked to breast cancer. In particular, dioxin is a byproduct of industrial processes and the incineration of PVCs. It is released into the environment and found in food, especially meat, poultry, and dairy. In addition, vinyl chloride is released during the manufacture of PVCs and is found in air and water.
- Trace metals, including cadmium, have been found in plastic materials, including food packaging [Nomura et al., 2000]. They are released into the environment during incineration of plastics and are found in air, food and water. Cadmium exposure has been been shown to be associated with an increase in a number of different types of cancer, including perhaps breast cancer [Garcia-Morales et al., 1994].
How do these chemicals enter the body?
Plastic additives such as bisphenol-A and phthalates are not bound within the plastic matrix structure. This allows these chemicals to leach from the plastic products into their surroundings. For example, in the case of polycarbonate baby bottles, bisphenol-A may leach from the plastic when heated in the microwave, resulting in the detection of the chemical in the formula. In the case of plastic wraps made from PVC and containing additives such as phthalates, the chemicals move from the plastic into the food, especially foods with high fat content, such as meat and cheese. For children’s toys made out of PVC, children may be exposed orally to plasticizers when the toy is placed in their mouths. Many of these chemicals are also released in both the production and disposal of plastics. Traces of chemicals can be found in indoor air, food products, water, and soil. As a result, many of these chemicals are taken into the body through the ingestion of contaminated food and water and breathing in air containing these chemicals. Once these chemicals enter they body, they are stored in fat and may persist for many years.
What are the mechanisms by which these substances might increase the risk for breast cancer?
Plastic additives alter cellular activity in a variety of ways. One way in which these chemicals may affect breast cancer risk is by either mimicking or disrupting normal endocrine (hormone) functions of breast cells. These chemicals therefore can have effects that disrupt cellular processes more generally, either directly through the estrogen pathway or through other hormone-sensitive processes. Some of these impacts include promoting or inhibiting cell proliferation and growth, altering cell metabolism and enzyme activity, and stimulating or hindering the replication of DNA during the formation of new cells. Disruption of the normal checks-and-balances of cellular activity in mammary tissue is associated with increased rates of mutations, and therefore increased risk of breast cancer [Markey et al., 2001].