The Resin Identification Code (RIC) #7, often labeled as “Other,” is a broad category encompassing any plastic that does not fit into the six specific classifications from #1 through #6. Because it is a catch-all for diverse materials, this designation is the core reason for public concern about its safety in water bottles. The most significant health question surrounding plastic #7 relates to the inclusion of Polycarbonate (PC). Polycarbonate is widely used in hard, clear, reusable water bottles, relying on Bisphenol A (BPA) for its chemical structure. The possibility of BPA leaching into the water prompts closer scrutiny of all products marked with the #7 code.
Understanding the Category of Plastic 7
The #7 designation is not a single material but a mixed collection of polymers, which makes a blanket statement about its safety impossible. Within the context of water bottles, the category primarily includes polycarbonate (PC) and newer, often proprietary, plastics. Polycarbonate has traditionally been the material of concern because it is synthesized using Bisphenol A, a compound that can migrate out of the plastic and into the contents.
To address consumer worries, many manufacturers have shifted from PC to “BPA-free” alternatives, such as the copolyester Tritan or polylactic acid (PLA). These alternatives are still marked with the #7 code because they do not fit into the other six categories. However, the label “BPA-free” simply means BPA was not used, and it does not guarantee the absence of other similar compounds.
In many cases, the original BPA has been replaced with structural analogs like Bisphenol S (BPS) or Bisphenol F (BPF). Research suggests that these bisphenol substitutes share similar chemical structures with BPA and may exhibit comparable hormonal activity. Tritan, for instance, is often marketed as being free of all bisphenols, but the safety of these newer compounds is still under scientific investigation.
The Mechanism of Endocrine Disruption
The primary health concern with chemicals like BPA, BPS, and BPF is their ability to act as endocrine-disrupting chemicals (EDCs). Endocrine disruptors are exogenous substances that interfere with the body’s natural hormones, which are chemical messengers regulating numerous functions like metabolism, growth, and reproduction. These chemicals often mimic a hormone, most notably estrogen, due to a structural similarity that allows them to bind to the body’s hormone receptors.
Once bound to a receptor, the chemical can inappropriately activate or block the hormone’s natural signaling pathway. This disruption can lead to adverse effects on the reproductive, neurological, and immune systems. Low-dose exposure to EDCs is a particular concern, as these compounds can interfere with the body’s signaling at levels far below those that cause overt toxicity.
The effects of these compounds are thought to be most significant during critical developmental windows, such as the prenatal and early postnatal stages. Studies have linked exposure to EDCs to issues like altered sexual maturation, lower fertility, and potential impacts on metabolism and neurological function. Even the structural substitutes like BPS and BPF have been shown to have hormonal effects in laboratory settings, sometimes exhibiting potency similar to BPA.
Environmental Factors Affecting Chemical Release
The rate at which chemicals migrate, or leach, from plastic #7 water bottles is significantly influenced by environmental and usage factors. Heat exposure is a major accelerator of this process, causing the polymer chains to break down and release constituent chemicals. Leaving a polycarbonate bottle in a hot car, exposing it to direct sunlight, or washing it in a high-temperature dishwasher can dramatically increase the amount of chemical release into the water.
Prolonged storage time is another factor contributing to increased leaching, even when the bottle is kept at room temperature. Over time, the chemical bonds within the plastic slowly degrade, allowing more of the chemical components to seep into the liquid. Physical wear and tear also play a role in promoting chemical release. Scratches and abrasions on the surface of the plastic can compromise the material’s integrity, creating more pathways for chemicals to leach into the water.
Choosing Safer Materials for Water Storage
Given the ambiguity and potential for chemical migration in plastic #7, many people opt for alternatives generally considered more stable for water storage. Non-plastic options offer the greatest assurance of chemical inertness. Glass is highly recommended because it is non-porous, does not degrade with repeated use, and does not leach chemicals into the water.
Stainless steel is another excellent alternative, prized for its durability and ability to maintain beverage temperature. When choosing a stainless steel bottle, it is best to ensure it is made of food-grade steel and does not have an inner plastic lining. For those who prefer plastic, options with a more consistent safety profile are available. These plastics are generally considered more stable and are not known to contain the endocrine-disrupting bisphenols found in many #7 formulations.
Safer Plastic Alternatives
- Polyethylene Terephthalate (#1 PET)
- High-Density Polyethylene (#2 HDPE)
- Low-Density Polyethylene (#4 LDPE)
- Polypropylene (#5 PP)