Health and environment: a closer look at plastics
Plastics have transformed modern society, providing attractive benefits but also befouling waterways and aquifers, depleting petroleum supplies and disrupting human health.
Rolf Halden, a researcher at Arizona State University’s Biodesign Institute has been following the chemical trail of plastics, quantifying their impact on human health and the environment. In a new overview appearing in the journal Reviews on Environmental Health, Halden and his co-author, ASU student Emily North, detail the risks and societal rewards of plastics and describe strategies to mitigate their negative impacts, through reconsideration of plastic composition, use and disposal.
“We are in need of a second plastic revolution. The first one brought us the age of plastics, changing human society and enabling the birth and explosive growth of many industries. But the materials used to make plastics weren’t chosen judiciously and we see the adverse consequences in widespread environmental pollution and unnecessary human exposure to harmful substances. Smart plastics of the future will be equally versatile but also non-toxic, biodegradable and made from renewable energy sources,” says Halden.
Plastics are made up of a network of molecular monomers linked to form macromolecules. These versatile chemical structures come in enormous varieties and today over 20 major forms of plastics exist. Plastics are typically lightweight and biocompatible. Along with their myriad uses in everyday life, plastics fulfill many needs in the public health arena, where they are found in items including absorbable sutures, prosthetics and engineered tissues.
Further, plastics may be manufactured at low cost using little energy and their adaptable composition allows them to be synthesized in soft, transparent or flexible forms suitable for a broad range of medical applications. Because they can be readily disposed of, items like latex gloves, dialysis tubes, intravenous bags and plastic syringes eliminate the need for repeated sterilization, which is often costly and inefficient. Such single-use items have had a marked effect on reducing blood-borne infections, including hepatitis B and HIV.
Many consumer products, such as water bottles and product containers, are made from various types of plastic. The Society of the Plastics Industry (SPI) established a classification system in 1988 to allow consumers and recyclers to properly recycle and dispose of different types of plastic. Manufacturers follow a coding system and place an SPI code, or number, on each plastic product, which is usually molded into the bottom. Although you should always verify the plastic classification number of each product you use, this guide provides a basic outline of the different plastic types associated with each code number.
Plastic marked with an SPI code of 1 is made with Polyethylene Terephthalate, which is also known as PETE or PET. Containers made from this plastic sometimes absorb odors and flavors from foods and drinks that are stored in them. Items made from this plastic are commonly recycled. PETE plastic is used to make many common household items like beverage bottles, medicine jars, peanut butter jars, combs, bean bags, and rope. Recycled PETE is used to make tote bags, carpet, fiberfill material in winter clothing, and more.
Plastic marked with an SPI code of 2 is made with High-Density Polyethylene, or HDPE. HDPE products are very safe and they are not known to transmit any chemicals into foods or drinks. HDPE products are commonly recycled. Items made from this plastic include containers for milk, motor oil, shampoos and conditioners, soap bottles, detergents, and bleaches. Many personalized toys are made from this plastic as well. (Please note: it is NEVER safe to reuse an HDPE bottle as a food or drink container if it didn’t originally contain food or drink!) Recycled HDPE is used to make plastic crates, plastic lumber, fencing, and more.
Plastic labeled with an SPI code of 3 is made with Polyvinyl Chloride, or PVC. PVC is not often recycled and it can be harmful if ingested. PVC is used for all kinds of pipes and tiles, but it’s most commonly found in plumbing pipes. This kind of plastic should not come in contact with food items. Recycled PVC is used to make flooring, mobile home skirting, and more.
Plastic marked with an SPI code of 4 is made with Low-Density Polyethylene, or LDPE. LDPE is not commonly recycled, but it is recyclable in certain areas. It is a very healthy plastic that tends to be both durable and flexible. Plastic cling wrap, sandwich bags, squeezable bottles, and plastic grocery bags are all made from LDPE. Recycled LDPE is used to make garbage cans, lumber, furniture, and more.
Plastic marked with an SPI code of 5 is made with Polypropylene, or PP. PP is not commonly recycled, but it is accepted in many areas. This type of plastic is strong and can usually withstand higher temperatures. Among many other products, it is used to make plastic diapers, Tupperware, margarine containers, yogurt boxes, syrup bottles, prescription bottles, and some stadium cups. Plastic bottle caps are often made from PP as well. Recycled PP is used to make ice scrapers, rakes, battery cables, and more.
Plastic marked with an SPI code of 6 is made with Polystyrene, also known as PS and most commonly known as Styrofoam. It is commonly recycled, but it is difficult to do so and often ends up in landfills anyway. Disposable coffee cups, plastic food boxes, plastic cutlery, packing foam, and packing peanuts are made from PS. Recycled PS is used to make insulation, license plate frames, rulers, and more.
The SPI code of 7 is used to designate miscellaneous types of plastic that are not defined by the other six codes. Polycarbonate and Polylactide are included in this category. These types of plastics are difficult to recycle. Polycarbonate, or PC, is used in baby bottles, large water bottles (multiple-gallon capacity), compact discs, and medical storage containers. Recycled plastics in this category are used to make plastic lumber, among other products.
Consumers can make better plastic-purchasing decisions if they understand SPI codes and potential health hazards of each plastic, and recyclers can more effectively separate plastics into categories. Always check a product’s classification code prior to recycling it or re-using it. It’s important to stay educated about plastic classification numbers and plastic types; remember, informed consumers can demand that plastics manufacturers provide better products.
Many varieties of polymers are produced to meet the expanding needs of modern medicine. Polymer chemistry is used to produce sophisticated drug delivery systems for the pharmaceutical industry; material to cement bone for hip replacements is made with polymer polymethylmethacrylate and polymer scaffolds are revolutionizing the practice of tissue engineering.
Researchers like Halden have shown, however, that the benefits of global plastics use can come at a steep price in terms of both human and environmental health. Continuous contact with plastic products, from the beginning to the end of life has caused chemical ingredients - some with potentially harmful effects - to form steady-state concentrations in the human body.
In recent years, two plastic-associated compounds have been singled out for particular scrutiny, due to their endocrine-disrupting properties: Bisphenol A (BPA) and di-(2-ethylhexyl)phthalate (DEHP). Studies of bioaccumulation have shown that detectable levels of BPA in urine have been identified in 95 percent of the adult population in the U.S. and both BPA and DEHP have been associated, through epidemiological and animal studies, with adverse effects on health and reproduction. These include early sexual maturation, decreased male fertility, aggressive behavior and other effects. Concern over BPA exposure, particularly for highly vulnerable members of the population, has recently led the Food and Drug Administration to place a ban on BPA use in infant bottles, spill proof cups and other products intended for infants and toddlers.
Similar issues exist with DEHP, a plasticizer found in polyvinyl chloride (PVC). Because this additive is not tightly bound to the plastics in which it is used, the potential exists for DEHP to leach out and enter the body, causing unwanted exposure and affecting health. Both animal and human studies suggest DEHP may produce harmful effects, including insulin resistance, increased waist circumference and changes to male and female reproductive systems.
A variety of other plastic-related chemicals are currently under evaluation by Halden’s group for their adverse effects on health and the environment. These include polyhalogenated flame retardants, polyfluorinated compounds and antimicrobials containing plastic additives such as triclosan and triclocarban.