Caltech Science Exchange / Topics / Sustainability / Plastic Problem
This article was reviewed by a member of Caltech's Faculty.
Plastic is incredibly useful in modern life, but its widespread use may impair human sustainability. The production and disposal of plastic generates greenhouse gases and hazardous waste. Plastic and the chemicals it emits are building up on land and in oceans, lakes, rivers, ice, and air, and the resulting damage to human and ecological health is currently poorly understood. Most plastic is not recyclable and the vast majority does not biodegrade. Further, plastic products often break down into very small fragments called microplastics that can pollute ecosystems and harm organisms.
Why Plastic Pollution Is a Problem
Plastic is everywhere, from bags and single-use bottles and packages to car parts, pipes, and siding. Likewise, plastic waste is ubiquitous. It has been found, for example, in Arctic sea ice, beer, farm soil, trout and other wild freshwater fish, shrimp and other shellfish, songbirds and seabirds, human placentas, the Great Pacific Garbage Patch, midoceanic atolls, sea caves, the air and rain, and national parks and wilderness areas. While the impact of plastic pollution on sea life is well documented, scientists are just beginning to measure plastic's effects on humans and human fertility, land ecosystems, and crops and other plants.
The United States alone generated 35.7 million tons of plastic waste in 2018. Of that, 27 million tons was landfilled, 5.6 million tons incinerated, and three million tons, or 8.7 percent may have been recycled. (Some reports suggest that plastic scrap shipped abroad for recycling may instead end up in landfills and waterways.)
Researchers estimate that nearly 7,000 million tons of virgin plastic have been manufactured around the world as of 2015. Of that, 9 percent may have been recycled, 12 percent has been incinerated, and the rest is in landfills, still in use, or in our environment. Globally, about one fourth of plastic waste is never collected. In less wealthy countries, waste plastic is sometimes burned in the open, releasing toxic chemicals into the air.
What is plastic made of?
The main ingredients in plastic come from oil and natural gas processing. Different molecules are used to make different types of plastic, giving them distinctive properties and chemical structures. Manufacturers also mix in additives to give specific products their desired qualities. These chemicals, such as colorants, plasticizers, flame-retardants, stabilizers, fillers, reinforcing fibers, and biocides sometimes contain hazardous substances, including lead, arsenic, and cadmium compounds, as well as BPA.
Caltech chemists and their colleagues are designing molecules and nanoscale catalytic devices that may make it possible to produce plastic from chemicals derived from carbon dioxide rather than fossil fuels, with the goal of reducing the climate impact of plastic manufacturing.
What types of plastic can be recycled?
Many consumer plastic products are imprinted with triangular recyclable symbols. But only two kinds of plastic commonly end up recycled: #1, PET or polyethylene terephthalate, and #2, HDPE or high-density polyethylene, and within those, usually only bottles, tubs, and jugs (generally not, for example, salad containers, berry boxes, or clamshell packages). Together, these account for a small fraction of all plastic waste.
Plastics that are recyclable are typically downcycled rather than fully recycled. This means that they are turned into products of lesser value that often cannot be recycled again. When plastic waste is turned into a more valuable product, such as clothing or shoes, that is called upcycling.
Recycling results in a product of equivalent value that can be recycled multiple times. However, the number of times a plastic can be effectively recycled is currently limited.
Recycling Innovation
Chemical recycling is an emerging method that chemists are trying to develop. It would break plastics down into their basic, raw materials, sometimes through the use of customized enzymes, so that they can be remade and recycled an infinite number of times. Using similar approaches, polymers that are more difficult to recycle could potentially be turned into biodegradable compounds and used in cleaning products.
Because different types of plastics have varying properties, plastic products need to be sorted before they can be recycled. Some packaging, usually used to keep food fresh, cannot be sorted or recycled because it is made from layers of different types of plastic. Scientists are working on solvents that could separate multilayer packaging into its component polymers, which could then be used instead of new plastic. Others are making molecules that would allow multiple types of polymers to mix and still create viable recycled materials.
Dive Deeper
Production, use, and fate of all plastics ever made
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Caltech and UCLA Researchers Discover Effective Pathway to Convert Greenhouse Gas into Valuable Products
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