Why ditching plastic saves more than just turtles

April 17th, 2021. By Audrey Tam '22

It's no secret that plastics are bad for the environment. But why? The answer lies in the chemistry of plastics – in what they are made of and how they are produced.

What Are Plastics Made Of?

Plastics are polymers of non-renewable resources like coal, natural gas, and oil. Other examples of polymers include starches (polymers of sugars), proteins (polymers of amino acids), and DNA (polymers of nucleotides).

Polymers are large molecules composed of many repeating monomers bonded together. As shown in the diagram below, there are many ways monomers can combine with themselves or each other. As a result, there are many different types of plastics with different properties.

There are a few ways these monomers can combine to form plastic polymers. Two methods are condensation reactions and addition reactions.

1. In condensation reactions, two molecules combine through the loss of a smaller molecule. For example, in the diagram below, water is produced and the remaining electrons between the monomers form a covalent bond. This reaction continues over and over again until a long chain of copolymers is created.

2. In addition to reactions, the double bonds within a monomer rearrange to form single bonds with other molecules. This is similar to two people (monomers), both with arms crossed (double bond), standing close to each other. When they unfold their arms, they can create a link by holding hands (single bonds). Now, they act as a combined unit.

While plastics are polymers with biomaterial, they cannot biodegrade. Organisms that decompose, say an apple, are able to do so because they evolved to attack common bonds found in nature. Because the long chain of monomers created in these reactions is not natural, it is impossible for organisms to break down plastic.

How Are They Produced?

On an industrial scale, chemists and engineers prepare raw materials and monomers, carry out polymerization reactions, process the polymers into final polymer resins, and produce finished products.

1. They start with raw materials that make up the plastics’ monomers. Since plastic is derived from substances such as natural gas, petroleum, and oil, this requires seismic blasting and hydraulic fracking in the ocean. Seismic blasting emits loud noises to locate oil and gas, and it often interferes with the many marine animals that depend on sonar to communicate. Likewise, from water pollution to soil contamination, fracking also poses threats to the environment and our safety.

It is also worth noting that transportation from the extraction sites to plastic processing facilities also has its fair share of consequences. For example, car crashes or leaks in pipelines can cause oil spills and release large amounts of CO2. Even without accidents, the Center for International Environmental Law (CIEL) estimated that 12.5 to 13.5 million metric tons of carbon dioxide equivalent are emitted per year during this process in the United States.

2. Next, the monomers undergo polymerization reactions in polymerization plants. The end products are polymer resins, which must be collected and further processed. The final polymer resins are usually pellets or beads. To form plastics, these polymer resins are then heated, molded, then cooled. For something like plastic water bottles, polyethylene resin pellets are heated and compressed into a tube before chilled in a mold and blasted with compressed air.

This plastic refinery is also a greenhouse-gas-intensive process. In 2015, emissions from manufacturing ethylene, the building block for polyethylene plastics, were 184.3 to 213 million metric tons of carbon dioxide equivalent, which is about as much as 45 million passenger vehicles emit during one year, according to the CIEL report. We aren’t slowing down either. Globally, carbon dioxide emissions from ethylene production are projected to expand by 34% between 2015 and 2030.

3. Since most plastics are used for packaging, most plastics are also single-use. The turnaround from production to use to disposal is extremely short. For disposal, there are three main options: landfill, incineration, or recycling.

a. Plastics in landfills and the environment break down into smaller microplastics. Microplastics scatter all across the globe, where they bind with toxins and are easily ingested by wildlife. Additionally, when phytoplankton ingests these microplastics, the growth of microalgae and the efficiency of photosynthesis reduces-- even less carbon dioxide is removed from the atmosphere.

b. Yet waste incineration has the largest climate impact. Burning plastics not only emits tons of carbon dioxide but also releases huge amounts of toxins. Unfortunately, incineration facilities are also built disproportionately near communities of color and low-income populations, meaning they are exposed to more of these dangerous substances.

c. Recycling is the best option, but it comes with its own set of problems. Compared to the cost of other materials, recycled plastics are relatively high cost and low value. Even then, research suggests that only 2% of plastics are recycled into products with the same function. Another 8% are “downcycled” to something of lower quality.

For many years, the United States and other Western countries sent contaminated waste to China, but in 2018, China stopped accepting contaminated recycling. However, instead of managing waste production or increasing its recycling capabilities, the United States now sends waste to other countries like Thailand, Malaysia, and Vietnam. These temporary solutions reveal the uncomfortable notion that there are simply too many single-use plastics. As Claire Arkin stated to Yale Climate Connections, “We can’t recycle our way out of the plastic pollution crisis.”

When we think of plastics and their impact, sometimes immediate ideas include pollution or garbage patches. We think about plastic straws stuck in turtles’ noses or shopping bags floating around in the distant sea. While plastics certainly pose a threat to marine life, the production and decay of plastic also bring an equally sinister set of effects. At every stage of their life cycle, plastics generate heat-trapping gasses and contribute to climate change.


EarthHero. “Why Is Plastic Bad? | Learn with the EarthHero Blog | Sustainability Made Simple.” EarthHero, 15 Oct. 2019, https://earthhero.com/why-is-plastic-bad/.

HowStuffWorks. “How Plastics Work.” HowStuffWorks, 14 Dec. 2007, https://science.howstuffworks.com/plastic.htm.

Natalie Wolchover. “Why Doesn’t Plastic Biodegrade?” Livescience.Com, March 2011, https://www.livescience.com/33085-petroleum-derived-plastic-non-biodegradable.html.

Yale Climate Connections. “Why Plastics Can Be Garbage for the Climate.” Yale Climate Connections, 20 Aug. 2019, https://yaleclimatemediaforum.org/2019/08/how-plastics-contribute-to-climate-change/.