Waste isn’t new, and neither is humanity’s role in creating it. Since the dawn of industrialization, our ability to pollute has scaled alongside our innovations.
In 1862, British inventor and metallurgist Alexander Parkes unveiled the world’s first man-made plastic: Parkesine. However, what Parkes didn’t know at the time was that his semi-synthetic thermoplastic material made from cellulose treated with nitric acid and a solvent would spark a revolution. This cellulose-based thermoplastic sparked a new era of material science.
Fascinated by plastic’s versatility, potential, and durability, other inventors quickly began modifying and multiplying it. This resulted in a wave of new materials such as celluloid, Bakelite, PVC, nylon, PET, and many more, that would rapidly begin to take over everyday life.
The early warning signs of a durable pollutant
In the late 1960s, the consequences of plastic began to surface. While carrying out plankton research in the Sargasso Sea, scientists Edward J. Carpenter and K. L. Smith Jr. of the Woods Hole Oceanographic Institution (WHOI) came upon numerous small plastic particles mixed with the seaweed.
This showed that plastic pollution wasn’t just a small issue, but rather an emerging threat. In response, engineers turned to recycling – a waste management method that turns plastic into raw materials that can be reused for new, valuable products.
But while it first seemed like a smart solution as it reduced waste, conserved resources, and kept a significant amount of plastic out of the ocean, the process began revealing its limitations decades later. Not only is it costly and at times inefficient, it is also linked to concerns over toxicity and pollution.
Recycled plastics also contain harmful chemicals, and they can release microplastics back into the environment. This raises a crucial question: Is recycling still the most effective way to address the global plastic crisis, or is it time to engineer a better solution?
The mechanics of plastic recovery
While recyclable materials can be processed through mechanical, chemical, or energy recycling, all methods begin with three common steps. These include collecting the waste, separating the recyclables, and converting the residue back into raw material.
Mechanical recycling is the most widely used method for processing plastics such as polyethylene terephthalate (PET) and high-density polyethylene (HDPE). It typically consists of collection, sorting, washing, drying, grinding, and finally compounding and pelletizing. To this day, it remains the only form of plastic recycling widely implemented at a commercial scale.
In contrast, chemical recycling is a relatively new technology that aims to restore plastics from any stage of degradation back to their original high-quality raw materials. This method targets hard-to-recycle plastics, such as snack bags, ready meal trays, and certain films, that mechanical recycling can’t efficiently process.
It can be done through pyrolysis, where polymers are heated without oxygen and broken down into smaller components that behave like oil; gasification, where polymers are heated with oxygen and water, resulting in a mixture of gases; hydro-cracking where large plastic molecules are broken down into smaller ones with the help of hydrogen; and finally, depolymerization, in which polymers are broken down into monomers, producing raw material which is directly usable for making new plastic.
Ultimately, energy recycling involves burning the plastic to produce heat, which can then be used to generate electricity or heating. This method turns plastic into fuel by using its energy content; however, it doesn’t recover the material itself.
Breaking down the costs
Despite its prevalence, mechanical recycling is far from cost-free. With operating expenses typically ranging from USD 50 to 200 per ton, recycling the 460 million metric tons of plastic produced annually could cost up to USD 92 billion, if it were even possible. Many plastics can’t be mechanically recycled due to contamination or material limitations.
Meanwhile, chemical recycling comes at a significantly higher cost, ranging from USD 300 to 1,000 per ton. Nonetheless, the technology is still in its early stages and is currently limited to demonstration plants and smaller factories.
While data on energy recycling is limited, energy use across all plastic recycling methods accounts for about one-third of total operating costs, according to industry estimates.
Still, the process offers significant environmental benefits. Recycling a single ton of plastic can save up to 5,774 kilowatt-hours (kWh) of energy, 16.3 barrels of oil, and 30 cubic yards of landfill space. In comparison to producing virgin plastic, it can reduce energy use by more than 80 percent.
What’s really inside recycled polymers?
Recycling may give plastic a second life, but it does not fully remove the harmful chemicals present in plastic waste. This is because certain substances can either leach out or persist throughout the recycling process, ultimately contaminating the recycled material.
A 2023 Greenpeace report suggests that recycled plastics often carry elevated levels of harmful substances, including flame retardants, carcinogens, and hormone-disrupting chemicals, as well as persistent environmental pollutants like brominated and chlorinated dioxins.
What’s more, chemical recycling processes like pyrolysis can emit pollutants such as mercury, arsenic, formaldehyde, carbon monoxide, nitrogen oxides, and sulfur dioxide, leading to air and water pollution.
At the same time, mechanical recycling can generate new toxins when plastics are heated. Even small amounts of contamination, like PVC in PET, can produce benzene, a known human carcinogen linked to leukemia and other serious health effects.
A recent study by researchers from the University of Gothenburg and Leipzig found that a single recycled plastic pellet can contain more than 80 different chemicals.
“We identified common plastic chemicals, including UV-stabilizers and plasticizers, as well as chemicals that are not used as plastic additives, including pesticides, pharmaceuticals, and biocides,” Eric Carmona, researcher at the Department of Exposure Science, Helmholtz Centre for Environmental Research in Leipzig, said in a statement.
Designing for end-of-life, not just performance
As the world looks beyond conventional plastic recycling, more companies are exploring innovative solutions like mushroom-based packaging and advanced biopolymers, promising low-impact alternatives to traditional plastics.
Meanwhile, recycled cardboard and paper remain the most widely used biodegradable alternatives to plastic packaging. However, experts say the real solution lies in reducing plastic dependency and rethinking the entire system.
Both researchers and policymakers stress that sustainable change requires more than just changing materials. They add that plastic recycling can’t be considered safe unless hazardous chemicals are completely removed from the equation.
Elsa Olivetti, PhD, an MIT professor of materials science and engineering, emphasizes that clear regulations and standards are essential for scaling recycling. “To be effective, policies need to not just focus on increasing rates of recycling, but on the whole cycle of supply and demand and the different players involved,” Olivetti said.
“We cannot safely produce and use recycled plastics if we cannot trace chemicals throughout production, use, and waste phases,” added Bethanie Carney Almroth, PhD, a professor at the University of Gothenburg.
Until then, even the most innovative recycling processes will remain constrained by the same chemistry that made plastic such a durable miracle in the first place.