Chloe Zhang
Sunlight has been shown to break down plastics, a process which could help reduce plastic waste in the environment. While it was previously assumed that sunlight only physically fragmented plastics into smaller particles, recent studies have found that sunlight also chemically transforms plastics into tens of thousands of compounds, including carbon, that can be broken down further by bacteria. This process is known as photochemical transformation or photodegradation and has been observed in both marine and terrestrial environments. The development of sun-sensitive plastics that break down more quickly could also be a potential solution to plastic pollution. However, the impact of these breakdown products on aquatic ecosystems and biogeochemical processes is still unknown, and the dilution of these byproducts in the ocean may be a cause for concern in smaller water sources such as rivers or streams.
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What You'll Learn
Sunlight chemically alters plastic
The chemical structure of plastic is altered by sunlight, specifically the UV light component. UV light from the sun slowly breaks down plastics on the ocean's surface, turning them into smaller, invisible nanoplastic particles that spread across the water column. This breakdown can also produce molecules found in crude oil, which can be further broken down by bacteria.
The specific chemical changes that occur during the breakdown of plastic by sunlight depend on the type of plastic and the additives it contains. For example, polystyrene, a common plastic, has been found to degrade into dissolved organic carbon and trace amounts of carbon dioxide when exposed to sunlight. The additives in polystyrene, which determine its colour, flexibility, and other physical features, also play a role in the breakdown process by absorbing different frequencies of sunlight.
A recent study examined the breakdown of four different single-use consumer polyethylene plastic bags from major retailers under sunlight. The bags were found to contain complex formulations of chemical additives, and the breakdown process produced a suite of transformation products that no longer resembled the original material.
Additionally, a new type of environmentally degradable plastic has been developed, which breaks down in about a week in sunlight and oxygen, leaving behind only succinic acid, a non-toxic small molecule. This process is different from the breakdown of other degradable plastics, which often leave behind microplastic fragments.
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Sunlight breaks down plastic into nanoplastics
It was previously assumed that sunlight exposure simply fragmented plastics into microplastics, which would persist indefinitely in the environment. However, recent studies have revealed that sunlight also chemically alters plastic, breaking it down into tens of thousands of compounds that can dissolve in water. This process is known as photochemical transformation, and it has been shown to occur in both marine and freshwater environments.
In the ocean, sunlight breaks down floating microplastics into smaller, invisible nanoplastic particles that spread throughout the water column. This breakdown is facilitated by UV light from the sun, which can account for the disappearance of about 1.7-2% of visibly floating plastic from the ocean surface each year. Over time, this can add up to a substantial amount of plastic degradation.
The breakdown of plastics by sunlight can lead to the production of water-soluble compounds, including molecules found in crude oil, and carbon-based compounds such as organic carbon and carbon dioxide. Some of these compounds can be further broken down by bacteria, while others may have unknown impacts on aquatic ecosystems and biogeochemical processes.
The development of degradable plastic polymers that can break down in sunlight and air is an emerging area of research. These plastics can decompose rapidly, transforming into non-toxic molecules that do not leave microplastic fragments behind. While this technology may not be suitable for all plastic products, it offers promising solutions for reducing plastic pollution in the environment.
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Sunlight breaks down plastic into compounds that can be broken down by bacteria
Sunlight, particularly UV light, has been found to break down plastics on the ocean's surface. Floating microplastics are broken down into smaller, invisible nanoplastic particles that spread across the entire water column. These nanoplastics can then be broken down further into compounds that can be degraded by bacteria.
Laboratory experiments conducted by Annalisa Delre and colleagues at the Royal Netherlands Institute for Sea Research, NIOZ, on Texel, calculated that about 2% of visibly floating plastic may disappear from the ocean surface each year due to this process. Over time, this can add up to a substantial amount of plastic being degraded.
The breakdown of plastics by sunlight is not limited to the ocean's surface. A study published in the Journal of Hazardous Materials found that four different types of post-consumer microplastics collected from the waters of the North Pacific Gyre dissolved into organic carbon when placed under a solar simulator. This process may be even more concerning in smaller water sources such as rivers or streams, where the byproducts of chemical reactions are less diluted and can cause more localized harm.
While the breakdown of plastics by sunlight can be beneficial for reducing plastic pollution, it is important to note that the resulting chemicals may have unknown impacts on the environment. Additionally, the breakdown of plastics can also lead to the release of additives, which can have their own environmental effects.
Furthermore, not all plastics are equally susceptible to degradation by sunlight. The presence of additives, such as those that determine color, flexibility, and other physical features, can influence how fast a plastic breaks down. For example, black foam and black coffee lids, often made of polystyrene, are more likely to end up in landfills as they are more challenging to recycle.
Recent advancements in plastic design have led to the development of environmentally degradable plastics that can break down in sunlight and air within about a week. This new plastic degrades into succinic acid, a naturally occurring non-toxic small molecule, without leaving behind microplastic fragments. However, such sun-sensitive plastics may not be suitable for products that need to last longer than a week.
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Sunlight breaks down plastic into carbon that can be used by microbes
The idea that sunlight can break down plastics is not new. Anyone who has observed sun-bleached plastic playground toys, park benches, or lawn chairs has witnessed this process in action. However, recent studies have revealed that sunlight does more than just physically break down plastics into smaller particles; it also chemically alters them.
A study published in the Journal of Hazardous Materials found that when four different types of post-consumer microplastics collected from the North Pacific Gyre were exposed to a solar simulator, they dissolved into organic carbon. This carbon can then be consumed by microbes and turned into food.
While this process may seem beneficial for reducing plastic pollution, it is important to note that the byproducts of these chemical reactions can be harmful. The breakdown of plastics can release contaminants, and in higher concentrations, these pollutants can cause more localized harm. Additionally, one of the four plastics tested in the study actually harmed the bacteria.
Furthermore, the breakdown of plastics can also lead to the release of carbon dioxide, although the levels produced are currently far too low to impact climate change. Nevertheless, as the plastic undergoes this transformation, it creates entirely new byproducts that are invisible to the naked eye, making it challenging to estimate the true amount of plastic in the environment.
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Sunlight breaks down polystyrene faster than expected
Sunlight breaks down polystyrene, one of the world's most ubiquitous plastics, faster than expected. While it was previously thought that polystyrene would take thousands of years to fully break down, recent studies have shown that it may degrade in decades or centuries when exposed to sunlight. This is because the ring-based backbone of polystyrene, which makes it difficult for microbes to break down, is the perfect shape and size to catch certain frequencies of sunlight.
The process by which sunlight breaks down polystyrene involves the absorption of energy by the plastic, which breaks apart its carbon bonds. In a laboratory setting, researchers exposed commercially available polystyrene samples to sunlight using a solar simulator, a lamp that replicates sunlight frequencies. They then collected the resulting CO2 and compounds that had dissolved into the water. Using chemical tools, they traced the origins of the carbon atoms found in both the CO2 and filtered water, confirming that sunlight had transformed the polystyrene into CO2 and other compounds.
The implications of these findings are significant. Firstly, it challenges the assumption that polystyrene lasts forever in the environment, which has been a justification for policies banning its use. Secondly, understanding how sunlight breaks down polystyrene can help estimate the amount of plastic in the environment, as the original form of the plastic disappears, and new byproducts are formed that cannot be seen by the naked eye. Additionally, the presence of additives in polystyrene, which determine its colour and physical features, can also influence the breakdown process by absorbing different frequencies of sunlight.
While the faster breakdown of polystyrene may seem positive, the impact of the resulting chemicals on the environment is still unknown. Furthermore, the breakdown of plastics in smaller water sources such as rivers or streams, where plastic concentrations are higher, may be more concerning due to the potential release of contaminants during degradation. Nevertheless, these findings provide actionable approaches for creating less persistent plastics in the future. By modifying the ingredients, the plastic industry can make their products more susceptible to breakdown once they reach the end of their useful lifespan.
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Frequently asked questions
Sunlight breaks down plastic through a process called photo-oxidative degradation, in which sunlight irradiation breaks the polymer’s double- and triple-bonded carbon backbone.
Plastic breaks down into carbon that some microbes turn into food. It also breaks down into molecules that one also finds in crude oil, which can be further broken down by bacteria.
It depends on the type of plastic. Polystyrene, for example, may degrade in decades or centuries when exposed to sunlight, rather than the thousands of years as was previously thought.
Sunlight breaking down plastic could help reduce plastic pollution in the environment. However, it is important to note that the byproducts of plastic degradation could be harmful to the environment and aquatic ecosystems.
