Plastic Waste in the Ocean and Possible Degradation by Bacteria
An Escalating Problem
Plastic use is increasing rapidly in many parts of the world today and is changing human lives. Plastics are certainly useful, but the tendency of many people to throw away them away when they're no longer needed is creating a major pollution problem. They break down very slowly and may release toxic substances as they degrade. Some of the discarded items enter the ocean, where they harm and kill marine animals.
Plastic in the ocean exists not only as chunks and pieces but also as microplastic. Microplastic fragments are less than five millimeters long. The fragments form as larger pieces of plastic in seawater slowly degrade. They are also released into the sewage system when clothing made of plastic fibres, such as polyester and acrylic, is washed. Microplastic is widespread in the ocean and is especially concentrated in the so-called "garbage patches". These are places in the ocean where water currents trap garbage or pollutants in the area.
Bacteria help to decompose many types of waste. According to the present state of our knowledge, though, there don't seem to be many bacteria that can break down plastic. Some bacteria can decompose bioplastics, which are made from plants such as corn. Researchers have discovered that microplastic in the Atlantic Ocean has been colonized by a group of bacteria that may be able to degrade the particles. Other researchers have found a specific species of bacteria that can break down one type of plastic. Despite these discoveries, the problem of removing the material from the ocean is far from being solved.
What Is Plastic?
A plastic is a synthetic material made of an organic polymer. The word "organic" means that the molecules making up the material contain carbon atoms. A "polymer" is a long chain of molecules joined together. Most plastics are made of petrochemicals (chemicals produced from petroleum or natural gas).
Plastics usually contain additives to improve them in some way. Examples of these additives include pigments, flame retardants, stabilizers, plasticizers to improve softness and flexibility, and reinforcers to make the material tougher.
Sources of Plastic Waste
The list of plastic items in many people's lives is a long one. A partial list is given below. Sometimes an alternate product can be found with the same function as a plastic item, but not always.
- storage containers
- lunch bags and food wrap
- shopping bags
- grocery bags
- drink bottles
- food packages, such as breads bags, frozen meal containers, yogurt containers, and some milk containers
- containers for cosmetics, shampoo, and laundry detergents
- microbeads in cosmetics such as exfoliating facial scrubs and cleansers
- medication containers
- utensils and cutlery
- furniture such as chairs and tables
- cases for electronic devices and plastic accessories for these devices
- credit cards, shopping cards, ID cards, and driver's licenses
- items made of vinyl, nylon, acrylic, polyester, polycarbonate, polyethylene, polypropylene, polybutylene, polystyrene, ABS plastic (acrylonitrile butadiene styrene), PLA plastic (polylactic acid), or plastic resins
How Does Plastic Enter the Ocean?
Plastic waste may be deposited in the ocean directly or indirectly. Some is deliberately dropped off ships or offshore platforms or is blown or washed off. Some is tossed into the sea by people on land. The rest is blown off the land or washed off by moving water. Plastic deposited in land fills or casually dropped on the ground may eventually reach the ocean.
Altogether, these methods deposit a significant amount of plastic into the ocean every year. The old idea that the oceans are so vast that anything dropped into them will be diluted and have no effect is no longer valid.
It is estimated that about 80% of marine debris originates as land-based trash and the remaining 20% is attributed to at-sea intentional or accidental disposal or loss of goods and waste.— Environmental Protection Agency
World Oceans Day Statement About Pollution
A commonly held belief is that plastic doesn't break down, apart from the new, biodegradable plastics. This isn't true, however. Regular plastic does break down, but usually very slowly.
Ultraviolet light from the sun breaks some plastics down in as little as a year, while others are thought to need hundreds of years to break down. The light breaks the bonds holding the building blocks (or the monomers) of the polymer chain together.
Although degradation of plastics sounds like a good thing, it may not be so wonderful. Research suggests that when the materials degrade, they don't disappear but become small pieces of microplastic.
Microplastic fragments enter the bodies of animals. The effects of microplastics on living things aren't known for certain, but their presence worries some researchers, especially as their concentration is increasing. The term "plastic soup" is sometimes used for a region in the ocean that is laden with microplastic particles.
Another problem that develops from plastic degradation is that as the material disintegrates it releases the additives that were used to improve its properties. Some of these additives are known to be harmful to living things, including humans.
Some people think that biodegradable plastics can be left in a landfill and will then be broken down by bacteria. Unfortunately, this isn't the case. When they are buried in a landfill, they aren't exposed to enough oxygen, light, and moisture to break down.
One type of biodegradable plastic is the bioplastic family. Bioplastics are derived from living things, such as corn. They must be sent to a commercial composting plant to be decomposed by specific bacteria under specific environmental conditions. If this isn't done, they are as dangerous for the environment as regular plastics.
Waste and Recycling Statistics in the United States
According to the Environmental Protection Agency or EPA, the following statistics were obtained from 2017 with respect to municipal solid waste. (Comparable statistics from more recent years are unavailable at the moment.) The numbers are rounded to one decimal place.
- 35.4 million tons of plastic waste was generated.
- 3.0 million tons was recycled (8.5% of the amount generated).
- 5.6 million tons underwent combustion with energy recovery.
- 26.8 million tons entered landfills.
As the table in the first reference at the end of this article shows, the amount of plastic waste generated each year in the United States is still increasing. In addition, the percentage of waste that was recycled in 2016 (9.2%) was higher than in 2017. Our love of plastic is creating a major problem.
Effects of Plastic on Marine Animals
Plastic pollution can have serious consequences for ocean life. Large pieces of the material may be mistaken for prey and eaten. Sea turtles and whales may mistake a billowing plastic bag for a squid, for example. The bag may block the animal's airway, causing suffocation, or block the stomach, leading to starvation. It may also prevent food absorption though the intestinal wall or leach toxic substances, poisoning the animal.
In 2013, a dead sperm whale washed up on a Spanish beach with over 37 pounds of plastic debris in its stomach. The material existed in the form of 59 different items and included thick plastic sheets, bags, rope, hosepipe, two flower pots, and a plastic spray canister. The animal is believed to have died from starvation.
The items in the whale's stomach came from a huge greenhouse industry nearby. The greenhouses occupy almost 99,000 acres and can be seen in satellite views of Earth. Much of the plastic waste produced by the industry is treated in special centers, but a significant amount escapes into the ocean.
Unfortunately, the sperm whale's fate was not unique. Dead whales containing plastic in their digestive tract are still being discovered. In 2019, a curvier beaked whale in the Philippines was found to have 88 pounds of plastic inside its body.
Another problem that develops from plastic waste is that some animals become trapped in the six-pack rings used to carry canned drinks. The rings may cause the animal to suffocate or starve. They may also cause an infection if they injure the animal's skin. Yet another problem that may arise is that plastic debris may cover and kill seaweeds or coral. This may indirectly harm the creatures that depend on the seaweeds or coral for survival.
Pellets or Nurdles
One of the most common forms of visible plastic in the ocean and on beaches is the plastic nurdle. Nurdles are small pellets that are used to make larger objects. Birds and aquatic animals may eat these, mistaking them for fish eggs. Like larger pieces of plastic, nurdles can cause suffocation, starvation, or poisoning. Nurdles may contain toxic substances added during their formation and may also absorb toxins from their environment.
Nurdles are sometimes called "mermaid tears". They enter the marine environment when they are spilled during their production or transport. Unfortunately, they mix with the sand on beaches, making it very hard to remove them.
The Ocean Garbage Patches
The Great Pacific Garbage Patch isn't covered by a blanket of large, easily visible pieces of trash, as some people imagine. Instead, it contains a high concentration of microplastic.
Microplastics are fragments of plastic that are less than 5 mm in length or diameter. They are made from the breakdown of larger pieces of plastic. They're also shed from clothing made from synthetic fibers as the clothing is washed in a washing machine. The microbeads in cosmetics and some industrial products are usually microplastics, too.
Plastic pollution combined with ocean circulation patterns is responsible for the creation of the Great Pacific Garbage Patch, an area in the Pacific Ocean with an unusually high microplastic concentration. Microplastic is found far beyond the garbage patch, however. As scientists do tests in different parts of the world, they are discovering that it has a very widepread distribution.
It's impossible to remove microplastics from sea water. Their particles are too small, too numerous, and too widespread. While larger pieces of plastic and some of the substances leached from them are known to be harmful, the effects of microplastics are not so clear. Researchers know that the particles are entering the bodies of marine animals and being stored there. They may leach toxic substances, just like larger pieces of the material, but this has yet to be confirmed.
Leached Toxins from Plastic
Two examples of potential toxins leached from plastic are bisphenol A (or BPA) and chemicals known as phthalates.
Bisphenol A is used in the manufacture of clear polycarbonate plastic and epoxy resins. It's an endocrine disruptor (a substance that interferes with the action of hormones). The view of the NIH (National Institutes of Health) is that at current exposure levels BPA is not harmful for adult humans, but there is "some concern" about the exposure of fetuses, infants, and children to the chemical. BPA is dangerous for at least some marine animals.
Different kinds of phthalates exist. The chemicals are added to polyvinyl chloride to increase its softness and are also added to cosmetics. Phthalates are thought to be endocrine disruptors in humans and animals. Some members of the family seem to be more dangerous than others. As is the case with BPA, research is ongoing. One type of phthalate is thought to be a carcinogen (cancer causer) in humans. High levels of another kind may interfere with reproduction or development.
One type of bioplastic is polylactic acid, or PLA. PLA is made from corn starch in North America but is also produced from tapioca roots and sugarcane.
Two environmentally friendly ways to get rid of unwanted PLA plastic exist. One method is to use bacteria to break the material down into carbon dioxide and water. The bacteria are added to the plastic at a high temperature in a commercial composting facility. The decomposition process generally takes three to six months.
The other way to deal with unwanted PLA plastic is to melt it and then pass it through an extruder, which will form a new shape from the material. Other types of plastic can also be recycled in this way. Some extruders are cheap enough for many consumers to buy. This is good because of the growing popularity and affordability of 3D printers. Consumer-level 3D printers produce solid objects from hot, melted plastic, so it's important that a good way to deal with unwanted objects is available.
Making Plastic From Corn
Possible Degradation by Bacteria in Nature
In June 2011, scientists from the Marine Biological Laboratory in Woods Hole, Massachusetts, reported that they had collected bits of microplastic from the North Atlantic Ocean and found that they had bacteria on their surface. The bacterial community in the "plastisphere" habitat was different from the community in the surrounding water.
The microplastic fragments had tiny pits on their surface. The pits matched the shape of the bacteria. In addition, the researchers identified plastisphere bacteria that could break down hydrocarbons, which are found in plastics. These observations led the scientists to believe that the bacteria were degrading the microplastic. It's unknown whether the bacteria in the plastisphere convert plastics into harmless chemicals or instead release toxins from the plastic as they degrade it (if in fact they do degrade it). The bacteria may be beneficial, harmful, or both at the same time.
Other bacteria have been found to break down plastic in lab experiments, although as in the above example it's unknown how significant this is in natural environments. It's possible that plastic-degrading bacteria may one day be useful to us. We are in no way ready to release the bacteria into the ocean and may not be so for a long time, however. Though the research is continuing and may eventually be useful, we need solutions to the plastic problem now.
A Bacterium That Can Live on PET
In 2016, researchers at Kyoto University in Japan announced that they had found a bacterium that can live on a plastic called PET, or polyethylene teraphthalate. PET is used to make bottles and clothing. The researchers have named the bacterium Ideonella sakaiensis. When they placed the bacterium in a container containing pieces of PET and a few other nutrients, the plastic disappeared within a few weeks.
The scientists have made another potentially important discovery. They have identified the enzyme that the bacterium uses to break down PET and have found the DNA sequence in the microbe that codes for the enzyme. In addition, they have been able to make the enzyme. This might lead to a new way to remove one type of plastic waste.
Since the monomers of a plastic contain carbon, they should in theory be a good food source for bacteria. The problem is that most bacteria don't have suitable enzymes to break a plastic up into its constituent monomers. The discovery of one that does is exciting.
How to Make a Corn Bioplastic at Home
A Plastic Waste Poll
How do you deal with the plastic waste that you create in your life?
Reducing the Use of Plastic
Plastic is so ubiquitous in most people's lives that it may be hard to avoid it. There are many websites that either help people lead plastic-free lives or help them to greatly reduce their use of the material. If a person searches for "living plastic free" on the Internet, they'll find page after page of useful links.
A plastic-free lifestyle does require some creative thinking. In some cases the lifestyle is too inconvenient or too expensive for a family or individual to follow rigidly. Sometimes it simply isn't possible to avoid plastic. After all, a person can't refuse to accept a needed medication just because it's in a plastic container.
The best solution for the problem is to encourage people to reduce their use of the material significantly and to find better ways to either recycle their plastic or break it down. Lobbying companies to find alternatives for plastic containers or products may be helpful, but not if the alternate product is more expensive.
Researchers and inventors are investigating new types of biodegradable plastics. These may be very helpful in the future, as long as they have other necessary properties (such as strength) in addition to being biodegradable.
We definitely need to change the way in which we deal with plastic. We are harming ocean life with our debris. Since humans eat marine animals such as fish, we may also be harming ourselves.
- Plastic waste and recycling data from the Environmental Protection Agency
- Toxicological threats of plastic from the EPA
- Information about phthalates from Tox Town (a National Institutes of Health site)
- Facts about bisphenol A (BPA) from Tox Town
- Information about the garbage patches from NOAA (National Oceanic and Atmospheric Administration)
- A report about a dead sperm whale full of plastic from The Guardian
- A report about another plastic-filled whale from National Geographic
- Marine microbes digest plastic from the Nature journal
- A bacterium that digests plastic from a University of Hull lecturer via The Conversation
Questions & Answers
© 2013 Linda Crampton