Plastic or the Planet?

Sasha Tetu and Lisa Moore are microbial ecologists at Macquarie University in Australia. They study how microscopic organisms respond to changes in their environment. Moore is one of the world’s top experts on a type of bacteria called Prochlorococcus, or “Pro” for short.

Pro is the tiniest—and the most numerous—photosynthetic organism on Earth. Like plants, the bacteria make their own food using photosynthesis. They harness sunlight to change water and carbon dioxide gas into sugar that they use for energy. Because Pro remove carbon from the atmosphere, they’re a crucial part of our planet’s carbon cycle. This is the process by which carbon moves through the environment between the atmosphere, living creatures, rocks, and water (see Microbes and the Carbon Cycle).

Sasha Tetu and Lisa Moore are microbial ecologists at Macquarie University in Australia. They study how microorganisms respond to changes to their environment. Moore is one of the world’s top experts on a certain type of bacteria. It’s called Prochlorococcus, or “Pro” for short.

Pro is the tiniest and most common photosynthetic organism on Earth. Like plants, the bacteria make their own food through photosynthesis. They use sunlight to change water and carbon dioxide gas into sugar. Then they use the sugar for energy. Pro remove carbon from the atmosphere, so they’re an important part of Earth’s carbon cycle. In this process, carbon travels through the environment. It moves between the atmosphere, living creatures, rocks, and water (see Microbes and the Carbon Cycle). 

Pro release oxygen as a waste product of photosynthesis: one molecule for every molecule of carbon dioxide they take in. That makes them vital to life on Earth. “It’s been estimated that 1 in every 10 breaths of oxygen you breathe is thanks to these little guys,” says Moore. “Yet almost nothing is known about how marine bacteria such as Prochlorococcus respond to human pollutants.”

That prompted the scientists to investigate how toxins released by one of the ocean’s most abundant pollutants—plastic—affect one of the ocean’s most abundant and important microbes. They set up lab experiments in which they exposed Pro to two widely used kinds of plastic: high-density polyethylene (HDPE) from shopping bags and polyvinyl chloride (PVC) from carpet padding.

The scientists cut the plastics into tiny bits and mixed them with artificial seawater that contained Pro bacteria. The result? “The chemicals that leach from the plastics interfered with growth and photosynthesis in Prochlorococcus,” says Moore. The chemicals also caused changes to the way the bacteria’s genes—units of hereditary material—functioned, resulting in most of the bacteria dying. Now, Moore and Tetu want to find out if plastic pollution has a similar effect on these microbes in the actual ocean.

Oxygen is a waste product of photosynthesis. Pro release one oxygen molecule for every molecule of carbon dioxide they take in. That makes them vital to life on Earth. “It’s been estimated that 1 in every 10 breaths of oxygen you breathe is thanks to these little guys,” says Moore. “Yet almost nothing is known about how marine bacteria such as Prochlorococcus respond to human pollutants.”

That’s why the scientists decided to look at toxins released by plastic. The material is one of the ocean’s most common pollutants. How does it affect one of the ocean’s most common and important microbes? In lab experiments, scientists exposed Pro to two widely used kinds of plastic. One was high-density polyethylene (HDPE) from shopping bags. The other was polyvinyl chloride (PVC) from carpet padding.

The scientists cut the plastics into tiny bits and mixed them with artificial seawater. The water contained Pro bacteria. The result? “The chemicals that leach from the plastics interfered with growth and photosynthesis in Prochlorococcus,” says Moore. The chemicals also affected the bacteria’s genes, or units of hereditary material. The changes in the genes caused most of the bacteria to die. Does plastic pollution have the same effect on these microbes in the actual ocean? Now Moore and Tetu want to find out. 

Plastic pollution is a widespread issue. Plastic trash has been spotted in just about every part of the world’s seas, even remote places like the Mariana Trench—the deepest point in the ocean. “I do a lot of my research out in the open ocean,” says Anne Thompson, a biological oceanographer at Portland State University in Oregon. “It’s shocking and depressing how much plastic is out there.”

In terms of innovation, plastic has been a miraculous invention. The substance is a polymer containing large molecules organized into repeating units. It’s durable, it’s cheap, and it can be transformed into just about anything. Plastics also have a vast range of properties, from strong and virtually unbreakable (think Kevlar, the material used in bulletproof vests) to flimsy and flexible (think plastic wrap and shopping bags). But these same qualities are also what make plastic a problem.

Once manufactured, plastic sticks around for a long, long time. Throwing it away doesn’t mean it’s gone. Most plastic isn’t biodegradable. It doesn’t break down in the environment like food, cotton, wood, and other natural substances do. Plastic decomposes extremely slowly, if at all. That explains why it keeps piling up on the planet—and showing up in places where it doesn’t belong, like the ocean. By the year 2050, experts predict, Earth’s oceans will contain more plastic trash, by weight, than fish!

Plastic pollution is a widespread problem. Plastic trash has been seen all through the world’s seas. It’s even in remote places like the Mariana Trench. That’s the deepest point in the ocean. “I do a lot of my research out in the open ocean,” says Anne Thompson, a biological oceanographer at Portland State University in Oregon. “It’s shocking and depressing how much plastic is out there.”

Plastic has been an amazing invention. The substance is a polymer, with large molecules arranged into repeating units. It’s long-lasting and cheap, and can be shaped into just about anything. And plastics can have many different qualities. Some are strong and nearly unbreakable. For example, Kevlar is a plastic material used in bulletproof vests. Some are flimsy and flexible, like plastic wrap and shopping bags. But these same qualities also make plastic a problem.

After plastic is made, it sticks around for a long, long time. If you throw it away, it isn’t gone. Most plastic isn’t biodegradable. It doesn’t break down in the environment like food, cotton, wood, and other natural substances do. Plastic breaks down very slowly, if at all. That’s why it keeps piling up on the planet. And it keeps showing up in places where it doesn’t belong, like the ocean. Experts think the world’s oceans will contain a huge amount of plastic by the year 2050. This trash will weigh more than all the fish in the oceans! 

According to the United Nations, at least 800 species worldwide are affected by marine debris—and 80 percent of that debris is, you guessed it, plastic trash. An estimated 14 million tons of the almost indestructible stuff ends up in the ocean each year. That’s the equivalent of a garbage-truck load’s worth every minute.

The plastic debris littering the ocean falls into two categories. There’s macroplastic—the large pieces that float around, wash up on beaches, ensnare animals, and turn up by the bushel in whales’ stomachs. And then there’s microplastic—tiny plastic pieces, less than 5 millimeters (0.2 inches) long, that are literally everywhere. They’ve been found on the ocean floor, the snow-capped peak of Mount Everest, and icebergs in Antarctica. They’ve even been detected in foods we eat and in animal feces—including our own.

Macroplastic is easy to see and therefore has been studied for a while now. “But what you can’t see are the chemicals being released by plastics as they break down,” says Thompson. “And you also can’t see microbes like Prochlorococcus. The question of whether plastic is toxic to Pro is so important because the two are clashing in the ocean right now. We need to know what the consequences of that are.”

Marine trash affects at least 800 species around the world, according to the United Nations. And guess what 80 percent of that trash is? Plastic. Around 14 million tons of the long-lasting material ends up in the ocean each year. That’s the same as a garbage-truck load every minute.

The plastic litter in the ocean falls into two classes. One is macroplastic. These large pieces float around, wash up on beaches, and get tangled around animals. Large amounts also turn up in whales’ stomachs. The other class is microplastic. These tiny plastic pieces are less than 5 millimeters (0.2 inches) long, and they’re everywhere. They’ve been found on the ocean floor, the snowy peak of Mount Everest, and icebergs in Antarctica. They’ve even been found in foods we eat and in animal feces, including our own.

Macroplastic is easy to see, so it’s been studied for a while now. “But what you can’t see are the chemicals being released by plastics as they break down,” says Thompson. “And you also can’t see microbes like Prochlorococcus. The question of whether plastic is toxic to Pro is so important because the two are clashing in the ocean right now. We need to know what the consequences of that are.”