What are Microbiomes?

Microbes are tiny organisms—such as bacteria, fungi, and viruses—that are so small we cannot see them without the help of microscopes. Many microbes are so small (about 1/1,000,000 of a meter) that thousands of them can fit inside a single raindrop. Microbes live together in communities called microbiomes. Microbiomes are found almost everywhere, living inside our bodies to the soil beneath our feet. For example, microbes in our stomach help us digest food, protect us from harmful germs, and even make vitamins to keep us healthy. Microbes found in the soil are just as important but often receive far less attention. Soil microbes can make the soil fertile so plants can grow, recycle nutrients such as nitrogen and carbon, and even store gases from the air to help keep the planet cooler (Figure 1). But the important roles soil microbes play may be disrupted by changes in the environment, including pollution. Because microbes are important for life on Earth, it is up to us to understand how these changes affect them and what we can do to protect them.

How Does Pollution Affect Living Things?

Pollution happens when harmful substances enter the environment and cause damage. Pollution can hurt people by causing problems like itchy eyes, coughing, headaches, or making them feel sick to their stomach. Over time, pollution can lead to more serious health problems, such as damage to the brain, trouble breathing, or even cancer [1]. However, pollution not only harms humans but also affects plants and other animals. For example, when pollution enters lakes or oceans, it can cause certain algae (plant-like organisms that live in water) to grow too much. These algae can use up the oxygen in the water, which can make it hard for fish, turtles, and even birds to survive. In a similar way, polluted soils can affect organisms on land by making it hard for plants to grow and harming worms and other helpful organisms that help keep the soil healthy. Pollution in one part of the environment can start a chain reaction, like dominoes falling one after another. A small change in water or soil can lead to much bigger problems for plants, animals, and people—disrupting life all around us.

Pollution comes in many forms. Throwing garbage or chemicals into rivers and lakes causes water pollution. The gases released from cars and factories can pollute the air we breathe. Bright city lights can create light pollution that can confuse birds and other wildlife. Even loud sounds, such as traffic or airplanes, create noise pollution that can stress both people and animals. As our world continues to grow and change, people are becoming more aware of different kinds of pollution. One of these is microplastics, which are tiny pieces of plastic, smaller than 5 mm, that were discovered polluting the environment in the 1960s. Scientists have only recently started to pay attention to these tiny plastic particles because they are now found almost everywhere, from the soil in our backyards to inside the human body.

What are Microplastics and Where do They Come From?

Many microplastics are about the size of a pencil eraser, but some can be much smaller—some as small as a grain of sand or too tiny to see without a special microscope. Microplastics come in many different sizes, shapes, and types: small beads, thin films, short fibers, or broken bits from larger plastic items [2]. Microplastics are made up of long, repeating chains of atoms called polymers. The polymers usually contain carbon and other elements, and they are built to be very strong and last a long time. Because of this, microplastics do not break down easily and can stay in the environment for a very long time.

Microplastics can be grouped into two types based on how they are made. Primary microplastics are made to be small on purpose. These include tiny plastic beads in some personal care products, such as toothpaste, sunscreen, body wash; as well as tiny plastic fibers used to make synthetic clothing (made from man-made materials such as polyester). Secondary microplastics start out as larger plastic items. These items can include plastic bags and bottles, which can break down into smaller pieces over long periods of time when they are exposed to sunlight, wind, or water (Figure 2).

Many microplastics come from everyday activities and items, some of which we may not even think about. For example, when car tires wear down on the road, they release microplastics. Washing synthetic clothes can shed tiny plastic fibers that end up in waterways. If personal care products contain plastic beads, these can also wash down the drain and enter the environment [3]. Additionally, plastics that are not thrown away properly, like plastic bottles or food wrappers, can break into smaller pieces that end up in parks, oceans, or the soil. Microplastics can build up in the environment, especially when they are not cleaned up or recycled. Once microplastics are out in the environment, they can move around a lot. Their small size makes it easy for them to travel long distances through wind and water.

How do Microplastics Affect Soil Microbiomes?

So, what happens when microplastics stay in the soil? A lot can change, especially for the community of microbes living there. Microplastics can change how tightly the soil sticks together, how much water it can hold, and how easily air can flow through it [4]. These things might not seem like a big deal at first, but microbes need the right conditions to do their jobs. Just like people, microbes need the right balance of air, water, and space to stay alive and active. If those conditions change too much, many microbes may not survive.

When the soil is filled with microplastics, helpful microbes or those that support plant roots might begin to disappear. In their place, other microbes that cannot do these jobs may thrive instead. Sometimes microplastics can even allow harmful microbes to take over. Some microbes might even use microplastics as a new home, including harmful bacteria that can stick to its surface (Figure 3) [4]. Over time, these types of changes can affect the entire environment.

Protecting Soil Microbiomes from Microplastics

The world produces around 400 million metric tons of plastic waste every year. That is a lot! In fact, it is the same as the weight of 4,000,000 blue whales, the largest animal on Earth. This huge amount of plastic waste makes microplastics a serious problem. Scientists are still working to understand all the ways microplastics affect soil microbiomes. However, what we do know is that too much plastic in the environment is not good. When plastic builds up in the soil, it can harm the microbes we depend on to support life on Earth. While we need more research to understand the long-term effects, there are simple things we can do to help prevent microplastics from getting into the soil.

One way we can help protect soil microbiomes is by reducing the use of plastic in our daily lives. Simple choices like using reusable water bottles, avoiding plastic bags, or choosing clothing made from natural fibers can go a long way. Recycling is another important step. By properly recycling and disposing of plastic, we can prevent it from polluting the soil. If we all make an effort to reduce microplastics, we can protect microbiomes in the soil. Together, we can make a big impact and create a safe, healthy worth for future generations!

Glossary

Microbiome: ↑ A community of microbes that live and interact with each other.

Pollution: ↑ Harmful substances introduced by humans into the environment.

Microplastics: ↑ Plastic pieces that are smaller than a pencil eraser.

Polymers: ↑ Long chains made up of small molecules that are connected, like beads on a string.

Primary Microplastics: ↑ Plastics that are made to be small on purpose.

Secondary Microplastics: ↑ Plastics that are the result of the breakdown of primary plastics.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

AI Tool Statement

The author(s) declared that Generative AI was not used in the creation of this manuscript.

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