Core Concept Earth Sciences Collection Article Published: October 25, 2021

How Are Microplastics Invading the World?


Microplastics are tiny plastic pieces, <5 mm, which is smaller than a pencil eraser. Did you know that you can find microplastics everywhere? They are in the air, water, soil, and within living creatures. You can find them from the deep sea to the snow in the Arctic. You can find them across beaches in California, and in the San Francisco Bay waters. Many living organisms ranging from zooplankton to whales contain microplastics in their bodies, including aquatic creatures from California. In this article, you will learn about the origin of microplastics, where you can find them, why they are a concern, how they can affect the Sacramento-San Joaquin Delta, and how you can help to reduce their global invasion.

What Are Microplastics and How Do They Originate?

Microplastics are little plastic pieces <5 millimeters (mm), or about 1/5 inch, in size. Depending on their origin, these plastic pieces can be considered primary or secondary microplastics. Primary microplastics are originally manufactured as this tiny size for industrial use. For example, plastic microbeads are used in personal care products, like toothpastes and skin creams. Secondary microplastics originate from the fragmentation of larger plastic materials, such as plastic bottles, bags, straws, and containers, which break down in the environment over time to become microplastics (Figures 1A,B).

Figure 1 - Microplastics suspended in water.
  • Figure 1 - Microplastics suspended in water.
  • Microplastics can be classified as (A) primary microplastics, which are created as small particles and used to create larger plastic objects or in personal care products like toothpastes, or (B) secondary microplastics, which result from the breakdown of larger plastic objects, such as a plastic bottle. Microplastics can exist as (C) pellets, (D) fragments, (E) fibers, (F) foams, (G) films, or (H) granules. Some microplastics can act as fomites, transporting (I) hazardous chemicals, or (J) pathogens.

When classified by their visual appearance, microplastics can be pellets, fragments, fibers, foams, films, or granules (Figures 1C–H). Pellets are manufactured as little spheres to produce bigger plastic items, whereas fragments originate from plastic bottles or other plastic items that break down over time. Fibers typically come from synthetic clothes, while foam usually comes from single-use Styrofoam containers. Films enter the environment from plastic bags or food packaging, and granules come from personal care products like toothpaste. Pellets and granules are both are round, but pellets are much larger.

Why Are Microplastics a Concern?

Microplastics are a growing environmental concern because they can act as fomites for chemicals and disease-causing organisms called pathogens (Figures 1I,J) [1, 2]. This means that dangerous chemicals and harmful germs can use microplastics to hitchhike through the environment. Microplastics are also a concern because they are so tiny and often look like food, so they can be eaten by aquatic and marine animals of all sizes. Zooplankton, little organisms living in aquatic environments that mainly eat tiny algae, will eat less food after ingesting microplastics [3]. Microplastics can become entangled within the zooplankton gut and lead to starvation, a state in which the animal no longer gets enough energy from food to survive. On a much larger scale, whales that eat massive amounts of plankton end up filtering out and consuming these microplastics, some of which carry toxic chemicals. Both the microplastics and the chemicals can accumulate in their bodies [4]. Thus, microplastics have multiple ways of harming the health of many marine animal species.

Where Are Microplastics and How Can They Affect the Sacramento-San Joaquin Delta?

Microplastics are everywhere around the world! They have made it into all the environmental compartments of an ecosystem: air, soil, water, and biota (living organisms) (Figure 2). For instance, synthetic microfibers (manmade fibers that come primarily from clothing) have been found in water, on beaches, and even in air [5, 6]. A study in the San Francisco Bay found that there are more than 1 million microplastic particles per square mile of surface water [5]. This is the same as finding over 300 microplastic pieces on a credit card-sized area! Moreover, microplastics (consisting mainly of microfibers) were found everywhere across California beaches, from Marin County in the San Francisco Bay to more than 560 miles away in San Diego, the southernmost county in California [6]. Biota of the San Francisco Bay can contain and generate microplastics, too. Pacific mole crabs and mussels accumulate microplastics in their bodies, while other marine crustaceans can generate microplastics by digging in big blocks of foam [68].

Figure 2 - Microplastics in the four environmental compartments of a freshwater ecosystem: air contains floating synthetic microfibers; soil contains diverse microplastics and plastic debris; water contains suspended microplastics that interact with chemicals, bacteria, sediment, and living organisms; and biota such as fish contain microplastics in their guts.
  • Figure 2 - Microplastics in the four environmental compartments of a freshwater ecosystem: air contains floating synthetic microfibers; soil contains diverse microplastics and plastic debris; water contains suspended microplastics that interact with chemicals, bacteria, sediment, and living organisms; and biota such as fish contain microplastics in their guts.

The Sacramento-San Joaquin Delta is a unique ecosystem where freshwater mixes with seawater, generating conditions that support diverse animal, plant, and insect species. Furthermore, the Delta serves as an important source of drinking water and agriculture for millions of people in California. The conservation of this valuable ecosystem is everyone’s responsibility. San Francisco Bay area is to the west of the Sacramento-San Joaquin Delta. Higher concentrations of microplastics have been found in the San Francisco Bay waters than in the waters around other urban areas of the United States [5], and further studies are currently in progress in the Delta. Microplastic contamination in the Delta appears inevitable. There is also contamination from pesticides and other environmental contaminants that can combine to affect the health of the organisms living there. Around the world, microplastics have been found in drinking water (see Video) and fish. However, are there microplastics in California drinking water? Do people consume fish with microplastics in them? Do microplastics affect human health? These are some important questions that are still unsolved in the Sacramento-San Joaquin Delta region.

What Can We Do to Fight This Invasion?

Did you know that, in 2017, only about 8% of plastic in the United States was recycled, and almost 27 million tons of plastic were added to landfills? As it breaks down over time, all this plastic will become secondary microplastics. Can you imagine how many tons of microplastics will be generated on Earth over the next 10 years? Remember that 27 million tons is only the plastic waste from one country in one year. Just imagine how much plastic trash we generate worldwide! This plastic overuse comes primarily from our reliance on single-use plastic products, including plastic bags, straws, plastic bottles, and foam containers.

One possible solution is to redesign the plastic industry to use new types of plastic or alternative materials that will not harm the environment. Another helpful action is to ban single-use plastics and personal-care products containing microbeads. In San Francisco, California, single-use plastic bags have been banned in grocery stores. However, these actions are not enough. Eliminating all single-use plastics will take a lot of time and effort. Many scientists are already working on alternative materials, but you can help with your own ideas, too. We invite you to brainstorm creative solutions with your science teachers and friends, by playing, experimenting, and testing.

There are other ways that you can prevent the current environmental invasion of microplastics. For example, you can avoid the unnecessary use of plastics in your daily life. Do you bring your sandwich to school in a plastic bag every day or drink water from single-use plastic bottles? Replace these with reusable containers. Do you use toothpaste with microbeads? Check the ingredients and use the internet to choose brands that do not contain microplastics. Do you use plastic straws to drink your soda? Choose a biodegradable straw or better yet, do not use one at all! You have the power to make choices that help the planet. You can also help limit the microplastic invasion by spreading the word and telling your friends and family why microplastics are a global concern. It is important that as many people as possible raise awareness of the danger that microplastics pose for our planet, and now you know enough to help with this mission!


Microplastics: Plastic particles that measure <5 mm in size.

Primary Microplastics: Microplastics originally manufactured as tiny particles for industrial use such as microbeads in personal care products, or microfibers in synthetic textiles.

Secondary Microplastics: Microplastics formed overtime from the breakdown of large plastic pieces in the environment.

Fomites: Inanimate objects that transport disease-causing pathogens such as viruses and bacteria.

Pathogens: Tiny agents of disease, such as viruses, bacteria, and parasites.

Zooplankton: Small, animal-like organisms that inhabit aquatic environments.

Ecosystem: A system of interactions between living organisms and their environment.

Biota: The living organisms (plants and animals) of a specific ecosystem.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


CL-V studies were supported by the fellowship Beca Doctorado en el Extranjero, contract N° 236-2018, FONDECYT from the Peruvian Government.


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