The global plastic pollution problem is not something new. This once beholden miracle substance has found its way to every corner of the world through the various forms plastic waste can take. Being positioned at the forefront of environmental discussions, scientists, politicians, and activists have dedicated time and energy to replacing or remediating this material. But is there another option beyond recycling plastic? Yes, and that answer is compostable plastic. 

New plastics have recently begun to enter the market, touting the ability to be composted and biodegraded, further diverting plastic from the waste stream. But is this biodegradable plastic actually what they claim to be, or is this just another attempt at clever greenwashing?

Let's begin with a dive into the topic of what are compostable plastics?

Compostable plastic is a plant-based plastic manufactured and designed to break down into natural substances through the composting process. The decomposition yields carbon dioxide, water, and soil conditioning material without leaving any toxic residue.

According to a European Bioplastics e.V. 2020 report, of the current plastic products on the market, only around 1% of them can be considered compostable. These plastics are manufactured from plant-based materials and designed to look and feel like traditional fossil-fuel plastics. But don't be fooled, as placing these plastics back into the recycling stream can disrupt the process.

Various organizations are setting the standard on how we label items as compostable. One example is that of The American Society for Testing and Materials (ASTM) International. This group has defined compostable plastic as "a plastic that undergoes degradation by biological processes during composting to yield carbon dioxide (CO2), water, inorganic compounds, and biomass at a rate consistent with other known compostable materials and that leaves no visible, distinguishable, or toxic residue." This definition acts as a baseline to help differentiate between traditional, compostable, and biodegradable plastics.

Here are just a few of the groups that are setting the standards for compostable plastics:

American Society for Testing and Materials (ASTM) International

European Committee for Standardization (CEN)

International Organization for Standardization (ISO)

TUV Austria Begium NV

Biodegradable Products Institute (BPI)

Thanks to these companies, a better understanding of compostable plastics is becoming a regular part of the plastic industry. But even though these companies have defined them as such, are these plastics compostable?Yes, compostable plastic is really compostable. But that doesn't mean it's approved to go into your backyard compost bin beside your food waste. Compostable plastics require specific composting conditions to guarantee it breaks down; conditions achieved at industrial composting facilities.

The wonder of composting comes from a specific biodegradation process known as decomposition. In this process, complex organic material will break down into simple organic and inorganic matter with the correct usage of heat, moisture, oxygen, particular microorganisms, and time. This means that the result of the decomposed (or composted) product becomes a soil conditioning material and inorganic materials like carbon dioxide, water, sugars, and salts. But not all composting and compostable materials are the same!

The most significant factor in the composting environment is the heat generated. Composting, when done correctly, can sustain temperatures high enough to sterilize soil-borne pathogens, leftover seeds, and harmful soil bacteria. When conditions are incorrect, the temperature drops and the process slows. Industrially compostable plastics require a tailored composting environment with prolonged high heat to guarantee an efficient breakdown. In proper commercial composting facilities, the biodegradable and compostable plastics should take roughly two to six months to break down, a process at the same rate as composting organic materials.

Always check your plastic before you compost. Introducing non-compostable plastic into a compost pile or commercial composting location can disrupt the breakdown process. Similarly, adding petroleum-based plastic to a compost bin can cause problems. For example, as plastic products slowly break down, they release microplastics that enter the natural environment. A compost bin exposed to microplastics may adversely affect the beneficial insect life. Worms exposed to microplastics have shown signs of stunted growth and loss of weight, which can significantly impact the surrounding ecosystem.

So how can you tell which plastics are for composting? Sorting errors happen, but putting the wrong plastic in the wrong bin can do more than reduce the quality of the recyclable plastics bale. Since compostable plastics don't behave like petroleum-based plastics, they can't withstand recycling. But with two easy tricks and a little research, anyone can be well on their way to separating compostable from recyclable plastics.

The first step on the journey to recognizing compostable plastics is understanding the current Resin Indicator Code (RIC). Currently, compostable plastics fall under recycling group "No.7," a group of miscellaneous plastics. This group of Code 7 plastics includes not only the plastics made of polylactic acid (No.7/PLA), which may be approved compostable, but also acrylic, fiberglass, and nylon, which are not. So, when examining recently purchased plastic containers, the best place to begin is the recycling Mobius to see if your product is in the correct category.

Beyond learning your RICs, there is another label that will better guide you towards choosing the correct plastic bin. Typically located beside the recycling Mobius is a compostable label. We are used to seeing these labels appear on our cardboard products, so it may surprise us when we pick up a plastic product with similar signage. It is important to note that just because something reads as compostable does not mean it's for home composting and may require industrial composting.

Finally, suppose you're looking to reduce your household's environmental impact. It may be best to research which companies provide compostable plastic alternatives. For example, the Biodegradable Products Institute (BPI) allows you to search by product and company for approved compostable products. This capability enables you to find new plastics that would best suit your needs and shows just how many of these compostable plastics are already on the market today.