Microplastics in compost: What we found and what you need to know
What are plastic-coated paper products?
Plastic-coated paper products are a common type of food packaging made from paper and coated with plastic to prevent liquid absorption or freezer burn, or to otherwise enhance product performance. Almost all plastic-coated paper products are coated by an impregnation process with low-density polyethylene (LDPE). This and other petroleum-based coatings used for these applications do not biodegrade. These products include milk and juice cartons, hot and cold paper drinking cups, frozen food containers, plastic-lined paper bags, take-out containers and some paper plates.
What happens when plastic-coated products are composted?
The plastic-coated paper products currently being collected by many composting programs produce both macro- and micro-fragments of non-biodegradable plastic which contaminate the finished compost. Once these plastics are dispersed into the environment, they have not been shown to biodegrade and are suspected of causing detrimental effects to organisms in a variety of ecosystems. We can expect these fragments to persist indefinitely and to be so widely dispersed that it will be impossible to clean them up. Compost collection programs and compost facilities must exclude plastic-coated paper products from their guidelines to prevent future harm.
How can I tell if a paper product is coated with a petroleum-based plastic?
There is no fail-safe method for determining whether a paper product is coated with petroleum-based plastic. There are far more manufacturers using polyethylene (PE) coating on paper products than a compostable PLA coating and these PE-coated products are much more readily available. While most PE-coated paper products are not marketed as compostable, they are accepted by many composting programs, or they may have misleading marketing claims such as “biodegradable” or “earth-friendly.” Only products that meet ASTM 6400, EN 13432 or BPI standards can be safely composted.
What guidelines do you recommend for composting facilities for accepting foodservice products and packaging?
Only certified tested products—using ASTM 6400, EN 13432 or the Biodegradable Products Institute (BPI) standards—should be allowed in food waste collection programs. No other plastic-coated paper products should be accepted. Soiled paper products, such as tissues, paper napkins and paper towels, are suitable for composting. Paper products such as cardboard, office paper, shredded paper and uncoated paperboard do biodegrade but recycling these materials should be given highest priority. Milk and juice cartons should be recovered through recycling facilities.
The City of Seattle's guidelines (right) and Eco-Cycle's guidelines for Boulder County are good examples of programs that exclude plastic-coated paper products that are not certified compostable.
Should I stop using compost?
No! Compost is an excellent soil amendment with numerous benefits:
- Suppresses plant diseases and pests
- Reduces or eliminates the need for chemical fertilizers
- Promotes higher yields of agricultural crops
- Improves soil structure (tilth) which improves water holding capacity and erosion control, and improves drainage and permeability by keeping aeration channels open
- Buffers soil acidity
- Facilitates reforestation, wetlands restoration, and habitat revitalization efforts by amending contaminated, compacted and marginal soils
- Cost-effectively remediates soils contaminated by hazardous waste
- Removes solids, oil, grease, and heavy metals from storm water runoff
- Captures and destroys 99.6% of industrial volatile organic chemicals (VOCs) in contaminated air
- Offers stronger protection against changing climate conditions.
However, it is imperative we deploy best management practices to the growing number of compost collection programs in the U.S. and Canada in order to maintain the integrity of our compost and ultimately our soils. Learn more about the benefits of composting at www.cool2012.com.
Why aren’t plastics removed from compost during the screening process?
Most composters use a ½ inch (12 mm) sieve to screen contaminants from their finished compost. This removes many common plastic contaminants such as plastic bags. Under dry conditions, a 3/8 inch (9 mm) sieve may be used. Particles smaller than the sieve size, such as micro-plastics, are not removed through the screening process and will contaminate the finished compost.
FAQs about microplastics in compost:
Macro-plastics have been defined as being greater than or equal to 5mm and micro-plastics have been defined as less than 1mm. For practical purposes in a composting process, macro-plastics can be defined as those that can be screened out and micro-plastics as those that pass through the screening process.
Macro-plastic particles are introduced into the composting process from a variety of products such as plastic bags, plastic-coated paper products, diapers and other contaminants. These particles are larger than ½ inch in size and are generally removed from the composting process during screening. They do, however, add to the cost of processing compostable materials.
Micro-plastic particles are smaller than ½ inch in size, and may be as small as 100 microns (a micron is one-millionth of a meter). Because of their small size, micro-plastic particles are not removed by the compost screening process and contaminate the finished compost. Eco-Cycle and Woods End research found all plastic-coated paper products tested were shedding micro-plastic particles into the compost during decomposition.
No! Composting your food scraps and yard debris returns valuable nutrients to our soils and keeps organic materials out of landfills. Landfills are a top source of methane, a greenhouse gas 72 times more powerful than carbon dioxide. Landfills can also contaminate groundwater and contribute to local air pollution. By composting in your backyard or through a curbside composting program, you’re part of a win-win solution for our environment, our climate and our communities.
Yes, pizza boxes, paper towels, tissues and paper napkins are safe for composting. These products, often referred to as “soiled paper,” are made entirely of paper fibers and can be composted in a home compost bin or through a curbside composting program. (Frozen pizza or other frozen food boxes and hand or surface wipes are not compostable.)
Milk cartons and juice boxes can be recycled through many recycling programs across the U.S. and efforts are underway to expand these recycling options to all communities. To find out if these materials can be recycled in your local recycling program or to learn more about adding these materials to your recycling program, visit www.recyclecartons.com.
Other plastic-coated paper products, such as paper cups, take-out food packaging and frozen food boxes, cannot be recycled. The same plastic coating that inhibits the decomposition process also makes these products difficult to recycle. The paper fibers cannot be separated from the plastic coating so these materials are a contaminant in the recycling bin.
Oxo-biodegradable products are petroleum-based plastic products that are designed to disintegrate when exposed to heat and oxygen. These products are commonly used for plastic foam items, plastic carryout bags, film plastics and agricultural mulch films. These products do not meet composting standards and should not be included in composting programs. The environmental benefits of these products, as well as their ability to degrade or biodegrade, are all under debate. A series of recent tests by Woods End and Mother Earth News calls into question how well these bags actually fragment; after exposure to several months of hot, arid conditions, no fragmentation occurred. It is also under debate whether or not the fragmented plastics are eventually taken up by micro-organisms to be biodegraded, or if they remain in the environment.
Consumers often assume that a product labeled degradable is actually biodegradable.This is not the case. A degradable product disintegrates into smaller pieces when exposed to environmental conditions. It is not broken down completely unless it is biodegradable, and therefore, it will add to the growing problem of plastic pollution in the environment. Something that is truly biodegradable can be completely consumed or decomposed by living organisms, becoming beneficial to the environment.
Beware of products that claim to biodegrade in 1 to 5 years.These claims are debated and any product that does not biodegrade in the normal 90 day cycle at a compost facility can do harm when released into an ecosystem. In addition, products made with a mix of non-biodegradable plastic and a compostable material (such as plant starch) should be avoided because the plastic fragments will remain after the compostable component decomposes.
The landfilling of organic materials such as food scraps, yard debris, paper products and compostable plastics produces methane, a greenhouse gas 72 times more powerful than carbon dioxide. Landfills also produce a liquid leachate that can seep out and contaminate groundwater, and volatile organic compounds and other toxic substances that contribute to local air pollution. By composting our organic materials instead, we can replenish our soils with valuable nutrients, reduce greenhouse gas emissions and create jobs.
Only products that meet ASTM 6400, EN 13432 or BPI standards can be safely composted in a commercial-scale compost facility.Look for these labels or use the BPI website to find companies with compostable products. Avoid products that say “biodegradable” or “compostable” without any reference to a measurable standard.
We've pulled together a comprehensive list of BPI certified products, as well as some explanations of the different products and choices, to help you make the right decisions.
Durable, reusable tableware is the best choice for our environment and the most efficient use of our natural resources. For larger events or gatherings, you can rent these materials from event/party rental companies, or pick up your own supply cheaply at a secondhand store.
Microplastics in compost 