The terms “biodegradable” and “compostable” are frequently used interchangeably by manufacturers, creating widespread confusion for consumers seeking environmentally friendly disposal options. This misuse often leads to products being purchased with the false assumption they will break down harmlessly in any environment, such as a landfill or a backyard compost pile. The misunderstanding is complicated by a lack of universal regulatory definitions and clear labeling, which obscures the actual end-of-life requirements for these materials. To make informed choices, it is important to distinguish between a product that merely degrades and one that is certified to nourish the earth. Understanding the science behind each term reveals why not all bags labeled as biodegradable can be considered truly compostable.
Defining Biodegradable Materials
A product is labeled as “biodegradable” if it can break down into smaller, natural components through the action of living microorganisms, such as bacteria and fungi. This definition is broad and does not specify a required timeframe for the decomposition process to be completed. A biodegradable plastic bag could take many years, even decades, to fully disintegrate, meaning its environmental benefit is often negligible. The term is largely unregulated, allowing manufacturers to use it on products that break down only under highly specific, non-natural conditions.
The decomposition of many so-called biodegradable bags frequently leaves behind toxic residue or fragments known as microplastics. These small plastic pieces can persist in the environment, contaminating soil and water and ultimately entering the food chain. Because the term “biodegradable” lacks stringent standards for the final breakdown products or the required timeline, it does not guarantee a complete and non-harmful return to nature.
The Strict Standards of Compostable Products
The classification of a product as “compostable” carries a more rigorous scientific meaning than “biodegradable.” A truly compostable material is certified to decompose into water, carbon dioxide, inorganic compounds, and non-toxic biomass, which is rich in nutrients and supports plant growth. This breakdown must occur within a specific, short timeframe, typically 90 to 180 days, and must not leave behind any visually distinguishable or toxic residues. The process is strictly controlled and relies on optimized conditions of moisture, oxygen, and high temperatures.
It is important to differentiate between home composting and industrial composting environments, as they operate under significantly different conditions. Home composting relies on lower, fluctuating temperatures (generally \(20-30^{\circ}\text{C}\)), making it unsuitable for breaking down most certified compostable bags. Industrial composting facilities maintain stable, high temperatures (often \(55-70^{\circ}\text{C}\)), which are necessary to trigger the chemical reaction and microbial activity required for rapid breakdown. Without access to these controlled, high-heat systems, many compostable bags will not decompose as intended.
Identifying Certified Bags
Because the “biodegradable” label is unreliable, consumers must look for evidence of third-party certification to ensure a bag is genuinely compostable. The most recognized certification in North America is provided by the Biodegradable Products Institute (BPI), which verifies compliance with specific industry standards. A product displaying the BPI certification mark has been scientifically tested to meet the requirements of the American Society for Testing and Materials (ASTM) D6400 standard. This standard confirms the material will fully disintegrate and biodegrade without harming the quality of the finished compost in a municipal or industrial composting facility.
Generic terms like “eco-friendly,” “plant-based,” or “made from corn starch” are not sufficient proof of compostability and should be viewed with skepticism. These phrases are often used without external verification, a practice commonly referred to as “greenwashing.” The BPI certification mark, often a green circle with the acronym, is a visual guarantee that the product has passed the rigorous testing needed for processing by commercial composters.
If a bag does not have a recognizable certification logo, it is likely to be merely biodegradable and unsuitable for composting infrastructure.
Understanding Proper Disposal Pathways
Even after confirming a bag is certified compostable, proper disposal is necessary, as placing it in the wrong bin defeats its environmental purpose. Certified bags are engineered for the thermophilic, high-heat environment of an industrial composting facility, which is not available to most households. Consequently, these bags should not be tossed into a curbside recycling bin, as they are considered contaminants that disrupt the recycling process for traditional plastics. They should also not be placed in a home compost bin, where insufficient heat and microbial levels prevent a complete breakdown.
The most effective disposal method is to check with your local municipality or waste hauler to see if they offer a food-scrap collection or commercial composting program that accepts BPI-certified materials. If such a program is available, the bag can be used to line the collection bin and then processed through the specialized facility. Without this infrastructure, the bag must be placed in the regular trash bin. Placing a certified compostable bag in an anaerobic environment like a landfill prevents it from breaking down as intended, because the decomposition process requires oxygen.