Compostable or biodegradable?

Compostable, biodegradable or oxo-biodegradable—at first glance, these words seem to mean the same thing, but what are the nuances that distinguish them? Every day, more and more products appear on the market that seem to offer a good green option. Whether they be compostable cups, biodegradable utensils or oxo-biodegradable plastic bags, what do these products contain and what really becomes of them?

Compostable products

According to the Bureau de normalisation du Québec (BNQ), products certified “compostable” can be composted industrially—that is, at centralized composting sites. They are not necessarily compostable in a domestic composter. Nevertheless, certified compostable products will eventually biodegrade in a home composter, but at a relatively slow pace, depending on the conditions.

Industrial composting versus domestic

When composting is done on a large scale or in a bioreactor, the temperature can reach up to 65–70°C, which is high enough to prevent the proliferation of potentially dangerous bacteria such as salmonella or E. coli from animal waste such as bones, meat or fish. Compost we make at home with our garden and kitchen waste will never reach such high temperatures. Since the speed of biodegradation is relatively slow, it is also preferable not to add products labelled “compostable” (certified or not) such as coffee cups or fruit and vegetable trays to your home compost heap. To learn how to make compost at home, see the Compost Council of Canada’s website , the home composting guide (French only) or the City of Montréal’s Handy Guide to Home Composting.

Municipal organic food waste collection programs

If you have access to food waste collection (i.e. brown bin), it is important to contact your municipality to make sure that compostable-certified products, including bags, are accepted. Some municipal organic food waste collection programs do not accept compostable plastic bags due to the higher potential for contamination (confusion with plastics labelled biodegradable but not compostable, conventional plastic, etc.). On the other hand, it is important to know that some compostable plastic products are made from cornstarch or sugarcane, which means that agricultural land must be used to make them. This controversial practice has an impact on the production of corn to feed local populations (i.e. scarcity, increased cost of corn-based food). The standard for certification of compostable plastic bags (BNQ9011-911/2007) stipulates that a product must decompose by 90% within 180 days (approximately six months).

“Biodegradable” products

Products labelled as biodegradable but without any mention of certified compostability should be avoided. In fact, the term “biodegradable” is not synonymous with “compostable,” meaning that these products do not decompose at the same rate as organic waste. They contaminate compost.

Oxo-biodegradable or oxo-degradable products

Oxo-biodegradable products, such as garbage bags, are conventional petroleum-based plastic products with an additive to make them break down into small pieces in the presence of light, heat or oxygen. This is polyethylene, often bearing the triangular symbol (Möbius strip) denoting plastic number 2 or 4. As the additive can reduce the quality of the plastic, oxo-biodegradable products are not accepted in most recycling centres in Québec despite the Möbius strip symbol. They contaminate the batch and reduce its value. They are also not compostable, and most contain metal ions that could affect the quality of compost. In a landfill site—in the absence of light and oxygen—oxo-biodegradable products break down at a relatively slow rate. To date, no scientific studies have shown any environmental advantages of using these products over conventional plastics, which have a longer lifespan and can be reused several times before being recycled.

Few advantages of using oxo-biodegradable products

According to the makers of oxo-biodegradable products, their primary advantage is that they can decompose within a few years when left in nature. In short, there are very few advantages of using these products instead of conventional plastics, which can be recycled.

Recyc-Québec recommendations on shopping bags

“From an environmental standpoint, reduction at the source, when applicable, remains the best solution. Reusable bags come second. As for which single-use bags to favour, this depends on several factors. Overall, conventional plastic bags win over degradable and paper bags, as long as they are reused or recycled. With regard to compostable bags, including paper bags, they constitute added value in the context of municipal organic waste collection.” Recyc-Québec

In conclusion…

Aside from kitchen and garden waste, which can be composted at home, products labelled “compostable” will only break down quickly in industrial composting conditions. If you have access to brown bin collection, find out what materials are accepted. For all intents and purposes, if you are environmentally conscious and have no intention of abandoning them in nature, oxo-biodegradable products are unnecessary. However, in some places, shopping bags and all kinds of other conventional plastic abandoned in nature—especially in waterways and the ocean—do pose a major threat to biodiversity. In conclusion, we should always keep the good old principle of the 4Rs (Reducing, Reusing, Recycling and Recovering) in mind before resorting to substitute products.

References Organisation for Economic Co-operation and Development (OECD)