Biodegradable Plastic May Be Even Worse for the Environment

Biodegradable plastic bags that were available in stores just a few years ago have disappeared. But disposable cutlery made out of biodegradable plastic is gaining popularity. At the same time the eco-friendliness of bio-based polymers is being questioned. What happens to biodegradable plastic after it’s been used is the main reason for all the confusion.

Biodegradable plastics are biological polymers derived from renewable resources that in favorable conditions decompose almost entirely. The name “biodegradable plastics” is also used for other non-petroleum polymers which don’t decompose entirely. This in turn creates confusion and myths about biodegradable plastic. Biodegradable plastic, which is composed of carbon compounds, would ideally decompose into CO2 and water. In reality the decomposition of biodegradable plastic depends on the environment it ends up in.

Plastic bottles on a beach. Photo: Let's Do It! World

Plastic bottles on a beach. Photo: Let’s Do It! World

Biodegrading Does Not Equal Composting

It’s important to understand the difference between biodegradation and composting. Technically, all plastic (even petroleum-based) is biodegradable – meaning, that in favorable conditions and with the help of microorganisms, it’s capable of degrading. For a regular plastic bag that process would take around a thousand years. Biodegradable plastic isn’t always compostable because only material that decomposes in one composting cycle is regarded as compostable. In addition, material that decomposes in one composting cycle but decomposes into non-biodegradable micro-particles is also not considered compostable.

If 90% of a material degrades in up to 6 months, it can be considered compostable (EU standard EN 13432). Additionally, if the material is left to decompose with organic waste, less than 10% of the original quantity of the material can be more than 2mm in size after 3 months. The decomposing can’t have negative residual effects such as heavy metals, volatile solid substances or changes in the pH or salinity of the surrounding areas.

The speed of the decomposition of biodegradable plastic is affected by:

  • the composition and quantity of the decomposing material
  • the moisture levels and acidity of the environment
  • aeration
  • carbon nitrogen ratio
  • ammonia and inorganic salts

The last points on the list have a direct effect on the living conditions of the microorganisms that cause the decomposing process.

Not All Biodegradable Plastics Compost

Over half of the biodegradable plastic goods that are on the market are made of starch (mainly corn, coconut, potato and rice starch but also soy proteins and sugarcane). In addition to above-mentioned agricultural goods, bioplastic could also be made from petroleum-based plastics, such as used plastic bottles, by using microorganisms and adding agents that help with the decomposing process.

Most known biologic plastics:

  • PLA – made of corn or sugarcane, will decompose entirely.
  • PHA – polymers that are produced by bacteria, may be derived from plants or petroleum, may be entirely biodegrading.
  • PSM – a mixture of starch and PP, one of the few heat resistant plastics.
  • Cellophane, plastic made out of cellulose – produced from wood, cotton or hemp fibers, compostable.
  • Biopolyethylene – produced by fermenting starch or sugar, doesn’t biodegrade but is recyclable.
  • Polyamide also known as nylon – produced by chemical processes from petroleum or natural oils, does not compost.

Plastic bags may be marked as “biodegradable” when cornstarch has been added to regular plastic. That way the plastic will partially decompose, but the tiny plastic pieces left over from this process may be even more dangerous for the environment. Faster decomposing plastic bags are used in a similar way, in which case additives (often metals) make the bags friable in nature. This kind of plastic seems to disappear but in reality the same microplastics are left over. Microplastics endanger marine animals and are easily assimilated into the food chain. Almost every person tests positive for microplastics in their bloodstream, which definitely was not the case just decades ago.

The Scientific Certification System has been trying to make marking bioplastics more coherent by issuing a “Certified Biodegradable” label, which means that in 4 weeks more than 70% of the product will decompose into compounds that are safe for marine life.

Ethical Dilemma: Should Farmlands Be Used to Produce Short-Lived Plastic?

Producing bioplastics isn’t petroleum free, even if the source material is agricultural. To make plastic out of starch, petroleum is used to farm, harvest, transport, and process the crop, to fertilize, to make pesticides and to spray the land. In addition, genetically modified crops are often used which have an unknown effect on the ecosystem.

Materials to produce bioplastics come from industrial farming, which reduces natural diversity and promotes desertification. Still, the biggest problem is using land suitable for growing food to make products like packaging that are easily substituted. Especially when comparing the environmental effect of producing traditional plastic and bioplastics – the production of bioplastics uses only about 25% less fossil fuel than regular plastic.

Estiko Plastar, one of the leading manufacturers of plastic packaging in the Baltics, no longer emphasizes the production of bioplastics, although they have the capability and technology for it. Their main reasons for stopping production are the negative side effects related to corn-based biodegrading plastic. According to scientists it’s ecological footprint is 1.7 times bigger than when using petroleum-based polyethylene granules (if you take into account the whole production cycle beginning with petrol used for farming). As well, the human population is growing faster than the amount of land fertile enough for growing food. With bioplastics, it’s very important to keep in mind that even if the polymeric material is biodegradable, the ink used to design it often is not.

Biodegradable plastic bags fulfill their purpose only if they are composted in a suitable environment and decompose entirely. Unfortunately the biodegradable products that make their way into landfills produce methane when decomposing which is a greenhouse gas 20 times stronger than CO2. Only very few waste disposal facilities use the available methane as an energy source. This means that in a landfill biodegradable products are no more environmentally friendly than regular refuse.

In conclusion: truly compostable products are plastics that consist only of materials eaten by bacteria that fulfill their purpose only if the products are properly composted after they’re used. Throwing away biodegradable plastic with household waste is not suitable and is just as burdening to the environment as regular plastic.

The best environmental solution would be to reuse plastic bags and packaging. More important than choosing between a plastic bag made of biopolymer or fossil fuels, is the proper recycling of the product. All biodegradable plastics need to be composted and regular plastic recycled where it will be melted and have a new life.

Written by Kadri Kaarna, NGO Estonian PackCycling environmental manager

Translated by Marianne Torm-Johnson, Let’s Do It! Newsletter team