The plastic problem is something most of us our familiar with — too much ends up in the natural environment where it stays for hundreds of years to come. Is biodegradable plastic the answer? Lara Dixon investigates.

Plastic consumption is expected to rise around 60% before 2060, and leakage into the environment will triple, according to a 2022 OECD report. Once plastic ends up in the natural environment it can persist for hundreds of years, posing a threat to marine life and accumulating in the environment over time.

Biodegradable plastic has been hailed as a potential mitigation strategy to plastic accumulation, due to its ability to completely or partially convert to water, CO2, methane, energy and new biomass in the presence of microorganisms. If use is scaled up, it is hoped to free up landfill space and reduce the life of plastic that ends up in our oceans.

Most biodegradable plastics are produced from biobased sources too, such as starch and sugar cane, meaning they can also help to reduce the reliance of the plastic industry on fossil fuels. As things stand, the market for this plastic is a small fraction of the total, currently just 0.3%, but its use is growing rapidly.

Are biodegradable plastics actually better?

In short, yes and no. The biodegradability of plastics in the ocean can vary drastically, making it hard to discern whether they create a marked improvement for the oceans or not.

One study on the performance of common biodegradable plastics, PHB and PBSe, in various ocean environments found the half-lives were between 54 and 2614 days, depending on the plastic type and location. This is not hugely surprising given the effects of temperature, UV exposure, pH, biosurfactants and enzymes on biodegradation rate — all of which vary greatly in different parts of the oceans.

Plastics lying on the shoreline, for example, are exposed to more UV and higher temperatures, and so oxidise and fragment rapidly. Once these fragments sink and become buried in sediment, however, the rate of degradation slows. Although this half-life is a reduction from virgin petroleum plastic, its wild variation creates difficulty when defining biodegradability standards.

Essentially, as long as waste infrastructure failures allow plastic to leak into the natural environment, we cannot be sure where the material will reach its end of life, and cannot accurately predict its biodegradability.

In addition, plastics labelled as compostable are only biodegradable under industrial conditions, typically at temperatures greater than 60 °C. These are not present in the natural environment and therefore will be of no use where plastic has reached our seas.

Biodegradable plastics still create nano plastic

In another study, comparing the fragmentation of a biodegradable plastic (PBaT) and a non-biodegradable plastic (LDPE) in a marine environment, it was found that the biodegradable plastic actually produced much larger quantities of microplastic more quickly. These microplastics could potentially linger for a long time in an environment that favours a slow degradation rate, as previously noted. Not only that, they can further degrade into nano plastics, which are also known to have detrimental effects on marine health.

Despite the relatively small scale of these studies, the evidence still suggests that we cannot rely on biodegradable plastic to decrease plastic abundance in the ocean in the short term. In the long term, it is not certain whether the increased degradation rate of biodegradable plastics would affect the abundance of plastic in the ocean to a measurable extent, and it may be a risk to rely on this, especially given the observed health hazards from micro and nano plastics.

“Without waste being sent to the correct disposal site […] it is not guaranteed plastic will avoid accumulating in the ocean”.

Is it feasible to scale biodegradable plastic production?

Regardless, it seems that biodegradable plastics will be part of the solution to plastic pollution, although there are important barriers to scaling up production that must be considered first.

  • Reduced mechanical strength compared to their petroleum-based counterparts. Carbon and glass synthetic fibres are currently used to strengthen materials, even though these are not biodegradable. There has been investment to develop ecologically friendly alternatives, such as lignocellulosic fibres, but more research is required if biodegradable plastic is to be used in strength-based applications.
  • Biodegradable plastic production is more expensive than conventional plastic and, given this, financial incentives may be required for consumers to make the switch.
  • A further issue is the need to create a separate recycling stream for biodegradable plastic. If it is recycled with conventional plastic, it may decay in the recycled product causing premature material failure. The technology for separating these waste streams is available but very expensive at the moment.
  • Lack of public awareness around plastic types. Most individuals interviewed in a German study (62%) said they would recycle biodegradable plastic if they could identify it, however, only 7% interviewed knew exactly what bioplastics were.

This lack of public awareness, coupled with technologically lagging waste management infrastructure for biodegradable plastics, represents the biggest challenge in scaling the market effectively. Without waste being sent to the correct disposal site, the biodegradability of the plastic will be highly dependent on the environment, and it is not guaranteed plastic will avoid accumulating in the ocean.

Is it still valuable to scale biodegradable plastic?

The apparent value of using biodegradable plastic will be the highest in applications where the loss of plastic, macro or micro, to the environment is intrinsic to its use.

Boat and fishing gear, for example, is consistently lost in the ocean. This can be extremely harmful to marine life due to a phenomenon known as ‘ghost fishing’, where discarded fishing gear continues to trap marine organisms, reducing local fish populations. The feasibility of the use of biodegradable fishing nets was tested in a study, which revealed that biodegradable nets could hold up against the durability of commercial fishing nets, up to their lifetime of 2 years, and even had the advantage of catching fewer smaller fish, increasing profit per catch.

There is also movement in the tyre industry towards the use of sustainable rubber, made from dandelions. The microplastics shed from tyres during use makeup 28% of the microplastic pollution in the ocean. Although the use of dandelion rubber wouldn’t inherently prevent microplastic shedding, the faster speed of degradation would greatly reduce the persistence of the plastics once shed.

These two interventions have perceivably more impact in reducing ocean plastic accumulation than scaling biodegradable plastic use in packaging applications, for example, which have less guaranteed loss to the environment.

Because of this, clothes and textiles should be an area of interest for their implementation, as these will be a growing source of ocean plastic build-up by 2060.

“We can tackle the ocean plastic pollution crisis”.

Looking to the future

There are lots of exciting biodegradable plastic innovations coming to the forefront. For example, start-ups creating nature-based plastics that biodegrade in a home compost environment will reduce our reliance on waste infrastructure to properly biodegrade plastics. More innovation in this field is happening all the time.

In particular, headway has been made in the packaging industry, which is today facing increasing regulation on its plastic use. If you’re interested, why not check out these three packaging start-ups hoping to revolutionise our day-to-day relationship with plastic:

  • Shellworks — Plastic made by bacteria that is truly home compostable and will degrade in six weeks.
  • Notpla — Material made from seaweed and plants that disappears naturally. Notpla recently won an Earthshot Prize too.
  • Mushroom Packaging — Polystyrene alternative by Ecovative for use in shipping/transportation. The material is made from hemp hurd and mycelium and is home compostable in just 45 days.

Despite the drawbacks, biodegradable plastic will likely play a key role in the transition away from traditional plastic, even if it’s not the silver bullet some may have hoped. Focusing its use in sectors with the most intrinsic plastic loss to the environment will be the most impactful use of this intervention. Coupled with an increase in waste management infrastructure to reduce environmental losses and a reduction in consumer plastic use in the first instance, we can tackle the ocean plastic pollution crisis.