Caution urged over biodegradable bags – Expert reaction

Plastic bags are the current public enemy number one, but are biodegradable bags any better?

European experts argue that the existing industry standards and testing methods are insufficient to predict the biodegradability of single-use plastic carrier bags within lakes, rivers and oceans. They say we don’t know enough about how these materials will break down in the environment, which is essential to figure out before we jump into another type of bag that may cause a different set of problems.

The SMC asked experts to comment on the review paper, please feel free to use these comments in your reporting.

Professor Thomas Neitzert, Professor of Engineering, AUT; President of Engineers for Social Responsibility, comments:

“This research helps destroy the thinking a plastic bag with a label ‘biodegradable’ is safe for the environment. The current standards are not taking properly into account real-life conditions and are therefore underestimating the break-down times of plastic materials. The standards are also not accounting for the damage of break-down particles on marine life when they are digested. A biodegradable plastic bag is potentially dangerous to marine life from the moment it enters the water until it dissolves into micro- or nanoparticles over many years.

“The co-existence of conventional plastic bags and so-called biodegradable plastic bags of compostable materials is also upsetting current recycling operations and is confusing the general public. Biodegradable plastic bags are in many cases made from crude oil, requiring carbon-based production processes and are emitting CO2 or methane when degrading. On the way to a low carbon economy, we should, therefore, carry a reusable bag made from cloth or jute, like our parents did.

“As with many standards, there is a gap between laboratory testing and the outside world with its constant changing conditions in this case concerning seasons, temperatures and concentrations of chemicals. Plastics exists in wastewaters, freshwater and the marine environment and standards never cover all of them. The standards are usually underestimating the life of a plastic product by years and sometimes decades. The test durations are usually only up to six months, apart from marine conditions where they go out to two years. The test conditions are not precisely described in terms of inocula and material sizes. Sometimes powders are being used which deteriorate faster than film material because of different surface to volume ratios. Statistical replications can be insufficient, composites and plastics with additives are insufficiently considered. This also applies to environments colder than 13 degrees, sandy sediments and coastal waters, where freshwater and marine water mix. Only one conformity mark scheme considers toxicology aspects, but insufficiently again.”

No conflicts of interest declared.

Professor Kim Pickering, School of Engineering, University of Waikato, comments:

“What I can say on my brief look is that it provides an excellent overview of the current state of art on the assessment of biodegradability of plastic bags and films including its shortfalls. It is important to assess how long things take to degrade in real situations and also what they break into and the consequences of that and we need to address such shortfalls.

“If it is to be assumed that we cannot prevent some plastic products getting into the environment, then biodegradable plastics could be a step in the right direction (depending on the product), but it shows that there are great uncertainties regarding the impact these could have on the environment and so we should still assume responsibility of waste plastic and consider its disposal, whether biodegradable or not. In moving forward, a lot is dependent on the expectations we can have on responsible human behaviour in terms of stewardship (education, legislation) but there is much to be done in ensuring as little environmental impact as possible through e.g controlled degradation and ensuring the products of this are not harmful.

“Generally it would be best to design products from the outset with end of life in mind (e.g. consider what additives are used in simple products like biodegradable plastic bags and films) and look for ways to add value to waste plastic (taking more account of the environmental cost in their price so things are more likely to be used more than once and recycling/upcycling (work going on in my research group). We should be thinking carefully before describing things as “single-use” plastics.”

No conflicts of interest declared.

Dr Ivanhoe Leung, Co-Deputy Director of the Centre for Green Chemical Science, and Senior Lecturer at the School of Chemical Sciences, University of Auckland, comments:

“Plastic pollution is one of the most challenging environmental issues that is facing the world today. In New Zealand, retailers like the Warehouse, Noel Leeming, Countdown and New World are planning to stop offering customers plastic shopping bags, and to replace them with different products ranging from reusable tote bags to paper bags to biodegradable/compostable bags.

“The science and technology behind biodegradable/compostable plastics have gone a long way since they were first developed. Given the right conditions, biodegradable plastics can be broken down into harmless materials within a few months. The challenge, however, is to separate these biodegradable plastic materials from the waste stream so that they can be broken down under the right conditions. For example, undesirable substances like acids or methane gas can be produced from biodegradable plastics if they are broken down in places that lack oxygen. These could be landfill sites, or anaerobic marine habitats like saltmarshes or brackish waters.

“One of the challenges when developing biodegradable plastics is that the biodegradability of these materials under controlled conditions, such as those inside a laboratory, do not necessarily translate to the open environment. The lack of clear and standardised guidelines mean that temperature, or the size, form and shape of the materials are often being ignored during testing, even though they are important parameters that determine the biodegradability of a material.

“There is no single magic bullet to solve the plastic pollution problem. Governments, industries and universities need to work together from different angles. It is important that governments and the international community to review current international standards and testing methods so that we can get realistic models to predict the biodegradability of plastic materials in different environments. Research funding should be spent so that universities and industries alike can develop materials that have better properties, balancing the needs for durability and biodegradability. Alternative methods, such as the use of plastic-eating bacteria, should be investigated so that we can find new ways to break down and recycle existing plastic wastes in a more efficient manner.”

No conflict of interest.

Professor Sally Brooker, Department of Chemistry, University of Otago, comments:

“We are not active in the end of life side of developments, but I completely agree with the authors of the embargoed article that this is a challenging and important area of research in its own right.

“Overall, we definitely need a multi-pronged approach:

  • Reduction in unnecessary use of packing materials (i.e. packing materials just to look pretty should be discouraged)
  • Incentives for use of easily reused/recycled materials eg. milk/fizzy back in glass bottles which are reused as in the past
  • Development of ways to reliably recycle plastics
  • Development of better understanding of how to handle the potentially compostable plastics – so as to ensure they do fully break down in less controlled (non-lab) environments.
  • Development of better plastics (and the catalysts to make them)”