Monday, December 27, 2021

In Praise of Plastic

From New Scientist:

Social media can be a powerful force for positive change, especially when it comes to environmental issues. A seemingly perfect example is the drive to stem the tide of single-use plastic, particularly when it comes to food packaging.

Huge campaigns – including organised groups descending on supermarkets to strip and dump all packaging from their purchases and leaving it at the till in what is known as a “plastic attack” – have led to some quite dramatic changes, both in business and government. But it is possible that these sorts of well-intentioned moves, based on simple, social-media-friendly messages, can have unintended consequences.

The less geeky among us might overlook the fact that fruit and veg are still living plants, constantly interacting with the world around them in complex ways, some of which degrade the product. Under supermarket strip lights, they are still photosynthesising, making new compounds, breaking down others and even emitting growth regulators into the air that affect the behaviour of neighbouring crops on the shelves around them.

Understanding these incredibly sophisticated interactions and how to control them has spurred the creation of a branch of study called post-harvest technology. Over the past half century or so, this has led to a suite of ingenious inventions, including wrapping, that have dramatically extended the shelf life of crops. Waste has been slashed and nutritional quality and flavour improved.

Take, for example, a study published in 2011 showing that shrink-wrapped cucumbers lost a lot less water in a typical journey from farm to fork than the unwrapped equivalent, extending shelf life by up to 60 per cent.

Ditching this wrapping would therefore have a significant impact on food as, much of the time, the crop would go off before being eaten.

The upsides of plastic packaging don’t stop with shelf life, but can retain the nutritional value of the crops too. Broccoli is a good example. It can lose up to 80 per cent of its glucosinolates, a group of phytochemicals thought to be responsible for some of the crop’s key health benefits, when loose on supermarket shelves, versus the shrink-wrapped version in the chiller. Such effects have been found in a wide range of crops, which is one of the key reasons retailers go to the extra expense of using wrapping in the first place.

It can be easy to assume that biodegradable food waste has nowhere near the same environmental impact as plastic waste that can persist for hundreds, if not thousands, of years. However, assessing this isn’t that straightforward. While fruit and vegetable waste does break down fast into compounds, many benign, the environmental cost of producing these foods in the first place can be surprisingly high.

The United Nations Food and Agriculture Organization estimates that one-third of all food is wasted, and so many resources are dedicated to its production that, if food waste were a country, it would come third after China and the US in terms of carbon emissions. This is equivalent to 87 per cent of all road transport emissions. Based on such stats, growing this wasted food requires almost 13 per cent of the planet’s farmland and, if all waste was averted, it would be enough to feed 2 billion people.

Admittedly, comparing measures like carbon emissions and land use with plastic pollution is getting into apples and oranges territory (excuse the pun), but given the importance of the issue, some research has tried to calculate the net effect.

A recent study published ahead of formal peer review, from the Swiss Federal Laboratories for Materials Science and Technology, looked at cucumber production and found that plastic packaging was responsible for only 1 per cent of the total environmental impact of this food, yet each cucumber that had to be thrown away because it spoiled has the net environmental impact of 93 plastic wraps. The study concluded that, in the context of reducing food waste, the plastic was beneficial: by extending shelf life, the net environmental benefit of wrapping cucumbers was 4.9 times higher than not bothering. This shows wrapping is a complex and confusing issue.

Given the clear benefits of using some plastic packaging on some crops, I wonder whether we should move away from the idea of blanket bans and instead review which types are genuinely of benefit for shelf life, and thus the planet, and which are simply there for marketing or presentation. And what about a third approach of swapping to alternative, more recyclable or perhaps even biodegradable packaging, for those instances where plastic does play a useful role, rather than ditching it altogether – even if such an approach doesn’t get quite as many shares on social media.

Read more:

1 comment:

Peter Spendelow said...

Matt - this is a great article. Thanks for posting it here. Here is another issue to consider. If people think food waste is innocuous because it biodegrades, they are not considering where much of that food waste ends up - solid waste landfills. A huge misperception of the general public is that it is good for materials to biodegrade in landfills, but that is not true at all. Food waste decomposes fairly rapidly in a landfill - long before the landfill operators can turn on the landfill gas collection system. The decomposition of food and other material quickly use up the oxygen in the landfill, and so most of the food decomposes anaerobically, producing methane as a biproduct. Methane, of course, is a major contributor to greenhouse gas - about 30 time more potent than carbon dioxide on a 100-year time scale, and I think about 80 times more potent on the shorter 20-year times scale. Plus, another common byproduct of anaerobic decomposition is organic acids, which will leach heavy metals out of the surrounding garbage which creates a very toxic leachate. Contrast that to what happens to plastic in a landfill - essentially nothing. All that carbon bound up in the plastic just sits there, sequestered in the landfill and not contributing to greenhouse gases. In a sense the carbon has gone full circle, being pumped out of the ground to form plastic, and then returning to the ground in a landfill. Those of us who work with landfills understand that we generally do not want materials in landfills that degrade. Stable materials do not cause problems in landfills the same way degradable ones do. I don't intend these comments to in any way diminish the concerns over the environmental damage that manufacturing plastic resins creates, but as this article points out, plastics are sometimes at least the best option for packaging - especially for food.

Peter Spendelow (