Biodegradable plastic sounds like a wonderful idea when you first hear about it. Most plastics are notorious for how long they stick around and how hard it is to break them down naturally, so to think that all those bits of plastics that end up scattered to the four winds could just melt away harmlessly sounds almost too good to be true. And well, once you read the fine print, it kind of is...
A new report by the United Nations looks at these so-called biodegradable plastics and their impact on oceans, and compared to the theory, reality is a lot less rosy. The biodegradable plastics rarely actually degrade because they require long-term exposure to high-temperatures (around 122F, or 50C), like those found in large municipal composters, to actually break-down. Those conditions are not found very often in nature, and especially not in the oceans.
To add insult to injury, once those biodegradable plastics are in the oceans, the water reduces UV and oxygen exposure, so they degrade even slower than they would otherwise... Basically, biodegradable label or not, those plastics will be there for a very long time. And even when they do break down, after years, the small pieces still pose a threat and just add to the existing microplastics problem that we've written about in the past.
On top of all this, biodegradable plastics are less recyclable than regular plastics, and they can contaminate the feed of recycling plants:
"If you're recycling plastic you don't want to have anything to do with biodegradable plastics," says Peter Kershaw, one of the authors of the UNEP study. "Because if you mix biodegradable with standard plastics you can compromise the properties of the original plastic."
So unless we can somehow make biodegradable plastics that actually degrade under regular conditions fairly rapidly without causing problems, and that can also be easily recycled, or at least kept out of recycling plants, maybe these aren't the best idea. It might make people feel good when they see the label, but if they don't work as intended, then it's just greenwashing.