BLUE- SKY THINKING

THE PROBLEM OF PLASTIC IN OUR OCEANS HAS SUDDENLY BECOME A MOUNTAINOUS MAINSTREAM ISSUE BUT TRULY SUSTAINABLE ALTERNATIVES ARE FEW AND FAR BETWEEN

In the battle against plastic

pollution, where to next?

WE ARE ADDICTED to plastic in all its guises: bottles, cups, containers, clingfilm and general packaging, but the singleuse plastic bag is the most insidious and damaging of the lot. They waft about on the wind, drift down rivers into the sea, smothering birds and strangling the insides of countless animals that mistake them for food.

A trillion bags are produced globally every year. If we could curtail the environmental disaster created by them alone, we’d be doing well. But where science initially showed a consciencesalving glimmer of hope in the form of biodegradable plastic bags, it has now revealed that we don’t actually have a clue whether these alternatives are any friendlier to the environment at all.

European researchers published a study in May in the journal Royal Society Open Science that reviewed a broad selection of published papers looking into the end- of-life fate of biodegradable plastic bags. It found them to be so wide-ranging in their protocols, and the real-life testing so inadequate, that they don’t give us any information that could usefully inform policies - such as whether a tax or ban on plastic bag-use and incentives to use biodegradable or compostable replacements would make an appreciable difference.

A compostable conundrum

The problem is that even biodegradable plastic bags that supposedly break down harmlessly within a few months in the environment can perform very differently in landfill when mixed in with regular plastic and other household trash. They can also leach acids or release gases in anaerobic marine habitats such as salt marshes or brackish waters.

Biodegradeable plastics, for which there are established standards, are typically made from plantbased materials featuring everything from corn starch to kiwifruit skins, rather than disposable bags which are made from petro-chemicals. The European Commission led the way in developing testing standards that measure the disintegration of bioplastics, heavy metal concentration and “microbial respiratory gas evolution”.

The International Organization for Standardization (ISO) standards play a significant role in regulating bioplastic production here in New Zealand. A number of New Zealand companies are producing biodegradable plastics and even compostable plastics that can break down to harmless mulch in as few as 90 days. The problem is that the materials need to be dealt with properly at the end of their life through dedicated composting and recycling schemes to perform as intended.