Researchers developing plastics that biodegrade in seawater

Plastics that biodegrade in seawater are being developed by French researchers to attack global waste at source, rather than through clean-ups that seem doomed to fail.

Bacteria are both the start and end of the process

Bacteria can create PHA polymers that then become a food source for bacteria in the sea.

Jean-François Ghiglione, research director at the Oceanological Observatory in Banyuls, Pyrénées- Orientales, said: “When this polymer is introduced into an environment like the sea, bacteria use it as a growth booster and feed off it, effectively getting rid of the plastic.”

Although PHA polymers’ properties have been known for some time, little was known of the most effective bacteria for making them and how they would react in a variety of elements, including seawater.

This basic research is what Dr Ghiglione and his team have been working on for eight years.

“We are at the stage now where there is a good chance that in four or five years we will have industrialists interested in producing PHA-based plastics,” he told The Connexion.

“There are two main obstacles: PHA polymers are four times the cost of conventional, oil-based ones, and the reticence of industrialists, who invested heavily in first-generation starchbased biodegradable plastics, only to discover they did not find the markets they were promised.”

Costs of PHA are expected to drop significantly when there is demand for the product and more suppliers.

Bacteria manipulated to produce it can be grown in large fermentation vats, using procedures similar to those used in the microbiology industry.

The first-generation biodegradable plastics did not meet with great success as they were based on starch. Green groups, and others, were unhappy that maize, which requires large amounts of water and pesticides, was the main source of the starch.

In real-life conditions, the plastics did not work as well as hoped. They were designed to break down in compost heaps but this did not happen as domestic compost heaps seldom reach the temperatures of industrial ones.

Dr Ghiglione said PHA plastic would be most effective in single-use plastic objects, which account for most of the plastic and microplastic found in the seas of the world.

“It will require action from plastic manufacturers and political will from governments to get it done, but I am confident it will happen,” he said. Political pressure is being applied by commercial groups who want to use PHA, but EU rules treat it like other single-use plastics, which are banned."

The Banyuls institute already has links with a major plastic manufacturer, which cannot be named for commercial reasons.

Fears that biodegradable plastics in the sea could lead to the bacteria dominating the eco-system have proved unfounded

Dr Ghiglione said: “The bacteria latch on to the plastic and multiply but once the plastic has gone, they die off. The only residue is sometimes a foam, like you get when you boil rice, and that quickly disperses.”

Dr Ghiglione and his research partner Anne-Leila Meistertzheim have formed a start-up company called Plastic@sea to highlight the problems caused by plastics in the ocean. Last year, he took part in an expedition on the research yacht Tara, which checked nine large European rivers for the amount and size of plastic and plastic particles in the water.

“Our findings overturned previous theories on plastics in oceans, which thought microplastic particles – bits smaller than 5mm – came from erosion and grinding down in the ocean."

“We found 95% of the plastics in the rivers was already at microplastic size. Collecting plastic from the ocean will have only a negligible effect on the overall amount. The only way to stop non-biodegradable plastics getting in the ocean is not to use them on land.”

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