Saving the oceans with chitosan: are prawns the new plastic?

Earlier in the year, I wrote a post concerning a new, extremely strong, material derived from limpet teeth. Bearing in mind our current reliance on oil-derived materials, another form of marine life may hold the key to the global plastic pollution crisis.

Every year over six million tons of crab, lobster and shrimp is processed as seafood. This industry's by-products include the chitin-rich carapaces of all these creatures. Chitin is a substance found in fungi and invertebrates, with a range of uses from making paper to food processing and biotech to water treatment. In the past five years, research has been gaining momentum for another use for chitin which may prove to be a game changer (and for once, this hyperbole could well prove an understatement).

Currently about 335 million tons of plastics are produced annually, of which one-third is for single (and therefore disposable) use. Only about twenty percent of the total is recycled. We have all seen news items about the Great Pacific Garbage Patch and the large numbers of wildlife species affected by ingesting such material. We are now also beginning to understand that we humans too are ingesting microplastic particles that contaminate our food chains, to the tune of forty to fifty thousand particles per person per year. Quite apart from the plastic itself, the unwanted materials in our food may contain absorbed chemicals and heavy metals known to be toxic. And that's separate to all the microplastic that rains down on us and our food from practically every manmade structure we enter.

In 2014 a biodegradable polymer was developed from chitosan, a material made by subjecting the chitinous carapaces of marine arthropods, primarily crustaceans, to a range of treatments. Chitosan has been in use for some decades in diverse fields such as medicine, as a biopesticide and as a filtration and clarification material. However, the acids used to produce it have markedly affected its green credentials. Over the past five years a rather more ecologically-friendly set of processing techniques, including ultrasonics and microwaves, have been developed. The upshot of this means that chitosan could eventuate into one of the most ubiquitous materials on the planet. Pioneering companies have been set up around the world to convert chitosan into biodegradable packaging.

One such corporation is the Scottish-based CuanTec, who are developing food packaging that is antimicrobial while also being compostable. They claim to be the first company able to use bacterial fermentation to extract chitin from langoustine shells on an industrial scale, which is subsequently processed into chitosan. The antimicrobial properties of the packaging means that the foodstuffs it contains will have a longer - possibly even doubled - shelf life, with protection against the likes of Salmonella, Listeria and E. coli.

The first three types of packaging are said to be a food film wrap, single-use milk bottles and beer can collators (the latter incidentally for a company who produce their alcohol from stale bread rolls!) However, to date CuanTec has sought crowd-funding in order to begin commercial operations, which seems astonishing. Their products are predicted to cost slightly more than the petro-chemical alternatives, but hopefully industry will realise that the advantages far outweigh this.

Across the Atlantic from CuanTec other companies are climbing on a similar bandwagon. Mari Signum in Virginia, USA, is utilising an ionised liquid (including vinegar) technique to extract chitin for the development of various products, including 3D-printed alternatives to plastic packaging. As a recognition of their efforts, last year the U.S. Environmental Protection Agency presented them with their Green Chemistry Challenge Award. They're not the only American company to investigate the potential of swapping plastics with chitosan: the California-based CruzFoam have expanded their research from chitin-derived surfboard cores to packaging aimed to replace polyurethane foam.

Universities in various nations are also working with chitin to produce bioplastics that combine with other materials such as cellulose. The National University of Singapore has combined grapefruit seed extract with chitosan to produce a composite film for use a food packaging which can extend the shelf life of perishables such as bread. In a nation as humid as Singapore, you can clearly see the savings to the consumer if such materials become commercially available - assuming the affected food producers don't buy up and block the relevant patents, that is!

Clearly, chitosan looks like a material whose time has come. Apart from the potentially vast reduction in plastics, the widespread use of chitosan-derived food packaging would likely lead to much less food being thrown away because it has spoiled. It's unlikely that chitosan manufacturers would run out of their raw material either, since chitin is the planet's second most abundant biopolymer - climate change effects on marine crustaceans not withstanding. I can't help but ponder just how many more natural substances are waiting their turn to be the next wonder material?

PET projects: can nature destroy plastic pollution?

One of key markers of the Anthropocene - the as yet unofficial term for a human-impacted global environment - is the deposition of manmade pollutants on land and in the oceans. A prominent component of these pollutants is plastic-based consumer waste; as I mentioned in March 2010, the UK was then using 17.5 billion plastic bags each year. Happily, the introduction of a charge on lightweight plastic shopping bags in the UK has reduced usage by a fantastic 85%. Various nations have introduced similar or even better legislation, but unfortunately in that key polluter the USA only California has had any success in overcoming corporate lobbying. The situation in Trump's America looks unlikely to change any time soon, since several states have even prohibited such bans at a county level!

Therefore, despite the best endeavours of some nations, most recently Kenya, around 80 million tonnes of polyethylene-based packaging and bags are still being produced worldwide each year. The amount that is recycled varies considerably from nation to nation, with the US Environmental Protection Agency recording only 12% of America's plastic as being recycled. As a result, it is estimated that about 12 million tonnes of plastic is annually deposited in the oceans, with even deep-sea species found to have been contaminated.

We've all seen images of beaches on the most remote, uninhabited islands smothered by tiny, multicoloured pieces of plastic, but apart from being unsightly, what are the potential dangers to the global ecosystem and humans in particular? By ingesting plastics, animals risk either choking or starving to death, or being poisoned by chemicals leaching from the material. Even if the latter doesn't quickly kill the critter (which could be anything from sea birds to turtles to baleen whales), substances such as Bisphenol A can build up in their system. In addition to the damage caused to the animals themselves, toxins can upset a species' reproductive cycle. For instance, some of the leached chemicals mimic estrogen, potentially inhibiting development of male offspring.

Of course, with such a range of species being affected, isn't it feasible that there will be knock-on effects to the human food chain? Even if there aren't obvious reductions in commercially-caught species, there is a high likelihood that wider food webs could be severely altered - and not for the good - or even that we on the verge of ingesting copious amounts of microscopic plastic particles. Even people who never eat seafood won't be able to avoid it, since animal feed may contain contaminated fishmeal.

It isn't just the obvious items that are the key pollutants, either: plastic microbeads (i.e. less than 1mm along their longest side) are prominent in rinse-off personal care products. Whoever invented them clearly has zero environmental credentials, bearing in mind there's no ability to recycle or reuse them; in fact, about 8 quadrillion microbeads get washed down the plug hole every day.  The World Trade Organisation is making some inroads into their removal - here in New Zealand their manufacture and sale will be banned by the middle of next year - but research has found they are already pretty much ubiquitous in the environment wherever these products are in use.

Therefore it makes sense to tackle the problem as soon as possible. Since some countries are reticent to implement legislation, or like China and India are having difficulties enforcing it, there is much to be said for seeking ways to degrade plastic waste in the most efficient way possible. Research over the past decade has revealed an astonishing conclusion: only about 1% of the expected amount of waste material has been found in the oceans. Either it is rapidly being buried in the sea bed, or more likely, something is breaking it down. Is this possible? Last year, a team of Japanese researchers found a microbe called Ideonella sakaiensis that is able to digest polyethylene terephthalate (PET), which is used in such mass-produced items as drink bottles. This suggests that there may be marine microorganisms with a taste for human waste, diligently destroying our plastic rubbish and preventing even worse effects on ocean life.

The Japanese research hints that it may be possible to use vats of these microbes to break down at least waste PET and then recycle it, with a much greater efficiency than is currently possible. Without interference, PET is thought to take between four hundred and one thousand years to completely degrade, presumably depending on the shape and thickness of the item. In contrast, Ideonella is able to digest the material in only six weeks. About 56 million tonnes of PET, mostly for bottles, is produced each year. Here in New Zealand, less than half of this material is recycled, the first (conventional) PET recycling plant having started work in August. So there's plenty of scope for a natural solution, should it become usable on an industrial scale.

This begs the question: are there any other critters with similar capabilities?  Last month a team at Texas Tech University reported that caterpillars of the pantry moth Plodia interpunctella have been able to thrive on polyethylene. Research showed that their digestive system contains various species of bacteria - different from the gut microbes in caterpillars that eat natural foods - which are capable of breaking down the plastic. However, what worries me is that if these microbes become selected for in the wild, will this change have the same sort of disastrous result that the inadvertent artificial selection of MRSA has had?

Some worm species are known to eat natural polymers similar to man-made plastics, such as the beeswax in hives, and so have been tested for their ability to break down plastic as well. Further research is required to determine whether the work is being done by microbes in the worms' digestive systems, but one issue with worm-digested plastic is that by-products include the toxic ethylene glycol. Apart from bacteria, Chinese researchers using plastic waste from Pakistan have found that the fungus Aspergillus tubingensis can degrade polyester polyurethane. After some years of disappointing results in mycoremediation (the use of fungi to break down man-made materials) this may prove to be a breakthrough.

The big question then is has nature done it again? After all, it does have about three and a half billion years' head start on the human race. Plastic waste is clearly a big issue and for the majority of humanity who live away from the sea (or rubbish dumps, for that matter) it's fairly easy to think "out of sight, out of mind". However, it pays to highlight the potential danger of changing ecosystems on a global scale, including the extinction of unseen and unknown species, including microbes that are vital to maintaining stability. I've previously mentioned the problems with concentrating on a few key 'poster' organisms at the expense of those that may play a pivotal role - now, or in the future - to our nutritional, pharmaceutical or technological needs. Therefore we need to be certain that the solution won't be as bad as the problem, when it comes to using nature itself to destroy the waste we unthinkingly generate. Surely a good compromise would be to minimise the amounts of plastic rubbish we generate in the first place?