The literature defines microplastics as plastic particles varying in diameter from 1 micrometre to 5 millimetres. A distinction is made between primary and secondary microplastics: primary microplastics are plastics that are produced specifically as small particles, while secondary microplastics originate from larger plastic parts that are broken down, through temperature and UV light among other things.
The primary microplastics are used in various applications. One major market is cosmetics, for which microbeads are worked into shampoos, face creams and toothpaste. The reason? The beads have a scrubbing effect on hair, skin and teeth.
This abrasive effect is why microbeads are also incorporated in both industrial and domestic cleaning products. Beads are also used to a lesser extent as carriers in medicines.
Large share for PE
These beads are manufactured on the basis of different plastics. PE takes a large share in cosmetics. Apart from its share in microbeads, polyethylene is globally the plastic with the most bulk: by 2018 the worldwide production will reach around 100 million metric tonnes, while double this amount is anticipated for 2050.
Primary microplastics can also have polypropylene, polystyrene, PET, PVC and other polymers as their basis, often with additives such as softening agents or fire retardants. In brief, they are non-degradable plastics that end up in the environment.
It is extremely difficult to estimate the volumes involved with the use of microplastics. The Nova Institute made a rough assessment of the European consumption, based on an American study. The research institute came up with a yearly volume of 3,125 tonnes, but remained very non-committal. It remains a tricky business, because there is no earlier research and data is not always available.
Gap in knowledge
The same applies to the volumes of microplastics that flow through the drains towards waterways and open waters every year. There is a gap in our knowledge in this area, according to the Nova Institute. Do water purification plants filter out a portion, and if so, how much? And what proportion eventually reaches the seas and oceans?
Because primary and secondary plastics in open waters are composed of similar constituents, it is also extremely difficult to specify which proportion is primary and which proportion is secondary.
According to the Ocean Cleanup, the initiative of Boyan Slat, only a comparatively small portion of the microplastics will end up in open waters. ‘There is a good chance that they are carried back to the coast, sink on their way or are eaten by marine animals,’ according to Joost Dubois. ‘We believe that it is mainly secondary microplastics that accumulate in open waters in the so-called gyres (editor’s note: areas of concentration of plastics and microplastics). We expect to be able to use our technology to remove these particles, with diameters measuring from 0.5 millimetres.’
Back to the source?
As Dubois already stated, a proportion of the microplastics ends up in the food chain. Mainly the so-called filter feeders, such as oysters, mussels and other shellfish, feed themselves by filtering large amounts of water. A study by the French Research Institute for Exploitation of the Sea shows that oysters absorb the microplastics and that this has a negative effect on their reproduction. Because filter feeders also form a source of nourishment for other marine animals, the microplastics can also ‘travel’ higher up the food chain. These microplastics could eventually return to the ‘source’: humans. For the time being this does not seem to be the case. This also requires more detailed research.
Whatever the case, the question is whether primary microplastics should enter the environment at all. All the more so because they are produced specifically and do not arise through the breakdown of larger plastic pieces.
Obama signs ‘anti-bead act’
That is why Barack Obama signed the Microbead-Free Waters Act last year. Manufacturers in the United States are now forbidden as of 1 July 2017 to use microbeads in personal care products. This applies to both fossil-based and biobased plastics. As of 1 July 2018, such products may no longer be sold. ‘A very important step in the fight against plastic soup and a strong signal to the rest of the world,’ according to the Plastic Soup Foundation, which organised the international campaign Beat the Microbead.
Things are not that far in Europe yet. Cosmetics Europe prefers to promote a voluntary phase-out (until 2020) instead of a strict ban as in the USA. According to the sector organisation, there are enough alternatives for fossil-based microbeads and several of its members have already phased out microbeads.
Manufacturers and retailers in the Netherlands have also taken these steps. Unilever already made the decision in 2014, while other players such as L’Oréal, P&G, Kruidvat, Etos and De Tuinen have likewise said farewell to the microbeads.
‘At the time we took the decision as a reaction to the publicity about the enormous increase of microplastics in the environment,’ according to a spokeswoman of Unilever. ‘Previously, in a limited number of our personal care products we used microbeads based on PE for their scrubbing effect. For that matter, these microbeads were totally safe for humans and the environment. We have replaced them now by largely organic materials such as ground apricot shells, walnut shells or shell particles, ground pumice and silica.’
Possibilities for biopolymers
As Unilever already indicated, there are more than enough substitutes on the market for microbeads based on PE. At the German personal care trade fair In-Cosmetics, dozens of (chemical) companies presented their solutions. For example, Evonik has developed a synthetic variation on natural sand, largely for hygienic reasons. The American company Micropowders sells polyactides based on corn starch while the Swiss Permcos offers body scrubs that are made on the basis of hydrogenated palm oil.
Besides these beads from natural materials, the Nova Institute also sees possibilities for polymers like TPS, PBSA and PHA that are biodegradable in seawater. The research institute does not commit itself, however, because the environmental impact of these biopolymers in a microbead application has not been sufficiently investigated. In any case it does not consider oxo-degradable bioplastics as a solution, because they contribute precisely to the microplastic soup.
PHAs (polyhydroxyalkanoates) are an interesting option, according to Jan Ravenstijn (ex-DSM, Dow), bioplastics consultant. ‘In principle PHAs are highly suitable because they can be absorbed and digested by the human body, but also because they form part of the metabolism of vegetable and animal organisms. PHAs are already used in medical applications for soft tissue engineering. Now the USA has included bioplastics in its ban on microbeads. PHAs will have no effect on this market now. However, there are countries that do not exclude bioplastics in advance. So there is a possible market for certain PHA blends with the right properties.’
Alarm set too late
Ravenstijn does point out that it will take at least five years to develop these blends for a specific application. The large cosmetics and personal care manufacturers have already been working with the previously mentioned alternatives for several years. ‘I have the idea that PHA manufacturers have set the alarm too late. If they had responded to this development earlier, buyers might have still been interested. Unless PHA manufacturers can make a better business case, for example based on price and/or functionality of the end product. To achieve this, we will have to form alliances with players in the value chain so that these PHA beads can be developed and then tested to see what happens to them in fresh water and seawater. To be honest, I am more inclined to see a market for biobased and bio-degradable plastics in other applications, such as packaging film. There is a market demand there too for plastics that break down in a watery environment without causing damage to it.’
The Nova Institute estimated that 4,360 tonnes of microbeads from EU countries ended up in the sea in 2012. Six to ten percent of the global plastics production ends up in the sea. These are mainly secondary plastics that then disintegrate into smaller parts, including microplastics. In 2008 an average of 752,100 pieces of plastic per square kilometre were floating in the Pacific Ocean.