Can UV be a solution to the microplastic problem?

It is down to us to make lasting positive change happen and the public’s views on worldwide issues such as water quality, are continuing to evolve as we become more and more aware of the potential damage that our lifestyles and demands are causing.

We have previously looked at PFAS (known as forever chemicals, these are incredibly durable and do not break down over time) and how new ideas and techniques including using ultraviolet light may be a way of removing these from the water supply. You can read more on this in our PFAS blog here.

This blog is taking a look at another growing issue that is occurring in both our oceans and drinking water supply, that of plastic contamination.

Plastics and Microplastics – what do we mean and are they a problem?

Much has been talked about the amount of plastic pieces and microplastic particles now in the world's oceans, and the damage it is doing to the marine ecosystems, but plastic in fresh and wastewater supplies is a growing concern. These accumulate in much the same way and arguably can cause a more immediate impact on human life in the short term.

Microplastics are tiny particles of plastic – typically smaller than 5mm’s in size. Our increased use of plastic goods has directly contributed to the microplastic problem as we typically only recycle (burn) around 9% of the plastic produced each year. The rest, once used, ends up in landfill, our oceans and ecosystems.

Microplastics come not only from larger items breaking down but also are produced for use in microform in many cosmetics, shower products and toothpastes. These are added to our water systems directly from homes and end up in rivers, oceans, soil and recycled water supplies.

The impact on marine life has been studied and it is known that microplastics can cause direct damage to fish (i.e. their mouths) as well as accumulating in their stomachs which obstructs their ability to feed.

Humans consume microplastics through the food chain, fresh water, bottled supplies and consumer products. At this moment in time, research into the effects of microplastics on the human body is in its early stages but there is a growing concern as evidenced by this report of microplastics now appearing in human hearts and blood. Whilst there is no current proof that these cause lasting harm it has to be remembered that all research is recent and that there are no long-term studies available to reference.

The challenge in having plastic pieces and microplastics in our water is that plastic is very, very hard to break down. Plastic is not a natural product and so cannot be easily dealt with via natural ecosystems. A piece of plastic is likely to exist in water for an estimated 450 to 600 years* and with our never-ending and continuing increase in demand for plastic goods, the amount we will have to deal with, and the potential for more harmful effects is likely to continue to grow.

Is the water treatment industry the good or the bad guys?

Of course, water treatment companies are aware of the plastic problem and engage in the removal of large pieces of plastic as part of their water treatment process. But, right now, water treatment plants that release biosolids (waste sludge) are a main source of microplastics being added to environmental waters.

Also, with plastics being very hard to break down and the microplastic pollution problem being relatively new, national and international regulatory demands are still developing to catch up. This means water treatment systems are not necessarily currently configured to remove them in any adequate way.

So, what more can be done?

Plastic can undergo changes in its structural composition and ‘age’ in an open environment (albeit very slowly). This ageing process happens due to several factors that include breakage, heat or light degradation and biodegradation. As part of these processes, the microplastics can start to release chemical contaminants which come from additives such as stabilisers, plasticisers, fillers and antioxidants. 

It is known that ultraviolet light plays a critical part in the light (or photo) degradation process of polymers, including ones in plastic. So, with our ability to utilise UV light to speed up processes such as curing and bonding, perhaps now is the time to invest in more research on how ultraviolet light can help bring the microplastic problem under control?

How can UV affect plastic composition?

Plastic composition is made up of polymer strands. Polymers are essentially large macromolecules that have many repeating subunits within them. They are usually structured as interconnected strands. When plastic polymers are exposed to UV light, they absorb it which creates free radicals. (Free radicals are molecules that are unpaired and so are capable of independent existence). These free radicals interact with oxygen to create more free radicals which in effect accelerates the ‘ageing’ process and eventually leads to a collapse of the polymer chains.

Research carried out (Combined Effects of UV Exposure Duration and Mechanical Abrasionon Microplastic Fragmentation by Polymer Type, Song et al. 2017) on the effects of plastics exposed to UV light at 254nm over a 2 to 6 month time period proved the increased break up of plastic particles, some to the degree of undetectable sub-micron particles. However, it also noted that the increased salinity of seawater inhibited the absorption of UV, slowing down the degradation process. The research proved that natural UV light is part of the reason for an increase in microplastics in the marine ecosystem, but also points to a possible solution to tackling the problem in the future.

For further information on how polymers interact with UV light during the curing, bonding or coating process please take a look at our ‘How Does UV work’ series of blogs on our sister site Alpha-Cure.

What other research is out there?

There has been some research already undertaken to look at UV light and its effect on degrading microplastic composition in water treatment systems.

In 2020 research was published under the title ‘Ultraviolet-C and vacuum ultraviolet inducing surface degradation of microplastics’. This piece of work first looked at what effect a standard dose of UV light in a typical water treatment process had on microplastics. The result is very little to no effect. But the research also tested when the UV dose was increased to twenty times the normal amount. This resulted in ‘significant alterations on surface morphology, chemical features and hydrophobicity of the plastic’ – essentially a high dose of UV created cracks as it weakened the way the plastic’s chemicals bonded together. It is thought that this could result in a potential reduction in trace organic contaminants (TrOCs).

 Another piece of research titled ‘UV Light Causes Structural Changes in Microplastics Exposed in Biosolids’ was published in 2022. This looked at how UV-A and UV-C light may accelerate microplastic degradation, on three types of plastic when treated at 70°C.

It found that ultraviolet light did have an effect on microplastic composition. It worked better when the plastic was in a biosolid suspension (perhaps aided by the presence of other organic matter and water). It also noted that UV-A light appeared more effective than UV-C. The conclusion was that UV light, when used with raised temperatures can aid in accelerated plastic polymer degradation.

A third piece of research published again in 2022 (Investigation of the effect of microplastics on the UV inactivation of antibiotic-resistant bacteria in water) looked at the effect microplastics had on the effectiveness of UV treatment of water. It found that plastics can help ‘block or protect’ bacteria from UV disinfection. A conclusion to be drawn from this research would be that as the microplastic content of water continues on its upward trajectory then users of UV treatment systems will need to continue to monitor and recalculate their UV treatment times to take microplastics into account.

Conclusions

Whilst research into how UV light can help deal with the growing problem of plastics and microplastics is at an early stage, the good news is that it is beginning to happen. The research done so far clearly shows there is scope for ultraviolet light to help in breaking down microplastics, but it will require more investment and new, more powerful UV treatment systems.

This means it is still some way off being an effective solution to the microplastic problem but should be considered as a credible option to be explored. To make it happen we need funding to be made available to continue research and develop activities in this field.

Alpha-Purify is a world leader in the production of high-quality ultraviolet light lamps used in disinfection, germicidal and purification systems around the world.

If you'd like information on our products...

*source: US’ National Oceanic and Atmospheric Administration (NOAA) and Woods Hole Sea Grant