By now, most of you have probably heard about the five ocean gyres, wrongly called plastic islands, where discarded plastics have been gradually accumulating since they first started being manufactured. Surely you have seen pictures of turtles, whales, birds and other charismatic species stuffed with plastics, as well as some other plastics being washed up on formerly beautiful, paradise beaches. You might even have collected some of that rubbish from your own local stretch of coastline. Something you might not be as familiar with, however, is the term microplastics and how they are linked to the freshwater ecosystem.
Discarded plastics have become one of the greatest environmental challenges of the 21st century, while also being the single greatest material of our contemporary age. They are light, durable, easy to manufacture and cheap. Everywhere you look you will find plastics – plastic bags, food containers and cosmetics (polyethylene), clothes (nylon and polyester) or buildings (polyvinylchloride) among many other examples. And then, if you connect the dots between your plastic products and the refused already drifting in the oceans, you might realise where they are coming from.
Yes, mostly cities – 80% of all plastic pollution actually comes from land sources such as wastewater treatment plants, landfill, polymer manufacturers and mismanaged city waste. Much of which finds its way into our rivers which, in turn, continuously deliver our rubbish to the sea. Some of these plastics, however, never make their way to the sea, instead remaining as fragments in the rivers water column or sediment.
So what are microplastics?
Well, in short, they are synthetic pieces or fragments made of oil-based plastic polymers. They can be up to 5 mm in size, but are usually smaller than 1 mm; thus beads, fibres, films, fragments, pellets, foam and other microscopic polymers are all defined as microplastics. These materials can be divided into two categories according to their source; with primary microplastics stemming from microbeads found in cosmetics or toiletries, and secondary microplastics from the degradation of larger plastic items. Microfibres, for example, come from the shed of clothes made of synthetic polymers, while the most straight forward source of microplastic pollution results from the beads found in facial scrubs.
The presence and accumulation of microplastics in aquatic environments can vary depending on different factors, among these wind, currents, proximity to urban areas and volume of the microplastics released. This makes it very difficult to estimate and report an accurate number of microplastics within the freshwater environment as a whole. However, even though the research and understanding of microplastics in the freshwater environment is in its infancy, microplastics have already been sampled from rivers and lakes worldwide, indicating that the threat posed by these minute particles is, in fact, very real. Large microplastic fibres have, for example, been found at many different points along the River Thames.
There are increasing concerns about microplastics, stemming largely from their microscopic size – which allows these synthetic particles to be easily consumed by a wide range of organisms. According to the scant literature produced so far, freshwater habitats and the species within them are very susceptible to pollution from microplastics. The threat is greatest in urban areas that are being polluted constantly, day in and day out.
My PhD focuses on the toxicological effects that microplastics may have on different freshwater species. It is believed that microplastics follow a very similar route into the freshwater food chain as they do in its marine counterpart. The processes of bioaccumulation within the ecosystem, or whether they occur at all, as well as the toxic effects of the plastics are still unknown. However, we can already guess which species could be classified as higher risk should we nd that microplastics are toxic for them. Among these, certain endangered freshwater species might nd microplastics represent yet another major pressure to overcome. Species such as the critically endangered pearl mussel, the Atlantic salmon or one of the many declining riparian bird species covered by the Habitats Directive, could be at risk.
Until we find out what is happening in the freshwater environment and to what extent changes are occurring, and until policies, monitoring programmes and other solutions are put into place, there are simple ways for you to stop this problem at the source and do your bit for the freshwater environment. Try reducing your plastic waste by swapping plastic shopping bags for cloth bags, by giving up bottled water and using a refillable bottle instead, refusing excess packaging, choosing microplastic free cosmetics products and by joining your local beach or indeed, river, clean-up team. While much about microplastics remains unclear, what is certain is that each of us can make a difference when it comes to cleaning up our rivers and safeguarding their precious wildlife.