| In today's lecture, I'm going to be talking about microplastics. |
| Microplastics are tiny pieces of plastic smaller than five millimetres in size. |
| Recently, there's been a greater awareness that there are large quantities of plastic waste - big and small - in the environment. |
| The amount of plastic waste in the oceans has received widespread attention, |
| but far less is known about the effects of microplastics in freshwater and particularly in soil. |
| Microplastics can enter the environment via a number of different sources. |
| Threads and microfibres detach from synthetic clothing every time they're put in a washing machine, |
| and these find their way into the water system. |
| Other sources include big pieces of plastic waste that are already in the environment, |
| and these break down into microscopic particles over a period of time. |
| On a larger scale, factory waste is another route, |
| as are tyres which wear down as cars, lorries and so on travel along road surfaces. |
| We already understand some of the impacts of microplastics from studies involving fish and other animals. |
| There is evidence that microplastics harm small creatures in a variety of ways, |
| such as by damaging their mouths, |
| or by impairing their ability to feed, |
| for example, when microplastics get lodged in their digestive system. |
| Surprisingly perhaps, it is likely that humans consume microplastics, |
| as these have been detected in a wide range of food and drink products, including bottled water, |
| as well as in water that comes direct from the tap. |
| What's more, salt and many kinds of seafood have also been found to contain microplastics. |
| However, it's important to underline that there is not yet conclusive proof |
| that microplastics cause significant harm to people. |
| In many countries, including here in the UK, |
| there is legislation which prevents manufacturers from adding plastic microbeads to shower gels, facial cleansers and toothpaste. |
| It is very difficult to accurately estimate the total amount of microplastic particles in the soil |
| as they can be hard to detect, |
| but we do know they are carried in the air and deposited in the soil by rain. |
| What's more, many of the fertilisers used by both farmers and gardeners contain microplastics. |
| A team from the Anglia Ruskin University in Cambridge |
| has carried out a study of the effects of microplastics on the digestive tracts of earthworms. |
| These worms, which live in topsoil, are an essential component of our agricultural system. |
| By feeding on soil, they mix nutrients into it, thereby making it more fertile. |
| The researchers set out to discover whether the introduction of microplastics into the soil, |
| and the subsequent ingestion of these by earthworms, |
| would impact soil quality and ultimately inhibit plant growth. |
| The short answer was, yes, it did. |
| After placing three different types of microplastic particles into the soil, |
| they planted perennial rye grass. |
| The particles of microplastic, which included biodegradable PLA and conventional high-density polyethylene, or HDPE, |
| were then ingested by the earthworms in the soil. |
| The result was that the worms lost weight rapidly. |
| What's more, a lower percentage than normal of the rye grass seeds germinated, |
| and the researchers concluded |
| that this was a direct result of the earthworms being unable to fulfil their normal role in making soil more fertile. |
| The team also discovered that there was an increase in the amount of acid found in the soil, |
| and this was attributed mainly to the microplastic particles from conventional HDPE plastic. |
| The conclusions of the study make for very interesting reading. |
| I've included the reference in the notes to give you at the end of this session. |
| To summarise, the authors proposed the idea that we need to regard soil as we would regard any other process in nature. |
| This means we should accept the implications of soil being dependent on decaying and dead matter |
| constantly being passed through the bodies of earthworms. |
| That is, when soil becomes impoverished by the presence of microplastics, |
| not only ecosystems but also the whole of society are negatively impacted. |