1In today's lecture, I'm going to be talking about microplastics.
2Microplastics are tiny pieces of plastic smaller than five millimetres in size.
3Recently, there's been a greater awareness that there are large quantities of plastic waste - big and small - in the environment.
4The amount of plastic waste in the oceans has received widespread attention,
5but far less is known about the effects of microplastics in freshwater and particularly in soil.
6Microplastics can enter the environment via a number of different sources.
7Threads and microfibres detach from synthetic clothing every time they're put in a washing machine,
8and these find their way into the water system.
9Other sources include big pieces of plastic waste that are already in the environment,
10and these break down into microscopic particles over a period of time.
11On a larger scale, factory waste is another route,
12as are tyres which wear down as cars, lorries and so on travel along road surfaces.
13We already understand some of the impacts of microplastics from studies involving fish and other animals.
14There is evidence that microplastics harm small creatures in a variety of ways,
15such as by damaging their mouths,
16or by impairing their ability to feed,
17for example, when microplastics get lodged in their digestive system.
18Surprisingly perhaps, it is likely that humans consume microplastics,
19as these have been detected in a wide range of food and drink products, including bottled water,
20as well as in water that comes direct from the tap.
21What's more, salt and many kinds of seafood have also been found to contain microplastics.
22However, it's important to underline that there is not yet conclusive proof
23that microplastics cause significant harm to people.
24In many countries, including here in the UK,
25there is legislation which prevents manufacturers from adding plastic microbeads to shower gels, facial cleansers and toothpaste.
26It is very difficult to accurately estimate the total amount of microplastic particles in the soil
27as they can be hard to detect,
28but we do know they are carried in the air and deposited in the soil by rain.
29What's more, many of the fertilisers used by both farmers and gardeners contain microplastics.
30A team from the Anglia Ruskin University in Cambridge
31has carried out a study of the effects of microplastics on the digestive tracts of earthworms.
32These worms, which live in topsoil, are an essential component of our agricultural system.
33By feeding on soil, they mix nutrients into it, thereby making it more fertile.
34The researchers set out to discover whether the introduction of microplastics into the soil,
35and the subsequent ingestion of these by earthworms,
36would impact soil quality and ultimately inhibit plant growth.
37The short answer was, yes, it did.
38After placing three different types of microplastic particles into the soil,
39they planted perennial rye grass.
40The particles of microplastic, which included biodegradable PLA and conventional high-density polyethylene, or HDPE,
41were then ingested by the earthworms in the soil.
42The result was that the worms lost weight rapidly.
43What's more, a lower percentage than normal of the rye grass seeds germinated,
44and the researchers concluded
45that this was a direct result of the earthworms being unable to fulfil their normal role in making soil more fertile.
46The team also discovered that there was an increase in the amount of acid found in the soil,
47and this was attributed mainly to the microplastic particles from conventional HDPE plastic.
48The conclusions of the study make for very interesting reading.
49I've included the reference in the notes to give you at the end of this session.
50To summarise, the authors proposed the idea that we need to regard soil as we would regard any other process in nature.
51This means we should accept the implications of soil being dependent on decaying and dead matter
52constantly being passed through the bodies of earthworms.
53That is, when soil becomes impoverished by the presence of microplastics,
54not only ecosystems but also the whole of society are negatively impacted.