You will hear part of a lecture about microplastics and their effects on wildlife, soil, and plants.
First, you have some time to look at questions 31 to 40.
Now listen carefully and answer questions 31 to 40.
In this lecture, I'll be discussing microplastics.
These are fragments of plastic measuring less than 5 millimeters.
People have become much more aware of the enormous volume of plastic waste in the environment, from large discarded objects to particles too small to see.
Plastic in the oceans has attracted a great deal of attention, but much less is understood about microplastics in fresh water and especially in soil.
They reach the environment by several routes.
Whenever synthetic clothing goes through a wash cycle, threads and minute fibers come loose and enter the water system.
Larger plastic items already in the environment gradually fragment into microscopic particles.
Industrial waste is another source, while vehicle tires also wear away as cars and lorries move over road surfaces.
Studies involving fish and other animals have already shown several effects.
Small creatures may suffer damage to their mouths.
Their feeding can also be disrupted when plastic particles become trapped in the digestive system.
It may be surprising, but people probably consume microplastics as well.
They have been identified in bottled water and in water taken directly from the tap.
Researchers have also found them in salt and in many varieties of seafood.
Even so, there is still no conclusive evidence that microplastics seriously damage human health.
Nevertheless, laws in a number of countries, including the UK, stop manufacturers from adding plastic microbeads to shower gels, facial cleansers and toothpaste.
Estimating how much microplastic is present in soil is extremely difficult because the particles are not easy to detect.
We do know that some travel through the air and are deposited by rain.
In addition, many fertilizers used by farmers and gardeners contain microplastics.
A research team at Anglia Ruskin University in Cambridge investigated how microplastics affect the digestive tracts of earthworms.
These creatures live in topsoil and are vital to agriculture.
As they feed, they mix nutrients through the earth, which helps to make it fertile.
The researchers wanted to discover whether putting microplastics into soil and then having earthworms ingest them would reduce soil quality and ultimately restrict plant growth.
The answer was clearly yes.
They added three forms of microplastic to soil and planted perennial ryegrass.
The materials included biodegradable PLA and conventional high-density polyethylene, or HDPE, and the worms then consumed the particles.
The earthworms lost weight rapidly.
Fewer ryegrass seeds than usual germinated because the worms could no longer perform their normal role in maintaining fertile soil.
The researchers also recorded an increase in the amount of acid in the soil, which they linked mainly to particles from HDPE plastic.
The study's conclusions are worth reading, and the full reference is included in the notes for the end of this session.
In summary, the authors argue that soil should be understood as a natural process rather than as an inactive substance.
It depends on decaying and dead material continually passing through earthworms.
When microplastics impoverish the soil, the damage extends beyond ecosystems to society as a whole.
