As part of a joint project, Oldenburg scientists are investigating how much microplastic enters the North Sea through the Weser and what it consists of. Detective work for the chemists.
In the seabed beneath the Great Barrier Reef, in Arctic sea ice or in the deep sea - tiny, often invisible pieces of plastic, known as microplastics, have long been found in even the most remote places in the world's oceans. According to an estimate published in 2015, around 4.8 to 12.7 million tonnes of plastic waste ended up in the oceans in 2010 alone. The vast majority of this waste comes from land and enters the oceans via rivers.
Experts define microplastics as particles that are smaller than five millimetres and larger than one micrometre, i.e. thousandths of a millimetre. "This is anything from the size of an ant to the size of a bacterium," says Dr Barbara Scholz-Böttcher, Head of Central Organic Analysis at the university's Institute of Chemistry and Biology of the Marine Environment (ICBM). The particles are formed, for example, when larger plastic, often packaging waste, decomposes through light, reaction with oxygen and the influence of waves. A significant proportion of this is already released into the marine environment as microplastics; textile fibres and tyre abrasion make up the largest proportion of this, according to an estimate by the International Union for Conservation of Nature (IUCN).
From the source to the North Sea
Scientists still know too little about where exactly the particles come from, how they are composed, how they are distributed in the environment and how harmful they actually are to living organisms. The aim of a large joint project, in which environmental chemist Scholz-Böttcher from Oldenburg, oceanographer Dr Thomas Badewien from the ICBM and biology didacticist Prof Dr Corinna Hößle are involved, is to investigate this more comprehensively. "Using the Weser as an example, we are analysing an entire river system - from the source to the estuary and into the North Sea," explains Scholz-Böttcher.
The various project partners are not only analysing samples from the river and the North Sea, but also from sewage treatment plants and the air in order to clarify the exact origin of the particles. They are also analysing mussel samples from the past 30 years to gain an impression of how polluted the animals are - and how this has changed over time. Other project partners are shedding light on the health risks for humans and how the plastic particles affect microorganisms. "This cross-ecosystem approach is new in Germany," emphasises Scholz-Böttcher.
Low concentrations
In order to tackle the task, scientists from the University of Frankfurt, the research centre Jülich, the Thünen Institute in Braunschweig and the Lower Saxony State Agency for Water Management, Coastal Defence and Nature Conservation on Norderney are involved in the project "Microplastic contamination in the Weser - Wadden Sea National Park model system: a cross-ecosystem approach" (PLAWES), which is led by the University of Bayreuth and the Alfred Wegener Institute in Bremerhaven (AWI). The BMBF is funding the project, which was launched last autumn, for three years and with around 2.9 million euros.
This April, the project partners took samples from the Weser and the estuary for the first time in a concerted effort - from ships and from land. All those involved are analysing the same samples using different methods in order to obtain as comprehensive a picture as possible of the pollution. For example, scientists from the AWI are using methods to count the particles and record their size and composition. "Our approach is complementary to this," explains Scholz-Böttcher. "Because we analyse the different types of plastic in relation to the total mass of microplastic." The researchers are carrying out detective work: microplastics can now be found everywhere in the environment. However, the concentrations are very low and therefore difficult to detect. What's more, plastic is a mixture of many different, often very complex chemical compounds - such as polyethylene and polystyrene from packaging or polyester from textiles.
A different approach to plastic
Together with colleagues, Scholz-Böttcher has developed and refined a new method in recent years: in order to get at the small plastic particles, the scientists pump large quantities of water through filters 10 micrometres in size, for example. During the sampling in April, doctoral candidate Maurits Halbach and Christopher Dipke treated several thousand litres of water in this way. Any material remaining on the filter has to be processed by the researchers to ensure that neither sand nor the smallest living organisms contaminate the plastic samples. The final step is pyrolysis: the material is decomposed at 590°C in the absence of oxygen. Depending on the type of plastic, this produces characteristic fragments that the chemists can separate using a gas chromatograph and then analyse using a mass spectrometer.
"This gives us an idea of the basic load and pathways of microplastics in the ecosystem," explains Scholz-Böttcher. The data is also important for feeding into mathematical models that scientists use, for example, to describe and predict how microplastics spread. For the environmental chemist, these are all important steps towards being able to assess the risks to the environment. Scientists are still finding it difficult to prove whether and if so how harmful the small plastic particles are. Whether harmful or not, the chemist is already calling for a different approach to plastic: "Plastics are durable - using them for short-lived packaging is a waste of resources."