Plastics are synthetic laboratory creations, materials developed by human beings with properties that tend not to be encountered in nature in the same form and combination. What is a blessing in the applications for which individual polymers are used proves to be a curse for Mother Nature, who does not have a plan to integrate them in her evolutionary concept. Once they have reached the environment, hardy plastics can become a problem – particularly in the marine context. Extensive information and reports have already been published about the severe pollution of oceans by plastics and the consequences of this – in this series too, incidentally (Topic of the Month January 2014 and October 2012). Very little research has, however, been done in the past about the situation of our inland waterways (see the Topic of the Month November 2013in this connection too). According to plans made by the industrial, political and scientific communities, this is to be changed now. The initial step has been taken: ongoing research projects are focussing on an analysis of the origin and consequences of microplastics in inland waterways.
It is not a new discovery and no-one seriously disputes it: plastics should not be disposed of in the environment in general and in water in particular. Even though recycling concepts have been established successfully, up to now there has, however, been a lack of effective strategies for raising collective awareness at the international level that plastics should be considered as valuable materials rather than waste when their service life is over and that they should therefore be treated accordingly. Appropriate information and education are essential here.
At the present time, very little is known about the behaviour and impact of plastics in and on inland waterways. In most cases, we only notice the plastic waste that is floating around the world’s oceans – a long way away in our subjective opinion – and that gets there primarily via rivers when such debris and other waste reach coastal regions. This is probably the reason why no-one realised for such a long time that rivers are not just a transport route for plastic residue; rivers themselves are also suffering from extensive consequences of plastic litter.
Along river banks are found residues of waste and plastics. (Source: iStockphoto)
A walk along the Rhine or other busy waterways reveals that there is every reason to speculate that this probably is the case. Sascha Klein, a doctoral student and a member of the scientific staff of the chemistry and biology faculty at Fresenius University in Idstein / Germany, points out that it is obvious from a close look at river banks that not just sand and stones but also any amount of plastic can be found there. This observation led to a research project, which Klein recently presented .
Plastics attract chemicals
In his work, Klein takes a look, on the one hand, at plastic debris that can be found on river banks, while the scientist, on the other hand, tries – with the help of analytical chemistry – to highlight the profound influence polymers can have on the aquatic environment and its inhabitants. It is in the nature of polymer materials that such effects can be expected.
Plastics are extremely tough, hardy structures. Although they are susceptible, for example, to high-energy sunlight or mechanical stresses, they never disintegrate completely and thus disappear entirely as far as is known at the present time. In the course of time, a plastic breaks down into increasingly small and fine particles known as microplastics. The latter include, incidentally, not only artefacts but also plastic granulates that are used to manufacture plastic products, cosmetics or personal products. What are problematic about microplastics are the small size of a few millimetres or micrometres as well as the situation outlined below.
In chemical analysis, plastics like polydimethylsiloxane (PDMS) are used to extract organic compounds from liquid / aqueous media, in order to determine the exact nature and volume of them afterwards with the help of suitable analytical chemical instruments and methods. The organic compounds that are considered to be critical by environmental experts include active substances in medical drugs, pesticides, herbicides, hormones, polyaromatic and polycyclic hydrocarbons, plasticisers [phthalates] and other chemicals which fulfil a deeper purpose in their particular application area but are nasty pollutants as a residue in ground or surface water, where they are a threat not only to the ecosystems affected but also to mankind in general. For this reason, the government restricts the amount of pollutants present in drinking water and food products to what is believed to be an acceptable level.
Young fish larva (about 12 mm) from the Danube with a plastic particle in its intestines. (Copyright: R. Krusch)
It is considered a physical law that the ratio of the surface of an object increases as its volume decreases. The smaller an object is, the larger its surface area. Applied to plastic residue in rivers and oceans, this means: the smaller a microplastic particle is, the more pollutants can collect on its surface. This sounds as if a way has as a result been found to liberate the world’s oceans from chemical pollutants. In actual fact, however, microplastics have demonstrated conclusively that they are a serious danger to the organisms that live in water.
Out and about on the beautiful Danube
Scientists from Vienna University known as limnologists, who study the structure as well as the material and energy balance of inland waterways, have published alarming results: in the course of a research project about young fish in the Danube, they for the first time estimated the volume of plastic in Europe’s second-largest river. They found out that the Danube carries more plastic particles than fish larvae in the areas close to its banks between Vienna and Bratislava .
The fish in turn confuse the plastic particles that are floating in the water with food, including small crabs, insect larvae or fish eggs. It is not difficult to work out what this means: the fish suffer either from malnutrition – due to a “fake” feeling that they have eaten enough – or from constipation or from intestinal injuries, which can lead sooner or later to premature death. Vienna University  reports that there is in addition plenty of evidence that the intake of plastic particles can lead to a bioaccumulation of soluble compounds (active substances of medical drugs, pesticides, herbicides, hormones, polyaromatic and polycyclic hydrocarbons, plasticisers [phthalates] and other chemicals) in the food chain. In other words: in the final analysis human beings suffer from microplastic pollution of inland waterways too, when they eat fish.
Different categories of plastic that were quantified in the Danube: pellets (diameter: about 4 mm), flakes (length: about 2.8 mm), spherules (about 2.9 mm), other material (about 15.0 mm). (Copyright: A. Lechner)
4.2 tonnes of plastic per day
The Viennese research scientists say by way of summary that they found not only fish larvae but also a substantial number of small, macroscopically visible plastic particles in practically all the drift samples they took of water from the Danube. Industrial raw material in many different forms, such as pellets or flakes, accounted for most of these particles (about 80 per cent). The rest consisted of other particles that it was not possible to classify in any detail but probably came from municipal waste. All in all, the scientists come to a worrying conclusion: Hubert Keckeis from the Department of Limnology and Oceanography at Vienna University explains that the estimated volumes demonstrate that the Danube on average transports 317 plastic particles (4.8 g) and 275 fish larvae (3.2 g) per 1,000 cubic metres of water in the areas close to the banks between Vienna and Bratislava. Extrapolated conservatively, this amounts to an estimated input of about 4.2 tonnes of plastic waste per day from the Danube into the Black Sea.
So far, however, it has not been possible to quantify the volume of pollutants that can be absorbed by microplastic particles and can ultimately enter the food chain. Sascha Klein from Fresenius University in Idstein will be studying this aspect in his ongoing research work.
Our next Topic of the Month in October will be dealing with “microplastic” too. It will include an interview between k-online and the scientist Professor Dr Christian Laforsch from Bayreuth University, one of the leading microplastic research scientists in Germany.
 Aaron Lechner, Hubert Keckeis, Franz Lumesberger-Loisl, Bernhard Zens, Reinhard Krusch, Martin Glas, Michael Tritthart, Elisabeth Schludermann: "The Danube so colourful: a potpourri of plastic litter outnumbers fish larvae in Europe’s second largest river". In: Environmental Pollution, http://authors.elsevier.com/sd/article/S0269749114000475, DOI: 10.1016/j.envpol.2014.02.006