3.9 million plastic items per square kilometer …
Given the fact that microplastic debris is so widespread, it’s probably no surprise that the Rhine — Europe’s workhorse river — has been found to be among the most polluted by plastic.
The Rhine-Ruhr metropolitan area has the highest concentration, at about 2,333,665 particles per square kilometer, with a peak at Rees on the Nederhijn, where 3.9 million plastic items per square kilometer (or 21,839 particles per 1000 cubic meters) were found in a single water sample. In general, extreme peaks may be reached after heavy rain or accidents.In a similar sampling effort, Austrian scientists found that plastic pollution sometimes outweighs biomass in the Danube.
The data was compiled by researchers with the University of Basel, who evaluated, for the first time, the plastic concentration at the surface of one of the big European rivers. The results have been published in the journal Scientific Reports.
“The Rhine’s microplastics concentrations are .. among the highest so far studied worldwide,” said biologist Professor Patricia Holm from the Department of Environmental Sciences at the University of Basel.
Europe’s lakes are also saturated with plastic waste, including Lake Geneva and Lake Maggiore, where 220,000 particles per square kilometer have been reported by other studies. In comparison, Lake Erie has only about 105,503 items per square kilometer
The tiny — smaller than five millimeters — plastic bits are ubiquitous in the world’s waterbodies. They occur as intermediate products in plastic production or as pellets for cleansing and care products or result from fragmentation of plastic debris. They are released into the environment due to improper handling.
In the oceans, they contribute to the great garbage patches and are ingested by many organisms, from protozoa to baleen whales. Although as much as 80 percent of this marine plastic is emitted by rivers to the oceans, not a single great river has yet been scientifically studied for the microplastics load over its length.
Along with quantifying the plastic pollution, the environmental scientists also tried to classify the different types of plastic by taking 31 water samples at 11 locations over a stretch of 820 kilometers. Microplastics were found in all samples in different concentrations, with an average of 892,777 particles per square kilometer (or 4,960 particles per 1000 cubic meters).
The findings reflect the major potential sources of environmental pollution along the Rhine, such as metropolitan areas and industrial plants, waste water treatment plants and weirs, as well as the particular current conditions.
“If we assume an average microplastics concentration on the day we took the water sample in Rees, we can say that the Rhine contributes a daily load of more than 191 million plastic particles to the North Sea, and that only takes into account the surface,” Holm said.
“Even though, in terms of weight, this only corresponds to roughly 25 to 30 kilos a day, this adds up to 10 tons a year. Each one of these billions of plastic items can be ingested by organisms and have negative effects on their health,” she added.
Origins partially unclear
The scientists concentrated on the detection of microplastics found in large numbers in production worldwide and of low specific density, such as polyethylene, polypropylene and polystyrene. The types of plastics are used in the plastic industry e.g. for packaging, office equipment and vehicle construction and float on the water surface for long distances. Samples were mostly taken from boats of the Rhine Police Basel-Stadt and the Waterways and Shipping Administration in Germany and the Netherlands.
The researchers found microplastics in the shape of opaque and transparent spherules as well as of fragments and fibers.
“The extremely high proportion of more than 60 percent spherules in certain parts of the river is striking. Where they come from and what their former use was, is largely unclear so far”, said Thomas Mani, first author of the study and PhD student at the Department of Environmental Sciences of the University of Basel.