In the meantime, tyre abrasion is regarded in technical discussions as an important source where discharges of microplastic into the environment are concerned. Car tyres are regarded as "rubber products" and not as "plastics", which is why the BKV has not so far included tyre abrasion in its model "From land to sea – model for the documentation of land-sourced plastic litter". On the other hand, more and more studies on the subject of marine litter also deal with the discharges from tyre abrasion, which are classified there as microplastics.
Discharges of tyre abrasion into the waterways are as yet still largely unresearched. Although the joint project RAU (tyre abrasion in the environment) does deal with the topic as part of the BMBF (German Federal Ministry of Education and Research) research focus "Plastic in the environment", no detailed results are as yet available on this. Conversio has now, within the "From land to sea" model, developed a new flexible approach for estimating discharges from Germany into the North Sea, Baltic Sea and Black Sea, which can in future constantly add fresh data to the calculations to provide an ever more accurate assessment. Until now, it is only possible at all levels to identify an approximate range or bandwidth.
How much tyre abrasion is produced is dependent on several factors, for example, the type of vehicle. In this respect, based on figures cited in the technical literature, the authors quote a fluctuation range of 80,000 to 125,000 tonnes a year. As far as discharges into the waterways are concerned, there are still a number of uncertainties that make it difficult to estimate volumes, for example how much remains in the atmosphere, how much is removed in street cleaning and how much is washed on to the fields. Against this background, the authors estimate the quantity discharged into rivers and lakes at approx. 6,200 to 9,700 tonnes, and the volume discharged into the seas at between 3,000 and 4,800 tonnes. If the assumptions made in the "From land to sea" model are taken as the basis, around 88 percent of the litter gets into the seas via rivers, the majority of it into the North Sea.
In view of the still many uncertainties because of the insufficient data situation, the authors recommend that the assumptions made in this model and also the data are continuously updated and validated. For this reason, they call their estimate a "discussion paper", which, they hope, will give rise to further surveys of valid data.
The BKV discussion paper on the topic of tyre abrasion ("Bericht: Diskussionspapier Reifenabrieb", only in German) can be ordered free of charge from the BKV website: https://www.bkv-gmbh.de/infothek/studien.html. Click under Marine Litter: Bericht und Sonderbetrachtungen zum Modell "Vom Land ins Meer".
Photo: © Fotolia / Mario Hoesel