Although the presence of microplastics in the environment is raising concerns, the amount of microplastics in air and water is small compared to another polymer that pollutes air and water: micro rubber. These are the finest particles resulting from tire abrasion, which enter soil and air via the road surface or are removed by artificial turf.
Empa researchers have now calculated that over the last 30 years, from 1988 to 2018, 219 ± 22 kilotonnes of micro rubber have accumulated in the environment in Switzerland.
This work used dynamic probabilistic material flow analysis to quantify the flows of rubber particles from tires to roads and further onto soils and surface waters of Switzerland. The model considered the whole life-cycle of tires from import over the use phase to the end-of-life and the re-use of scrap tires. Uncertainties of model parameters and data variability were considered by using a probabilistic approach. Mass flows onto soils and through road drainage by both uncontrolled dispersal and engineered systems are considered. In addition, the release of rubber from artificial turfs was included.—Sieber et al.
The researchers from Empa’s “Technology and Society” lab identified car and truck tires as the main source of micro-rubber. Only three percent of the rubber particles emitted come from rubber granulate from artificial green areas. Tire abrasion is responsible for the remaining 97%.
Of the particles released into the environment, almost three-quarters remain on the left and right side of the road in the first five meters, 5% in the remaining soils and almost 20% in water bodies.
The team based its calculations on data on the import and export of tires and then modeled the behavior of rubber on roads and in road waste water. Since the year 2000, the guidelines for the recycling of water and the prevention of soil pollution have been significantly tightened. Through measures such as the construction of road wastewater treatment plants (SABA), part of the microrubber can now be removed from the water.
A part of the micro rubber is first transported by air into the first five meters left and right of the road, deposited and partly whirled up again. Christoph Hüglin from Empa’s “Air Pollution / Environmental Technology” lab estimates the impact on humans to be low, as a study from 2009 shows.
The proportion of tire abrasion in inhaled fine dust is also in the low single-digit percentage range at locations close to traffic.—Christoph Hüglin
Ramona Sieber, Delphine Kawecki, Bernd Nowack (2019) “Dynamic probabilistic material flow analysis of rubber release from tires into the environment,” Environmental Pollution, doi: 10.1016/j.envpol.2019.113573.