Every winter, thousands of tonnes of salt are spread out on Norwegian roads. Road salt improves driving conditions on slippery roads, but also damages cars, plants, soil and fresh water. Previous studies have pointed out the presence of microplastics in ordinary table salt and Elisabeth Støhle Rødland has now been investigating their presence in road salt, as a PhD project with NIVA and CERAD/NMBU. Her research shows that there are indeed microplastics in road salt, but it is a very small proportion of all the microplastics found on roads.
Microplastics in road salt
In a recently published study, Rødland and her colleagues from NIVA, CERAD/NMBU, the Norwegian Public Roads Administration and the University of Queensland in Australia investigated road salt used in Norway, Sweden and Denmark. They examined three types of sea salt from the Mediterranean and one type of rock salt from Germany, and concluded that all contained microplastics. They found ten different types of plastic, including PET and PE, typical from bottles and food packaging. The microplastics in sea salt partly originate from contaminated seawater, but production and transport of both sea salt and rock salt further add microplastics.
Is road salt a large source of microplastics?
The study showed that there was less microplastic in rock salt compared to sea salt, but the difference was very small. Based on their findings, the authors calculated that road salt releases around 150 kg of microplastics on Norwegian roads each year. We still know little about the distribution processes and where the microplastics from road salt end up. Some of it will find its way to freshwater courses and into the sea, and some will be left along the roads.
The 150 kg of microplastics from road salt may seem considerable, but is in fact a negligible proportion of all microplastics on the roads. Annually, car tires contribute around 5,000 tonnes of microplastics, road paint 100-300 tonnes and polymer-modified asphalt 30 tonnes, making road salt's contribution only 0.003 per cent of the total.
CERAD is involved in this PhD project due to its competence and experience in characterizing various particles. Our research director Ole Christian Lind is co-supervisor of Elisabeth Støhle Rødland.
Read more about this study in Rødlands article at forskning.no (in Norwegian)
Read more about this research at nrk.no (in Norwegian)
Rødland ES, Okoffo ED, Rauert C, Heier LS, Lind OC, Reid M, Thomas KV, Meland S. «Road de-icing salt: assessment of a potential new source and pathway of microplastics particles from roads». Science of the Total Environment, 2020. DOI: 10.1016/j.scitotenv.2020.139352