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Road de-icing salt: Assessment of a potential new source and pathway of microplastics particles from roads
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Road de-icing salt used in cold climates was found to contain microplastic contamination, adding roads as a previously overlooked source of microplastics entering the environment. This has implications for how microplastics reach groundwater and surface water systems during winter months.
Roads are estimated to be the largest source of microplastic particles in the environment, through release of particles from tires, road markings and polymer-modified bitumen. These are all released through the wear and tear of tires and the road surface. During the winter in cold climates, the road surface may freeze and cause icing on the roads. To improve traffic safety during winter, road salt is used for de-icing. Knowledge of microplastic (MP) contamination in road salt has, until now, been lacking. This is contrary to the increasing number of studies of microplastics in food-grade salt. The objective of this study was to investigate if road salt could be an additional source of microplastics to the environment. Fourier-Transform Infrared spectroscopy (FT-IR) and Pyrolysis gas chromatography mass spectrometry (GC-MS) were employed to identify and quantify the polymer content in four types of road salts, three sea salts and one rock salt. The particle number of MP in sea salts (range 4-240 MP/kg, mean ± s.d. = 35 ± 60 MP/kg) and rock salt (range 4-192 MP/kg, 424 ± 61 MP/kg, respectively) were similar, whereas, MP mass concentrations were higher in sea salts (range 0.1-7650 μg/kg, 442 ± 1466 μg/kg) than in rock salts (1-1100 μg/kg, 322 ± 481 μg/kg). Black rubber-like particles constituted 96% of the total concentration of microplastics and 86% of all particles in terms of number of particles/kg. Black rubber-like particles appeared to be attributable to wear of conveyer belts used in the salt production. Road salt contribution to MP on state and county roads in Norway was estimated to 0.15 t/year (0.003% of total road MP release), 0.07 t/year in Sweden (0.008%) and 0.03 t/year in Denmark (0.0004-0.0008%) Thus, microplastics in road salt are a negligible source of microplastics from roads compared to other sources.
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Deicing salts release micro- and nano-plastics and accelerate their photoaging and algal toxicity in urban waters
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The road salt used to melt ice in winter contains tiny plastic particles, and once these particles hit salty water, they break down faster and become more toxic to algae, a key organism at the bottom of the food chain. Since algae support aquatic ecosystems that eventually connect to our food and water supply, this research suggests winter deicing may be a hidden source of harmful plastic pollution that's been largely overlooked.
Microplastics (MPs) in urban roadside snowbanks: Quantities, size fractions and dynamics of release
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Tire wear particles and road wear particles were found to dominate microplastic contamination in urban roadside snowbanks in northern Sweden, with MPs detected across multiple size fractions. The study documented a large pulse of MP release when snowbanks melt in spring, identifying snowmelt as a seasonal point source of microplastics entering urban waterways.
Occurrence of tire and road wear particles in urban and peri-urban snowbanks, and their potential environmental implications
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Researchers analyzed urban and peri-urban snowbanks in Norway and found significant concentrations of tire and road wear particles, confirming roads as a major source of microplastic pollution. The study is among the first to measure mass concentrations of these particles in snow, providing important data on how they accumulate and are transported in cold climates. The findings suggest that snowmelt may carry substantial loads of tire-derived microplastics into waterways each spring.
Microplastics pathways in the urban environment: Urban roadside snowbanks
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Researchers sampled urban roadside snowbanks in a Canadian city and found high concentrations of microplastics, with tire wear particles and synthetic fibers most abundant. The study demonstrates that urban snowbanks accumulate microplastics throughout winter and release a pulse of contamination into waterways when they melt in spring.
Characterisation and spatial distribution of tyre wear particles in Swedish highway snow: Loads into roadside ditches and risk of emissions with snowmelt
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Researchers measured tire wear particles (TWPs) — a major but underappreciated source of microplastic pollution — in snow alongside a Swedish highway and found concentrations up to 1,300 mg/L, with particles decreasing in concentration farther from the road. Because large amounts of TWPs can be rapidly released into waterways when snow melts, the study calls for better snow management practices to prevent this pulse of microplastic contamination.
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