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Deicing salts release micro- and nano-plastics and accelerate their photoaging and algal toxicity in urban waters
Summary
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.
Commercial deicers may represent an overlooked seasonal source of micro- and nanoplastics (MNPs) in urban aquatic environments. This study quantified MNP occurrence and polymer composition in six commercial deicers based on NaCl-, CaCl-, and CHCOOK and examined their subsequent transformation and biological effects. MNP mass concentrations ranged from 14.5 to 112.6 mg/kg in the >0.22 μm fraction and from 5.0 to 36.3 μg/kg in the <0.22 μm fraction. The tested chloride-based products generally contained higher MNP loads than the organic alternatives, with polypropylene predominating in both fractions. During 10-d photoaging at a fixed anion concentration of 500 mmol/L, saline media enhanced particle oxidation and fragmentation relative to ultrapure water, with CHCOOK generally producing the greatest dimensional reductions. Salt-aged particles exhibited 7-d EC values of 19.2-82.0 mg/L for Chlorella pyrenoidosa, compared with 76.6-233.9 mg/L for pristine particles. NaCl-aged particles generally had the lowest EC values, indicating that fragmentation alone did not determine toxicity. Direct salt-particle co-exposure at 1.4 mmol/L produced salt- and polymer-dependent responses associated with changes in particle surface charge and particle-cell interactions. One year of government procurement records indicated a potential application-stage MNP input of 7.13 t Together, these findings provide a basis for deicer-product screening and targeted roadside snowmelt management while highlighting the need to consider salinity-mediated particle transformations in ecological risk assessment.