Assessing the Toxic Effects of “Eco-Friendly” Road De-Icer Alternatives on Freshwater Plankton Communities

Abstract

Increasing use of de-icing salt on roads and paved surfaces is contributing to rising salinity in freshwater, threatening aquatic ecosystems. In response, novel road de-icers advertised as “eco-friendly” have been developed and are widely used in cities across North America. Despite this, testing of the toxicity of road salt alternatives rarely extends beyond individual aquatic species, and community and ecosystem-level testing remain limited. We used outdoor mesocosms at the Queen’s University Biological Station to test how zooplankton communities, important primary consumers in aquatic systems, responded to multiple levels of three de-icers: road salt (NaCl), an organic alternative (beet-juice & salt-brine), and an inorganic alternative (NaCl, CaCl2, MgCl2). We found that both alternatives were toxic to zooplankton and decreased total abundance and affected community indices. Cladocerans and copepods were more sensitive than rotifers to all de-icers. We saw various impacts at the zooplankton species level, indicating differential sensitivities that could impact community composition, species interactions, and ecosystem function. However, the mechanisms of toxicity among de-icers may have differed; a decline in oxygen in the organic alternative correlated with the decline in zooplankton abundance not observed in the other de-icers tested. The inorganic and road salt de-icers also increased the chlorophyll a concentration at the end of the chloride gradient, while the organic de-icer decreased it. These results suggest that some de-icer alternatives might not be as environmentally friendly as advertised despite their recommended and growing use across North America, although more research is needed in impacted lakes.