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A preliminary evaluation of the environmental toxicology of road salts on plant root dynamics

Abstract. Although critical for the deicing of roads and bridges throughout the winter season in North America, road salts continue to have yearlong negative impacts on both anthropogenic and biological systems. Our objective was to measure the impact of four commonly used road salt ingredients on the dynamics of plant growth and development. Using onions as a model system, we hypothesized that exposing plants to different concentrations of sodium chloride, calcium chloride, potassium chloride, and magnesium chloride treatments would allow us to calculate the environmental concentration at which root development is halted by each road salt. We found that root growth decreased with sodium chloride, calcium chloride, and potassium chloride treatments, but increased with magnesium chloride. We used a linear model of root growth rates and concentrations to calculate the level at which each road salt becomes toxic to plants in the surrounding environment. We also apply the ecological theory of the principle of allocation to discuss how the chemical induction of root growth by magnesium chloride road salts may result in a life history trade-off that reduces investment toward plant-defense. The predicted trade-off in plant defense suggests that crop species in urban environments would be more susceptible to herbivory and as such would rely more on agricultural pesticides to sustain food security. We propose further studies to evaluate applications of plant defense theory in an urban context.