For my sixth grade science fair project, I raised sweet potatoes in water in mason jars, and added various substances to the water to determine the short and long term effect of the substance on the tater. One substance I added was liquid from a bucket of melted ice that I scooped of a cindered and salted road and I can report with some confidence that halides kill sweet potatoes. 🙂 It was for the same purpose as questioned originally - what is the effect of common items on growing items? Motor oil didn't work very well for sweet potatoes either (think of all the oil and detergent that gets washed off asphalt or concrete when it rains, and where it goes).
In addition to the spray trucks, there are bridges across the state that are equipped with automatic de-icing - essentially, if it gets cold enough to ice, and there is moisture in the air, there are sensors that spray the de-icer. When it runs off, through the drains in the bridge, most likely, it most likely drops into the streams or rivers below.