Which property of a pesticide increases its likelihood to move in surface water runoff?

The property that increases a pesticide's likelihood to move in surface water runoff is high solubility. When a pesticide is highly soluble, it can easily dissolve in water and thus readily mix with runoff water during rainfall or irrigation events. This allows the pesticide to be transported over a greater distance—ultimately reaching surface water bodies, which can lead to contamination of these ecosystems.

In contrast, low toxicity refers to the harmful effects a substance might have on living organisms but does not directly correlate with the pesticide's movement through water. High volatility relates to a pesticide's tendency to evaporate into the atmosphere rather than moving through water. Lastly, a large particle size makes it more likely for the pesticide to remain on the surface rather than being washed away, as larger particles are less easily suspended in water.