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

High solubility is the property of a pesticide that significantly increases its likelihood of moving in surface water runoff. When a pesticide is highly soluble, it means that it can easily dissolve in water. This allows the pesticide to be carried away by rainwater or melting snow, which can lead to surface runoff. In agricultural or landscaped areas, when these conditions occur, the dissolved pesticide can contaminate nearby waterways, posing risks to aquatic ecosystems and possibly human health.

Other properties, such as low volatility, refer to a pesticide's tendency to evaporate. A low volatility means it is less likely to enter the atmosphere, which is more relevant to airborne transport than water runoff. High toxicity relates to the potential harmful effects of the pesticide on living organisms but doesn't directly affect its movement through water. Similarly, heavy molecular weight can result in a compound being less mobile in water, as heavier molecules tend to settle rather than remain dissolved and transported in runoff. Thus, high solubility is the key factor in facilitating the transport of pesticides through surface water runoff.