A pesticide that is ______ reduces the likelihood of groundwater contamination.

• A. Persistent
• B. Highly water soluble
• C. Loosely adsorbed to soil particles
• D. Strongly adsorbed to soil particles

Answer: (B)

Groundwater movement of pesticides mainly depends on how much the chemical sticks to soil versus how much it dissolves in water. When a pesticide is strongly adsorbed to soil particles, it binds tightly to the soil and is less likely to dissolve in infiltrating water. That means it doesn’t travel downward with percolating water as readily, so the chance of it reaching groundwater is reduced.

If a pesticide is highly water soluble, it dissolves easily in water moving through the soil, increasing its downward transport and the potential for groundwater contamination. Loosely adsorbed pesticides can be washed away by infiltrating water more readily, also increasing leaching risk. Persistence indicates how long the chemical remains in the environment, but it doesn’t by itself determine how mobile it is or its likelihood of reaching groundwater. So the best fit for reducing groundwater contamination is strong adsorption to soil particles.