Which statement about diquat's interaction with soil is correct?

• A. Diquat rapidly degrades in water within hours.
• B. Diquat does not bind to soil at all.
• C. Diquat strongly binds to soil particles; once bound, not effective.
• D. Diquat is highly volatile and evaporates.

Answer: (C)

Diquat’s behavior in soil revolves around adsorption to soil particles and what that means for its ability to affect weeds. Diquat is a contact herbicide used on plant foliage, and when it ends up in soil it tends to bind strongly to soil surfaces, especially where there are clays and organic matter. This strong binding makes the chemical relatively immobile in the soil and prevents it from moving to plant roots to be absorbed. As a result, once diquat is bound to soil particles, it isn’t effective for weed control via soil movement or root uptake. That’s why the statement describing strong soil binding and loss of effectiveness once bound is the correct one.

Other ideas don’t fit because diquat does bind to soil rather than staying free, it isn’t characterized by rapid degradation in water within hours as the primary behavior to rely on, and it is not a volatile compound that would evaporate from soil.