Regarding residues, which statement is true for phenoxy and dipyridyl (paraquat) herbicides in exposed livestock?

• A. High residues are common
• B. Residues are moderate
• C. Residues are low
• D. Residues are unpredictable

Answer: (C)

Residue behavior in exposed livestock is driven by how the chemical distributes and clears from the body. Phenoxy herbicides (like 2,4-D) and dipyridyl herbicides (paraquat) are not highly lipophilic and do not accumulate in fatty tissues. They tend to stay in extracellular fluids and are eliminated rapidly, mainly through urine and bile, so tissue residues in edible products are typically very low by the time animals are slaughtered. Paraquat, while highly toxic and capable of focal accumulation in certain organs with very high exposure, does not persist long in edible tissues and overall residue levels remain minimal. Thus, low residues best describe their disposition in exposed livestock. The idea that residues would be high, moderate, or unpredictable isn’t supported by their pharmacokinetic properties, which favor quick clearance and limited tissue storage.