Which compounds are classic examples of persistent organic pollutants?

• A. Sodium chloride
• B. Ammonia
• C. Oxygen
• D. PCBs, DDT, and dioxins

Answer: (D)

Persistent organic pollutants are chemicals that resist environmental breakdown, persist for long times, bioaccumulate in living tissues, and can travel long distances through air and water. PCBs, DDT, and dioxins fit this profile because they are organic, halogenated compounds that stay in ecosystems for years, accumulate in fatty tissues of organisms, and become more concentrated as they move up the food chain. They can spread far from where they were released, which is a hallmark of POPs. In contrast, sodium chloride is simply a stable inorganic salt, ammonia is an inorganic nitrogen compound, and oxygen is a basic atmospheric gas; none of these share the persistence and bioaccumulation characteristics that define persistent organic pollutants.