Which statement describes persistence of PCBs?

Which statement describes persistence of PCBs?

• A. They break down rapidly under sunlight
• B. They do not easily break down in the environment
• C. They biodegrade only in water
• D. They require biological metabolism to degrade quickly

Answer: (B)

The key idea here is environmental persistence: PCBs are highly stable chemicals that resist breakdown, so they tend to remain in the environment for long periods. Their structure, with multiple chlorine atoms attached to the biphenyl rings, makes them resistant to photolysis, chemical attack, and most biological degradation. As a result, they do not easily break down in air, water, or soil, leading to long-term presence in ecosystems and potential accumulation in organisms. This is why the description that best fits persistence is that PCBs do not easily break down in the environment. The other statements imply rapid or selective degradation that simply doesn’t apply to PCBs, which are known for their slow, limited, or condition-dependent breakdown rather than quick, universal degradation.

The key idea here is environmental persistence: PCBs are highly stable chemicals that resist breakdown, so they tend to remain in the environment for long periods. Their structure, with multiple chlorine atoms attached to the biphenyl rings, makes them resistant to photolysis, chemical attack, and most biological degradation. As a result, they do not easily break down in air, water, or soil, leading to long-term presence in ecosystems and potential accumulation in organisms. This is why the description that best fits persistence is that PCBs do not easily break down in the environment. The other statements imply rapid or selective degradation that simply doesn’t apply to PCBs, which are known for their slow, limited, or condition-dependent breakdown rather than quick, universal degradation.