OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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When are chemicals classified as dioxins produced?

During the production of natural fertilizers
When plastics containing chlorine are burned
When organic waste is composted
During the refining of crude oil

The correct answer is: When plastics containing chlorine are burned

Dioxins are a group of chemically-related compounds that are known to be environmental pollutants. They are produced as unintentional by-products of various industrial processes, particularly those involving chlorine-containing substances. The primary method of dioxin formation occurs when plastics that contain chlorine, such as PVC, are burned. During the combustion process, the chlorine reacts with organic materials to form dioxins. In contrast, the other processes mentioned, such as the production of natural fertilizers, composting of organic waste, and refining of crude oil, do not typically produce dioxins. Natural fertilizers and composting are processes focused on organic materials and usually aim to enhance soil health without the involvement of chlorine. The refining of crude oil can produce various pollutants, but dioxins are not a direct by-product of this procedure.