Which of the following is NOT a priority pollutant?

Radon is classified as a naturally occurring radioactive gas and is not typically listed as a priority pollutant under environmental regulations. Priority pollutants are those substances that are identified by regulatory agencies, such as the Environmental Protection Agency (EPA), as harmful to public health and the environment. These pollutants include a range of substances like heavy metals (which can be toxic to aquatic life and humans) and pathogens (which can cause diseases). Nutrients, while often not classified as traditional pollutants, can contribute to issues like eutrophication in water bodies, leading to oxygen depletion and harming aquatic ecosystems. Therefore, the other options represent pollutants identified as critical concerns for environmental monitoring and regulation, while radon does not fit this classification.