Does the definition of a pollutant include substances such as water oxygen and carbon-dioxide which are needed for life on earth but in strong doses are toxic?

Answer 1

The difference among the substances you describe is a matter of degrees. Oxygen and water are not naturally present in the environment in magnitudes that would be toxic. I know you probably heard that they are toxic in large doses, which they are, but they would have to be extraordinarily large doses. You would experience physical pain before you experienced water toxicity. Similarly, oxygen is not present in air in high enough concentrations to be toxic.

Similar to oxygen, carbon dioxide is not present in high enough concentrations to be directly toxic to organisms. However, the concentration of carbon dioxide in the atmosphere has been artificially increased by human activities and these concentrations are having an adverse impact on the environment. And that is the reason it is a pollutant.

So in answer to your question, the definition could include these types of substances, but it is a matter of magnitude. Just because carbon dioxide is naturally occurring does not mean it is not a pollutant.

Answer 2

No, the definition of a pollutant typically refers to substances that are harmful or toxic to the environment or living organisms in excessive amounts. While water, oxygen, and carbon dioxide are essential for life, they can become pollutants if they are present in concentrations that disrupt the balance of ecosystems or pose a threat to human health.