What defines a pollutant?

A pollutant is defined as a harmful chemical or substance present in the air, water, or soil that can adversely affect the environment and living organisms. The key aspect of this definition is the emphasis on the harmful nature of the substance, which distinguishes pollutants from harmless or beneficial substances. Pollutants can originate from various sources, including industrial discharges, agricultural runoff, and vehicle emissions, and they often contribute to health risks and environmental degradation.

The other options describe substances that either do not have a harmful impact or are beneficial in nature, thus failing to capture the essence of what constitutes a pollutant. A beneficial substance in small doses may not pose any risk and can even be essential for health, meaning it does not fit the criteria for a pollutant. Similarly, a harmless chemical found in nature does not cause adverse effects, while a naturally occurring mineral, although it can have ecological significance, does not inherently qualify as a pollutant unless it poses environmental or health risks in certain contexts.