What is classified as a pollutant?

A pollutant is defined as a substance that introduces harmful effects to the environment, typically by contaminating air, soil, or water. This definition directly correlates with the notion of waste material that adversely impacts the ecosystem, health, or the balance of natural processes. The correct choice highlights that any waste material—which can originate from industrial, agricultural, or domestic sources—can contaminate these essential elements of our environment and therefore qualifies as a pollutant.

In contrast to the correct answer, the other options do not align with the definition of a pollutant. For instance, plants that grow in water can be part of healthy aquatic ecosystems, and they do not inherently harm the environment. Similarly, a pH-neutral chemical does not designate itself as a pollutant simply based on its neutrality; its impact depends on its nature and the context in which it is found. Lastly, naturally occurring minerals may have roles in ecosystems and can be beneficial, thereby not meeting the criteria for pollutants under normal conditions.