Which term refers to harmful materials that can enter the biosphere?

The term that refers to harmful materials capable of entering the biosphere is "pollutants." Pollutants are substances that can cause adverse effects on the environment and living organisms when they are introduced into ecosystems. These can come from a variety of sources, such as industrial discharge, agricultural runoff, or waste materials. Pollutants can affect air, water, and soil quality, leading to negative impacts on health, biodiversity, and ecological balance.

While contaminants, toxins, and hazards may relate to harmful materials, they have more specific meanings. Contaminants can refer to any substance that alters the purity of an environment, not necessarily implying harm. Toxins specifically refer to poisonous substances produced by living organisms. Hazards are risks or dangers that might not always involve an actual harmful material but indicate the potential for harm. Therefore, "pollutants" is the most appropriate term for materials that cause contamination and harm within the biosphere.