Which definition best fits the term "contaminate"?

The definition that best fits the term "contaminate" is accurately identified as making something impure due to exposure to pollutants. Contamination typically refers to the introduction of harmful substances or pollutants into a clean environment, which compromises its integrity. This can occur in various contexts, such as water, air, soil, or even food.

Understanding contamination is critical in fields such as environmental science, public health, and law enforcement, where protecting communities from harmful substances is paramount. The other definitions provided do not align with the meaning of contamination. For instance, purifying an environment represents the opposite action, as does increasing quality or monitoring for safety, which do not involve making something impure.