Which action is classified as microbial action in regard to pesticide degradation?

Microbial action refers specifically to the processes carried out by microorganisms, such as bacteria, fungi, and protozoa, that lead to the breakdown of substances, including pesticides, in the environment. The correct choice reflects the natural degradation of chemicals through the metabolic activities of these soil microorganisms.

Microorganisms can effectively utilize certain pesticide compounds as a food source, leading to their transformation into less harmful or inactive forms. This process not only helps in detoxifying the pesticides but also contributes to nutrient cycling within ecosystems.

In contrast, the other options pertain to different physical and chemical processes that do not involve microorganisms. For instance, the breakdown of chemicals due to sunlight is a physical process known as photodegradation, which does not involve microbial action. Pesticide vaporization refers to the transition of a pesticide from a liquid or solid state into a gas, and while significant, it does not involve biological degradation. Lastly, a chemical reaction in water, such as hydrolysis, involves the reaction of water with the pesticide but does not necessarily involve microbial action. Thus, the natural degradation by soil microorganisms is the key process that categorizes the action as microbial action in pesticide degradation.