What is the main cause of photodegradation?

Photodegradation is primarily the breakdown of substances through exposure to sunlight. This process is driven by light energy, specifically ultraviolet (UV) light from the sun, which causes chemical changes within the compound. As these substances absorb sunlight, they undergo reactions that can lead to their degradation, altering their structure and rendering them less effective or harmful to the environment.

While water, a chemical reaction, and soil erosion can interact with substances and potentially influence their stability and lifecycle, they are not the main drivers of the photodegradation process. Sunlight directly provides the energy necessary for the photochemical reactions that lead to the breakdown of materials, such as pesticides, in the environment. Therefore, the significant role of sunlight in facilitating this degradation process identifies it as the correct answer.