Which process involves the direct breakdown of herbicides by sunlight?

The process that involves the direct breakdown of herbicides by sunlight is photo-decomposition. This specific process occurs when the energy from sunlight triggers chemical reactions that break down the herbicide molecules. Sunlight can cleave chemical bonds within the herbicide compounds, leading to their degradation and reducing their efficacy and potential environmental impact.

In contrast, microbial decomposition refers to the breakdown of substances by microorganisms, which involves biological processes rather than direct sunlight interaction. Chemical decomposition generally describes processes that can involve heat, pressure, or other chemical agents but do not specifically target sunlight as the primary catalyst. Absorption relates to the uptake of substances by organisms or materials and does not involve the breakdown process. Thus, photo-decomposition is accurately defined as the direct action of sunlight on herbicides, making it the correct answer.