What is the primary mechanism by which UV radiation deactivates pathogens?

The primary mechanism by which UV radiation deactivates pathogens is by damaging genetic material within cells. When UV light penetrates the cells of microorganisms, it primarily affects their DNA or RNA. This damage leads to the formation of pyrimidine dimers, which disrupt the normal structure of the DNA and interfere with the cell's ability to replicate and perform vital functions. As a result, bacteria and viruses are rendered inactive and incapable of reproduction, thereby effectively reducing the potential for infection and disease transmission.

In contrast, other options do not accurately describe the mechanism of UV disinfection. Inducing chemical changes in organic matter typically refers to processes involved in other forms of treatment, like oxidation, rather than the targeted action of UV. Increasing water temperature is related to thermal treatment methods and does not pertain to UV’s mechanism of action. Creating chlorine residuals is relevant to chlorination processes, which differ fundamentally from UV treatment in terms of how pathogens are neutralized. Thus, the focus on UV radiation's ability to damage genetic material stands out as the correct explanation for its deactivation of pathogens.