Ultraviolet (UV) germicidal limits: What is a key drawback of UV as a sterilizing/decontaminating agent?

Introduction:
UV-C (around 254 nm) inactivates microorganisms primarily by inducing DNA pyrimidine dimers, leading to replication arrest. Although effective for surface/air disinfection, its physical limitations restrict when and how it can be used.

Given Data / Assumptions:

• Consider typical UV-C lamps used for surfaces, biosafety cabinets, and air handling.
• Assess penetration and line-of-sight constraints.

Concept / Approach:
UV-C has very poor penetration. It works best on directly exposed surfaces and air streams but does not pass through opaque materials, dust, or deep into multi-layered items. Therefore, microbes hidden in crevices, shadows, or internal parts of objects may survive. Also, high doses or prolonged exposure are required for spores; while UV can inactivate spores with sufficient dose, it is less efficient.

Step-by-Step Solution:
Identify the physical limitation: minimal penetration and line-of-sight action. Apply this to objects with centers or shaded zones: organisms there are not exposed adequately. Select the drawback emphasizing poor penetration.

Verification / Alternative check:
Engineering controls specify direct exposure and appropriate distances; shadowing is a known failure mode of UV workflows.

Why Other Options Are Wrong:

• Failure to kill bacteria in general: Incorrect; UV can kill many bacteria when directly exposed.
• Failure to kill spores under any circumstance: Overstated; spores are harder to inactivate but not invulnerable.
• Failure in closed environments: Many UV systems operate in closed ducts/cabinets effectively.
• Failure to inactivate DNA: False; DNA damage is the main mechanism.

Common Pitfalls:
Overreliance on UV for complex instruments; it is not a substitute for validated sterilization of internal surfaces.

Final Answer:
The major drawback is poor penetration, leaving microbes in shaded/inner areas unaffected.