The most significant biological effect of short-wavelength ultraviolet (UV-C) radiation on living organisms is its impact on biopolymers – proteins and nucleic acids. These molecules contain cyclic carbon-nitrogen groups that strongly absorb radiation at 260-280 nm. The absorbed energy migrates through molecular chains until reaching weak atomic bonds, breaking them in a process called
photolysis. This produces molecular fragments with potent biological effects – for example, converting histidine to histamine (a compound that dilates blood capillaries).
UV radiation also causes
protein denaturation: at specific wavelengths, molecules lose electrical charge, clump together, and become biologically inactive (losing enzymatic, hormonal, and antigenic functions).
Key Mechanisms- Photolysis: Dominant at 280–302 nm
- Denaturation: Dominant at 250–265 nm
- These concurrent processes determine UV’s cellular effects.
Biological Impact- Most sensitive cellular function: Division
- Dose of 10⁻¹⁹ J/m² stops division in 90% of bacteria (without killing them)
- Lethal dose (causing mutations/protein synthesis inhibition): 10⁻¹⁸ J/m²
- DNA damage affects growth, reproduction, and heredity.
- DNA’s uniqueness makes it critical: it encodes all cellular proteins.
- Damage can cause irreversible harm or severe dysfunction.
Applications and Limitations- Sterilization uses: Water, air, and surface disinfection.
- Not fully sterilizing: Ineffective against some bacteria, fungi, and prions.
- Optimal wavelength: 265 nm (peak DNA absorption), though common low-pressure lamps emit at 253.7 nm.
- Mechanism: Causes thymine dimers in DNA, preventing replication.
UV Technologies- Bactericidal Lamps:
- Used in air/surface sterilizers (e.g., recirculators).
- "Quartz lamps" refer to quartz glass enclosures, not the mechanism.
- Water Treatment:
- UV disinfection: Safe and chemical-free but lacks residual effect (unlike chlorination).
- Works by disrupting microbial DNA at 260.5 nm.
- Often paired with chlorination/ozonation for comprehensive treatment.
- SODIS method: Uses sunlight’s UV component to purify water in developing regions.
Advantages Over Chemicals- No prolonged environmental toxicity (e.g., unlike chlorine).
- Immediate microbial inactivation without byproducts.