come in contact with the cell. Microorganisms are inactivated by UV light due to its damage to nucleic acids, such as DNA and RNA. The light penetrates the outer membrane and inactivates microorganisms by altering DNA through the formation of thymine dimers. Once the DNA is damaged, the microorganism is no longer able to reproduce and cause disease. UV-C has been proven to be effective against pathogens such as E. coli, Salmonella, Listeria monocytogenes and research is ongoing to validate uses in irrigation water systems. The effectiveness of UV-C on pathogens depends on exposure time, level of radiation, and the technology used.
Figure 5 - The electromagnetic spectrum including ultraviolet light wavelengths. (Adapted from: http://www.irinamacare.com/the-most-important-things-you-need-to-know-about-the-connection-between-the-sun-ultra- violet-light-and-vitamin-d/ )
Advantages and disadvantages of UV Light Disinfection
UV light offers several advantages. They can be combined with disinfectants to improve efficacy. There is a low cost associated with the system once the initial investment is made. UV light provides no downstream activity to interact with other compounds, such as fertilizers or pesticides. There are a few disadvantages to the UV light that may hinder a grower from choosing to implement this type of system. Water turbidity may limit effectiveness, particularly for less expensive units. Because the UV light must make contact and penetrate DNA, turbidity within the water from plant material or soil may actually block UV light penetration into the microorganism. For this reason, water treatment systems may include an initial filtration step. Furthermore, unlike residual chlorine, for example, there is no downstream biocidal activity to prevent or control the formation of biofilms after treatment. Over time, the lamp will need
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