Treatment Process

EFFECT OF UVC ON DNA

DNA or deoxyribonucleic acid is a long polymer made from repeating units called nucleotides. The DNA chain is 66 to 78 x 10^-10  feet wide and 10 x10^-10  feet  long.

Information in the DNA is stored as a code made up from 4 chemical bases ; adenine (A) , guanine (G) , cytosine (C) and thymine (T). Human DNA consists of 3 billion bases , with more than 99% of these bases the same in all people. The largest human chromosome, chromosome number 1 is approximately 220 million bases long.

The order or sequence of these bases determines the information available for building and maintaining an organism. DNA bases pair up with each other; A with T and C with G to form units called base pairs.  Each base pair is also attached to a sugar molecule and a phosphate molecule. Together, the base, sugar and phosphate is called a nucleotide. 

The nucleotides are arranged in 2 long strands that form a spiral or double helix. The double helix is like a twisted ladder; the base pairs forming the ladders rungs, and the alternating sugar and phosphate forming the vertical sides of the ladder. Each strand of DNA in the double helix can serve as the pattern for duplicating the patterns of the bases

The base pairs are linked together by hydrogen bonds. These bonds are responsible for all of the interactions between the complimentary base pairs, and this  link is critical for all of the functions of living organisms. 

These hydrogen bonds are ruptured by UV light in the 260nm light region, and when the cross bonds are broken , new bonds called dimers form between adjacent bases. This process is almost instantaneous, taking approximately 1 Pico second to occur. Once the cross bond is broken, normal cell function including replication, assimilation of food and respiration cease.  The organism is rendered non viable, and it poses no further infectious threat.

A number of research groups have shown that this phenomena can be reversed for very low doses of UV light; this makes the design of the UV system and  regular maintenance very important. Photo-repair does not occur at a normal disinfection dose.

Healthy organisms can replicate and quickly spread infection or cause product spoilage. UV light effectively prevents cell replication and routine cell functions. Equipment design needs to ensure that the delivery of UV dose is uniform, that the optical path is not blocked, and that inlet bends or baffles used to overcome poor hydraulic designs do not permit breakthrough or cause shadows.

The majority of organisms have been studied and their  susceptibility to UV, known as their D₁₀   value has been determined. This value indicates the dose in mJcm^-2   that is required to achieve a 90% (or 1 log) reduction of a challenge species. Typical UV doses can achieve 99.9999% reduction of the target species. Certain species demonstrate higher resistance to UV; molds and yeasts for example do require a higher UV dose than many common waterborne species.  Contact ETS UV Technology if you have concern about a particular nuisance organism that you are trying to ensure does not become a problem, or would like to review our research database.