Whole human blood DNA degradation associated with artificial ultraviolet and solar radiations as a function of exposure time.

Laboratory investigations were conducted to evaluate the effect of ultraviolet radiation components and solar radiation exposure as a function of time on the degradation of whole human blood DNA from the standpoint of forensic analysis. Ten μL of whole human male blood samples were exposed to UV-A, UV-B, UV-C, and solar radiation at 20 min intervals up to 120 min. Allele frequencies of 16 short tandem repeat (STR) markers were monitored by employing current forensic typing DNA techniques. The STR markers were grouped into high, medium, and low molecular weight categories. Results revealed that even 20 min exposure to 4.89 eV UV-C photons (ʎ = 254 nm) with radiation intensity of 1200 μW/cm would degrade whole human male blood DNA samples significantly, making them unfit for human identification due to the breakdown of high molecular weight STRs. Exposure of blood samples to 4.11 eV UV-B photons (ʎ = 302 nm) with radiation intensity of 900 μW/cm resulted in complete degradation of high molecular weight STRs after 60 min. Partial breakdown of medium and low molecular weight STRs started after 80 min exposure. The degradation index (DI) values appear to show that the degradation of the DNA template molecule was relatively less in the low molecular weight DNA fragments as compared with high molecular weight DNA fragments. This finding indicates that genetic profiles obtained from whole human male blood exposed to this radiation for 60 min will give inconclusive results. Samples exposed up to 120 min to 3.40 eV UV-A photons (ʎ = 365 nm) and 3.10-3.94 eV photons of solar radiation did not appear to produce appreciable degradation in any of three molecular weight STRs in the whole human blood DNA samples.