Exposure of the artificially contaminated slides at a distance of
8 cm from the UV source led to a reduction of the contamination
by 83.4% (DNA) and 56.2% (saliva), with no relation to exposure
time. A distance of 48 cm reduced the contamination by 70.7%
(DNA) and 53.5% (saliva) on average, showing that the distance
between the samples and the light source has an effect on the
reduction of the amount of contamination. Furthermore, our
findings indicate that isolated DNA is more susceptible to UV
irradiation than saliva. Using a wavelength of 254 nm the
reduction of unwanted DNA was higher than by using 312 nm
(data not shown). These results show that the shorter wavelength
eliminates the contamination more efficiently than the longer
one. However DNA contamination could not be eliminated
completely. The experiments with different chemicals indicate
that in most cases isolated pure DNA is more susceptible to the
tested chemicals than saliva (Fig. 1). Even though the results are
ambivalent, our study demonstrates that the procedures of DNA
decontamination with UV irradiation are rather inefficient. UV
irradiation can only reduce the contamination but does not
eliminate it completely, demonstrating the importance of
contamination avoidance prior to genetic analysis.