Seasonal variations in spontaneous levels of DNA damage; implication in the risk assessment of environmental chemicals.

The alkaline comet assay was used to investigate DNA damage levels in white blood cells of 45 normal healthy subjects. Therefore blood was sampled at four different periods, namely in February, June, August and November of the same year. Higher DNA damage levels were found in summertime, as well as higher levels of 1-hydroxypyrene in urine in this period. This suggests a higher exposure to polycyclic hydrocarbons in the summer compared with other periods of the year. The observed seasonal variation in DNA damage levels is in agreement with some, but in contradiction with other data. Seasonal variations in DNA damage levels can easily be explained by the existence of different confounders that may influence the results of a biomonitoring study. Besides sunlight and environmental pollution, also diet, allergy and physical exercise, for example, were already identified as important influencing factors. The investigation confirms that the blood sampling period is crucial in the planning and interpretation of biomonitoring studies.