Objectives The aim of the study was to detect single-strand breaks in deoxyribonucleic acid (DNA) in mononuclear blood cells of fire fighters exposed to o-nitroanisole and other substances released into the environment during an accident in a chemical plant.

Methods The level of DNA single-strand breaks in mononuclear blood cells was detected by alkaline elution. The results for 16 fire fighters who worked in a contaminated area for about 8 h and two references groups (one of fire fighters who had not worked in the contaminated area and one of persons without any apparent occupational exposure to genotoxic substances).

Results The mean normalized elution rate (nER) 19 d after the accident was slightly but statistically significantly (P<0.05) higher for the exposed fire fighters [mean 1.48 ± 95% confidence interval (95% CI) 0.21] than for reference group I (mean 1.21 ± 0.21) or reference group II (mean 1.17 ± 95% CI 0.18). No statistically significant difference was found between reference groups I and II. Another analysis was performed three months after the first. The level of DNA single-strand breaks (mean nER 1.12 ± 95% CI 0.11) was no longer increased in comparison with the levels of the reference groups. Conclusions DNA single-strand breaks were increased in fire fighters exposed to o-nitroanisole and other substances. In comparison with the extent of DNA strand breaks found in other occupational groups the increase was only moderate. The observed decrease in DNA single-strand breaks to the reference level in exposed fire fighters three months later suggests a DNA repair mechanism for single-strand breaks caused by o-nitroanisole.

Key terms acute toxicity; biomonitoring; dna single-strand breaks; fire fighter; human mononuclear blood cells; o-nitroanisole