''Dioxin exposure permanently affects the reproductive system and there is an inhibition in infancy and stimulation in puberty. When mature there is no effect,'' lead researcher Paulo Mocarelli, of the Hospital of Desio in Milan said.
The study used 400 volunteers who were infants, boys or young men at the time of the explosion to uncover the effects of dioxin exposure on male fertility.
It was found that men exposed to dioxins from the explosion when aged 1 to 9 had reduced fertility 22 years later. Their average sperm counts were reduced by 43 per cent compared with the control group.
However, men who were aged 10-17 at the time of the explosion had sperm counts 62 per cent higher than the control group. The sperm counts of men over 17 when exposed were not permanently affected.
Another finding was that levels of the female hormone oestradiol in men exposed to dioxins were permanently lowered. This was detectable 22 years after exposure, the Daily Telegraph reported.