Men who are exposed to the toxic chemical 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD or dioxin) father more female babies, according to new data from Seveso, Italy.

Researchers measured the dioxin concentrations in blood samples from parents potentially exposed during an explosion at a herbicide manufacturing plant in 1976. The ongoing research which followed the blast has previously shown a relative increase in the number of female births. This latest analysis of blood samples collected from 239 men and 296 exposed women was done to determine whether sex and/ or age at time of exposure influenced the sex ratio of their offspring.

While mothers' exposure to dioxin was not influential in determining the sex of their offspring, fathers exposed when they were younger than 19 years old sired significantly more girls than boys. This effect was noted with blood concentrations of less than 20 ng per kg of bodyweight.

Many of the offspring were conceived years after the exposure, suggesting, say the researchers, that either the effect of dioxin exposure before or during puberty may cause permanent hormonal changes or that concentrations remain higher than previously thought many years after exposure. These data tend to support the former theory, suggesting that the time before and during puberty may be a very sensitive period for dioxin toxicity in men (Lancet, 2000; 355: 1858-63).

Austrian officials have taken action to limit the amount of dioxin in the feed of chickens and pigs. The move follows the recent Belgian scandal in which significant amounts of dioxin found their way into the food chain via contaminated animal feed.

The new guidelines, which limit the allowable amount of dioxin in animal feed to 2 pg toxic equivalents (TEQ) per grams of feed, recently helped officials to identify poisoned animals and to quickly trace the source of contamination, thus averting another public disaster. The report suggests that these guidelines could have prevented the unfortunate Belgian episode.

More than 90 per cent of human exposure to dioxins comes from food, mainly animal fat (Lancet, 2000; 355: 1883).