Mothers’ exposure to dioxins affects children

Mothers’ exposure to environmental contamination can affect the health of their offspring, a joint Italian and US study has shown. Babies born to mothers with a history of high exposure to dioxins suffered from decreased thyroid function.

Women most heavily contaminated with dioxins following the 1976 Seveso pesticide factory explosion in Northern Italy later gave birth to babies more likely to suffer from hypothyroidism - an underactive thyroid gland - researchers have found.1 If untreated in infants, the disease can cause mental and physical retardation.

The 1976 explosion of a trichlorophenol reactor released a cloud of chemicals including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic dioxin. The surrounding area was not evacuated for some time because the adverse effects were not immediately apparent.

Since then, research on those who were exposed has allowed scientists to link dioxins to a catalogue of negative health effects. For instance, a study of men exposed as children showed the chemicals had marked and permanent effects on semen quality (ENDS Report 396, pp 4-5 ).

Although background levels in the environment have fallen since the 1970s (ENDS Report 380, p 18 ), TCDD has an extremely long half-life in humans. This is especially true for women: it takes about ten years for half of the chemical to be cleared.

In the Seveso explosion’s aftermath, the contaminated area was divided into three zones with decreasing soil dioxin levels. For the study on thyroid function, Italian and US scientists based in Milan, Boston and Maryland compiled data on 1,772 women who lived in the two most contaminated zones A and B, at the time of the disaster. For comparison, an equal number of age-matched women from nearby but uncontaminated areas were selected.

All babies born between 1994 and 2005 to sample or control mothers were tested for thyroid stimulating hormone (TSH). Post-natal testing of TSH is common, as elevated levels are a sensitive indicator of hypothyroidism. The test allows infants with the problem to be identified early.

Babies born to mothers living in the contaminated areas were at higher risk of hypothyroidism. The proportion of infants with elevated TSH was 2.8% for the controls, 4.9% for zone B and 16.1% for zone A. Average TSH levels were similarly increased.

These figures were based on a proxy measure of maternal dioxin exposure - the zone in which mothers lived in 1976. To check if the relationship held when maternal dioxin exposure was measured precisely, the researchers also looked at infants’ TSH for 51 mothers with known blood dioxin concentrations. Once again, a positive correlation between dioxin levels and TSH was found.

The researchers plan to follow up this work by tracking the intellectual and physical development of the children studied.

The study is an example of heritable effects which affect the next generation. These may or may not presage transgenerational effects which are passed on indefinitely (ENDS Report 397, p 27 ).

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