Breast-fed sons have lower sperm quality when mothers are exposed to low doses of dioxins, Italian scientists have reported.
The findings are part of the legacy of the 1976 Seveso disaster in northern Italy, when a pesticide plant explosion exposed thousands to 2,3,7,8-tetrachlorodibenzodioxin (TCDD), the most toxic dioxin.
Research has revealed a catalogue of adverse health effects, including reduced sperm counts in men who were aged 1-9 at the time (ENDS Report 396, pp 4-5).
It has been suggested that exposure to dioxins and other endocrine-disrupting chemicals could explain declining male fertility over the past 60 years (ENDS Report 412, p 6).
Work led by Professor Paolo Mocarelli of the Hospital of Desio in Milan suggests the adverse effects of exposure can be passed to children.1
Tests on the sperm quality of 39 sons born to mothers exposed to dioxins in the Seveso accident found 21 of those breast-fed had lower sperm levels as adults. On average their sperm counts were 36.3 million per millilitre of semen compared with breast-fed boys born to unexposed mothers, who had 86.3 million/ml.
Lower scores were also found for total sperm count and sperm motility, a measure of the ability to move towards the egg.
Eighteen sons of exposed mothers who had been formula-fed and 22 formula-fed sons of unexposed mothers, all had no sperm-related differences.
Exposed mothers had on average 19 parts per trillion of TCDD in their blood at conception, compared with 10ppt in their unexposed counterparts.
The results show dioxin exposure via breast milk, even at levels just above the background, can permanently impair the reproductive system. The authors’ semen quality observations were reinforced by corresponding changes in hormone levels for the breast-fed exposed group.
Exposure during the first four or five months after birth seems to be particularly damaging, they say. This period is known as the neonatal ‘mini-puberty’, when testes almost double their volume.
Levels of dioxins in the environment are now ten times lower than in the 1970s (ENDS Report 380, p 18), so harmful effects might be expected to have reduced.
Background levels of exposure at the time of the Seveso accident were about 10ppt in blood. Lower dioxin levels in the environment mean women aged 20-40 now have less than 2ppt on average. This is below the level that would be expected to cause harm, say the authors.