Breast-fed sons have reduced sperm quality when their 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 an explosion at a pesticide plant left thousands exposed to 2,3,7,8-tetrachlorodibenzodioxin (TCDD), the most toxic dioxin.
Research on those exposed has revealed a catalogue of adverse health effects, including reduced sperm counts in men who were aged between 1-9 years at the time of the explosion (ENDS Report, January 2008).
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, May 2009).
Work led by Professor Paolo Mocarelli of the Hospital of Desio in Milan suggests the adverse effects of exposure can have inter-generational effects. The researchers tested sperm quality in 39 sons born to mothers exposed to dioxins in the Seveso accident.
Twenty one of the boys who had been breast-fed had lower average sperm concentration as adults with 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 in total sperm count and sperm motility, a measure of the ability to move properly towards the egg.
Eighteen sons of exposed mothers who had been formula-fed, and 22 formula-fed sons of unexposed mothers, 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 that dioxin exposure via breast milk, even if only marginally above background levels, can lead to permanent impairment of the reproductive system. The authors’ observations of semen quality were reinforced by corresponding changes measured in hormone levels for the breast-fed exposed group.
Exposure during the first four or five months of life 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, September 2006), so harmful effects might be expected to reduce.
Background levels of TCDD were about 10ppt in blood at the time of the Seveso accident. Current environmental levels mean women aged between 20 and 40 now have less than 2ppt on average. This is below the level expected to yield adverse effects, say the authors.