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 Researchers studied men and women who were employed between 1969 and
1984 at a plant in New Zealand making what’s known as phenoxy
herbicides, chemicals sprayed on plants to prevent uncontrolled
growth. The chemical blend included several types of
tetrachlorodibenzo-p-dioxin (TCDD) that are linked to a range of
health issues including decreased odds of male offspring.
“Twenty years ago, it was first reported that men that had been
exposed to high levels of dioxin as a result of an industrial
accident in Seveso, Italy, on average fathered less boys than girls
compared to men exposed to background levels of dioxin,” said lead
study author Andrea ’t Mannetje, a public health researcher at
Massey University in Wellington, New Zealand.
Since then, only a few studies have been done on people exposed to
dioxin; some found a similar effect on the gender of children but
others did not.
“This study, which was conducted in a group of former producers of
dioxin-contaminated herbicides, adds to the number of studies that
have observed this effect,” she added by email. “This study also
provides evidence that the effect is dose-dependent (the higher the
dioxin exposure, the bigger the effect) and male-mediated (the
effect was observed in men with high dioxin exposure, not in women
with high dioxin exposure).”
Dioxins are mainly byproducts of industrial activities but can also
be produced by natural events like volcanic eruptions and forest
fires. These chemicals typically accumulate in the food chain,
mostly in the fatty tissue of animals.
TCDD is the most toxic type of dioxin, according to the World Health
Organization. Long-term exposure is linked to impairment of the
immune system, the developing nervous system, the endocrine system
and reproductive functions.
For the current study, researchers analyzed data on 127 men and 21
women who reported conceiving a total of 355 children after they
started working at the New Zealand herbicide plant.
This group of kids included 197 boys and 158 girls, which translated
to an overall sex ratio of 0.55, meaning 55 boys and 45 girls per
100 births, researchers report in Occupational and Environmental
Medicine.
All of the workers in the study provided blood samples in 2007 and
2008 for researchers to test for concentrations of TCDD. Researchers
used the results to estimate blood levels of the chemical for the
parents at the time their babies were born.
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For fathers with blood concentrations of TCDD of at least 20
picograms per gram (pg/g) at the time of birth, the sex ratio was
0.47, meaning these men were more likely to have girls than boys.
When fathers had blood concentrations of at least 100 pg/g at the
time of birth, the sex ratio was 0.45, making boys even less likely
for fathers with greater exposure to the herbicides at the plant.
Researchers didn’t find an effect in women.
One limitation of the study, however, is that it didn’t include
enough female workers to produce statistically meaningful results
about their babies. Researchers also lacked data on blood
concentrations of TCDD for many of the workers at the plant,
reducing the number of employees that could be included in their
analysis.
Still, the findings add to results from research at the accident
site in Italy, that also found the decrease in male births was more
pronounced when people were exposed to larger amounts of dioxin,
said Michele Marcus, a public health researcher at Emory University
in Atlanta who wasn’t involved in the New Zealand study.
“This is important because the sex ratio was proportional to the
dose of the exposure,” Marcus said by email. “This makes it more
likely that the exposure is causal.”
SOURCE: http://bit.ly/2cEDes0 Occupational and Environmental
Medicine, online August 31, 2016.
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