Those working in flour mills might have fewer male children and more female. Experts wonder whether certain toxic exposures in the mills might affect men's reproductive function or the survival of male fetuses.
Using data from the Washington State health department, researchers found that the children of men who worked in flour mills were disproportionately female. Of 59 children born to these workers between 1980 and 2002, 37 — or roughly 63 percent — were girls.
In contrast, just over 51 percent of children born in Washington during that period were boys, according to the findings published in the American Journal of Industrial Medicine.
While the reason for the discrepancy is not certain, on-the-job exposure to chemicals may be involved, according to Dr Samuel Milham and Eric M Ossiander, the health department researchers who conducted the study.
Flour mill workers are exposed to a range of pesticides used to keep insects out of stored grains and flour. One pesticide, known as DBCP, has been banned because of its effects on men's fertility and on male births, Milham and Ossiander point out.
The current findings suggest that some pesticides used in flour mills may have similar effects, the researchers speculate.
Traditionally, it's been expected that for every 100 girls born, there will be about 105 boys.
However, recent research suggests that this gap is narrowing. One study found that, across the US and Japan, male births have been declining since 1970. In the US, the proportion of males births dipped from 105.5 per 100 female births in 1970, to 104.6 in 2001, Reuters news agency reports.
Those researchers speculated that environmental toxins — whether pesticides, heavy metals, solvents or other pollutants — may partially explain this trend. Men's exposure to these chemicals may, for example, specifically damage sperm carrying the Y chromosome, and this could lead to fewer male fetuses. Male fetuses themselves may also be more vulnerable to such toxins.
The current study found that, besides the low prevalence of male births, boys born to flour mill workers also weighed significantly less than average. Their average birth weight was 7 pounds, compared with nearly 8 pounds among girls born to flour mill workers, and about 7 pounds, 12 ounces among boys born statewide.
According to Milham and Ossiander, this finding is 'unprecedented,' and could reflect another toxic effect of the fathers' chemical exposures.