During the study, the researchers found that among women from the San Francisco Bay Area, those exposed to higher levels of polychlorinated biphenyls (PCBs- a banned group of pollutants) during the 50s and 60s, were significantly more likely to give birth to female children.
PCBs are persistent organic pollutants identified worldwide as human blood and breast milk contaminants. They were widely used in industry as cooling and insulating fluids for electrical equipment, as well as in construction and domestic products such as varnishes and caulks
They also affect immune, reproductive, nervous, and endocrine systems.
The researchers analysed the levels of PCBs in blood taken from pregnant women during a Bay Area study in the 1960s and found that for every one microgram of PCBs per litre of serum, the chance of having a male child fell by 7pct.
"The women most exposed to PCBs were 33% less likely to give birth to male children than the women least exposed," said Irva Hertz-Picciotto, the lead author of the study.
"These findings suggest that high maternal PCB concentrations may either favour fertilization by female sperm or result in greater male embryonic or fetal losses.
"The association could be due to contaminants, PCB metabolites or the PCBs themselves," she added.
A study is published today in BioMed Central's open access journal Environmental Health.