Air and Water Pollution May Have Significant Effect on Gender Birth Ratios: Study

Lead, mercury and other pollutants commonly found in the air and water may be affecting how many boys and how many girls are born each year, according to the findings of new research that looked at more than half of the U.S. population and the entire Swedish population.

Side effects of pollutants in air and water have significant impacts on pregnancies and the unborn children. Exposure to the pollutants leads to imbalances that may prevent some pregnancies from coming to term. However, researchers from the U.S. and Sweden say they may also have an impact on gender.

In findings published this month in the journal PLOS Computational Biology, researchers conducted a statistical analysis of two very large population datasets incorporating electronic medical records. One dataset represents over half of the US population for a period of eight years, which included more than 150 million people. The other dataset covers the entire Swedish population, which is more than 9 million people, for over 30 years.

Researchers also studied factors like environmental quality measures, season and temperature, testing 100 hypotheses that focus on human sex ratio at birth, which is the ratio between the number of newborn boys and newborn girls born each year. Typically, the ratio is slightly greater than 1/2 with more boys than girls, but it varies across different geographical regions and time periods.

The study suggests that neither dataset nor any of the hypotheses supported the idea that the sex ratio changed seasonally or in response to variations in ambient temperature. However, the data indicated increased levels of a wide array of air and water pollutants were linked to lower sex ratios. This included increased levels of industrial and agricultural activity which served as proxies for water pollution.

Areas with increased mercury exposure had an increase in the ratio of boys to girls. Conversely, areas with more lead exposure in the soil than average had a higher ratio of girls to boys.

Researchers speculate environmental toxins may cause some pregnancies to terminate. Depending on the toxin, it may affect boys or girls more. Different substances seem to modify different parts of physiology in the different sexes.

Exposure to environmental factors, including environmental toxins, play a large role in how a fetus may develop. They can affect growth and proper development, but can also significantly affect a pregnancy, leading to the loss of the fetus.

Prior research has found that exposure to pollutants during pregnancy can increase a women’s risk of suffering a miscarriage and increases the risk the child will suffer heart dysfunction later in life. In fact, exposure to air pollution causes millions of preterm births every year.

Other research indicates exposure to toxins like heavy metals during pregnancy disrupts a woman’s hormones and can lead to long-term side effects for both mother and infant. Toxins like arsenic, nickel, and lead interfere with the normal levels of naturally occurring hormones in both mother and child, leading to inadequate fetal growth and increased risk of chronic disease.

Research published in 2019 warned exposure to pollutants during pregnancy can be especially dangerous because pollutants can cross the placenta during pregnancy, allowing toxins to impact the growing fetus.

“After testing more than 100 hypotheses, we showed that neither dataset supported models in which the SRB (sex ratio at birth) changed seasonally or in response to variations in ambient temperature,” the researchers concluded. “However, increased levels of a diverse array of air and water pollutants, were associated with lower SRBs, including increased levels of industrial and agricultural activity, which served as proxies for water pollution.”