Over 10% of births worldwide are preterm, meaning delivery occurs earlier than 37 weeks of pregnancy. It is a leading cause of neonatal mortality, and evidence suggests that exposure to heavy metals from the environment could be a risk factor. In the US, a major source of exposure to metals is private well water. The Environmental Protection Agency (EPA) sets standards and regulates levels of contaminants in public drinking water, but private well water isn’t regulated. This means private well water – which 13% of the US population receives drinking water from – is vulnerable to contamination. Indeed, studies have found metal contamination in private wells and that people who receive drinking water from private wells have more of these metals in their systems.

A recently published study set out to evaluate if exposure to toxic metals from private well water increased the risk of preterm birth. Because North Carolina (NC) has the largest state population using private well water, the researchers studied live births in NC that occurred from 2003-2015. From birth certificates, they could collect each pregnant person’s address at the time they delivered their babies. The researchers also used the NC-WELL database, which is a database of over 100,000 geocoded well water tests conducted from 1998-2019 from almost all census tracts in North Carolina. These tests include measurements of the concentrations of metals. The NC-WELL database allowed the researchers to assign each pregnant person’s address an estimate of their exposure to private well water and the concentrations of metals measured in that well water. Ultimately, the study included over 1.3 million births. This large sample size allowed the researchers to determine if increased metals in well water was associated with preterm birth.

The study found that people living in census tracts where over 25% of NC-WELL water tests exceeded EPA’s safe standard for cadmium had 11% higher odds of preterm birth than people who did not. People living in census tracts where over 25% of NC-WELL water tests exceeded EPA’s safe standard for lead had 10% higher odds of preterm birth than people who did not. These results indicate that cadmium and lead in private well water were each associated with preterm birth.

The study then modeled how the exposure to mixtures of metals was associated with preterm birth. This is particularly important because few studies assess the risks of multiple chemical exposures, even though it is highly likely people are exposed to more than one chemical at a time. When considering exposure to a mixture of seven metals present in private well water, the researchers found that exposure to the combination of cadmium and lead was associated with preterm birth.

In the US and NC, Black and Native American people have much higher rates of preterm birth than white people. Racial disparities in exposure to toxic chemicals could influence racial disparities in birth outcomes. As the study states plainly, “This is especially pertinent to consider when evaluating private well water-based exposure in NC, as structural environmental racism has led to poor and minority communities being more likely to rely on private well water.” This study found that when considering exposure to a mixture of seven metals present in private well water, the effect on preterm birth was most extreme for Native American people. It was associated with 20% higher odds of preterm birth for Native American people. The researchers say this disproportionate effect of metal exposure on preterm birth reflects the multiple environmental hazards and contaminants disproportionately forced on Native American people over several centuries. They also note that other studies have found that Native American pregnant people have higher levels of toxic metals in their systems than the national average.

This study used publicly available birth information and private well water testing to create a large cohort to study the effects of metals in private well water on preterm birth. The results make clear that private well water needs more regulation in order to ensure the levels of dangerous metals like cadmium and lead do not put people at risk. The results also make clear that not all people bear the same risks of exposure or health effects of exposure. People of color bear a disproportionate burden because they are more likely to receive private well water, which may contribute to disproportionate rates of preterm births.

For more information, CHEJ has previously written about the health effects of lead, cadmium, and the importance of considering the health effects of exposure to mixtures of chemicals.