Mimi Kirk is a contributing writer to CityLab covering education, youth, and aging. Her writing has also appeared in The Washington Post, Foreign Policy, and Smithsonian.
New research sounds the alarm on how high levels of lead in topsoil can reduce birth rates.
The relationship between lead and infertility has long been known in the U.S.: Over a century ago, pharmacists sold lead pills to women looking to end their pregnancies, and women who worked with lead in factories knew that they were less likely to have children and more likely to miscarry than those who didn’t.
More recently, research on the water crisis in Flint, Michigan, showed that fertility rates dropped by 12 percent and fetal deaths rose by 58 percent after lead contamination spiked in the city’s drinking water. A recent working paper from the National Bureau of Economic Research, “Toxic Truth: Lead and Fertility,” confirms this connection by providing, for the first time, causal evidence of the effects of lead exposure on fertility for large portions of the U.S. population, both male and female.
It’s a troubling new addition to the body of research examining the effects of lead poisoning on young people and families. American cities remain heavily laced with this toxic metal, which was once found in paint, plumbing, gasoline, and in various industrial usages. As the Flint water crisis demonstrated, its public health impacts are severe: Lead exposure in children is associated with serious health and developmental consequences. At least half a million American children under the age of five have blood lead levels higher than the point at which the Centers for Disease Control recommends public health intervention, and at least 4 million households are exposed to high levels of lead, the CDC says.
Many are clustered in low-income areas of cities like St. Louis, Cleveland, Baltimore, and Philadelphia, where the effects of lead poisoning span generations. Some researchers have posited that chronic lead exposure is partially responsible for poor educational outcomes and high crime rates in some cities.
But the connection between lead and fertility has received less attention. After seeing the Flint fertility drop, Edson Severnini, an economics and public policy professor at Carnegie Mellon University and a co-author of the paper, wanted to investigate whether the effects of lead exposure on fertility conclusively apply to an area much larger than the city of Flint. He and his co-authors, Karen Clay and Margarita Portnykh, didn’t have an effective way to measure lead in water for a significant share of the country, so they looked instead at lead in air and in topsoil: They used county data on airborne lead from 1978 to 1988 and on lead in topsoil in the 2000s, and accessed statistics on births for the same periods. The data allowed them to survey the effects of lead in air for a little over one third of the U.S. population and lead in topsoil for more than two thirds of it.
After the Clean Air Act of 1970 and the ban on leaded gasoline, levels of airborne lead in the U.S. began falling. During the decade they studied, Severnini and his colleagues found that fertility rates rose concurrently by 4.5 births per 1,000 women. Today, airborne lead in the U.S. remains at low levels.
Yet Severnini notes that “hot spots” for airborne lead persist, particularly around airports, as piston-engined planes are still powered by leaded gasoline. A Michigan research study published last year, for example, found that children’s blood levels of lead increased with their proximity to airports and the percentage of days in which the wind blew from the airports in the direction of their homes.
Residual amounts of lead are also in topsoil, especially in older cities. Land that once housed industrial sites or land around homes built before 1978, when lead paint was banned, is also likely to contain lead. In addition, demolition of older homes that contain lead-based paint can spread plumes of contamination into nearby areas. Severnini and his fellow researchers found that in counties with lead concentrations above the median in their topsoil, the fertility rate fell by 7.8 births per 1,000 women—about the same effect as from the contraceptive pill after it was introduced in the U.S. in 1957.
Severnini stresses that the use of the pill for comparison does not mean that both types of infertility are problematic. “The pill is a decision, whereas [lead-related] infertility is involuntary,” he said. Indeed, the study also found a positive correlation between levels of lead in the air and the probability of a person seeking treatment for infertility. “It could be that these people don’t know about their exposure to lead,” said Severnini.
The authors also point to the economic consequences of fertility. Lower levels of airborne lead have boosted births in the U.S. by 95,000 annually. If one assumes that parents obtain “utility” by having children that is at least equal to the money spent raising them, that adds up to utility gains of at least $18.3 billion per year. (They arrived at this figure by calculating USDA estimates of the costs of raising a child from birth to 18.) Cleaning up lead contamination in areas with higher levels of the toxic metal would annually bring about 166,000 more births, with yearly benefits of approximately $33.4 billion.
The topsoil findings, the authors write, “[are] particularly concerning, because [they] suggest that lead may continue to impair fertility today, both in the United States and in other countries that have significant amounts of lead in topsoil.” Moreover, while many Americans may be aware of the risk of lead in drinking water, paint, and air, they may not know of the dangers of lead in their soil. A simple blood test can confirm whether there are dangerous levels of lead in a person’s system.
Exposure to lead in soil can occur in a number of ways, says Mary Jean Brown, former chief of lead-poisoning prevention at the CDC and now a professor at Harvard’s School of Public Health. When children play in the dirt, for instance, they can ingest it directly, and both children and adults can consume it by eating fruits and vegetables grown in it.
Brown advises residents to get the land around their homes tested, and to find out what their local health department says about growing food in the area’s topsoil. She notes that USDA county extension services will check for lead in soil and may even advise residents on what specific types of fruits and vegetables are safe to grow in it. (Generally, root plants, such as carrots, are the riskiest, while a tomato growing from a tall plant will have less lead in it. Still, Brown notes that there will be lead on the tomato.)
If the soil’s lead level is high, it is safest to grow crops in raised beds with potting soil, and to put a layer of mulch on top of any other soil so children aren’t playing directly in it. Researchers have also come up with other fixes to neutralize lead in soil, such as by placing fish bones in it. The phosphate-rich bones combine with the lead to form pyromorphite, a crystalline mineral that the human digestive system can’t absorb.
Some cities are also working to contain the lead-laced dust kicked up by construction or demolition work. In Philadelphia, the city pledged last year to hose down parks and recreational facilities near construction sites several times a week, and Portland, Oregon, now requires contractors who are demolishing old homes to come up with a plan to control dust and to refrain from mechanical demolition when the wind is blowing over 25 mph. While completely cleaning soil is possible, it’s a very involved and expensive undertaking that is mostly limited to Superfund sites.
Severnini’s take: Americans need to be better informed about the risks of lead in soil, including the causal relationship between lead and infertility. While regulations on lead are made at the federal level, states and cities are usually responsible for mitigating the dangers of lead on the local level—and for disseminating information to residents about the risks of exposure. “This is particularly important because some groups, such as developers looking to build homes in an area where there’s a lot of lead in the soil, may be interested in containing such information,” he said.
“This knowledge must reach the public,” he added. “At least then people are aware and can make well-informed decisions.”
Funding from the Annie E. Casey Foundation was provided to support our project "The Kids’ Zone."