While in Australia last month I learned that female green sea turtles on the Great Barrier Reef now outnumber males by 116 to 1. Biologists blame it on the rising temperature of the sand on Australian nesting beaches: The warmer the sand, the more females hatch. In Sarnia, Ontario—known as Chemical Valley due to its 36 local petrochemical plants—emissions and runoff have halved the number of boys born in the area since the early 1990s, according to studies published in Environmental Health Perspectives.
Now a new study, published online last month in the journal Economics and Human Biology, shows that U.S. counties where lead in the topsoil exceeds the national average had twice the number of five-year-old boys with long-term cognitive problems. Five-year-old girls weren’t affected. Right from conception, it seems that environmental stress, especially pollution, discriminates on the basis of sex.
Edson Severnini, a professor of economics and public policy at Carnegie Mellon University, and his colleagues Karen Clay and Margarita Portnykh began with the United States Geological Survey’s recorded levels of lead in topsoil in 252 of the largest counties in the U.S. in 2000. They then turned to parents’ responses to a question on the 2000 census: Had their five-year-old experienced difficulties, for at least six months, with learning, memory, focus or decision making? The parents of over 77,000 children replied with a yes or a no.
We’ve long known lead to be dangerous, and adding the heavy metal to gasoline, house paint and pesticide has been banned now for decades. Nonetheless, we’re still living with lead’s legacy. Over the 20th century more than 6.5 million tons were released into the environment across the U.S., most of it still blowing around or sticking to soil particles. That is alarming because lead is a neurotoxin: It starves the brain—especially the frontal lobe of the developing brain—of protein and energy, and it doesn’t decompose.
To make matters worse, lead on painted windowsills and in garden soil tastes sugary. Innocently ingesting even tiny amounts of lead can translate to lower IQs and attentional and behavioral problems later on, researchers have found.
There is even evidence that higher levels of lead in the bloodstream can predict antisocial behavior and violence in adolescence and early adulthood, according to a 2012 study led by Tulane medical researcher Howard Mielke published in the journal Environment International.
The new Carnegie Mellon study reinforces the link between a child’s early lead exposure and an uncertain future. Preschoolers’ exposure to lead in their first five years of life increased their probability of compromised cognitive function, including a weaker ability to learn, solve problems and control one’s impulses. The study also adds two fascinating twists to the existing mound of scary data: Boys are twice as vulnerable as girls to early neural damage, and even levels of lead that are currently considered acceptable can exert a deleterious effect.
Our problems with lead aren’t history, this study shows. But it turns out that education can dampen lead’s harmful effects. “We actually show that if boys had some schooling, the [negative] effect was much smaller,” said Dr. Severnini. Except for restricting the lead in small aircraft fuel, which is still unregulated, and remediating contaminated soil where children live and play, we may not be able to control how much lead is still hanging around. But there is something we can do to protect our children’s brains, and it is called preschool