Researchers are looking into the possible ripple effects of lead exposure.
After the city of Flint switched to the Flint River for its drinking water, experts found the number of kids with elevated levels of lead in their blood doubled.
Even low levels of lead can cause kids to lose IQ points and end up with behavior problems.
Lead and DNA
A recent study suggests lead exposure can cause changes to DNA that might affect several generations.
Doug Ruden is the Director of Epigenomics at the Institute of Environmental Health Sciences at Wayne State University. He tested 35 moms and their babies in Detroit.
To do this, he tested blood lead levels in neonatal blood spots from the Michigan Neonatal Biobank. The biobank collects blood spots from all newborn babies in the state, and has done so since 1984.
“We recruited young mothers who were born after 1984 and got permission to measure their blood lead levels,” Ruden says.
They observed a correlation between elevated blood lead levels in the mothers and changes in DNA.
“If the mothers had high blood lead levels when they were born, then their grandchildren have changes in their DNA,” he says. “And the changes in the DNA we were looking at weren’t mutations — they weren’t permanent changes — but they’re what we call epigenetic mutations. They’re changes in DNA methylation.”
Ruden says these sorts of changes control gene expression.
“It’s thought that’s how lead causes neurobehavioral defects — or loss of IQ in children,” he says. “It’s not by directly mutating the DNA, but altering their DNA methylation.”
What does this mean?
Ruden says they don’t know if these changes in DNA are good, bad or neutral. He says they need to do more studies to learn what this could mean.
“Mothers who are exposed to lead in the water, for instance, can not only affect their children’s IQ but can also affect, potentially, the IQ of their grandchildren,” Ruden says. “We know the DNA is affected, but we don’t know right now — we’re continuing to study this — we don’t know right now whether these changes in the DNA in the grandchildren can also affect their IQ.”
A Russian nesting doll
Ruden says they’re studying how exposures in pregnancy can affect not just the baby a mom is carrying, but also her grandbabies.
“The way you think about it is: if a mother is pregnant with a baby, she’s also carrying the baby’s children too,” he says. “Because it’s like a Russian doll.”
He says a fetus develops fetal germ cells while still inside its mother.
“So all of the eggs that a person has in life are actually developed in the fetus, during the fetal period, and all the sperm progenitor cells in the boy babies, the boy fetuses, are also present in the fetus,” he says. “So when a mother drinks leaded water, like what happened in Flint, she’s exposing her fetus, so that’s going to directly affect brain development of her baby.”
But he says, there could be effects on the next generation too.
“What most people don’t realize is that you’re also expressing the germ line cells, and that can affect the grandchildren, and even potentially beyond that,” he says.
One important caveat here: this study is small. Ruden says it will need to be repeated on larger scales and in different populations.
“It is well established in animal models, though — like in mice and rats — that environmental exposures to compounds such as lead can have effects for many generations,” he says. “So this isn’t entirely surprising.”