Even relatively low levels of lead exposure can produce emotional disorders in children, according to a study conducted by researchers from the University of Pennsylvania and published in the journal JAMA Pediatrics on June 30.
“Our study is showing that even low levels of lead is associated with behavior differences,” lead author Jianghong Liu said.
Lead, a naturally occurring element and widely used industrial metal, is a potent toxin that affects every system of the body but is particularly damaging to the developing nervous systems of children. Studies have shown that even low levels of lead in children’s blood can lead to permanent behavioral and cognitive damage, including lowered IQ, hyperactivity, and behavior and learning problems. Lead has also been shown to produce anemia, slowed growth and hearing damage in children.
The new study reinforced many of these findings, and also added a new concern: emotional problems. In 2004 and 2005, the researchers tested 1,341 preschoolers from Jintan, China, finding that they had average blood levels of 6.5 micrograms per deciliter (µg/dl).
In 2012, the United States revised its “lead action levels” — the blood lead levels at which health intervention is needed — downward from 10 µg/dl to 5. China, however, still uses the old higher standard.
Even the 5 µg/dl level should not be considered “safe” though. According to the U.S. Centers for Disease Control and Prevention (CDC), “no safe blood lead level in children has been identified.”
After following up with the children at age six, the researchers found that those with the highest blood levels of lead also had the highest risk of pervasive developmental problems, as well as emotional disorders. Unlike lead-exposed adolescents, who have been shown to have higher levels of aggression and delinquency, the young children showed “internalizing problems,” such as anxiety and depression.
The researchers plan to continue to following the children as they age, to look for other effects of childhood lead exposure on neurological and cognitive development.
The health effects of pollution have become a national concern in China, which has been undergoing a boom in contamination keeping pace with its boom in industrialization. In addition to the use of lead in manufacturing, China phased out lead gasoline only in 2000 (five years after the United States) and still uses lead in paint — including on toys. In addition, the batteries used in China’s ubiquitous electric bicycles are also made with lead, which often ends up in municipal dumps and contaminates the environment.
“They don’t have a good recycling system,” Liu said.
In the United States, childhood lead exposure often comes from the consumption of lead-based paint, which was phased out in the 1980s. Yet lead is also notorious for traveling long distances in the air, then binding to soil particles or seeping into ground water far from its source. Original sources of lead contamination can include historic use of leaded gasoline, and historic or contemporary industrial pollution, ammunition, batteries and lead pipes. The CDC estimates that 4 million U.S. households contain children who are being exposed to high levels of lead, including half a million children with blood levels above the “action level” of 5 µg/dl.
Lead replaces calcium in the bones and is then released into the blood over the course of a lifetime. Although children are considered the most vulnerable to lead, the metal has also been linked to health problems in adults, including cardiovascular disease and kidney and reproductive dysfunction. Lead exposure during pregnancy has also been linked to premature birth and lower birth weight.
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