FLINT, MI -- Blood lead levels in Flint children ages 5 and younger hit an all-time low in 2016, according to a study published in the Journal of Pediatrics.
Researchers say results of the study suggest that efforts to abate the city's water crisis are working.
Researchers analyzed lead concentrations of 15,817 blood samples from children over an 11-year period. They found that between 2006 and 2016, the percentage of children with blood lead levels over five micrograms per deciliter dropped from 11.8 percent to 3.2 percent.
Blood lead levels dropped from 2.33 micrograms per deciliter in 2006, to 1.15 micrograms per deciliter in 2016. The mean blood lead level during the height of the water crisis in 2015 was 1.3, up from 1.19 in the previous year.
The Centers for Disease Control and Prevention recommends public health action when blood levels are at 5 micrograms per deciliter or higher.
"These findings suggest that, even when taking into account exposure to corrosive Flint water, long term public health efforts to reduce lead exposure in the community have been largely effective," said Dr. lead author Hernan Gomez, a medical toxicologist and pediatrician at Michigan Medicine said.
Since the water crisis, water filters, pipe replacements, a switch back to Lake Huron for the city's source of water and several fresh food initiatives have been implemented in an effort to abate the effects of lead exposure in the drinking water.
"There is no known safe blood level of lead, and the ultimate public health goal is for children to have zero amounts of lead in their system," Gomez said. "It's unacceptable that any child was exposed to drinking water with elevated lead concentrations. We wanted to provide a complete picture of blood lead concentrations of Flint children before, during and after their exposure to contaminated drinking water."
Lead is a potent neurotoxin and elevated blood lead levels are associated with increased risk of lower intelligence quotient scores, academic failure and aggressive behavior in children. Toxic effects for levels far higher than those reported during the crisis may also include anemia and kidney damage.
Childhood blood lead levels in the city have been steadily declining since 2006 with the exception of two spikes.
The first spike occurred between 2014 and 2015, when the city's water was contaminated with lead. A random second spike occurred in between 2010 and 2011 when the mean for blood lead levels went up from 1.75 micrograms per deciliter to 1.87.
The spike predates the water crisis by four years and authors say its unexplained and needs to be explored further.
"The fact that we managed to, with abatement efforts, not only lower from the peak levels during the crisis, but managed even to get it to a historic low: I think it's positive," Gomez said.
Lead exposure has been a long time problem in the United States. Pediatrician Dr. James Oleske and environmental health researcher John Bogden have been collaborating on lead research at Rutgers New Jersey Medical School.
"In the 1970s, almost all Newark children and most adults had blood lead levels greater than 5 micrograms per deciliter, but as in Flint, now only a small percentage do," Bogden said.
In the study, authors point to other communities in the state that have elevated blood levels.
During the period of the water crisis, 5.1 percent of children in Jackson, 8 percent of children in Grand Rapids and 7.5 percent of children in Detroit had elevated blood lead levels. It was also during this time that an average of 3.4 percent of children in the state and 3.3 percent of U.S. children had blood lead level above 5 micrograms per deciliter.
"Childhood lead exposure is a problem that existed long before the Flint water contamination," Gomez says. "Other communities continue to need resources to help prevent lead exposure for their youth."
The most recent source of exposure to lead for kids in Flint is the drinking water being contaminated in 2014. However, historically speaking, most children are exposed to lead through old infrastructure, such as lead in old paint.
Deteriorating paint in homes, old toys and furniture can create lead-containing dust in window sills, door frames and in yards that children may ingest.
The study notes that older homes may have lead pipes and fixtures that could also contaminate water.
Previously reported data showing that corrective measures, including switching back the city's water source and instructing residents to use filtered water for drinking and cooking, made significant progress in children's blood lead levels.
For Flint children, risks of the most severe consequences of lead exposure -- which are most concerning when exposure is prolonged over years -- are low compared to children growing up in the city a decade earlier, Gomez notes.
Authors of the study noted several limitations to their research.
The data likely account for about half of Flint children during the timeframe. No child young enough to be exposed to lead through water in formula was tested.
The study doesn't determine what source of lead was responsible for children's blood lead levels.
""The Flint story has raised national awareness of the important public health issue of lead exposure of young children. We are seeing health professionals across the nation evaluate potential lead exposure in their own communities," Gomez said. "Public health officials, legislators and clinicians should continue efforts and allocate resources to further decrease environmental lead exposure to children in all communities at risk."