A majority of the cities with widespread lead poisoning in young children are run by Democrats, according to a new study published in the Journal of Pediatrics.

The six-year study, which took place from 2009 to 2015, was based on more than 5 million blood samples of children under the age of six across the 50 states and the District of Columbia.

The study found that 3 percent of children tested across the nation had blood lead levels categorized as "high." It singled out six cities—Syracuse, Buffalo, and Poughkeepsie in New York, York and Oil City in Pennsylvania, and Cincinnati, Ohio—as especially troubled communities where more than 14 percent of children had high levels of lead in their blood.

Two thirds of those municipalities are controlled by Democrats and have been for some time.

In Syracuse, which had the nation's highest lead poisoning rate, 40.1 percent of children under six had high lead levels (between 5 and 10 micrograms per deciliter) and 16 percent had "very high" levels (exceeding 10 micrograms per deciliter). Syracuse has had Democratic mayors since 2001.

Buffalo, where 18.8 percent of children had high blood lead levels, has had a Republican mayor for only three years since 1952. Cincinnati (16 percent) has had a Democratic mayor since 1984 and York (14.4 percent) has had a Democratic mayor since 1994.

Both Poughkeepsie and Oil City currently have Republican mayors.

In Flint, Michigan, a study of blood lead levels in children under six years attracted national attention due to the finding that 4 percent of them had high lead levels. The study indicated that the decision to stop getting water from a Detroit pipeline caused the increase in children with significant blood lead levels.

Michigan's Republican Gov. Rick Snyder took heat for Flint’s lead problem, although some have pointed out that the city has had a Democrat-dominated government for years that was heavily involved in the decision to switch pipelines.

A new study from the American Academy of Pediatrics says that any amount of lead poisoning "can cause irreversible cognitive and behavioral problems."

Young children with lead in their systems have been shown to have lower IQ scores and to be more likely to develop "inattention, impulsivity, aggression, and hyperactivity," according to the study.