Lead was a problem for hundreds of San Diego children even before the latest scare involving San Diego Unified, records from the county health department show.

Last year, public health officials found hundreds of children in San Diego County with elevated levels of lead in their blood.

The children are at risk for a host of health problems, including behavioral disorders.

The county health department’s Childhood Lead Poisoning Prevention Program collected blood test data from 37,574 of the county’s 250,000 children under the age of 6, which is when children are at most risk of problems from lead exposure.

Of those, 91 had what the county considers especially dangerous levels of lead in their blood. Another 680 had elevated levels that could still be high enough to cause intellectual impairments.

Right now, parents and students have been alarmed by several schools that have found lead in the water because of decaying plumbing or fixtures inside of the school.

Any amount of lead in the water is considered unsafe, but water is not the leading cause of lead poisoning in San Diego. A survey of 105 serious cases of lead poisoning between 2009 and 2013 found only one case where leaded water was the likely culprit.

By contrast, 34 of those cases came from exposure to lead paint, which can be found chipping away on old buildings or can come free during remodeling.

Regulators have been struggling to reduce the amount of lead lingering around us for decades. In 1978, the federal government banned lead paint, but it’s still present in older homes. In 1986, it banned lead pipes, but some pipes from that earlier era have yet to be replaced. In 1996, lead was finally gone from gasoline.

Kids in the lowest-income neighborhoods are at the most risk of lead exposure.

Take Assembly District 80, for instance, which covers City Heights, Barrio Logan, San Ysidro and parts of Chula Vista and National City – some of the region’s lower-income, predominantly Hispanic communities. About a third of the lead poisoning cases in 2016 were there.

That’s one reason why Assemblywoman Lorena Fletcher Gonzalez, who represents the district, wants to make tests for leaded water mandatory for schools across the state, including preschools. Two of the three schools that have recently been discovered to have alarming levels of lead in their water were District 80.

There’s no single number that can point to an unsafe level of lead in a child’s blood. A frequently cited danger level is 10 micrograms of lead per decileter of blood, a ratio that would be like having several small grains of sand in a half a cup of water.

Other research has shown children can lose intelligence with even less lead in their blood.

“There’s a lot of factors that determine how much lead actually gets into the child’s body,” said Dr. Sayone Thihalolipavan, the county’s deputy public health officer.

A kid’s age, weight and even nutrition are all factors to take into account. Because calcium is chemically like lead, if a child consumes a lot of calcium, it will “outcompete the lead,” so the lead won’t be as harmful, Thihalolipavan said. In other words, calcium can act as a shield against lead poisoning.

He advised anyone who believes their child may have been exposed to lead to get a blood test. The county has resources for parents on its website.

Because the county blood testing data focuses mostly on kids too young to be in school, it might not catch problems caused by lead children encounter at school. Those encounters could be relatively fleeting, though, even at schools with lead in the water: While several schools in the county have elevated levels of lead in the water because of decaying plumbing or fixtures, not every faucet or fountain has lead. For instance, at San Marcos Middle School, officials tested five taps and found a single water fountain outside of the gym was releasing water that contained elevated amounts of lead.

At Emerson-Bandini Elementary School in San Diego, three of 10 taps tested had alarming levels of lead.

Tom Pellegrino, executive director of a charter school that shares a campus with Emerson-Bandini, said several worried parents have rushed to get their children’s blood tested for lead poisoning.

So far, he said, said no students at San Diego Cooperative Charter School or their parents have reported unhealthy lead levels.