Kataya Davidson was 26 years old when she hopped a freight train to New Orleans and took a job demolishing hurricane-damaged houses and buildings. Davidson, who'd left home in Washington State at age 14, had lost track of how many times she'd traversed the continent by rail.

This time, in 2007, she decided to stay put. She says that given her nomadic past, post-Katrina New Orleans was one of the "only places in America" where she could readily find work and housing.

Two years later, as a new mother, she was trading renovations for rent at a friend's bungalow in St. Claude, a neighborhood in the Upper Ninth Ward. As she sanded off layers of old paint, dust spun around her.

On a whim, Davidson, asked her baby's pediatrician to test for lead poisoning. She was shocked to learn that her daughter had levels of lead in her blood five times higher than the current federal guideline. Lead, among the best documented environmental threats to children, is linked to lower IQs, learning disabilities, attention problems, and other neurological effects.

The doctor, she recalls, wasn't surprised. "This is New Orleans," he said. "Everyone has lead."

In the aftermath of Hurricane Katrina, the number of children poisoned by lead mysteriously plummeted—a silver lining for New Orleans' poorest residents, who'd long been disproportionately exposed.

View Images From left, toddlers Jeremy George, Byron Bright, Amir Tobias, and China Scott play at New Orleans’ Kids Kingdom Academy Daycare. Soil at the day-care center was replaced by Lead Lab, a nonprofit project that helps communities clean up children's play areas. Photograph by Ben Depp, National Geographic

But a closer look reveals that the demographic turbulence that has altered the city in the decade since the devastation has also transformed the historic patterns of lead poisoning among its children. The percentage of African American women giving birth in New Orleans dwindled after Katrina; in some areas it dropped from about 65 percent to about 25 percent. Meanwhile, artists, musicians, volunteers, and counterculture aficionados—overwhelmingly young, white, and middle class—moved into the city's most lead-tainted neighborhoods, including parts of the Ninth Ward.

As a result, even though the average lead levels in the city's children and in much of its soil have declined since the hurricane, inner-city newcomers are now being exposed to a contaminant known to harm young children’s brains.

"It never occurred to me that I could be endangering my children," says Sarah Hess, a New Orleans native who'd lived in Australia, New York, and the San Francisco Bay Area before returning home in the hurricane's immediate aftermath. All three of her children have high lead levels.

Dangerous lead concentrations were recently discovered in the yards of almost two-thirds of New Orleans homes that were tested. In screenings done in 2013 alone, nearly a thousand children six years and younger—15 percent—had levels high enough to be deemed lead poisoning, according to the Louisiana Department of Health and Hospitals.

The 2005 storm exacerbated socioeconomic divides that had long existed in the city, and research shows that children facing social turbulence and economic stress can be more vulnerable to the effects of lead poisoning.

But the people of New Orleans are fighting back. They're cleaning up schools, parks, and yards in an effort to protect all the city's children.

View Images A worker uses a power sander as he helps renovate a house in the Lower Ninth Ward. Known as dry sanding, this is a primary cause of lead contamination in New Orleans. The white paint tested positive for lead in a wipe test by the photographer. Photograph by Ben Depp, National Geographic

Why Some Places Are Cleaner Post-Katrina

Over centuries, lead particles from flaking house paint, factories, and leaded gasoline have worked their way into the dust and soil. Homes built before 1978 usually contain lead-based paint, so renovation and demolition can release lead particles into the air and the soil. Before Katrina, more than 100,000 New Orleans homes had been built before 1950; an estimated 83 percent of them contained lead hazards.

Before Katrina roughly half of kids tested in neighborhoods with highly contaminated soil had lead poisoning, according to Tulane University researcher Howard Mielke, who has studied the effects of lead on children's health for more than 40 years. Three years after the hurricane, the rate had dropped to about 30 percent of kids in those same neighborhoods. In areas with less-contaminated soil, it declined even more—from roughly 25 percent before Katrina to 7.5 percent afterward. (Statewide, there was no apparent decline in lead poisoning.)

Levels of lead appear to have dropped in New Orleans soil, too, at least in some places. Between 2000 and 2006, median levels in soil dropped in more than 60 percent of the city's neighborhoods. Before Katrina, soil in 15 of the 46 neighborhoods tested exceeded 400 milligrams per kilogram of lead in soil, the amount deemed hazardous by the U.S government. After Katrina, only six neighborhoods exceeded that level.

The reasons for the drop are unknown. It could be that cleaner sediment from Lake Pontchartrain and the marshes was deposited when New Orleans was inundated, or that cleaner soil was brought in for new construction projects.

View Images Heat lightning cracks across the sky above New Orleans’ Seventh Ward, an area with a lot of lead contamination. Photograph by Ben Depp, National Geographic

But the problem hasn't gone away. The neighborhoods that remain highly contaminated were in the inner city, where flood damage was minimal. According to the United States Geological Survey, the storm surge and breached canals dumped sandy sediment on top of the city's lower-lying neighborhoods, but the cleaner sand didn't necessarily reach the higher-ground, inner-city neighborhoods.

"In the [higher-elevation] downtown and urban areas, we found shards of glass, brick fragments, Mardi Gras beads, and high levels of lead and other heavy metals," says Geoff Plumlee, a USGS research geologist. "It indicated to us that the floodwaters had essentially reworked contaminated local soils in those areas."

In many homes, lead remains elevated. The chances of getting lead poisoning are highest in inner-city blocks, which before Katrina were home to the most concentrated populations of African Americans.

Historically, black residents have been twice as likely as white residents to live in New Orleans neighborhoods with heavily contaminated soil. The lopsided burden of lead poisonings has long been a source of racial tension—which is worsened by the struggle of many African American homeowners to rebuild.

View Images Blue Wolters, 4, (at left), his mother, Marlo, and brother, Cylis, 7, live in the Ninth Ward. Tests showed high levels of lead in Cylis's blood and in the soil, so his mother covered the yard with fresh topsoil to protect her children from the metal, which can harm developing brains. Photograph by Ben Depp, National Geographic

"When the storm came through, it opened my eyes," Vanessa Gueringer, a civil rights activist and vice president of A Community Voice , a nonprofit organization in New Orleans' Upper Ninth Ward, said at a recent event. "Our neighborhoods should look like any other neighborhood. All babies deserve a healthy start, no matter the zip code."

Katrina "Jostled People Out of Households"

The demographics of some New Orleans neighborhoods shifted drastically after Katrina, says Richard Campanella, a Tulane University geographer. Many low-income black families who'd inhabited the inner city for generations—the folks Gueringer refers to as "the flavor, the gumbo, the cultural gatekeepers"—were uprooted and displaced.

"Even in unflooded areas," he says, "the trauma of Katrina jostled people out of households."

These inner-city neighborhoods, built on higher ground close to the Mississippi, largely escaped the floodwaters and the fresh soil they deposited. The subsequent housing crunch in those neighborhoods squeezed out many low-income tenants.

In the flood's aftermath, new middle-class, white residents began to settle in the high-ground neighborhoods, some drawn by construction jobs and recovery money. "Post-Katrina New Orleans was a very intense and provocative place to be," Campanella says.

View Images Sarah Hess hides the eyes of her son Thomas, 5, while he has blood drawn to check his lead levels. All three of her children have had elevated lead. Photograph by Ben Depp, National Geographic

What these newcomers didn't know is that their children—like those of earlier residents—would be poisoned by lead. Although low-income children are screened for lead through Medicaid or Head Start, many middle-income and high-income kids remain untested, even though it's a state law, according to Takeisha Davis, a pediatrician who is Louisiana’s director of public health.

A Daughter and a Son Poisoned

Sarah Hess, who moved back to New Orleans after her grandmother died in a helicopter evacuation during the flood, learned at her daughter Josie's one-year checkup that the girl had lead poisoning.

Hess and her husband, Josh, traced their baby's exposure to the crumbling lead paint inside their hundred-year-old home. They'd purchased a Faubourg St. John home from a couple who'd evacuated before Katrina and never returned.

Their two young sons have had high lead levels too. The family has spent more than $30,000 to scrub the lead from their home and yard. They take their shoes off at the front door, mop the floor, wash hands frequently, and even wipe down their four dogs to prevent lead dust from entering the house. "I feel like a crazy man wiping my dogs' paws with baby wipes each time I take them out," says Josh. "I have no clue where [the lead] is coming from."

View Images Josie Hess, 5, and Thomas Hess, 3, had high levels of lead in their blood. Their parents traced Josie’s exposure as a baby to crumbling lead paint inside their hundred-year-old home. They removed the lead, but her levels rose even higher—this time traced to a playground in the Bywater, a neighborhood along the Mississippi. Photograph by Ben Depp, National Geographic

Months after they removed the lead from their home, Josie's blood lead levels nearly doubled. This time the likely source was a playground in the Bywater, a narrow strip of a neighborhood along the Mississippi.

The playground soil contained more than 30 times the acceptable lead levels for soil, according to Mielke, the Tulane lead researcher. He and Hess worked to get the playground shut down and cleaned up. The city removed the contaminated topsoil.

Getting the Lead Out

Nearby, Marlo Wolters points to gray plastic poking out from under the woodchips and toys in her side yard. "Putting plastic on the ground is a necessary part of life here," she says.

Wolters, an herbalist and hospice worker, began squatting in an abandoned woodworking shop in 2009 and later acquired the rights to the property and two adjacent lots.

View Images Firefighters work to extinguish a burning blighted house in the Seventh Ward. Fires in structures built before 1978 can release into the air lead from old, lead-based paint. Photograph by Ben Depp, National Geographic

She discovered lead levels four times the federal guideline in the yard while testing her garden soil for nutrients. Her son, Cylis, had high lead levels too. Wolters sealed the lead-laced soil with a plastic barrier and covered it with four dump-truck loads of fresh dirt.

Wolters and Kataya Davidson's children had been poisoned by lead within blocks of each other in St. Claude, which escaped major flooding and is being gentrified. Davidson's daughter's lead levels dropped after they moved to a newer house.

Many children are not so lucky.

"I worry that children living in some communities are in the midst of a lead-dust-contaminated area with no resources to escape the situation," says Mielke.

View Images Amir Tobias, 2, plays at Kids Kingdom Academy Daycare. The play areas of many New Orleans day-care centers have been covered with clean soil to ensure that children are not exposed to lead. Photograph by Ben Depp, National Geographic

Using federal and nonprofit grants, Mielke has overseen soil cleanups at more than 30 child-care centers and church play areas, most of them in low-income and minority neighborhoods. He found that sealing off lead-contaminated soil, which may be safer and more cost effective than removing it, cost just $100 per child and significantly reduced the children's exposure.