Flint's water crisis has dominated headlines in the past month, as more and more details of the "man-made disaster" continue to come to light each day. But Flint is "just the tip of the iceberg," as famed environmental activist Erin Brockovich put it in an interview with Stephen Colbert last week.

According to a Washington Post article published Thursday, an "untold" number of U.S. cities have higher rates of lead poisoning than Flint.

The Washington Post reported:

Data collected by the Centers for Disease Control and Prevention [CDC] shows that over 40 percent of the states that reported lead test results in 2014 have higher rates of lead poisoning among children than Flint.

In Flint, 4 percent of kids aged five and under tested with blood-lead levels of at least five micrograms per deciliter, the threshold of lead intake that necessitates public health action, as defined by the federal government.

Elsewhere in the country, 12 states reported that a greater percentage of kids under six years old met or surpassed that threshold. The most egregious example is Pennsylvania, where 8.5 percent of the children tested were found to have dangerously high levels of lead in their blood.

And the problem could be much worse because very few children have even been tested for elevated lead levels.

The Washington Post said:

Only 27 states (including Washington, DC) reported childhood blood lead surveillance results to the CDC’s national database for 2014, the most recent statistical set available.

These represent just a slice of the infant population. In Texas, for instance, only 184 kids were tested for lead poisoning. The state’s population of kids under six exceeds 2 million.

On the federal level, then, there is no comprehensive understanding of the extent to which the population is being exposed to hazardous amounts of lead. While the percentage of children with more than 5 micrograms per deciliter of lead has been steadily declining, the CDC says no blood-lead level in children has been determined to be “safe.”

Flint may have in recent months become synonymous with lead contamination in America, but it is by no means the only—or the most extreme —example of how the toxic element can make its way into our bodies.

Take Cleveland for example. According to the Cleveland Plain Dealer, the number of children in Cleveland exposed to lead is 2.5 times the number of children poisoned in Flint at the height of the crisis.

"And those are only the children who get tested," the Plain Dealer said. "Most don't get screened for the toxin, recommended for all kids under the age of six because of the high prevalence of lead paint in the city's housing."

Experts say the most common source of lead poisoning is lead-based paints, which can be found in older homes across the country.

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Eleven New Jersey cities and several cities in Michigan have higher rates of lead poisoning than Flint, "again, not from the water but old paint and soil contaminated by factory emissions from yesteryears," The Washington Post explained.

Louisiana, Alabama, West Virginia, Kentucky, Indiana and Oklahoma are just some of the other states that have counties with lead levels higher than Flint's, according to Vox. One county in Alabama—Houston County—found that seven of the 12 children it tested had lead poisoning in 2014, which the CDC defines as kids who have more than five micrograms of lead per deciliter of blood.

As for what's being done to address the problem, local groups and politicians are working to hold agencies accountable for monitoring lead exposure and trying to get money allocated to remove lead from old homes.

"At a press conference in Trenton, New Jersey, this week, a coalition of groups led by community development nonprofit Isles, Inc. urged Gov. Chris Christie to devote $10 million towards the Lead Hazard Control Assistance Fund, which oversees the removal of lead from old homes and other lead abatement projects," The Washington Post reported.

In Ohio, U.S. Sen. Sherrod Brown announced last week he will introduce legislation to address the threat of lead exposure in the water supply after news broke of lead poisoning in the tap water of residents of Sebring, Ohio. Brown criticized the Ohio Environmental Protection Agency for failing to tell Sebring residents for five months that their water was contaminated with lead.

The new legislation would require the U.S. Environmental Protection Agency to notify the public of dangerous lead levels in their water within 15 days, and to put a cleanup plan into place within six months. The current law gives the state Environmental Protection Agency 18 months to enact a corrosion control plan to clean up lead from toxic water supplies, Sen. Brown told The Plain Dealer.

Cleveland City Council also held its third hearing since December on the city's lead poisoning problem. "The main task the city faces is sorting through a backlog of 3,000 lead poisoning cases identified by the Ohio Department of Health that have yet to be entered into the state's tracking system," the Plain Dealer reported.

Overall, "monitoring of lead exposure is hugely inadequate—even though it remains a significant problem, especially in the country's most vulnerable communities," Vox said. While blood lead levels have decreased dramatically in the last few decades, it's still a serious problem.

"There is no standard for how states should administer their childhood lead surveillance programs, and testing isn't mandatory, despite the fact that," according to Vox, "the CDC has said 'no safe blood level in children has been identified.'"

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