The nation's top housing official is proposing lowering the level of lead that must be detected in children's blood before triggering federal action to clean up the homes where they live.

U.S. Department of Housing and Urban Development Secretary Julian Castro made the announcement Wednesday after touring Providence homes where lead paint hazards have been cleaned up using federal funds.

The proposal would reduce the level that triggers intervention from 20 micrograms per deciliter of blood to 5.

Castro said the revisions will "allow us to act more quickly to make certain the homes we support are as safe as possible. The rule would also require a full environmental investigation rather than just a basic lead assessment, allowing us to more effectively locate and remediate the source of lead exposure."

Castro said that after a 60-day public comment period, the proposed change could affect about 2.9 million subsidized and public housing units built before the country's 1978 ban on residential lead paint. Any time there is a child under 6 years old living in HUD-assisted housing and found to have elevated lead blood levels above the threshold, the housing provider must report the case so HUD can launch an environmental investigation. If lead paint or soil is found to be the culprit, the hazards must be fixed.

The revisions would align HUD limits with recommendations made in 2012 by the U.S. Centers for Disease Control and Prevention.

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Castro chose to make the announcement in Rhode Island because of the prevalence of lead paint-based contamination in the state's old urban housing stock and a yearslong state effort to track and reduce childhood lead poisoning.

The state has the fourth-oldest housing stock and the oldest rental housing stock, said Barbara Fields, executive director of Rhode Island Housing, a public agency. The state's health department says the number of lead-poisoned children has declined by about a third over the past decade, but 935 children in the state will be entering kindergarten this year with elevated levels of lead in their blood, which can cause irreversible health, learning and behavioral problems.

Advocates have pushed for the federal change, and Castro said in an interview that his agency has been considering it for some time.

"HUD has been aware that the standard ought to change," Castro said. "We started advising our grantees they ought to use the (CDC) standard. ... Now we're making it official that it's required."