BALTIMORE — Scientists using federal grants spread fertilizer made from human and industrial wastes on yards in poor, black neighborhoods to test whether it might protect children from lead poisoning in the soil. Families were assured the sludge was safe and were never told about any harmful ingredients.

The Associated Press reviewed grant documents obtained under the Freedom of Information Act and interviewed researchers. No one involved with the $446,231 grant for the two-year study would identify the participants, citing privacy concerns. There is no evidence there was ever any medical follow-up.

Comparable research was conducted by the Agriculture Department and Environmental Protection Agency in a similarly poor, black neighborhood in East St. Louis, Ill.

The sludge, researchers said, put the children at less risk of brain or nerve damage from lead, a highly toxic element once widely used in gasoline and paint. Other studies have shown brain damage among children, often in poor neighborhoods, who ate lead-based paint that had flaked off their homes.

The idea that sludge — the leftover semisolid wastes filtered from water pollution at 16,500 treatment plants — can be turned into something harmless, even if swallowed, has been a tenet of federal policy for three decades.

Meanwhile, there has been a paucity of research into the possible harmful effects of heavy metals, pharmaceuticals, other chemicals, and disease-causing microorganisms often found in sludge. A series of reports by the EPA’s inspector general and the National Academy of Sciences between 1996 and 2002 faulted the adequacy of the science behind the EPA’s 1993 regulations on sludge. The chairman of the 2002 academy panel, Thomas Burke, a professor at the Johns Hopkins Bloomberg School of Public Health, says epidemiological studies have never been done to show whether spreading sludge on land is safe.

“There are potential pathogens and chemicals that are not in the realm of safe,” Mr. Burke told the AP. “What’s needed are more studies on what’s going on with the pathogens in sludge — are we actually removing them? The commitment to connecting the dots hasn’t been there.”

That’s not what the subjects of the Baltimore and East St. Louis research were told.

An Agriculture Department research agronomist who co-wrote the Baltimore study, Rufus Chaney, said the researchers provided the families with brochures about lead hazards, tested the soil in their yards, and gave assurances that the Orgro fertilizer was store-bought and perfectly safe. Mr. Chaney said the Baltimore neighborhoods were chosen because they were within an economically depressed area qualifying for tax incentives.

The Baltimore study concluded that phosphate and iron in sludge can increase the ability of soil to trap more harmful metals including lead, cadmium, and zinc, causing the combination to pass safely through a child’s body if eaten.

Another study investigating whether sludge might inhibit the “bioavailability” of lead — the rate it enters the bloodstream and circulates to organs and tissues — was conducted on a vacant lot in East St. Louis next to an elementary school, all of whose 300 students were black and almost entirely from low-income families. In a newsletter, the EPA-funded Community Environmental Resource Program assured local residents it was all safe.

Soil chemist Murray McBride, director of the Cornell Waste Management Institute, said he doesn’t doubt that sludge can bind lead in soil.

But when eaten, “it’s not at all clear that the sludge binding the lead will be preserved in the acidity of the stomach,” he said. “Actually thinking about a child ingesting this, there’s a very good chance that it’s not safe.”

Mr. McBride and others also questioned the choice of neighborhoods for the studies and why residents were not told about other, possibly harmful ingredients in sludge.