How long after exposure does it take for the first signs of lead poisoning to appear?

Variable: In baltimore there were old elegant homes that were decaying. Paint chips would be on the floor. Children in these homes would eat the chips and present to the hospital in coma due to lead toxicity. Children near freeways can have chronic exposure to lead in gasoline fumes that affects learning and behavior over many years. Blood levels can help determine degree of exposure and toxic risk.