IIRC the old standard was 40 micrograms per deciliter of blood. That was arbitrarily lowered to 20 micrograms/dl by EPA. Now a recent article states: “Pediatricians ring alarm bells when a child's blood tests show lead levels above 10 ug/dL (micrograms per deciliter) of blood. A microgram is a millionth of a gram; a deciliter is one-tenth of a liter.”
Does anyone know the hard science on lead poisoning? Why aren't all our ancestors brain damaged due to lead exposure as it was used so extensively in plumbing and most homes still have a lead water service?