“The American Conference of Industrial Hygienists (ACGIH) develops Biological Exposure Indices (BEI) as guidance values for assessing biological monitoring results in occupational settings by individuals trained in the discipline of industrial hygiene to assist in the control of potential workplace health hazards and for no other use. These values are not fine lines between safe and dangerous concentrations and should not be used by individuals without training in the discipline of industrial hygiene.” https://archive.cdc.gov/www_atsdr_cdc_gov/csem/leadtoxicity/safety_standards.html

The truth is none of the standards are based entirely on safe/not-safe levels - they know none of it is safe, but governments are hesitant to hold corporations responsible. And zero-lead is what “happens in practice” for responsible manufacturers. It’s not some unavoidable contaminant that can’t be removed.