There’s a section about this in the article. Plants take up lead from the soil they grow in (This phenomenon is actually well known and sometimes employed to decontaminate soil in brownfields; those plants aren’t used for human consumption though obvs) However, the companies don’t disclose where their raw goods are sourced from so it’s impossible to know for sure.
Most of the bad ones are “plant based”. Maybe extracting the protein also concentrates any trace lead.
There’s a section about this in the article. Plants take up lead from the soil they grow in (This phenomenon is actually well known and sometimes employed to decontaminate soil in brownfields; those plants aren’t used for human consumption though obvs) However, the companies don’t disclose where their raw goods are sourced from so it’s impossible to know for sure.