I've worked around lead and hexavalent chrome all my working career, I've come to the conclusion that it either affects different people worse than others or the math that sets the levels needs to be reworked.
Dear N of 1. Don't draw any conclusions from your data set. It's not yet a set.
Grandpa smoked all his life and never got lung cancer. Therefore smoking is safe.
Levels should be set for the most vulnerable. Not the least.