For lead, the overall mean dose for commercial broths was 1.73 μg, based on a mean 500 g serving size. This was compatible with a lead level of 7.01 μg/l found in the broth that had been made from chicken bone. Unfortunately, the method by which the chicken-bone broth was prepared in that study was not described .
Hsu, Der-Jen et al. “Essential and toxic metals in animal bone broths” Food & nutrition research vol. 61,1 1347478. 18 Jul. 2017, doi:10.1080/16546628.2017.1347478