From the article:

Overall, 43% of the products studied exceeded acceptable levels of lead and 35% exceeded cadmium levels, according to the study, which was based on a California law that sets maximum allowable dose levels for heavy metals in food. Food researchers often use the 1986 regulations, known as Prop 65, as a safety standard because the Food and Drug Administration doesn’t set limits on heavy metals in most foods, said Leigh Frame, director of integrative medicine at George Washington University School of Medicine and Health Sciences and lead author of the study.