I was just looking at this yesterday: there was a study where 75% of plant-based protein powders tested positive for lead, whereas animal-based protein powders performed much better. I think a lot of vegans drink soy and pea protein powders to get enough protein in their diet. And powders labeled "organic" did even worse on top of that. I think it would be interesting to do a study looking at vegans and exposure to heavy metals like lead/cadmium.

Here it is: https://www.cleanlabelproject.org/protein-powder/