https://www.consumerreports.org/health/food-safety/lead-and-cadmium-in-dark-chocolate-a8480295550/

70% of it is grown in Africa: https://en.wikipedia.org/wiki/Cocoa_bean

Lead and Cadmium have very different contamination patterns and sources. Cadmium (Cd) is taken up by the roots of the cacao trees and deposited in parts of the fruits. Mitigating this contamination includes changing the Ph of the soil, switching out tree stocks, reducing metals contamination from fertilizers and other inputs including water.

Lead has a more surprising origin. Lead contamination occurs from lead contamination at various stages of cacao production including the handling stage when cacao beans are removed from the pods, which are covered in very sticky mucilage, and fermented and dried often on the ground or on the side of the road. The origins of lead are generally human caused and may arise from the burning of leaded gasoline and diesel fuel, from leaded paint, the burning of plastics and/or garbage, the operation of smelters and other industrial processes, use of fertilizers, and emissions from coal-fired power plants, among others. Lead moves through air and gets mixed with dust particles ending up on the ground adhering to the sticky beans. These lead particles are primarily introduced during the harvesting, drying, and fermenting processes, and remain on the chocolate beans during transport to manufacturers, where they can contaminate chocolate batches during other manufacturing steps, including from deshelling and other handling processes.