It has been more than six years since America’s public companies began searching for African “conflict minerals” throughout their supply chains, and it remains difficult for trucking-related companies to know if some of their products are being made using tantalum, tin, tungsten or gold, or “3TG,” mined and refined in Congo and nine of its neighbor countries.

For the past five years, public firms across the United States have been searching out their supply chains for “conflict minerals” used to fund armed conflicts in Central Africa.