The use of lead, mercury, copper and cadmium should be limited because they all

According to the LEED v4: Building Design + Construction Guide, lead, mercury, copper and cadmium are examples of persistent bioaccumulative toxins (PBTs) that should be limited in building products. PBTs are substances that remain in the environment for long periods of time, accumulate in living organisms, and pose health risks to humans and wildlife. One of the prerequisites for the Materials and Resources Credit, Building Product Disclosure and Optimization - Material Ingredients, is to reduce the use of products that contain PBTs above certain thresholds1. References: LEED v4: Building Design + Construction Guide, Materials and Resources Credit, Building Product Disclosure and Optimization - Material Ingredients, Option 3: Product Manufacturer Supply Chain Optimization1