5 ppm in water is toxic to rats 1-10 ppm harms plants 40 mg inhaled is fatal to humans. It is taken up more readily if a person has a calcium deficiency. Lead is used in batteries, solders, pipes, shot, insecticides, pigments, glazes, and released from smelters. There is a drive to eat lead called a lead Pica. Effects of lead poisoning are cramps, renal failure, brain damage, anemia, lead line on gums.
Lead combines with proteins at sulfhydryl groups.
Mercury Mercury is a liquid and evaporates to toxic levels. When heated it evaporates faster. Used in vapor lamps, mercury switches, thermometers, batteries, dental amalgams, and to make plastics. It was also used to treat seeds to prevent rodent and insect damage. Methyl mercury forms where there is no oxygen.