Short answers, pulled from the story.
Cadmium is a soft, silvery-white metal with atomic number 48 and chemical symbol Cd. It belongs to group 12 of the periodic table alongside zinc and mercury, and is chemically similar to both. Its average concentration in Earth's crust is between 0.1 and 0.5 parts per million.
Cadmium was discovered in 1817 simultaneously by Friedrich Stromeyer and Karl Samuel Leberecht Hermann, both working in Germany. Stromeyer found it as an impurity in zinc carbonate sold in pharmacies; Hermann independently identified an impurity in zinc oxide. For 100 years after its discovery, Germany remained the only significant producer of the metal.
Cadmium accumulates in the kidneys, liver, and bones and has a biological half-life of 20 to 40 years, meaning the body eliminates it extremely slowly. The International Agency for Research on Cancer classifies cadmium and its compounds as carcinogenic to humans. Tobacco smoking is the most important single source of cadmium exposure in the general population, with as much as 50% of inhaled cadmium from cigarette smoke absorbed into the body.
Itai-itai disease is a painful condition involving severe bone fractures and kidney abnormalities that affected communities along the Jinzu River in Japan in the decades before World War II. Mining operations contaminated the river with cadmium, which accumulated in local rice crops. Victims were almost exclusively post-menopausal women with low iron and mineral stores.
In 2009-86% of cadmium was used in batteries, predominantly rechargeable nickel-cadmium batteries. Cadmium is also used in control rods of nuclear reactors as a neutron poison, in electroplating for aircraft components, in pigments for paints and artists' colors, and in cadmium telluride solar panels. Its use in coatings and pigments has declined sharply since the 1980s due to environmental regulations.
A Consumer Reports test of 28 brands of dark chocolate sold in the United States in 2022 found cadmium in all of them, with 13 brands exceeding California's Maximum Allowable Dose level. Cadmium accumulates in cocoa plants from soil and phosphate fertilizers. California requires food labels to carry a warning about potential cadmium exposure on products such as cocoa powder.