ABSTRACT
Cadmium contamination of rice in Japan caused the dreadful itai-itai disease. Cadmium is mainly used for surface treatment, as a stabilizing agent in plastic and many alloys. The major sources of cadmium dispersion are cadmium content in phosphorus fertilizers and air pollutants from coal-fired power plants. Cadmium forms chloride complexes that are less toxic than the cadmium ions. Formation of the complexes increases the solubility of cadmium in water. It is therefore important to consider the cadmium−chloride complexes by examination of cadmium pollution cases. It is recommendable to set up regional mass balances for all major toxic substances and particularly for the most toxic heavy metals such as mercury, lead, cadmium, and copper. A mass balance for Danish agriculture land is shown to illustrate the use of regional mass balance in environmental management. Cadmium has a carcinogenic and teratogenic effect. It is also highly toxic, as indicated by the LD50 value for rats—70−90 mg/kg. The uptake efficiency of cadmium from food is about the same as for other heavy metals—7−10%. Cadmium is accumulated mainly in the kidneys. It is possible to express the cadmium accumulation in the human body as a function of time by the following differential equation: dCd/dt = daily uptake − excretion coefficient * Cd = dCd/dt = 0.0025 − 0.0001 * Cd mg/24 hr. At steady state, the cadmium concentration becomes 0.0025/0.0001 = 25 mg, which (of course) is close to the average value at the age of 50 years.
