Many elements play a double role in the physiology of living organisms; some are indispensable, while most of them are toxic at elevated concentrations. The concern on the potential toxic effects of metal ions has been increasing in recent years. As a result of industrial activities and technological development, heavy metals released into the environment pose a significant threat to environment and public health because of their toxicity, accumulation in the food chain and persistence in nature.

In the sixties of last century the importance of controlling the concentration of toxic metal ions in waters for human use became apparent after the Four Big Pollution Diseases of Japan, a group of manmade diseases all caused by environmental pollution due to improper handling of industrial wastes by Japanese corporations.

Two of the Four Big Pollution Diseases of Japan, Minamata (1932-1968) and Niigata disease (1965), were due to mercury poisoning. The first one, first discovered in Minamata in 1956, is a neurological disease characterized by ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech, and in extreme cases, insanity, paralysis, coma and death. This poisoning was caused by the release of methyl mercury in the industrial wastewater from the Chisso Corporation’s chemical factory. The highly toxic mercury has been bio-accumulated in shellfish and fish in Minamata Bay and the Shiranui Sea, and human and animals deaths continued over more than 30 years. In March 2001, 2265 victims had been officially recognized (1784 of whom had died) and, in addition, individual payments of medical expenses and a medical allowance had been provided to 10072 people in Kumamoto, Kagoshima and Niigata for their mercury related diseases (http://www. nimd. go. jp/english/index. html).