The 26th Global COE seminar was held on July 28th, 2010 at the Center for Marine Environmental Studies (CMES), Ehime University, Japan. The guest speaker was Jurgen Gailer, a Professor in the Department of Chemistry and Environmental Science Program, University of Calgary, Canada. His talk was on “New insights into the etiology of human disease by probing the bioinorganic chemistry of the bloodstream”. This lecture was attended by many students, researchers, and members of CMES, scientists and professors from various departments and as well as members of the Southern Ehime Fisheries Research Center who has joined via teleconference. In his introduction, Dr. Gailer explained the ongoing anthropogenic emission of toxic metals and metalloid compounds into the global environment, and stated that certain populations are simultaneously exposed to increasing levels of toxic metals and metalloid compounds through their diet and drinking water. However, he said that the toxicity of a mixture cannot be accurately predicted because numerous antagonistic and synergistic effects are known to exist between and among individual compounds. Particularly, he stated that the arsenic hazard in Bangladesh and some parts of India appear as a ‘real disaster’, affecting many people physically, physiologically, mentally and economically. Dr. Gailer said 140 million people are now being affected in the world by arsenic in drinking water. Exposure to arsenic for 3-5 years with arsenic level above 200μg iAs/day can cause hyperkeratosis, liver cancer and kidney failure, etc. He also stated that the average concentrations of several toxic metals and metalloids in human blood are now firmly established, but interpretation of these results with regard to their health relevance is exceedingly difficult. Therefore, the etiology of human disease combined with the detection of several inorganic environmental pollutants in human blood suggests that a better understanding of the bioinorganic chemistry of toxic metals and metalloid compounds in the bloodstream may contribute to establishing functional connections between the exposure of humans to certain metals and specific diseases. He highlighted that in his research he found that, when rabbits are simultaneously injected with arsenite and selenite or mercuric chloride and selenite, compounds with As–Se and Hg–Se bonds were formed in the bloodstream. The combined application of liquid chromatography-inductively coupled plasma atomic emission spectrometry (ICP-AES) and X-ray absorption spectroscopy (XAS) has revealed the molecular structure of these toxicologically important compounds and provided insight into their mechanism of formation. Furthermore, Prof Gailer said that the glutathione-driven formation of these compounds in the bloodstream fundamentally links the metabolism of the environmental pollutants methyl mercury and arsenite with that of the essential ultratrace element selenium. Such a relationship establishes a feasible mechanism by which the chronic low-level exposure of various human populations to these toxic metals and metalloid compounds is linked to human diseases, including cancer and neurodegenerative diseases. In his conclusion, Prof Gailer said the molecular basis for the chronic toxicity of metals and metalloid compounds cannot be elucidated based on the reductionistic approach alone. Instead, the constant flux of essential and toxic elements through whole mammalian organisms must be taken into account and this could provide important and new insights into mammalian detoxification mechanisms. For me, the most surprising observation was his statement that in mammalian toxicology a lethal dose of selenium can be overcome by an otherwise lethal dose of arsenic. The lecture ended very much fruitful with lots of questions and suggestions by the attendees.