Toxicity frequently used metal

Flowever, some associated materials might be perceived as toxic. For example, complexes of osmium find frequent use as electron mediators, because of their rich chemistry, stability, and redox activity. Osmium metal and most compounds are considered nontoxic, but the neat tetroxide of osmium is a strong oxidizer and is considered highly toxic in the U.S. and very toxic by the European Union. On the other hand, the aqueous solution, osmic acid, has been injected at 1% concentration in several European clinical trials, starting in the 1970s, for treatment of arthritis and hemophilia. - No toxic effects were observed. Thus, osmium toxicity might be a question not of in vivo chemistry, but of manufacture, where a concentrated form of the oxide might need to be handled. ... 

By means of plants (used as food) and water, the soil pollutants threaten human and animal organisms and disturb natural cycles. Concentrations of heavy metals (Hg, Cu, Cd, Pb) and also other toxic metals, such as Zn, Se and As in soils are continually increasing by the action of intense human activity (civilization, industrialization, road transport). Frequently used pesticides and industrial fertilizers also make considerable contributions to the soil pollution. 

Presumptive positives are indicated by growth at 35 °C on Azide Dextrose broth, which also allows the organisms to be counted. The production of red colonies on Slanetz and Bartley s medium at 44 °C is also indicative of faecal streptococci, and this medium is frequently used in membrane filtration systems. These media may be in either the solid or liquid form, but solid media cannot be remelted once prepared. Azide is toxic and the manufacturer s advice for the preparation of these media should be followed. It may also become explosive in the presence of certain metals and should be disposed of carefully. Azide can be destroyed safely by treatment with excess sodium nitrite. 

Cobalt (II) complexes with Schiff base ligands are well known to activate dioxygen (16-18) and are frequently used to catalyze the oxidation of organic substrates (19) and to mimick mono and dioxygenases (20). This suggests that the Co-catalyzed oxidation of polyphenols could be a good alternative to the incineration of wastewaters rich in polyphenols. Moreover, the toxicity of Co(II) is much lower than that of other metal ions usually employed as oxidation catalysts. 

---