Organometallics in environment and toxicology

This volume, closely related to MILS-6, deals mainly with metal(loid)-alkyl derivatives but also with the rarer aryl compounds. Most of these (commonly toxic) compounds are formed in the environment by microorganisms, but some anthropogenic input occurs as well. MILS-7, providing a most up-to-date view, is of special relevance for researchers in analytical and bioinorganic chemistry, enzymology, environmental chemistry, physiology, toxicology, and related medical fields. Volume 7, devoted to the vital and rapidly expanding research area around metal-carbon bonds (see also MILS-6) focuses on the environment. With more than 2500 references, 35 tables, and nearly 50 illustrations, many of these in color, it is an essential resource for scientists working in the wide range from organometallic chemistry, inorganic biochemistry, environmental toxicology all the way through to physiology and medicine. In 14 stimulating chapters, written by 29 internationally recognized experts, Organometallics in Environment and Toxicology highlights in an authoritative and timely manner environmental cycles of elements involving organometal(loid) compounds as well as the analytical determination of such species. Organometallic compounds contain per definition a metal-carbon bond. Therefore, the present Volume 7 is related to the preceding Volume 6, Metal-Carbon Bonds in Enzymes and Cofactors, which, as follows from its title, focused on living organisms. Volume 7 opens with two general chapters; first, environmental cycles of elements, which involve organometal(loid)s, thus enhancing the element mobility, are discussed, and next the analysis and quantification of the pertinent species are critically reviewed. The discovery that the biologically active form of vitamin B12, its coenzyme 5'-deoxyadenosylcobalamin, and the corresponding methylcobal­amin are all compounds with a cobalt-carbon bond, opened up a new area in organometallic chemistry (MILS-6). In fact, the cobalt-containing corrin-like (B12) cofactor is similar to the nickel coenzyme F430 involved in bacterial methane formation as is pointed out in Chapter 3. Furthermore, it is now recognized that methanogens are obligate anaerobes that are responsible for all biological methane production on earth (ca. 109 tons per year). In Chapters 4 and 5 the organic derivatives of tin and lead, their synthesis, use, environmental distribution, and their toxicity are summarized. The next two chapters deal with organoarsenicals, their distribution and transformation in the environment, their uptake, metabolism and toxicity, including an evaluation of their adverse effects on human health. Chapter 8 is devoted to a further metalloid: Antimony has no known biological role and has largely been overlooked as an element of environmental concern though its biomethylation most probably occurs; yet, the concentrations of methylated antimony species in the environment are low and thus it seems unlikely that they could be of any great concern. In contrast to arsenic and antimony, no methylated bismuth species have ever been found in surface waters and biota. However, as reported in Chapter 9, volatile monomethyl-, dimethyl-, and trimethylbismuthine have been produced by some anaerobic bacteria and methanogenic archaea in laboratory culture experiments, and indeed, trimethylbismuthine has been detected in landfill and sewage sludge fermentation gases. Bismuth is an element that is relatively non-toxic to humans but it is toxic to some prokaryotes. Selenium, which is treated in Chapter 10, has one of the most diverse organic chemistries. It is also one of the few elements that may biomagnify in food chains. It is generaly assumed that organic selenium species exist in ambient waters, soils, and sediments, and that they play a key role in bio­accumulation. In contrast, the diversity of organotellurium compounds is small; so far it is limited in the environment to simple methylated tellurides. Chapters 11 and 12 are devoted to mercury: The most important mercury species in the environment is clearly monomethylmercury, which is normally not released into the environment, but formed by natural processes, mainly via methylation of Hg(II) by bacteria. Its biomagnification potential is enormous; it is accumulated by more than 7 orders of magnitude, i.e., from sub ng/L concentrations to over 106 ng/kg in piscivorous fish, and thus it is of main concern for human health, especially because methylmercury is a very potent neurotoxin; its mechanisms of toxicity are discussed including neurodegerative disorders like Parkinson's and Alzheimer's disease. The two terminating Chapters 13 and 14 are again of a more general nature. First the environmental bioindication, biomonitoring, and bio­remediation with all their consequences are considered; this is followed by an account of methylated metal(loid) species in humans. Interestingly, arsenic, bismuth, selenium, and probably also tellurium have been shown to be enzymatically methylated in the human body; this has not yet been demonstrated for antimony, cadmium, germanium, indium, lead, mercury, thallium, and tin, although the latter elements can be biomethylated in the environment. The assumed and proven health effects caused by alkylated metal(loid) species are emphasized.