Gases released from anaerobic wastewater treatment facilities contain considerable amounts of volatile methyl and hydride derivatives of metals and metalloids, such as arsine (AsH 3 ), monomethylarsine, dimethylarsine, trimethylarsine, trimethylbismuth (TMBi), elemental mercury (Hg 0 ), trimethylstibine, dimethyltellurium, and tetramethyltin. Most of these compounds could be shown to be produced by pure cultures of microorganisms which are representatives of the anaerobic sewage sludge microflora, i.e., methanogenic archaea (Methanobacterium formicicum, Methanosarcina barkeri, Methanobacterium thermoautotrophicum), sulfate-reducing bacteria (Desulfovibrio vulgaris, D. gigas), and a peptolytic bacterium (Clostridium collagenovorans). Additionally, dimethylselenium and dimethyldiselenium could be detected in the headspace of most of the pure cultures. This is the first report of the production of TMBi, stibine, monomethylstibine, and dimethylstibine by a pure culture of M. formicicum.Volatile methyl and hydride derivatives of metal(loid)s are found in gases released from natural environments such as sediments, wetlands (40), and hydrothermal springs (26), as well as from anthropogenic environments such as wastewater treatment plants and waste deposits (18). Some of the compounds are of anthropogenic origin, for example, alkylated tin and lead derivatives, whereas others are produced in environmental settings either due to chemical transalkylation or due to biologically mediated methylation and hydride formation (the addition of a formal hydride ion mediated by an organism) (11,36). The production of volatile metal(loid) compounds is a significant part of the biogeochemical cycles of metals (e.g., Bi, Hg, and Sn) and metalloids (e.g., As, Sb, Se, and Te) because of the increased mobility of the resultant compounds. Additionally, most of the volatile derivatives exhibit higher toxicity than their inorganic counterparts, since organic derivatives are lipophilic and are thus more biologically active (35,36). Exceptions are arsenic and selenium, in which cases the inorganic, nonmethylated forms are more toxic than the methylated derivatives (14).Following the pioneering work of Gosio (23) and Challenger et al. (6, 7), the mechanism for the biomethylation of arsenic has been studied extensively with various fungi (10, 15), bacteria (3), archaea (3, 30), and mammals (1, 38, 41), including humans (13). As proposed by Challenger, the biomethylation of selenium and tellurium follows the same mechanism as arsenic but, in general, studies investigating these processes are rather rare (16,22,38). Mercury biomethylation, on the other hand, has been studied in more detail because of poisonings by methylmercury compounds (4,8,29,33). Although stibine has been implicated as a cause in sudden infant death syndrome (31), up to now, only trimethylantimony was detected as a biovolatilization product of antimony in the headspace of soil samples (24) and of pure cultures of Scopulariopsis brevicaulis (12,27). The biomethylation of inorg...

No abstract

No abstract

No abstract

The biochemical modification of the metals and metalloids mercury, tin, arsenic, antimony, bismuth, selenium, and tellurium via formation of volatile metal hydrides and alkylated species (volatile and involatile) performs a fundamental role in determining the environmental processing of these elements. In most instances, the formation of such species increases the environmental mobility of the element, and can result in bioaccumulation in lipophilic environments. While inorganic forms of most of these compounds are well characterized (e.g., arsenic, mercury) and some of them exhibit low toxicity (e.g., tin, bismuth), the more lipid-soluble organometals can be highly toxic. Methylmercury poisoning (e.g., Minamata disease) and tumor development in rats after exposure to dimethylarsinic acid or tributyltin oxide are just some examples. Data on the genotoxicity (and the neurotoxicity) as well as the mechanisms of cellular action of organometal(loid) compounds are, however, scarce. Many studies have shown that the production of such organometal(loid) species is possible and likely whenever anaerobic conditions (at least on a microscale) are combined with available metal(loid)s and methyl donors in the presence of suitable organisms. Such anaerobic conditions can exist within natural environments (e.g., wetlands, pond sediments) as well as within anthropogenic environmental systems (e.g., waste disposal sites and sewage treatments plants). Some methylation can also take place under aerobic conditions. This article gives an overview about the environmental distribution of organometal(loid) compounds and the potential hazardous effects on animal and human health. Genotoxic effects in vivo and in vitro in particular are discussed.