Fungi arsenic volatilization

Some metals, arsenic and mercury for example, may be volatilized by methylation due to activity of anaerobic microorganisms. Arsenic can be methylated by methanogenic Archaea and fungi to volatile toxic dimethylarsine and trimethylarsine or can be converted to less toxic nonvolatile methanearsonic and dimethylarsinic acids by algae [42]. 

The methylation of arsenic is entirely or almost entirely biotic (Frankenberger and Arshad, 2002), 367. Specifically, certain fungi (including yeasts) and bacteria are capable of methylating arsenic ((Bentley and Chasteen, 2002), 257-260 (Cullen and Reimer, 1989), 717-724 Chapter 4). Only limited evidence exists for the chemical (abiotic) methylation of arsenic. As mentioned earlier, some volatile arsines have been produced in the laboratory from photochemical reactions involving As(III), carboxylic acids, and ultraviolet radiation (Guo et al., 2005 McSheehy et al., 2005). 

Perhaps as much as 26 200 t of arsenic may annually volatilize into the atmosphere from soils (Matschullat, 2000), 300-301. Much of this volatilization is due to microbial activity (Frankenberger and Arshad, 2002), 363-364. Under reducing conditions in soils, fungi and other microorganisms may produce gaseous arsine and methylated arsines, such as methylarsine, dimethylarsine and trimethylarsine ((Mandal and Suzuki, 2002), 205 (Lrankenberger and Arshad, 2002), 363 (Oremland and Stolz, 2003), 939 Chapter 4). 

The stability of a reference material is of great importance since the same material may be used over a period of many years. At issue is not only the question of whether it continues to be pleasant to handle (biological materials can of course be attacked by bacteria, fungi, insects and other pests), but also that, due to evaporation or chemical reactions, the concentrations and chemical binding of some of the elements of interest may change. This is obviously of greatest concern for elements that can exist in a volatile form such as mercury and arsenic, which could thereby be lost. 

Both fungi coverted AsjOj into volatile form 47 of arsenic with P. schweinitzii being the more efficient. The formation of volatile As was increased with increasing concentration of As(in) in the growth medium. The volatile arsenic was tentatively identified as TMA. 

Both oxidation and methylation are microbial transformations involved in the redistribution and global cycling of arsenic. Oxidation involves the conversion of toxic arsenite to less toxic arsenate. Bacterial methylation of inorganic arsenic under anaerobic conditions may be a mechanism of arsenic detoxification. Fungi also transform inorganic and organic arsenic compounds into volatile methylar-sines. However, unlike methylated selenium which is nontoxic, the volatile arsine... 

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