CHAPTER 14 • Occurrence, Formation and Fate of Organoantimony Compounds
277
verting the highly toxic inorganic arsenic compounds found in the environment to
methylated species that are much less toxic. It remains to be seen whether trimethylantimony formation by S. brevicaulis is a consequence of antimony substituting in
the biomethylation process for arsenic. Trimethylantimony production by anaerobic
soil/sediment enrichment culture has also been described recently (Giirleyiik et al.1997;
Gates et al. 1997; Jenkins et al. 1998c). Giirleyiik et al. (1997) reported the detection of
trimethylantimony in the culture headspace of soil bacteria enrichment cultures, when
supplied with inorganic antimony in the (III) or (V) oxidation states. The incubation
conditions were designed to promote bacterial growth through the use of nitrate as
terminal electron acceptor in anaerobic respiration. This report represents the first
characterisation of a volatile antimony compound thought to arise biogenically from
an inorganic antimony substrate, although the identity of microorganisms in soils
responsible for the biomethylation was unknown. Gates et al. (1997) have also reported
the detection of trimethylantimony in the culture headspace of undefined mixed cultures. In this work, pond sediment samples were incubated under conditions (highly
proteinaceous medium) that promote growth of fermentative bacteria and supplied
with potassium antimony tartrate. Jenkins et al. (1998c), have recently reported positive results for trimethylantimony with variable frequency for four of six soils tested
and for three types of enrichment culture, designed to encourage growth of fermentative, nitrate-reducing or methane-producing bacteria (Fig. 14.2). These authors proposed that, as for arsenic, different metabolic categories of prokaryotic organisms are
able to methylate antimony and that this capability is widely distributed in the natural environment. Unlike arsenic, however, all reports so far of antimony biovolatilisation
by soil bacteria suggest that the trimethyl form is the sole or principal species produced. We are not aware of reports in the literature of antimony biomethylation by
mono septic cultures of bacteria. There is evidence, however, that monoseptic cultures
of the methane-producing bacteria Methanobacterium formicicum and Methanosarcina barkeri are capable of methylating SbC1 3 with the formation of trimethylantimony (A.V. Hirner, personal communication), which is consistent with reports of
detection of methyl antimony species in landfill and sewage gases (Feldmann and
Hirner 1995; Feldmann et al. 1994).
14.3.2
Bioreduction and Bio-Oxidation of Antimony
Microbial reduction of inorganic antimony compounds has not been demonstrated
unequivocally. Detection of antimony trihydride (SbH 3 ) in landfill gas (Feldmann and
Hirner 1995; Feldmann et al. 1994) could reflect the capability for microbial reduction
of antimony in highly reducing environments. SbH 3 has also been detected in picogram quantities in aerobic cultures of S. brevicaulis supplemented with potassium
antimony tartrate (Andrewes et al. 1998), although the biological formation of this
trihydride is yet to be confirmed. SbH3 has never been detected in controlled laboratory experiments in which trimethylantimony has been generated from inorganic
antimony compounds by cultures of anaerobic bacteria (Giirleyiik et al. 1997; Gates
et al. 1997; Jenkins et al. 1998c). In contrast, certain soil bacteria have been shown to
produce arsine (AsH3) as the sole As containing product when incubated anaerobically in the presence of arsenicals (Cheng and Focht 1979). Bioreduction of trimethyl-
277
verting the highly toxic inorganic arsenic compounds found in the environment to
methylated species that are much less toxic. It remains to be seen whether trimethylantimony formation by S. brevicaulis is a consequence of antimony substituting in
the biomethylation process for arsenic. Trimethylantimony production by anaerobic
soil/sediment enrichment culture has also been described recently (Giirleyiik et al.1997;
Gates et al. 1997; Jenkins et al. 1998c). Giirleyiik et al. (1997) reported the detection of
trimethylantimony in the culture headspace of soil bacteria enrichment cultures, when
supplied with inorganic antimony in the (III) or (V) oxidation states. The incubation
conditions were designed to promote bacterial growth through the use of nitrate as
terminal electron acceptor in anaerobic respiration. This report represents the first
characterisation of a volatile antimony compound thought to arise biogenically from
an inorganic antimony substrate, although the identity of microorganisms in soils
responsible for the biomethylation was unknown. Gates et al. (1997) have also reported
the detection of trimethylantimony in the culture headspace of undefined mixed cultures. In this work, pond sediment samples were incubated under conditions (highly
proteinaceous medium) that promote growth of fermentative bacteria and supplied
with potassium antimony tartrate. Jenkins et al. (1998c), have recently reported positive results for trimethylantimony with variable frequency for four of six soils tested
and for three types of enrichment culture, designed to encourage growth of fermentative, nitrate-reducing or methane-producing bacteria (Fig. 14.2). These authors proposed that, as for arsenic, different metabolic categories of prokaryotic organisms are
able to methylate antimony and that this capability is widely distributed in the natural environment. Unlike arsenic, however, all reports so far of antimony biovolatilisation
by soil bacteria suggest that the trimethyl form is the sole or principal species produced. We are not aware of reports in the literature of antimony biomethylation by
mono septic cultures of bacteria. There is evidence, however, that monoseptic cultures
of the methane-producing bacteria Methanobacterium formicicum and Methanosarcina barkeri are capable of methylating SbC1 3 with the formation of trimethylantimony (A.V. Hirner, personal communication), which is consistent with reports of
detection of methyl antimony species in landfill and sewage gases (Feldmann and
Hirner 1995; Feldmann et al. 1994).
14.3.2
Bioreduction and Bio-Oxidation of Antimony
Microbial reduction of inorganic antimony compounds has not been demonstrated
unequivocally. Detection of antimony trihydride (SbH 3 ) in landfill gas (Feldmann and
Hirner 1995; Feldmann et al. 1994) could reflect the capability for microbial reduction
of antimony in highly reducing environments. SbH 3 has also been detected in picogram quantities in aerobic cultures of S. brevicaulis supplemented with potassium
antimony tartrate (Andrewes et al. 1998), although the biological formation of this
trihydride is yet to be confirmed. SbH3 has never been detected in controlled laboratory experiments in which trimethylantimony has been generated from inorganic
antimony compounds by cultures of anaerobic bacteria (Giirleyiik et al. 1997; Gates
et al. 1997; Jenkins et al. 1998c). In contrast, certain soil bacteria have been shown to
produce arsine (AsH3) as the sole As containing product when incubated anaerobically in the presence of arsenicals (Cheng and Focht 1979). Bioreduction of trimethyl-