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P.J. Craig· S.N. Forster· R.O. Jenkins· D.P. Miller· N.Ostah . L.M. Smith· T.-A. Morris
thyl antimony compounds, their detection in the natural environment (see Section 14.1)
suggests that a biomethylation pathway for antimony must exist. Over recent years,
concern regarding the postulated involvement of antimony in the toxic gas hypothesis for sudden infant death syndrome (SIDS) has fuelled interest in the possibility of
antimony biovolatilisation. Sbz0 3 had been incorporated as a fire retardant into PVC
cot mattress covers (Turner-Report 1995) and it has been hypothesised that antimony
trihydride (SbH3) is generated from cot mattresses by microbial action (Richardson
1994). S. brevicaulis, a known methylator of inorganic arsenic, was thought to be the
fungus involved. The toxic gas hypothesis for SIDS has been disputed by several researchers (see for example Jenkins et al. 1998a, Gates et al. 1997) and there is no evidence to support toxic gases being formed in a cot environment (Anon. 1998). Jenkins
et al. (1998b) reported the formation of trimethylantimony by S. brevicaulis, which was
the first report of antimony methylation by a characterized microorganism. The fungus was grown aerobically in the presence of inorganic antimony (e.g. potassium antimony tartrate, Sbz0 3, SbzOs), and volatile antimony evolved into the headspace above
the fungal cultures was quantified by remote trapping and analysis by ICP-MS. Antimony was mobilised from both the (III) and (V) oxidation states of the element, but
occurred far less readily from the latter state. The most productive phase of antimony
volatilisation in the liquid cultures (malt extract medium) was at the end of the linear
growth phase. Identification of trimethylantimony as the biogenic antimony species
involved was established by remote trapping onto Tenax-TA, and analysis by GC-MS
and by gas chromatography-electrothermal-atomic absorption spectrometry. Jenkins
et al. (1998b) reported that exclusion of oxygen in the culture experiments was necessary for the identification to avoid trimethylantimony being oxidized to less volatile
forms. No other volatile compound containing antimony was detected in S. brevicaulis
headspace gases by these researchers, even though other methylated forms of antimony
and antimony trihydride could be detected in derivatized standards. A subsequent
paper by Jenkins et al. (1998a), reported that the yields of volatilised antimony in relation to fungal biomass were around two-fold higher on a solid medium (ca.
6 jlg antimony (g dry weight biomassr 1 ), when compared to a liquid culture. The order of antimony substrates in relation to ease of biovolatilisation was reported as:
PAT »> Sbz0 3 »> SbzOs > KSb(OH)6' These researchers found no evidence of antimony volatilisation by other fungi (Penicillium spp., Aspergillus spp., Alternaria sp.)
or bacteria (Bacillus spp.) tested. The ability of S. brevicaulis to methylate inorganic
antimony has recently been confirmed by other workers (Andrewes et al. 1998) who
detected methylantimony compounds, principally (CH3hSbO, at concentrations up to
7.1 jlg Sb rl in culture media containing inorganic antimony(III) compounds. The other
volatile antimony compounds detected - SbH3, CH 3 SbHz, (CH3hSbH and (CH3)Sb -
were considered to be very minor products of S. brevicaulis metabolism. However, these
authors did not discount the possible oxidation of trimethylantimony to produce other
methylated forms of antimony in solution. Indeed the oxidation of a dimethylantimony
precursor could produce the reported environmental methyl stibonic acids. The production of only low quantities of methylantimony compounds by S. brevicaulis, and
the ability of this fungus to grow well at high concentrations of either antimony(III)
or (V) (Jenkins et al. 1998b, Andrewes et al. 1998), suggests that antimony biomethylation does not function as an antimony detoxification mechanism for the organism.
In contrast, biomethylation of arsenic is thought to have evolved as a process for con-
P.J. Craig· S.N. Forster· R.O. Jenkins· D.P. Miller· N.Ostah . L.M. Smith· T.-A. Morris
thyl antimony compounds, their detection in the natural environment (see Section 14.1)
suggests that a biomethylation pathway for antimony must exist. Over recent years,
concern regarding the postulated involvement of antimony in the toxic gas hypothesis for sudden infant death syndrome (SIDS) has fuelled interest in the possibility of
antimony biovolatilisation. Sbz0 3 had been incorporated as a fire retardant into PVC
cot mattress covers (Turner-Report 1995) and it has been hypothesised that antimony
trihydride (SbH3) is generated from cot mattresses by microbial action (Richardson
1994). S. brevicaulis, a known methylator of inorganic arsenic, was thought to be the
fungus involved. The toxic gas hypothesis for SIDS has been disputed by several researchers (see for example Jenkins et al. 1998a, Gates et al. 1997) and there is no evidence to support toxic gases being formed in a cot environment (Anon. 1998). Jenkins
et al. (1998b) reported the formation of trimethylantimony by S. brevicaulis, which was
the first report of antimony methylation by a characterized microorganism. The fungus was grown aerobically in the presence of inorganic antimony (e.g. potassium antimony tartrate, Sbz0 3, SbzOs), and volatile antimony evolved into the headspace above
the fungal cultures was quantified by remote trapping and analysis by ICP-MS. Antimony was mobilised from both the (III) and (V) oxidation states of the element, but
occurred far less readily from the latter state. The most productive phase of antimony
volatilisation in the liquid cultures (malt extract medium) was at the end of the linear
growth phase. Identification of trimethylantimony as the biogenic antimony species
involved was established by remote trapping onto Tenax-TA, and analysis by GC-MS
and by gas chromatography-electrothermal-atomic absorption spectrometry. Jenkins
et al. (1998b) reported that exclusion of oxygen in the culture experiments was necessary for the identification to avoid trimethylantimony being oxidized to less volatile
forms. No other volatile compound containing antimony was detected in S. brevicaulis
headspace gases by these researchers, even though other methylated forms of antimony
and antimony trihydride could be detected in derivatized standards. A subsequent
paper by Jenkins et al. (1998a), reported that the yields of volatilised antimony in relation to fungal biomass were around two-fold higher on a solid medium (ca.
6 jlg antimony (g dry weight biomassr 1 ), when compared to a liquid culture. The order of antimony substrates in relation to ease of biovolatilisation was reported as:
PAT »> Sbz0 3 »> SbzOs > KSb(OH)6' These researchers found no evidence of antimony volatilisation by other fungi (Penicillium spp., Aspergillus spp., Alternaria sp.)
or bacteria (Bacillus spp.) tested. The ability of S. brevicaulis to methylate inorganic
antimony has recently been confirmed by other workers (Andrewes et al. 1998) who
detected methylantimony compounds, principally (CH3hSbO, at concentrations up to
7.1 jlg Sb rl in culture media containing inorganic antimony(III) compounds. The other
volatile antimony compounds detected - SbH3, CH 3 SbHz, (CH3hSbH and (CH3)Sb -
were considered to be very minor products of S. brevicaulis metabolism. However, these
authors did not discount the possible oxidation of trimethylantimony to produce other
methylated forms of antimony in solution. Indeed the oxidation of a dimethylantimony
precursor could produce the reported environmental methyl stibonic acids. The production of only low quantities of methylantimony compounds by S. brevicaulis, and
the ability of this fungus to grow well at high concentrations of either antimony(III)
or (V) (Jenkins et al. 1998b, Andrewes et al. 1998), suggests that antimony biomethylation does not function as an antimony detoxification mechanism for the organism.
In contrast, biomethylation of arsenic is thought to have evolved as a process for con-