Environmental Engineering Reference
In-Depth Information
biomethylation of organotin compounds, were found both in silt and sand.
The methylation products are mono-, di-, tri- and tetra-methyl derivatives.
The tetraorganotins do not generally have highly physiologically active prop-
erties; therefore, they are used mainly as intermediates for the production
of other organotin compounds. The amount of monomethytin compounds is
abouthalfofthatofthetotalmethyltincompoundsinthesiltsampleandis
about 1
10 000 of that of TBT. Hence the total amount of these products is
very small compared with that of the TBT compounds. At present, the volatile
methyl derivatives are considered to be of little concern in causing environ-
mental problems.
Volatile butylmetyltin compounds formed by the biomethylation were re-
ported in the 1980s by Maquire and coworkers [120, 121], Rapsomanikis
and Harrison [101], recently by Yonezawa et al. [105], and Vella and co-
workers [104, 122-124]. In 1994, Yonezawa et al. [105] reported that these
biomethylations represent one path of degradation of the triorganotin com-
pounds through microbial activities in the sediment. The degradation of
the triorganotin compounds proceeds by two methylation reactions with
a sulfate-reducing microbial activity and debutylation with a nitrate-reducing
microbial activity.
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6
Degradation of Organotin Compounds by Organisms and Their Metabolites
Yamaoka et al. [125-134] screened TPT-degrading bacteria with a simple
technique using post-column high-performance liquid chromatography with
3,3
,4
,7-tetrahydro-fluavone as a post-column reagent for the determination
of TPT and its metabolite, DPT. They found that TPT degradation was cat-
alyzed by low-molecular-mass substances in the extract [126].
Yellow compound pyoverdins were isolated from
Pseudomonas chloro-
raphis
. The degradation of TPT by pyoverdin (20 mg) was carried out in
distilled water (30 ml) containing 6
gL
-1
concentration of TPT at 20
◦
Cfor
96 h in aerobic conditions. TPT and DPT in seawater were degraded to MPT
with pyoverdins [127]. The degradation of TPT in seawater increased with
elevating temperature between 4 and 37
◦
C. The optimum degradation of
TPT in seawater was observed at pH 7-8.5. The degradation of TPT and
DPT in distilled water can be faster than in seawater. Also, the degradation
of TPT in both water and seawater was faster than that of DPT while TBT,
DBT, MBT and MPT in water and seawater were not degraded by the py-
overdin [127].
The TPT-degrading bacterium
Pseudomonas chlororaphis
CNR15 produces
extracellular yellow substances to degrade TPT. F-I is suc-pyoverdin from
P. c h l o r o r a p h i s
ATCC 9446, which is a peptide siderophore produced by fluor-
escent pseudomonads. F-IIa and F-IIb are also pyoverdins [130]. F-I and F-IIa
µ
