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EC number: 249-820-2
CAS number: 29736-75-2
It has been reported that the use of high
concentrations of SbCl3dissolved in water have resulted in
precipitation of antimony (Brooke et al.,1986). What is most
likely being observed is an initial formation of chloroantimonate (III)
species, which in aqueous solutions are weak, and which then hydrolyse
to oxychloride (SbOCl), which has low solubility in water, and is
further hydrolysed to Sb2O3(Filella et al.,2002b;
Filella and May, 2003). The percentage of Sb lost from solution by
precipitation in the study by Brooke et al.(1986) during a 96-h
test ranged from a low 6% for the lowest exposure concentration
(nominally 25 mg Sb/L) to 76% for the highest concentration (nominally
50 mg Sb/L). The apparent trend was to lose a greater percentage of
antimony from solution with increasing nominal concentration. The
authors improved the methods by introducing mixing and filtering to
remove the precipitate from the solution. The maximum concentration
maintained in a solution without organisms for 96 h was 35.0 mg Sb/L,
using a nominal concentration of 250 mg Sb/L. Nominal bioassay
concentrations at 50 mg Sb/L and 100 mg Sb/L using Sb2O3resulted
in measured soluble concentrations of 3.4 and 5.0 mg Sb/L, respectively.
Solutions of Sb2O3in laboratory water at nominal
concentrations of 28, 58, and 110 mg Sb/L had measured dissolved
concentrations during the 96 h experiment period of 1.9, 2.6, and 3.3 mg
Similar observations of the removal of some
antimony species from solution over time have been observed in
transformation/dissolution tests on antimony compounds in some cases
Nominal concentrations will therefore be very
misleading guides to the actual amount of dissolved antimony. At equal
nominal concentrations, readily soluble compounds like SbCl3result
in more dissolved antimony during the exposure periods used in toxicity
experiments than less soluble compounds like Sb2O3.
However, even the readily soluble compound SbCl3may at high
nominal concentrations result in lower amounts of soluble antimony.
Filella and May (2003) conducted a critical
review of all available thermodynamic data on antimony and developed a
computer speciation model of antimony in multi-component solutions,
representative of different environmental conditions. Based on the
limited data set and the subsequent speciation calculations it was shown
that antimony is exclusively present as the pentavalent Sb(OH)-6in
oxic freshwater systems and as the trivalent Sb(OH)3in anoxic
conditions, at all pH values of environmental relevance for aquatic
systems. The formation of chloride-antimony species does not appear to
be of importance under environmentally relevant conditions, as no
Sb(III) -chloride was observed under seawater conditions, and the
concentration of possible Sb(V)-chloride could not be calculated due to
a lack of data. The very few studies available on Sb(V)-chloride binding
had been performed under extremely acidic conditions to prevent
hydrolysis and could thus not be used, as it was difficult to establish
the strength of such interactions under dilute conditions relative to
other antimony species. Therefore no thermodynamic relationship of this
kind has been published.
Based on the available information on
antimony there is nothing that indicates that the difference observed in
toxicity in aquatic systems between different inorganic antimony
compounds of the same valence, such as for instance SbCl3and
Sb2O3, would be due to different antimony species
exerting different degrees/kinds of toxicity. Instead, an observed
difference in toxicity at equal nominal doses of antimony is most
probably a reflection of differences in solubility, which means that a
more soluble antimony compound will result in more dissolved antimony
capable of exerting toxicity. However, it may be that higher
concentrations of Sb compounds also reflect an increased presence of
counter ions and/or protons.
Toxicity studies in the aquatic compartment
in which only nominal antimony concentrations are reported will
therefore not be considered to be reliable in this report. However,
studies will not be rejected based solely on which antimony compound was
used in the test, or whether or not a tri- or a pentavalent compound was
used, as long as the results are considered reliable and relevant. All
effect and no-effect concentrations are reported as a concentration of
the antimony ion.
The results from six studies, i. e. Brooke et
al. (1986), Kimbal (1978), TAI (1990), Heijerick and Vangheluwe (2003),
Heijerick and Vangheluwe (2004), and LISEC (2001), all provide valid
EC50s and NOECs for fish, invertebrates and algae.
Toxicity results for marine species are
scarce. Only the results from Takayanagi (2001) are considered reliable.
None of the NOECs used to derive the PNECs in
the aquatic compartment are considered to be confounded by the additions
of counter ions (i.e. chloride) and/or protons resulting from the use of
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