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EC number: 208-901-2
CAS number: 546-46-3
(72 h) NOEC 0.015 mg/L (r-a) P. subcapitata
data on toxicity of trizinc dicitrate (CAS 546-46-3) to algae are
available. A 72 h algae study is available for the parent acid of
trizinc dicitrate, citric acid 77-92 -9 with Scendesmus quadricauda,
showing the low toxicity of the parent acid (8 d NOEC 425 mg/L,
estimated, Bringmann and Kuhn 1982, rel. 2, see the CSA for citric acid
for further details). Additionally, studies with citric acid and algae
have been waived and not taken into consideration when assessing the
hazard of citric acid since citric acid is a complexing agent and
complexes essential nutrients, namely zinc, in solution (see CSA for citric
acid for further details).
dicitrate in solution is expected to behave in the same manner as the
parent acid and zinc counter-ion separately under the conditions of
the test. The toxicity of citric acid 77-92-9 to algae is negligible,
while the toxicity of zinc ion to algae is a 72 h NOEC value of 0.005
mg/L (De Schamphaere et al. 2003, cited in Zinc RAR 2008); therefore
the toxicity of trizinc dicitrate 546-46-3 is going to be driven by
the zinc counterion and
the assessment of this substance should be based on the toxicity of
toxicity of zinc to aquatic organisms has been reviewed in zinc metal
RAR (2008). The
authors of the Zinc metal RAR (2008) have reviewed numerous studies
available for zinc and selected reliable studies that fulfil the OECD
criteria for validity. The reliable studies in the zinc metal RAR
(2008) determine a range of NOECs for algae spp. in the range 0.005 to 0.124
mg/L (as dissolved zinc).
taking into consideration the NOEC of zinc ions and neglecting the
citric acid NOEC, the 72 h NOEC for Trizinc dicitrate with
Pseudokirchneriella subcapitata is 0.015 mg/L.
72 h NOEC for Zinc is 0.005 mg/L (Zinc RAR 2008), which is equivalent
to a 72 h NOEC value of 0.08 * 2.93 = 0.015 mg/L of Trizinc dicitrate
MW(trizinc dicitrate)/MW(zinc*3) = 574.37/(65.38*3) = 2.93]
is known that abiotic factors can greatly influence the toxicity of Zn
and therefore the toxicity of trizinc dicitrate to aquatic species.
For the purpose of this assessment some specific factors can be
is the most studied and important parameter. With increasing hardness
Zn becomes less bioavailable and thus less toxic because the zinc ions
form insoluble complexes with Ca and Mg ions. In a chronic study by
Paulauskis and Winner (1988) with D. magnait was demonstrated that by
increasing the total water hardness as CaCO3 y 50 to 200 mg/L, the
NOEC for reproduction increased 6 -fold, i.e. a decrease in toxicity.
The NOEC for survival was less affected
to hardness, with increasing pH the toxicity of Zn towards aquatic
organisms decreases since Zn becomes less bioavailable by binding to
H+ ions. In a study from De Schamphelaere et al. (2003) it was
demonstrated that pH changed the toxicity to invertebrates by a factor
of 3 to 4 with D. magna, by a factor of 2 to 3 with rainbow trout
Oncorhynchus mykiss, and by a factor of >20 with the algae
Pseudokirchneriella subcapitata. However a clear relationship between
toxicity and pH could not be established with the exception of algae
(Zinc metal RAR 2008).
background concentration of Zn will influence the test organism's
sucsceptibility to the metal. Higher background concentrations of zinc
ensure that the animals are more tolerant to zinc, and therefore a
decrease in toxicity is observed (e.g. Muyssen and Janssen, 2000 with
factors affecting the bioavailability and thus the ecotoxicity of Zn
to aquatic organisms are the DOC concentration (by Zn binding with the
organic carbon, Zinc metal RAR 2008) and alkalinity (by Zn binding
with the carbonates, Zinc metal RAR 2008).
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