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EC number: 231-901-9
CAS number: 7778-39-4
From the document “Proposed EQS for Water Framework Directive Annex VIII substances: arsenic (total dissolved)”, the most severe reliable reference for freshwater aquatic invertebrates, is a LOEC for reproduction toxicity of As as arsenic pentoxide to Daphnia pulex of 0.01 mg As/l, based on nominal concentration. According to the TGD, a NOEC can be calculated by dividing the LOEC by 2, in case no NOEC was observed in a study. Based on this, a NOEC of 0.005 mg/L was calculated for Daphnia Pulex and retained for risk assessment.
Beside the key toxicity study, other long term toxicity data are
The 21d chronic toxicity of Arsenic acid to Daphnia pulex was
studied under static conditions. Daphnids were exposed to control, and
test chemical at nominal concentrations in mg/L of: 0.25; 0.50; 1.0
mg/l. The 21d-NOEC was > 1 mg/L, based on the nominal concentrations.
This study is classified as acceptable and satisfies with the
guidelines requirements for an acute toxicity study with freshwater
Another data is available, for which the result is very low:
21 days NOEC = 20 µg/L. This study is based on FIFRA guideline 72-4
which requirements are less demanding than OECD guideline 211 (40
offspring per control female instead of 60 for instance). The main
end-points in such a study are survival and reproduction. No
dose-response relationship could be obtained for any endpoint including
growth. The only NOEC that could be calculated was based on growth
evaluated from surviving adult total length at the end of the exposure.
There is no guarantee that the various groups of daphnia used for the
different arsenic concentrations were equivalent in size at the start of
the experiment and comparing the absolute value of length (instead of
growth rate) is not reliable enough.
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