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Long-term toxicity to aquatic invertebrates

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Description of key information

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. 

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
0.005 mg/L

Additional information

Beside the key toxicity study, other long term toxicity data are available.

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 invertebrates.

 

 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.