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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

acute toxicity to freshwater algae: lowest EC50 0.136 mg Zn/l (Selenastrum capricornutum; single value) (neutral/high pH)
chronic toxictiy to freshwater algae: lowest NOEC 0.019 mg Zn/l (Pseudokircherniella subcapitata =Selenastrum capricornutum; geomean of 27 data)
chronic toxicity to marine algae: 12 species available which NOECs range between 0.0078 and 0.67 mg/l (dissolved concentrations)

Key value for chemical safety assessment

Additional information

Acute freshwater toxicity tests of high quality and relevancy performed according to standard protocol. Information is on 1 species which is in both the acute and chronic aquatic database on zinc the most sensitive. The lowest EC50 value is taken as reference value for classification for acute effect at neutral/high pH.

Chronic freshwater toxicity tests of high quality and relevancy according to standard protocol or equivalent. Data on 2 species, one of which the most sensitive of all freshwater organisms, second species is less sensitive.

Chronic seawater tests of high quality and relevancy according to standard protocol or equivalent. Data on 12 species, for which 3 species are in the low part of the species sensitivity distribution. One species of macro-algae is the second most sensitive of all seawater organisms.

Specific ecotoxicity of the substance

The ecotoxicity of the substance is mainly assessed by read across from information obtained on other zinc substances, i.e. ZnCl2 and ZnSO4. On zinc bis(dihydrogenphosphate), one specific algae ecotoxicity test was performed using P. subcapitata, according to OECD 201 standard protocol (Rzodeczko 2010). The observed 48hrs EC50 (growth rate) of this study was 0.28 mg Zn (measured, dissolved)/l, resulting from 0.37 mg Zn total loading/l; the observed NOEC values were 0.132 mgZn (measured, dissolved) resulting from 0.18 mg Zn/l total loading .

The species geomean EC50 value observed on P. subcapitata under similar test conditions (neutral-high pH, hardness >100mg CaCO3/l) in the soluble zinc salt studies was 0.137mg Zn (dissolved)/l. The NOEC for this substance following from the testing on soluble compounds is 19µg/l. Comparison of these reference values with the specific results obtained on the substance suggests that the ecotoxicity of the substance is similar to lower as compared to that of the soluble compounds, when the dissolved zinc fraction is considered. In other words, the validity of read across is confirmed by this specific test on P. subcapitata. It is noted that not all the zinc was dissolved from the substance in the ecotoxicity test.