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Toxicity to aquatic algae and cyanobacteria

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Granular Triple Superphosphate (GTSP) was tested for toxicity to algae (Pseudokirchnerella subcapitata) according OECD Guideline 201 (Alga, Growth Inhibition Test), under GLP conditions. GTSP produced a stimulation of algal growth (measured as increase in biomass) at all concentrations tested. Therefore, EbC50 and ErC50 values for inhibition of algal growth could not be calculated (> 87.6 mg GTSP/L or >100 mg/L nominal concentration). The NOEC was 87.6 mg GTSP/L (100 mg/L nominal concentration) based on the lack of significant inhibition or stimulation of algal growth (biomass and growth rate) as compared to the control.
In a study (limit test) according to OECD 201 (under GLP conditiosn) calcium sulfate dihydrate was tested for toxicity to the algae Pseudokirchnerella subcapitata. No inhibition of growth rate was observed and the LC50 was determined to be >100 mg/L..
Humic acid potassiium salt was tested in study performed according to EU Method C.3. The 72 hour - ErC50 (growth rate) was > 100 mg·L-1 (72 hour - EbC50  = 87 mg·L-1).

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Additional information

The following information on constituents of the submission substance and components of the humate-complexed superphosphate are available:

Triple Superphosphate:

Granular Triple Superphosphate (GTSP) was tested for toxicity to algae (Pseudokirchnerella subcapitata) according OECD Guideline 201 (Alga, Growth Inhibition Test), under GLP conditions. GTSP produced a stimulation of algal growth (measured as increase in biomass) at all concentrations tested that ranged from 6 to 24% compared to the control biomass.

Algal growth rate was inhibited or consistent with the growth rate of the control algae for the 4.83 and 21.6 mg GTSP/L concentrations. All other test concentrations demonstrated slight stimulation (2 to 5%) in the algal growth rate as compared to the control growth rate.

Therefore, EbC50 and ErC50 values for inhibition of algal growth could not be calculated (> 87.6 mg GTSP/L or >100 mg/L nominal concentration). The NOEC was 87.6 mg GTSP/L (100 mg/L nominal concentration) based on the lack of significant inhibition or stimulation of algal growth (biomass and growth rate) as compared to the control.

Potassium humate:

Humic acid potassium salt was tested in study performed according to EU Method C.3. Cell mass development was slightly inhibited, possibly due to the colour of the test substance and, in consequence, reduced light intensity in the test water. The 72 hour - ErC50 (growth rate) was > 100 mg·L-1 (72 hour - EbC50  = 87 mg·L-1).

Ca sulfate:

In a study (limit test) according to OECD 201 (under GLP conditions) calcium sulfate dihydrate was tested for toxicity to the alga Pseudokirchnerella subcapitata. No inhibition of growth rate was observed and the LC50 was determined to be >100 mg/L.

Taken these data together this shows that the submission substance, consisting of the humate phosphate complex and Ca sulfate does not possess aquatic toxicty to algae. A ErC50 of > 88 mg/L can be deduced from the data.