Phosphonic acid, calcium salt (2:1)

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

In the assessment of calcium dihydrogenphosphite (Ca(H2PO3)2, CAS 13780-04-6), a read-across approach is followed based on the information available for potassium phosphonate (KH2PO3/K2HPO3 EC 915-179-9). This read-across strategy is based on the hypothesis that the phosphite anion is the driver for the ecotoxicological and toxicological effects of both salts.The read-across hypothesis is justified by the immediate dissociation of calcium dihydrogenphosphate and potassium phosphonate upon dissolution in aqueous media. Both phosphite salts are highly soluble (>200 g/L) and are only present in their dissociated form in solution, i.e. the calcium or potassium cation and the phosphite anion. The transformation of the salts into the ions is rapid and complete in relevant environmental and physiological media and therefore no systemic exposure to the salts as such occurs. Exposure to the non-common cations (Ca2+ and K+) does not influence the prediction of the (eco)-toxicity because both elements are abundantly present in natural environments and emissions from these salts do not significantly increase the exposure concentration for calcium and potassium. Moreover, calcium and potassium are major essential element for living organisms.Further information is included as attachment in section 13 of IUCLID.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across: supporting information

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

ca. 18.5 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

act. ingr.

Remarks:

dihydrogenphosphite anion

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

ca. 92.7 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

act. ingr.

Remarks:

dihydrogenphosphite anion

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

ca. 23.1 mg/L

Nominal / measured:

estimated

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

ca. 115.7 mg/L

Nominal / measured:

estimated

Conc. based on:

test mat.

Basis for effect:

growth rate

Validity criteria fulfilled:

yes

Conclusions:

EC10 = 23.1 mg Ca(H2PO3)2 /LEC50 = 115.7 mg Ca(H2PO3)2 /L

Executive summary:

The influence of Potassium phosphonate (KH₂PO₃/K₂HPO₃) on the growth of the green algal species Pseudokirchneriella subcapitata, formerly known as Selenastrum capricornutum, was investigated in a 72-hour limit test according to the OECD Guideline No. 201, 2011.

For this purpose, exponentially growing test algae were exposed for 72 hours to an aqueous test medium containing the test item at only nominal concentration of 200 mg/L as active ingredient Potassium phosphonate, under defined conditions. Besides the concentration, a negative control without the test item was also prepared to check the acceptability of the algal inoculum.

The actual test concentration of phosphite were analytically confirmed at the beginning of the test (before and after having inoculated the test flasks) and at the end of the test.

Algal cell density was measured every 24 hours taking aliquots from each test concentration replicate and from negative control, diluting them in a NaCl 9 g/L solution and reading with an electronic particle counter.

At the end of the test, cell density in the negative control increased on average by a factor of 293. This value complies with the validity criterion of the test, according to OECD guideline No. 201, 2011, which indicates a minimum increase factor of 16.

The negative control also met the other validity criterion, with a coefficient of variation of daily growth rates at 72 hours of 25.9 % and a coefficient of variation of average growth in replicates negative control cultures during the test period of 1.1 %.

For the tested concentration, 200 mg/L, a significant biological effect was showed in comparison with negative control for both the endpoints, yield and growth rate, after 72 hours of exposure.

The 72-hour EC10 and EC50 values were calculated by linear interpolation. Values were recalculated for Ca(H2PO3)2 based on the assumption that the phosphite anion is the active ingredient reposonsible for the effects, resulting in predicted EC10 and EC50 values for growth rate of 23.1 mg Ca(H2PO3)2 /L and 115.7 mg Ca(H2PO3)2 /L, respectively.

Description of key information

EC10 72h (grow rate) = 23.1 mg Ca(H2PO3)2 /L

EC50 72h (grow rate) = 115.7 mg Ca(H2PO3)2 /L

Key value for chemical safety assessment

EC50 for freshwater algae:

115.7 mg/L

EC10 or NOEC for freshwater algae:

23.1 mg/L

Additional information

The influence of Potassium phosphonate (KH₂PO₃/K₂HPO₃) on the growth of the green algal species Pseudokirchneriella subcapitata, formerly known as Selenastrum capricornutum, was investigated in a 72-hour limit test according to the OECD Guideline No. 201, 2011.

For this purpose, exponentially growing test algae were exposed for 72 hours to an aqueous test medium containing the test item at only nominal concentration of 200 mg/L as active ingredient Potassium phosphonate, under defined conditions. Besides the concentration,a negative control without the test item was also prepared to check the acceptability of the algal inoculum.

The actual test concentration of phosphite were analytically confirmed at the beginning of the test (before and after having inoculated the test flasks) and at the end of the test.

Algal cell density was measured every 24 hours taking aliquots from each test concentration replicate and from negative control, diluting them in a NaCl 9 g/L solution and reading with an electronic particle counter.

At the end of the test, cell density in the negative control increased on average by a factor of 293. This value complies with the validity criterion of the test, according to OECD guideline No. 201, 2011, which indicates a minimum increase factor of 16.

The negative control also met the other validity criterion, with a coefficient of variation of daily growth rates at 72 hours of 25.9 % and a coefficient of variation of average growth in replicates negative control cultures during the test period of 1.1 %.

For the tested concentration, 200 mg potassim phosphonate /L, a significant biological effect was showed in comparison with negative control for both the endpoints, yield and growth rate, after 72 hours of exposure.

The 72-hour EC10 and EC50 values were calculated by linear interpolation. Values were recalculated for Ca(H2PO3)2 based on the assumption that the phosphite anion is the active ingredient reposonsible for the effects, resulting in predicted EC10 and EC50 values for growth rate of 23.1 mg Ca(H2PO3)2 /L and 115.7 mg Ca(H2PO3)2 /L, respectively.