Phosphonic acid, calcium salt (2:1)

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

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:

3 h

Dose descriptor:

NOEC

Effect conc.:

674 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

dihydrogenphosphite anion

Basis for effect:

inhibition of total respiration

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 674 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Remarks:

dihydrogenphosphite anion

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

841 mg/L

Nominal / measured:

estimated

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 841 mg/L

Nominal / measured:

estimated

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Validity criteria fulfilled:

yes

Conclusions:

Results indicate that KH2PO3/K2HPO3 did not induce a significant toxic effect on microorganisms up to 1000 mg/L. Values were corrected for Ca(H2PO3)2 based on the assumption that the phosphite anion is the active ingredient reposonsible for the effects, resulting in a predicted NOEC and EC50 value of 841 and >841 mg/L, respectively.

Executive summary:

The toxicity of Potassium phosphonate (KH₂PO₃/K₂HPO₃) to activated sludge was assessed in a respiration inhibition study according to  EU Commission Directive EC 440/2008, C.11.

For this purpose, aerobic activated sludge collected from the oxidation tank of the civil wastewater treatment plant “BRIANZACQUE” was incubated for 3 hours in presence of different concentrations of test item; additionally, two untreated negative controls were incubated under the same conditions.

Oxygen consumption was measured using a portable oxymeter and the inhibitory effect of the test item was expressed as percentage inhibition of the mean respiratory rate compared to negative controls.

The definitive test was carried out at five concentrations of test item in a geometric series, namely 10.0, 32.0, 100.1, 316.0 and 1000.0 mg/L as potassium phosphonate. Results are related to the nominal concentration of active ingredient, corrected on the basis of test item water content (46.16 % w/w) and of the exact weighed amount during test solutions preparation.

Moreover three abiotic controls were tested to measure the abiotic oxygen consumption. After 3 hours of exposure, abiotic controls did not show any significant oxygen consumption.

In the definitive test, after 3 hours of incubation respiration inhibition ranged from -7.3 % (in 10.0 mg/L solution) to 17.3 % (in 1000.0 mg/L solution).

Based on the obtained results, the EC50 value and the NOEC for potasium phosphonate were >1000 and 1000 mg/L, respectively. 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 a predicted NOEC and EC50 value of 841 and >841 mg Ca(H2PO3)2 /L, respectively.

Key value for chemical safety assessment

EC50 for microorganisms:

841 mg/L

EC10 or NOEC for microorganisms:

841 mg/L

Additional information

The toxicity of Potassium phosphonate (KH₂PO₃/K₂HPO₃) to activated sludge was assessed in a respiration inhibition study according to  EU Commission Directive EC 440/2008, C.11.

For this purpose, aerobic activated sludge collected from the oxidation tank of the civil wastewater treatment plant “BRIANZACQUE” was incubated for 3 hours in presence of different concentrations of test item; additionally, two untreated negative controls were incubated under the same conditions.

Oxygen consumption was measured using a portable oxymeter and the inhibitory effect of the test item was expressed as percentage inhibition of the mean respiratory rate compared to negative controls.

The definitive test was carried out at five concentrations of test item in a geometric series, namely 10.0, 32.0, 100.1, 316.0 and 1000.0 mg/L as potassium phosphonate. Results are related to the nominal concentration of active ingredient, corrected on the basis of test item water content (46.16 % w/w) and of the exact weighed amount during test solutions preparation.

Moreover three abiotic controls were tested to measure the abiotic oxygen consumption. After 3 hours of exposure, abiotic controls did not show any significant oxygen consumption.

In the definitive test, after 3 hours of incubation respiration inhibition ranged from -7.3 % (in 10.0 mg/L solution) to 17.3 % (in 1000.0 mg/L solution).

Based on the obtained results, the EC50 value and the NOEC for potasium phosphonate were >1000 and 1000 mg/L, respectively. 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 a predicted NOEC and EC50 value of 841 and >841 mg Ca(H2PO3)2 /L, respectively.