Bisguanidinium phosphate

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:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
please refer also to Read Across Statement attached in Section 13

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
In this read-across approach data on guanidinium phosphate (CAS 5423-22-3, EC 226-551-9) is used to fill data gaps for bisguanidinium phosphate (CAS 5423-23-4, EC 226-552-4), in accordance with Regulation No 1907/2006 (REACH), Annex XI. The basis for this read-across is the “Read-Across Assessment Framework” (RAAF) (ECHA 2017). The read-across hypothesis for the analogue approach is that both salts bisguanidinium phosphate and guanidinium phosphate result in the identical cat- and anion in a water based environment and have consequently similar (eco)toxicological and fate properties. According to the RAAF this approach is covered by scenario 2: “Different compounds have the same type of effect(s)”.
“This scenario covers the analogue approach for which the read-across hypothesis is based on different compounds with qualitatively similar properties. For the REACH information requirement under consideration, the property investigated in a study conducted with one source substance is used to predict properties that would be observed in a study with the target substance if it were to be conducted. Qualitatively similar properties or absence of effect are predicted. The predicted property may be similar or based on a worst-case approach” (ECHA 2017).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
In this read-across approach data on guanidinium phosphate (CAS 5423-22-3, EC 226-551-9) is used to fill data gaps for bisguanidinium phosphate (CAS 5423-23-4, EC 226-552-4).
The target substance bisguanidinium phosphate and the source substance guanidinium phosphate are phosphate salts of the base guanidine.
With a pKb of 0.4, guanidine is a strong base. Therefore, in neutral water guanidine occurs fully protonated as its conjugate acid guanidinium cation. Most guanidine derivatives are in fact salts containing guanidinium cation as the conjugate acid. The source and the target substances are phosphate salts of guanidine consisting of guanidinium cation as conjugate acid and phosphate anion as conjugate base. The relation between guanidinium cation and the phosphate anion is 2:1 in the target substance and 1:1 in the source substance. As a consequence, the conjugate base in the target substance is a hydrogenphosphate (HPO4), whereas in the source substance it is a dihydrogenphosphate (H2PO4).

3. ANALOGUE APPROACH JUSTIFICATION
Based on the structural similarity, the similarity in physical chemical properties and the QSAR predicted similarity in the (eco)toxicological profile, the read-across approach is justified. Thus, the available studies for the source substance guanidinium phosphate were used to fill data gaps for bisguanidinium phosphate for several environmental and toxicological endpoints. Since phosphates are endogenous compounds occurring in nature in considerable amounts, the guanidinium ions are considered to trigger the (eco)toxicity of bisguanidinium phosphate. To account for the higher guanidine content in the target substance bisguanidinium phosphate (2:1) when compared to the source substance guanidinium phosphate (1:1), the hazard values found for the source substance in experimental studies were calculated for the target substance (please refer to 'Any other information on results').
The source substance guanidinium phosphate was tested in a growth inhibition study in algae according to OECD 201 and GLP. Pseudokirchneriella subcapitata was exposed to guanidinium phosphate under static conditions at the following nominal concentrations (final test): 0 (blank control), 10, 22, 46, 100 and 220 mg/L. The test substance significantly reduced growth rate at 22 mg/L and higher. The EC50 (72 h) for growth rate reduction was 110 mg/L and the NOEC (72 h) for growth rate reduction was 10 mg/L based on analytically confirmed nominal concentrations. The study is considered to be reliable without restrictions. Considering the guanidinium content, these values correspond to an EC50 of 75.69 mg/L, an EC10 of 11.01 mg/L and a NOEC of 6.88 mg/L for the target substance bisguanidinium phosphate (please refer to 'Any other information on results').

4. DATA MATRIX
The data matrix is included in the Read Across Statement attached in Section 13

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

assessment report

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

75.69 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: value calculated for bisguanidine phosphate

Remarks:

for details on the calculation please refer to 'Any other information on results'

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

11.01 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: value calculated for bisguanidine phosphate

Remarks:

for details on the calculation please refer to 'Any other information on results'

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

6.88 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: value calculated for bisguanidine phosphate

Remarks:

for details on the calculation please refer to 'Any other information on results'

Details on results:

- Final test
Measured concentrations: actual concentrations were in agreement with nominal and remained stable during the test period (93-113%). Given this result the effect parameters were based on the nominal test concentrations.

Biological results: growth rate was in the range of the control at 10 mg/L during the 72-hour test period, whereas the growth rate of algae exposed to 22 mg/L and higher were increasingly reduced. Statistically significant reduction of growth rate was found at test concentrations of 22 mg/L and higher. Inhibition of yield increased with increasing concentration of Guanidine phosphate (1:1) from 10 mg/L upwards resulting in >90% inhibition at and above 100 mg/L. Statistically significant inhibition of yield was found at test concentrations of 22 mg/L and higher.

Microscopic observations at the end of the test revealed a normal and healthy appearance of the exposed cells when compared to the control.

Acceptability of the test:
1. In the control, cell density increased by an average factor of >16 within two days.
2. The mean coefficient of variation for section-by-section specific growth rates in the control cultures did not exceed 35%.
3. The coefficient of variation of average specific growth rates during the whole test period in replicate control cultures did not exceed 7%.

Results with reference substance (positive control):

Potassium dichromate: The EC50 for growth rate reduction (ErC50: 0-72h) was 1.1 mg/L (95% confidence interval: 0.71 to 1.6 mg/L)

calculation of hazard values for bisguanidine phosphate

Guanidinium content in guanidinium phosphate

MW (guanidinium phosphate) = 157.04 g/mol

MW (guanidinium ion) = 60.07 g/mol

proportion of guanidinium ion in guanidinium phosphate = MW (guanidinium ion) / MW (guanidinium phosphate) = 60.07 / 157.04 = 0.38

Guanidinium content in bisguanidinium phosphate

MW (bisguanidinium phosphate) = 216.11 g/mol

MW (guanidinium ion) = 60.07 g/mol

proportion of guanidinium ion in bisguanidinium phosphate = 2 * MW (guanidinium ion) / MW (bisguanidinium phosphate) = 2 * 60.07 / 216.11 = 0.56

EC50 (guanidinium phosphate) = 110 mg/L

EC50 (guanidinium ion) = EC50 (guanidinium phosphate) * 0.38 = 42.08 mg/L

EC50 (bisguanidinium phosphate) = 42.08 mg/L / 0.56 = 75.69 mg/L

EC10 (guanidinium phosphate) = 16 mg/L

EC10 (guanidinium ion) = EC10 (guanidinium phosphate) * 0.38 = 6.12 mg/L

EC10 (bisguanidinium phosphate) = 6.12 mg/L / 0.56 = 11.01 mg/L

NOEC (guanidinium phosphate) = 10 mg/L

NOEC (guanidinium ion) = NOEC (guanidinium phosphate) * 0.38 = 3.83 mg/L

NOEC (bisguanidinium phosphate) = 3.83 mg/L / 0.56 = 6.88 mg/L

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of the present study with Pseudokirchneriella subcapitata, guanidine phosphate (1:1) reduced growth rate of this fresh water algae species significantly at 22 mg/L and higher. The EC50 for growth rate reduction (72h-ErC50) was 110 mg/L. The 72h-NOEC for growth rate reduction was 10 mg/L. Considering the guanidinium content, for the target substance bisguanidinium phosphate, these values correspond to an EC50 of 75.69 mg/L, an EC10 of 11.01 mg/L and a NOEC of 6.88 mg/L.

Executive summary:

In a 72-h toxicity study conducted according to OECD guideline 201, microalgae (Pseudokirchneriella subcapitata) were exposed to guanidine phosphate (1:1) under static conditions at the following nominal concentrations (final test): 0 (blank control), 10, 22, 46, 100 and 220 mg/L. The test substance significantly reduced growth rate at 22 mg/L and higher. The 72-h EC50 for growth rate reduction was 110 mg/L (corresponding to 36 mg guanidine/L) and the 72h-NOEC for growth rate reduction was 10 mg/L (corresponding to 3.3 mg guanidine/L) based on analytically confirmed nominal concentrations. The study is considered to be reliable without restrictions. Considering the guanidinium content, for the target substance bisguanidinium phosphate, these values correspond to an EC50 of 75.69 mg/L, an EC10 of 11.01 mg/L and a NOEC of 6.88 mg/L.

Description of key information

Read across: OECD 201, GLP, P. subcapitata, EC50 (72 h) = 75.69 mg/L, EC10 (72 h) = 11.01 mg/L, NOEC = 6.88 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:

75.69 mg/L

EC10 or NOEC for freshwater algae:

11.01 mg/L

Additional information

The source substance guanidinium phosphate was tested in a growth inhibition study in algae according to OECD 201 and GLP. Pseudokirchneriella subcapitata was exposed to guanidinium phosphate under static conditions at the following nominal concentrations (final test): 0 (blank control), 10, 22, 46, 100 and 220 mg/L. The test substance significantly reduced growth rate at 22 mg/L and higher. The EC50 (72 h) for growth rate reduction was 110 mg/L and the NOEC (72 h) for growth rate reduction was 10 mg/L based on analytically confirmed nominal concentrations. The study is considered to be reliable without restrictions. Considering the guanidinium content, these values correspond to an EC50 of 75.69 mg/L, an EC10 of 11.01 mg/L and a NOEC of 6.88 mg/L for the target substance bisguanidinium phosphate.