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Short-term toxicity to aquatic invertebrates

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Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
24 MARCH 2010 AND 17 MAY 2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
See read-across justification report under Section 13 ‘Assessment Reports’.

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
In accordance with REACH Annex XI, Section 1.5, of Regulation (EC) No. 1907/2006 (REACH) the standard testing regime may be adapted in cases where a grouping or read-across approach has been applied.

The similarities may be based on:
(1) a common functional group
(2) the common precursors and/or the likelihood of common breakdown products via physical or biological processes, which result in structurally similar chemicals; or
(3) a constant pattern in the changing of the potency of the properties across the category

1. Both substances are inorganic salts of a monovalent cation from Group 1A of the periodic table, sodium or potassium, and phosphoric acid. Thus, they all share the Na+ or K+ cation and the PO43- anion as common functional groups. 2. All members of the group will ultimately dissociate into the common breakdown products of the Na+ or K+ cations and the PO43- anion. 3. Sodium and potassium orthophosphates have been shown to have a similar toxicological profile and physicochemical nature and therefore this data is considered to be adequate and reliable for use in read-across. Any further testing would not be scientifically justified as all substances will dissociate to their anionic and cationic forms in natural waters and these ions (Na+, K+ and PO43-) are all ubiquitous and are not considered to pose a risk of ecotoxicity.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
See read-across justification report under Section 13 ‘Assessment Reports’.

3. ANALOGUE APPROACH JUSTIFICATION
See read-across justification report under Section 13 ‘Assessment Reports’.

4. DATA MATRIX
See read-across justification report under Section 13 ‘Assessment Reports’.
Reason / purpose:
read-across: supporting information
Qualifier:
according to
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.2 (Acute Toxicity for Daphnia)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
Date of GLP inspection: 15/09/2009 Date of Signature on GLP certificate: 26/11/2009
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Chemical name: Phosphoric acid, potassium salt (2:3), dihydrate.
Synonyms (IUPAC name): Tripotassium trihydrogen diphosphate dihydrate.
Chemical formula: H3 O4 P . H2 O . 3/2 K
CAS number: 6922-99-4
Molecular weight: 346.29
Melting range: No complete melting up to 573 K
Solubility in water ( g/L, at 20 °C): 705 (pH 7)
Analytical monitoring:
yes
Details on sampling:
- Sampling method:
Water samples were taken from the control (replicates R1 – R4 pooled) and the 100 mg/l test group (replicates R1 – R2 and R3 – R4 pooled) at 0 and 48 hours for quantitative analysis.

- Sample storage conditions before analysis:
Duplicate samples were taken and stored at approximately -20°C for further analysis if necessary.

The method of analysis, stability, recovery and test preparation analyses are described in Appendix 1 (attached).
Vehicle:
no
Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION:
- Method:
A positive control (Harlan Laboratories Ltd Project No: 0039/1133) conducted approximately every six months used potassium dichromate as the reference item at concentrations of 0.32, 0.56, 1.0, 1.8 and 3.2 mg/l.
An amount of reference item (100 mg) was dissolved in reconstituted water and the volume adjusted to 1 litre to give a 100 mg/l stock solution. An aliquot (50 ml) of this stock solution was diluted in reconstituted water and the volume adjusted to 500 ml to give a 10 mg/l stock solution. Aliquots (16, 28, 50, 90 and 160 ml) of the 10 mg/l stock solution were each separately dispersed in a final volume of 500 ml of reconstituted water to give the test series of 0.32, 0.56, 1.0, 1.8 and 3.2 mg/l.
Each stock solution and prepared concentration was inverted several times to ensure adequate mixing and homogeneity.
Exposure conditions for the positive control were similar to those used in the definitive test.

The temperature was maintained at approximately 20°C.

Evaluation of data for the positive control

The EC50 value and associated confidence limits at 24 hours and the slope of the response curve and standard error were calculated by the maximum-likelihood probit method (Finney 1971) using the ToxCalc computer software package (ToxCalc 1999). The EC50 value and associated confidence limits at 48 hours were calculated by the trimmed Spearman-Karber method (Hamilton et al 1977) using the ToxCalc computer software package (ToxCalc 1999).
Probit analysis is used where two or more partial responses to exposure are shown.
When only one partial response is shown the trimmed Spearman-Karber method is appropriate.

Test organisms (species):
Daphnia magna
Details on test organisms:

TEST ORGANISM
- Common name:
Water Flea

- Source:
Derived from in-house laboratory cultures.

- Age at study initiation:
Gravid adults were isolated the day before initiation of the test, such that the young daphnids produced overnight were less than 24 hours old

- Feeding during test:
Received no food during exposure

ACCLIMATION
- Acclimation period:
Not stated


- Acclimation conditions:
Adult Daphnia were maintained in polypropylene vessels containing approximately 2 litres of reconstituted water in a temperature controlled room at approximately 20 degC.


- Type and amount of food:
Each culture was fed daily with a suspension of algae (Chlorella sp.).
The diet and diluent water are considered not to contain any contaminant that would affect the integrity or outcome of the study.

- Health during acclimation:
No mortality observed


Test Water:
The reconstituted water used for both the range-finding and definitive tests was the same as that used to maintain the stock animals.


Reconstituted Water
i) Stock Solutions
a) CaCl2.2H2O 11.76 g/l
b) MgSO4.7H2O 4.93 g/l
c) NaHCO3 2.59 g/l
d) KCl 0.23 g/l
ii) Preparation
An aliquot (25 ml) of each of solutions a-d was added to each litre (final volume) of deionised water with a conductivity of <5 µS cm-1. The reconstituted water had a pH of 7.8 ± 0.2 adjusted (if necessary) with NaOH or HCl and was aerated until the dissolved oxygen concentration was approximately air-saturation value.
The reconstituted water had an approximate theoretical total hardness of 250 mg/l as CaCO3.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
48 h
Hardness:
The reconstituted water had an approximate theoretical total hardness of 250 mg/l as CaCO3.
Test temperature:
Temperature was maintained at 20°C throughout the test.
The temperature was measured using a Hanna Instruments HI 93510 digital thermometer.
pH:
The reconstituted water had a pH of 7.8 ± 0.2 adjusted (if necessary) with NaOH or HCl.
The pH was measured using a WTW pH/Oxi 340I pH meter.
There were no treatment related differences for pH.
See Appendix 2 for results.
Dissolved oxygen:
The reconstituted water was aerated until the dissolved oxygen concentration was approximately air-saturation value.
Dissolved oxygen concentrations were recorded at the start and termination of the test. The dissolved oxygen concentration was measured using a dissolved oxygen meter.
See Appendix 2 for results.
Salinity:
not applicable
Nominal and measured concentrations:
The test concentration to be used in the definitive test was determined by a preliminary range-finding test.
In the range-finding test Daphnia magna were exposed to a series of nominal test concentrations of 0.010, 0.10, 1.0, 10 and 100 mg/l. The test item was dissolved directly in water.
An amount of test item (100 mg) was dissolved in reconstituted water and the volume adjusted to 1 litre to give the 100 mg/l test concentration. Serial dilutions from this were then performed to give further test concentrations of 10, 1.0, 0.10 and 0.010 mg/l.
Each prepared concentration was inverted several times to ensure adequate mixing and homogeneity.
Based on the results of the range-finding test a "Limit test" was conducted at a concentration of 100 mg/l to confirm that at the maximum concentration given in the OECD/EEC Test Guidelines, no immobilisation or adverse reactions to exposure were observed.

Details on test conditions:

TEST SYSTEM
- Test vessel:
As in the range-finding test 250 ml glass jars containing approximately 200 ml of test preparation were used. At the start of the test 5 daphnids were placed in each test and control vessel at random, in the test preparations. Four replicate test and control vessels were prepared. The test vessels were then covered to reduce evaporation and maintained in a temperature controlled room at approximately 20C with a photoperiod of 16 hours light and 8 hours darkness with 20 minute dawn and dusk transition periods. The daphnids were not individually identified, received no food during exposure and the test vessels were not aerated.
The control group was maintained under identical conditions but not exposed to the test item.
The test preparations were not renewed during the exposure period. Any immobilisation or adverse reactions to exposure were recorded at 24 and 48 hours after the start of exposure. The criterion of effect used was that Daphnia were considered to be immobilised if they were unable to swim for approximately 15 seconds after gentle agitation.

- Type (delete if not applicable):
closed

- Material, size, headspace, fill volume:
The test vessels were then sealed, with minimal headspace to prevent losses of the test material due to its volatile nature,

- Aeration:
None.

- Type of flow-through (e.g. peristaltic or proportional diluter):
None.

- Renewal rate of test solution (frequency/flow rate):
None.

- No. of organisms per vessel:
10 daphnids were placed in each test and control vessel at random, in the test preparations

- No. of vessels per concentration (replicates):
Duplicate test vessels were used for each test and control group.

- No. of vessels per control (replicates):
Duplicate test vessels were used for each test and control group.

- No. of vessels per vehicle control (replicates):
Duplicate test vessels were used for each test and control group.

- Biomass loading rate:
Not recorded.

- Source/preparation of dilution water:

Appendix 2 Reconstituted Water
i) Stock Solutions
a) CaCl2.2H2O 11.76 g/l
b) MgSO4.7H2O 4.93 g/l
c) NaHCO3 2.59 g/l
d) KCl 0.23 g/l
ii) Preparation
An aliquot (25 ml) of each of solutions a-d was added to each litre (final volume) of deionised water with a conductivity of <5 µS cm-1. The reconstituted water had a pH of 7.8 ± 0.2 adjusted (if necessary) with NaOH or HCl and was aerated until the dissolved oxygen concentration was approximately air-saturation value.
The reconstituted water had an approximate theoretical total hardness of 250 mg/l as CaCO3.

- Total organic carbon:
Not recorded

- Particulate matter:
Not recorded

- Metals:
Not recorded

- Pesticides:
Not recorded

- Chlorine:
Not recorded

- Alkalinity:
Not recorded

- Ca/mg ratio:
Not recorded

- Conductivity:
Not recorded

- Culture medium different from test medium:
The reconstituted water used for both the range-finding and definitive tests was the same as that used to maintain the stock animals.

- Intervals of water quality measurement:
Not recorded

OTHER TEST CONDITIONS

- Adjustment of pH:
The reconstituted water had a pH of 7.8 ± 0.2 adjusted (if necessary) with NaOH or HCl and was aerated until the dissolved oxygen concentration was approximately air-saturation value.

- Photoperiod:
a photoperiod of 16 hours light and 8 hours darkness with 20 minute dawn and dusk transition periods.

- Light intensity:
Not recorded

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Any immobilisation or adverse reactions to exposure were recorded at 24 and 48 hours after the start of exposure. The criterion of effect used was that Daphnia were considered to be immobilised if they were unable to swim for approximately 15 seconds after gentle agitation.

TEST CONCENTRATIONS

- Spacing factor for test concentrations:
Based on the results of the range-finding test a "Limit test" was conducted at a concentration of 100 mg/l to confirm that at the maximum concentration given in the OECD/EEC Test Guidelines, no immobilisation or adverse reactions to exposure were observed.

- Justification for using less concentrations than requested by guideline:
Not applicable

RANGE FINDING STUDY

- Test concentrations:

test concentrations of 0.010, 0.10, 1.0, 10 and 100 mg/l.

Reference substance (positive control):
yes
Remarks:
Potassium dichromate
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Remarks:
phosphate
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Remarks:
phosphate
Basis for effect:
mobility
Details on results:

- Behavioural abnormalities: Not recorded
- Other biological observations: None recorded

- Immobilisation of control:
Cumulative immobilisation data from the exposure of Daphnia magna to the reference material (Safepharm Laboratories Project No: 0039/0977) during the positive control are given in the following table. The relationship between percentage immobilisation and concentration at 24 and 48 hours is given in Figures 3 and 4 (see attached background material).

Inspection of the immobilisation data at 3 hours and analysis of the immobilisation data by the trimmed Spearman-Karber method (Hamilton et al 1977) at 24 hours and the probit method (Finney 1971) at 48 hours based on the nominal test concentrations gave the following results:

Time (h) EL50 (mg/l loading rate WAF) 95% Confidence limits
(mg/l loading rate WAF)
3 >3.2* -
24 0.97 0.85 - 1.1
48 0.70 0.62 - 0.80

The No Observed Effect Concentrations after 24 and 48 hours were 0.56 and 0.32 mg/l respectively. The No Observed Effect Concentration is based upon zero immobilisation at this concentration.
* A 3-Hour EC50 value was not calculated as less than 50% immobilisation occurred at this time point


- Other adverse effects control: No other effects observed.

- Abnormal responses: None recorded

- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: None recorded

- Effect concentrations exceeding solubility of substance in test medium: Observations on the test media were carried out during the mixing and testing of the WAFs.
At both the start and end of the mixing period and following the 1-Hour standing period WAFs were observed to have formed clear colourless water columns with an oily slick of test material at the water surface. Microscopic inspection of the WAFs showed no micro-dispersions or undissolved test material to be present.
Throughout the duration of the test all loading rates were observed to be clear, colourless solutions.
Results with reference substance (positive control):

- Results with reference substance valid?
Yes

- Mortality:
No mortalities recorded.

- EC50/LC50:

Cumulative immobilisation data from the exposure of Daphnia magna to the test item during the definitive test are given in Table 2.
There was no immobilisation in 20 daphnids exposed to a test concentration of 100 mg/l for a period of 48 hours. Inspection of the immobilisation data gave the following results:
Time (h) EC50 (mg/l)
24 > 100
48 > 100
The No Observed Effect Concentration after 24 and 48 hours exposure was 100 mg/l. The No Observed Effect Concentration is based upon zero immobilisation at this concentration.

DEFINITIVE TEST

Table 1.  Cumulative Immobilisation Data in the Range-finding Test

Nominal
Concentration
(mg/l)

Cumulative ImmobilisedDaphnia
(Initial Population: 10 Per Replicate)

24 Hours

48 Hours

Control

0

0

0.010

0

0

0.10

0

0

1.0

0

0

10

0

0

100

0

0

 


Table 2. Cumulative Immobilisation Data in the Definitive Test

Nominal
Concentration
(mg/l)

Cumulative Immobilised Daphnia
(Initial Population: 5 Per Replicate)

24 Hours

48 Hours

No. Per

Replicate

Total

%

No. Per

Replicate

Total

%

Control

R1

0

0

0

0

0

0

R2

0

0

R3

0

0

R4

0

0

100

R1

0

0

0

0

0

0

R2

0

0

R3

0

0

R4

0

0

 

 


Table 3. Cumulative Immobilisation Data in the Positive Control

Nominal
Concentration
(mg/l)

Cumulative ImmobilisedDaphnia
(Initial Population: 10 Per Replicate)

24 Hours

48 Hours

R1

R2

Total

%

R1

R2

Total

%

Control

0

0

0

0

0

0

0

0

0.32

0

0

0

0

0

0

0

0

0.56

1

1

2

10

3

2

5

25

1.0

7

7

14

70

10

10

20

100

1.8

10

10

20

100

10

10

20

100

3.2

10

10

20

100

10

10

20

100

 


R1– R4= Replicates 1 to 4

Validity criteria fulfilled:
yes
Conclusions:
The acute toxicity of the test item to the freshwater invertebrate Daphnia magna has been investigated and gave a 48-Hour EC50 of greater than 100 mg/l. Correspondingly the No Observed Effect Concentration was 100 mg/l.

Read-across is justified on the basis detailed in rationale for reliability above. This study is therefore considered to be of sufficient adequacy and reliability to be used as a key study and no further testing is justified.

Endpoint:
short-term toxicity to aquatic invertebrates
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
See read-across justification report under Section 13 ‘Assessment Reports’.

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
In accordance with REACH Annex XI, Section 1.5, of Regulation (EC) No. 1907/2006 (REACH) the standard testing regime may be adapted in cases where a grouping or read-across approach has been applied.

The similarities may be based on:
(1) a common functional group
(2) the common precursors and/or the likelihood of common breakdown products via physical or biological processes, which result in structurally similar chemicals; or
(3) a constant pattern in the changing of the potency of the properties across the category

1. Both substances are inorganic salts of a monovalent cation from Group 1A of the periodic table, sodium or potassium, and phosphoric acid. Thus, they all share the Na+ or K+ cation and the PO43- anion as common functional groups. 2. All members of the group will ultimately dissociate into the common breakdown products of the Na+ or K+ cations and the PO43- anion. 3. Sodium and potassium orthophosphates have been shown to have a similar toxicological profile and physicochemical nature and therefore this data is considered to be adequate and reliable for use in read-across. Any further testing would not be scientifically justified as all substances will dissociate to their anionic and cationic forms in natural waters and these ions (Na+, K+ and PO43-) are all ubiquitous and are not considered to pose a risk of ecotoxicity.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
See read-across justification report under Section 13 ‘Assessment Reports’.

3. ANALOGUE APPROACH JUSTIFICATION
See read-across justification report under Section 13 ‘Assessment Reports’.

4. DATA MATRIX
See read-across justification report under Section 13 ‘Assessment Reports’.
Reason / purpose:
read-across: supporting information
Reason / purpose:
read-across source
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Remarks:
phosphate
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Remarks:
phosphate
Basis for effect:
mobility
Details on results:

- Behavioural abnormalities: Not recorded
- Other biological observations: None recorded

- Immobilisation of control:
Cumulative immobilisation data from the exposure of Daphnia magna to the reference material (Safepharm Laboratories Project No: 0039/0977) during the positive control are given in the following table. The relationship between percentage immobilisation and concentration at 24 and 48 hours is given in Figures 3 and 4 (see attached background material).

Inspection of the immobilisation data at 3 hours and analysis of the immobilisation data by the trimmed Spearman-Karber method (Hamilton et al 1977) at 24 hours and the probit method (Finney 1971) at 48 hours based on the nominal test concentrations gave the following results:

Time (h) EL50 (mg/l loading rate WAF) 95% Confidence limits
(mg/l loading rate WAF)
3 >3.2* -
24 0.97 0.85 - 1.1
48 0.70 0.62 - 0.80

The No Observed Effect Concentrations after 24 and 48 hours were 0.56 and 0.32 mg/l respectively. The No Observed Effect Concentration is based upon zero immobilisation at this concentration.
* A 3-Hour EC50 value was not calculated as less than 50% immobilisation occurred at this time point


- Other adverse effects control: No other effects observed.

- Abnormal responses: None recorded

- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: None recorded

- Effect concentrations exceeding solubility of substance in test medium: Observations on the test media were carried out during the mixing and testing of the WAFs.
At both the start and end of the mixing period and following the 1-Hour standing period WAFs were observed to have formed clear colourless water columns with an oily slick of test material at the water surface. Microscopic inspection of the WAFs showed no micro-dispersions or undissolved test material to be present.
Throughout the duration of the test all loading rates were observed to be clear, colourless solutions.
Results with reference substance (positive control):

- Results with reference substance valid?
Yes

- Mortality:
No mortalities recorded.

- EC50/LC50:

Cumulative immobilisation data from the exposure of Daphnia magna to the test item during the definitive test are given in Table 2.
There was no immobilisation in 20 daphnids exposed to a test concentration of 100 mg/l for a period of 48 hours. Inspection of the immobilisation data gave the following results:
Time (h) EC50 (mg/l)
24 > 100
48 > 100
The No Observed Effect Concentration after 24 and 48 hours exposure was 100 mg/l. The No Observed Effect Concentration is based upon zero immobilisation at this concentration.

DEFINITIVE TEST

Table 1.  Cumulative Immobilisation Data in the Range-finding Test

Nominal
Concentration
(mg/l)

Cumulative ImmobilisedDaphnia
(Initial Population: 10 Per Replicate)

24 Hours

48 Hours

Control

0

0

0.010

0

0

0.10

0

0

1.0

0

0

10

0

0

100

0

0

 


Table 2. Cumulative Immobilisation Data in the Definitive Test

Nominal
Concentration
(mg/l)

Cumulative Immobilised Daphnia
(Initial Population: 5 Per Replicate)

24 Hours

48 Hours

No. Per

Replicate

Total

%

No. Per

Replicate

Total

%

Control

R1

0

0

0

0

0

0

R2

0

0

R3

0

0

R4

0

0

100

R1

0

0

0

0

0

0

R2

0

0

R3

0

0

R4

0

0

 

 


Table 3. Cumulative Immobilisation Data in the Positive Control

Nominal
Concentration
(mg/l)

Cumulative ImmobilisedDaphnia
(Initial Population: 10 Per Replicate)

24 Hours

48 Hours

R1

R2

Total

%

R1

R2

Total

%

Control

0

0

0

0

0

0

0

0

0.32

0

0

0

0

0

0

0

0

0.56

1

1

2

10

3

2

5

25

1.0

7

7

14

70

10

10

20

100

1.8

10

10

20

100

10

10

20

100

3.2

10

10

20

100

10

10

20

100

 


R1– R4= Replicates 1 to 4

Validity criteria fulfilled:
yes
Conclusions:
The acute toxicity of disodium hydrogenorthophosphate to the freshwater invertebrate Daphnia magna was estimated to have a 48-Hour EC50 of greater than 100 mg/l. Correspondingly the No Observed Effect Concentration was 100 mg/l.
Executive summary:

The EC50 (48h) was estimated to be greater than 100 mg/L for disodium hydrogen phosphate as found in the source study performed with tripotassium trihydrogen diphosphate dihydrate. As explained in the justification for type of information, the differences in molecular structure between disodium hydrogen phosphate and tripotassium trihydrogen diphosphate dihydrate are unlikely to lead to differences in the EC50 for aquatic invertebrates that are higher than the typical experimental error of the test method.

Description of key information

One key study to assess the short-term toxicity to aquatic invertebrates of disodium hydrogenorthophosphate exists. The study was performed under GLP conditions and to an appropriate guideline (OECD 202).
The additional supporting data provided were not considered to be adequate or reliable to fulfil neither the guideline nor the regulatory requirements. Further, there is no evidence within this data to suggest that essential validity criteria are met.
A number of literature papers relating to bioavailability and tolerance of inorganic phosphates in aquatic ecosystems are included in Section 6.6 to support the conclusions made in this endpoint.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
100 mg/L

Additional information

The acute toxicity of the test item to the freshwater invertebrate Daphnia magna has been investigated and gave a 48-Hour EC50 of greater than 100 mg/l. Correspondingly the No Observed Effect Concentration was 100 mg/l.

 

Read-across justification:

In accordance with REACH Annex XI, Section 1.5, of Regulation (EC) No. 1907/2006 (REACH) the standard testing regime may be adapted in cases where a grouping or read-across approach has been applied.

The similarities may be based on:

1. A common functional group

2. The common precursors and/or the likelihood of common breakdown products via physical or biological processes, which result in structurally similar chemicals; or

3. A constant pattern in the changing of the potency of the properties across the category

The source chemical and disodium hydrogenorthophosphate have the following similarities:

1. Both substances are inorganic salts of a monovalent cation from Group 1A of the periodic table, sodium or potassium, and phosphoric acid. Thus, they all share the Na+ or K+ cation and the PO43- anion as common functional groups.

2. All members of the group will ultimately dissociate into the common breakdown products of the Na+ or K+ cations and the PO43- anion.

3. Sodium and potassium orthophosphates have been shown to have a similar toxicological profile and physicochemical nature and therefore this data is considered to be adequate and reliable for use in read-across.

Any further testing would not be scientifically justified as all substances will dissociate to their anionic and cationic forms in natural waters and these ions (Na+, K+ and PO43-) are all ubiquitous and are not considered to pose a risk of ecotoxicity.