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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
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, and triphosphoric acid. Thus, they share the Na+ or K+ cation and P3O105- anion.
2. Both substances will ultimately dissociate into the common breakdown products of the Na+ or K+ cations and the P3O105- anion, resulting in further breakdown products of pyrophosphate and orthophosphate anions.
3. Sodium and potassium cations are ubiquitous in natural waters and are considered to possess similar toxicological and ecotoxicological profiles due in part to their similar behaviour and their existence as essential micronutrients. The triphosphate anion in both substances will breakdown in the environment via the processes of hydrolysis, biotic degradation and assimilation by organisms in the environment, resulting in the breakdown products of pyrophosphate and orthophosphate anions. Ultimately, pyrophosphate anions will also breakdown to orthophosphate. It is therefore considered to be scientifically unjustified to conduct further testing on pentapotassium triphosphate as the read across can be adequately justified.


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 for cross-reference:
read-across: supporting information
Qualifier:
according to guideline
Guideline:
other: AFNOR T95E - doc 50F
Deviations:
not specified
GLP compliance:
no
Remarks:
the study predates GLP
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
Concentrations of test material tested:
10, 32, 100, 320 and 900 (mg/l).
Test organisms (species):
Skeletonema costatum
Details on test organisms:
Seawater algae: Skeletonema costatum (Ifremer Algothèque in Nantes).
Test type:
not specified
Water media type:
saltwater
Limit test:
no
Total exposure duration:
7 d
Post exposure observation period:
No data.
Hardness:
No data.
Test temperature:
20 deg C.
pH:
Refer to table below.
Dissolved oxygen:
No data.
Salinity:
No data.
Nominal and measured concentrations:
No data.
Reference substance (positive control):
yes
Remarks:
sodium nitrilotriacetate
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
> 900 mg/L
Basis for effect:
growth rate
Details on results:
For the seawater algae, the test material and the reference substance have a very weak toxicity, non-measurable under the conditions of the test.

The EC50 was not calculated as the concentrations tested did stimulate the algae growth or did not inhibit the growth sufficiently. These concentrations were already very high for the environment, and therefore, further essays were not conducted.

With the seawater algae Skeletonema, the growth is very rapid. The frequency of two measures every 24 hours did not allow the calculation of the specific rate of growth.
Results with reference substance (positive control):
The reference substance has a very weak toxicity, non-measurable under the conditions of the test.
Reported statistics and error estimates:
No data.

Table 2 - Results

Substance

Method of Analysis

EC50 (mg/l)

Reliability Limit at 95% of EC50 (mg/l)

Reference Substance

(NaNitrilotriacetate)

Specific growth rate

>320

-

Surface under growth curve (4days – 90h)

Test Material

(Na Tripolyphosphate)

Specific growth rate

>900

-

Surface under growth curve (4days – 90h)

Standard Substance

(K2Cr2O7)

Specific growth rate

1.27

1.19-1.36

Surface under growth curve (4days – 90h)

Validity criteria fulfilled:
yes
Conclusions:
The toxicity (inhibition growth) of the test material to the seawater algae was very weak. The toxicity was non-measurable under the conditions of the test. Correspondingly, the EC50 was >900 mg/L.

Executive summary:

After an exposure of  7 days, concentrations of the test material of 10 to 320 mg/l stimulated the growth by comparison with the controls, whereas at 900 mg/l it was slightly inhibitory.

The algae growth was very low in the controls and the addition of the test material at 10 and 32 mg/l led to a steady increase of the algae growth indicating that the test medium is deficient in phosphates. With 100 and 320 mg/l the growth decreased regularly but at the end of the test it was still higher than in the controls.

It is suspected that the positive effect on the algae growth due to the o-phosphate formed by hydrolysis of the test material was counterbalances by the complexation of metals like Mg2 +, Cu2 +, Zn2 +, B3 + which are essential to the algae growth.

Description of key information

The toxicity of  the analogous substance sodium tripolyphosphate to Scenedesmus subspicatus was assessed by Herschke and Cellier (1985). The EC50 after 90 hours of exposure was found to be 160 mg/l and 69.2 mg/l, for the growth rate and the biomass respectively. The criteria of validity for the growth rate, set out in the OECD Draft Guideline 202 (July 2001), were fulfilled: the coefficient of variation for the daily growth rates in the controls was less than 35% and the coefficient of variation for the average growth in replicate controls was less than 15%. Therefore only the EC50 based on the growth rate is considered. No analysis of the substance into the test medium was performed. The study was in accordance with international standard methods (ISO/TC 147/SC 5/WG 5N 84). 
The key study was selected on the basis of its reliability both in terms of the guideline / regulatory requirement and the requirement for valid data for the calculation of PNEC's for use in risk assessment.

Key value for chemical safety assessment

EC50 for marine water algae:
900 mg/L

Additional information

Read across from pentasodium triphosphate to pentapotassium triphosphate is justified on the following basis:

Both substances are inorganic compounds containing a triphosphate anion and a group 1 alkali metal cation. Both sodium and potassium cations are ubiquitous in natural waters and are considered to possess similar toxicological and ecotoxicological profiles due in part to their similar behaviour and their existence as essential micronutrients. The triphosphate anion in both substances will breakdown in the environment via the processes of hydrolysis, biotic degradation and assimilation by organisms in the environment, resulting in the breakdown products of pyrophosphate and orthophosphate anions. Ultimately, pyrophosphate anions will also breakdown to orthophosphate.

It is therefore considered to be scientifically unjustified to conduct further testing on pentapotassium triphosphate as the read across can be adequately justified.