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Short-term toxicity to aquatic invertebrates

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Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Justification for type of information:
REPORTING FORMAT FOR THE CATEGORY APPROACH
Please refer also to the read-across statement attached in section 13

1. HYPOTHESIS FOR THE CATEGORY APPROACH (ENDPOINT LEVEL)
The target and the source substances are structurally similar substances that share the common organometallic core structure consisting of a central zinc metal bonded to four alkyldithiophosphate esters (ligands) by coordinate covalent bonds -Zn[(S2P(OR)2]2. Structural variations between the target and the source substances are related only to the alkyl (R) groups of the alkyldithiophosphate ligands. The substances in this category give thus rise to an (identical) common compound Phosphorodithioic acid moiety that can be released by the breakage of ester bonds and dissociation from the Zinc complex to which the organism would be exposed if the target substance was tested in the toxicity studies. Exposure to the parent compounds (non-transformed constituents) and to the counter alkyl alcohols, possibly released by hydrolysis of P-O bonds – non-common compounds – would not influence the prediction of the (eco)toxicological properties because they are considered to have the same biological targets and to cause the same type of effects through a common underlying mechanism due to the same functional groups (zinc cation, phosphorodithioic cation and aliphatic alcohol anionic moieties). The impurities of the target and the source substances are not expected to impact the prediction because they are identical or, if slightly structural different, belong to the same class of compounds with the same functional groups and their percentages are very low.

2. CATEGORY APPROACH JUSTIFICATION (ENDPOINT LEVEL )
The aquatic toxicity of the ZDDP category members is mainly influenced by the molecular weight (depends on the length of alkyl rests), and the water solubility. Numerous studies demonstrate decreasing toxicity with the increased chain length. Since the alkyl rests in the target substance are shorter (isobutyl, isopropyl and pentyl) than that of the source substance CAS 4259-15-8 (ethylhexyl) and the water solubility is higher (40.7 mg/L vs 9.1 mg/L for the target and the source substance, respectively) a higher bioavailability is expected for the target substance when compared to source substance CAS 4259-15-8. Regarding the source substance CAS 84605-29-8, the water solubility is with 2764 mg/L above the one of the target substance. Therefore, this source substance is expected to be more bioavailable than the target substance. Thus, data on CAS 84605-29-8 can serve as worst-case data for the target substance. In general, intrinsic toxicities of substances may be the same, because they have the same functional groups and thus the same mode of action. Therefore, taking into account the similar predicted environmental fate and behaviour, the target substance is considered not to possess significantly higher toxicity potential to aquatic environment then the source substance. Thus, the results of the acute toxicity studies in aquatic invertebrates and in algae available for the source substance are considered to be similar if these studies were conducted with the target substance. However, the target substance should be classified as aquatic toxic with long-lasting effects because its alkyl chains lengths are shorter (< C8) and thus aquatic toxicity potential cannot be ruled out.
Key result
Duration:
48 h
Dose descriptor:
EL50
Effect conc.:
75 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Remarks on result:
other: 65 - 87 mg/L
Duration:
48 h
Dose descriptor:
NOELR
Effect conc.:
32 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Details on results:
- Behavioural abnormalities: NDA
- Observations on body length and weight: NDA
- Other biological observations: NDA
- Mortality of control: 0
- Other adverse effects control: None noted
- Abnormal responses: NDA
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: not specified
- Effect concentrations exceeding solubility of substance in test medium: N/A
Results with reference substance (positive control):
EC50/LC50: A positive control using potassium dichromate as the reference material was conducted using test concentrations of 0.32, 0.56, 1.0, 1.8 and 3.2 mg/L. Exposure conditions for the positive control were the same as to those used in the definitive tests. Inspection of immobilisation results gave a 48 hour EC50 of 1.2 mg/L with 95% confidence limits from 1.0 to 1.3 mg/L. The No Observed Effect Concentration after 24 and 48 hours were 1.0 mg/L and 0.56 mg/L respectively. The results from the positive control with potassium dichromate were within the normal range for this reference material.
Reported statistics and error estimates:
An estimate of the EL50 value at 24 hours was given by inspection of the immobilization data. The EL50 value and associated confidence limits at 48 hours were calculated by the maximum likelihood probit method using the ToxCalc computer software package.

Table. Cumulative Immobilisation Data in the Definitive Test

Nominal Loading Rate (mg/L)

Cumulative Immobilised Daphnia (10 per replicate)

24 hours

48 hours

R1

R2

Total

%

R1

R2

Total

%

Control

0

0

0

0

0

0

0

0

10

0

0

0

0

0

0

0

0

18

0

0

0

0

0

0

0

0

32

0

0

0

0

0

0

0

0

56

0

0

0

0

2

1

3

15

100

0

2

2

10

8

9

17

85

Validity criteria fulfilled:
yes
Conclusions:
The acute toxicity of the test material to the freshwater invertebrate Daphnia magna has been investigated and gave a 48-h EL50 value of 75 mg/L nominal loading rate with 95 % confidence limits of 65 to 87 mg/L. The No Observed Effect Loading rate was 32 mg/l nominal loading rate.
Executive summary:

Introduction. A study was performed to assess the acute toxicity of the test material to Daphnia magna. The method followed that described in the OECD 202 Guidelines, “Daphnia sp, Acute Immobilisation Test and Reproduction Test”.

Methods.  Following a preliminary range finding test, twenty daphnids (2 replicates of 10 animals) were exposed to water accommodated fractions of the test material over a range of nominal loading rates of 10, 18, 32, 56, and 100 mg/L for 48 hours at a temperature of 21°C under static test conditions. The number of immobilized Daphnia were recorded after 24 and 48 hours.

 

Results.The 48 h EL50 for the test material to Daphnia magna based on nominal loading rates was 75 mg/L with 95% confidence limits of 65 to 87 mg/L.The No Observed Effect Loading rate was 32 mg/l nominal loading rate WAF.

Given that toxicity cannot be attributed to a single component or mixture of components but to the test material as a whole, the results were based on nominal loading rates only.

Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Justification for type of information:
REPORTING FORMAT FOR THE CATEGORY APPROACH
Please refer also to the read-across statement attached in section 13

1. HYPOTHESIS FOR THE CATEGORY APPROACH (ENDPOINT LEVEL)
The target and the source substances are structurally similar substances that share the common organometallic core structure consisting of a central zinc metal bonded to four alkyldithiophosphate esters (ligands) by coordinate covalent bonds -Zn[(S2P(OR)2]2. Structural variations between the target and the source substances are related only to the alkyl (R) groups of the alkyldithiophosphate ligands. The substances in this category give thus rise to an (identical) common compound Phosphorodithioic acid moiety that can be released by the breakage of ester bonds and dissociation from the Zinc complex to which the organism would be exposed if the target substance was tested in the toxicity studies. Exposure to the parent compounds (non-transformed constituents) and to the counter alkyl alcohols, possibly released by hydrolysis of P-O bonds – non-common compounds – would not influence the prediction of the (eco)toxicological properties because they are considered to have the same biological targets and to cause the same type of effects through a common underlying mechanism due to the same functional groups (zinc cation, phosphorodithioic cation and aliphatic alcohol anionic moieties). The impurities of the target and the source substances are not expected to impact the prediction because they are identical or, if slightly structural different, belong to the same class of compounds with the same functional groups and their percentages are very low.

2. CATEGORY APPROACH JUSTIFICATION (ENDPOINT LEVEL)
The aquatic toxicity of the ZDDP category members is mainly influenced by the molecular weight (depends on the length of alkyl rests), and the water solubility. Numerous studies demonstrate decreasing toxicity with the increased chain length. Since the alkyl rests in the target substance are shorter (isobutyl, isopropyl and pentyl) than that of the source substance CAS 4259-15-8 (ethylhexyl) and the water solubility is higher (40.7 mg/L vs 9.1 mg/L for the target and the source substance, respectively) a higher bioavailability is expected for the target substance when compared to source substance CAS 4259-15-8. Regarding the source substance CAS 84605-29-8, the water solubility is with 2764 mg/L above the one of the target substance. Therefore, this source substance is expected to be more bioavailable than the target substance. Thus, data on CAS 84605-29-8 can serve as worst-case data for the target substance. In general, intrinsic toxicities of substances may be the same, because they have the same functional groups and thus the same mode of action. Therefore, taking into account the similar predicted environmental fate and behaviour, the target substance is considered not to possess significantly higher toxicity potential to aquatic environment then the source substance. Thus, the results of the acute toxicity studies in aquatic invertebrates and in algae available for the source substance are considered to be similar if these studies were conducted with the target substance. However, the target substance should be classified as aquatic toxic with long-lasting effects because its alkyl chains lengths are shorter (< C8) and thus aquatic toxicity potential cannot be ruled out.
Key result
Duration:
48 h
Dose descriptor:
EL50
Effect conc.:
23 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mortality
Remarks on result:
other: 20 - 25 mg/L
Duration:
48 h
Dose descriptor:
NOELR
Effect conc.:
10 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mortality
Duration:
24 h
Dose descriptor:
NOELR
Effect conc.:
10 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Results with reference substance (positive control):
n/a
Reported statistics and error estimates:
Analysis of the immobilization data was by the probit method at 24 hours and the trimmed spearman karber method at 48 hours based on the nominal loading rates.

Table. Cumulative Immobilisation Data in the Definitive Test

Nominal Loading Rate (mg/L)

Cumulative Immobilised Daphnia (10 per replicate)

24 hours

48 hours

R1

R2

Total

%

R1

R2

Total

%

Control

0

0

0

0

0

0

0

0

10

0

0

0

0

0

0

0

0

18

1

0

1

5

2

1

3

15

32

2

4

6

30

10

10

20

100

56

2

5

7

35

10

9

19

95

100

5

5

10

50

10

10

20

100

Validity criteria fulfilled:
yes
Conclusions:
The acute toxicity of the test material to the freshwater invertebrate Daphnia magna has been investigated and gave a 48-Hour EL*50 value of 23 mg/L nominal loading rate with 95% confidence limits of 20 to 25 mg/L. The No Observed Effect Loading rate at 48 hours was 10 mg/l nominal loading rate.
Executive summary:

A study was performed to assess the acute toxicity of the test material to Daphnia magna. The method followed that described in the OECD 202 Guidelines, “Daphnia sp, Acute Immobilisation Test and Reproduction Test”. Following a preliminary range finding test, twenty daphnids (2 replicates of 10 animals) were exposed to water accommodated fractions of the test material over a range of nominal loading rates of 10, 18, 32, 56, and 100 mg/L for 48 hours at a temperature of 21 degrees C under static test conditions. The number of immobilized Daphnia were recorded after 24 and 48 hours. 

The 48-Hour EL50 for the test material to Daphnia magna based on nominal loading rates was 23 mg/L with 95% confidence limits of 20 to 25 mg/L. The No Observed Effect Loading rate was 10 mg/l nominal loading rate WAF.

Given that toxicity cannot be attributed to a single component or mixture of components but to the test material as a whole, the results were based on nominal loading rates only.

Description of key information

The acute toxicity of the test material (CAS 4259 -15 -8) to the freshwater invertebrate Daphnia magna has been investigated in a GLP compliant study according to OECD Guideline 202. The quality of the study was assessed with Klimisch 2. A 48-h EL50 value of 75 mg/L nominal loading rate with 95 % confidence limits of 65 to 87 mg/L was obtained. The No Observed Effect Loading rate was 32 mg/L nominal loading rate.

The acute toxicity of the test material (CAS 84605 -29 -8) to the freshwater invertebrate Daphnia magna has been investigated in a GLP compliant study according to OECD Guideline 202. The quality of the study was assessed with Klimisch 2. A 48-h EL50 value of 23 mg/L nominal loading rate with 95 % confidence limits of 20 to 25 mg/L was obtained. The No Observed Effect Loading rate was 10 mg/L nominal loading rate.

The values for both substances slightly differ, but this is in range with the category approach, where nevertheless the members of one category may have different values.

For CSA the lower value is choosen as worst-case-approach .

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
23 mg/L

Additional information

Based on the available data, which are slightly different, the lower value was choosen for the chemical safety assessment as a worst-case approach.

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