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Long-term toxicity to aquatic invertebrates

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Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Study period:
2013
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The QSAR program is validated for the substance type (organosulphur).
Justification for type of information:
QSAR prediction: migrated from IUCLID 5.6
Guideline:
other: REACH guidance on QSARs R.6, May/June 2008
Principles of method if other than guideline:
Toxicity estimated using ECOSAR class (Thioureas) and Neutral Organic SAR (Baseline Toxicity).
Dose descriptor:
other: Chronic Value (ChV)
Effect conc.:
0.079 mg/L
Remarks on result:
other: ECOSAR Class method (Thioureas). The toxicity value was determined from a predicted SAR using established acute-to chronic ratios and ECOSAR regression techniques which are documented in the supporting Technical Reference Manual.
Dose descriptor:
other: Chronic Value (ChV)
Effect conc.:
2.775 mg/L
Remarks on result:
other: Neutral Organic SAR method (Baseline Toxicity).
Details on results:
Thioureas :

For Fish and Daphnid Acute Toxicity Values: If the log Kow of the chemical is greater than 5.0, or if the compound is solid and the LC50 exceeds the water solubility by 10X, no effects at saturation are predicted for these endpoints.

For Green Algae Acute Toxicity Values: If the log Kow of the chemical is greater than 6.4, or if the compound is solid and the EC50 exceeds the water solubility by 10X, no effects at saturation are predicted for these endpoints.

For All Chronic Toxicity Values: If the log Kow of the chemical is greater than 8.0, or if the compound is solid and the ChV exceeds the water solubility by 10X, no effects at saturation are predicted for these endpoints.
Validity criteria fulfilled:
yes
Remarks:
QSAR validated for substance type (organosulphur)
Conclusions:
1,3-dihydro-4(or5)-methyl-2H-benimidazole-2-thione, zinc salt was estimated to have a Chronic Value (ChV) to Daphnia of 0.079 mg/l using the ECOSAR Class (Thioureas) method and a ChV to Daphnia of 2.775 mg/l using the Neutral Organic SAR (Baseline Toxicity) method.
Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
Refer to Section 13.2 for read-across justification.
Reason / purpose:
read-across source
Dose descriptor:
other: Chronic Value (ChV)
Effect conc.:
0.09 mg/L
Remarks on result:
other: ECOSAR Class method (Thioureas). The toxicity value was determined from a predicted SAR using established acute-to chronic ratios and ECOSAR regression techniques which are documented in the supporting Technical Reference Manual.
Dose descriptor:
other: Chronic Value (ChV)
Effect conc.:
6.779 mg/L
Remarks on result:
other: Neutral Organic SAR method (Baseline Toxicity).
Validity criteria fulfilled:
not specified
Conclusions:
1,1,3-dihydro-5-methyl-2H-benzimidazole-2-thione was estimated to have a Chronic Value (ChV) to Daphnia of 0.09 mg/l using the ECOSAR Class (Thioureas) method and a ChV to Daphnia of 6.778 mg/l using the Neutral Organic SAR (Baseline Toxicity) method.
Executive summary:

In a one-to-one read-across approach, the substance 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (source substance) is considered appropriate for direct read-across (one-to-one) to zinc 4-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide 7-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide (target substance) for the endpoint long-term toxicity to fish. In conclusion, the test item was estimated to have a Chronic Value (ChV) to Daphnia of 0.09 mg/l using the ECOSAR Class (Thioureas) method and a ChV to Daphnia of 6.778 mg/l using the Neutral Organic SAR (Baseline Toxicity) method. A full justification for the read-across approach is presented in IUCLID Section 13.2.

Endpoint:
long-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
Refer to Section 13.2 for read-across justification document.
Reason / purpose:
read-across source
Key result
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.035 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
0.103 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.103 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
mortality
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
0.372 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
mortality
Validity criteria fulfilled:
not specified
Conclusions:
After 21 days of exposure a NOEC (reproduction) of 0.0346 mg/L (measured) and a LOEC (reproduction) of 0.1035 mg/L (measured) for the test was determined.
Executive summary:

In a one-to-one read-across approach, the substance 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (source substance) is considered appropriate for direct read-across (one-to-one) to zinc 4-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide 7-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide (target substance) for the endpoint long-term toxicity to invertebrates. In conclusion, the 21 d NOEC of the test item to Daphnia magna was 0.0346 mg/L. A full justification for the read-across approach is presented in IUCLID Section 13.2.

Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study
Qualifier:
according to
Guideline:
EU Method C.20 (Daphnia magna Reproduction Test)
Deviations:
no
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 211 (Daphnia magna Reproduction Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Vehicle:
no
Details on test solutions:
Pre-treatment of the test item:
A stock solution was prepared to give the desired series of test concentrations. 4 mg of the test item were added to 1 litre of dilution water, treated for 1 h with an ultrasonic bath and stirred for 24 hours on a magnetic stirrer. Finally undissolved particles of the test item were removed by filtration using an aseptic filter (Sartobran sterile capsules) with a pore size of 0.45 μm + 0.2 μm. The pH was measured and ranged between 7.9 and 8.0. The concentration of the filtered stock solution was determined analytically by HPLC and the appropriate amounts of the filtered stock solution were diluted with dilution to produce the different test item concentrations. 100 mL per test item concentration were taken per replicate and one neonate was added to each replicate. For each test item concentration and the control 10 replicates were prepared.
Culture and dilution water:
Reconstituted water (so-called 'M4 medium' according to OECD 211) was used for both, the maintenance of the test animals and the preparation of stock and test solutions of the test item.
Test organisms (species):
Daphnia magna
Details on test organisms:
- Name: Daphnia magna STRAUS, parthenogenetic females
- Source: Strain of Bundesgesundheitsamt Berlin
- Maintenance and Acclimatisation: A population of parthenogenetic females of synchronized age structure has been maintained for more than 15 years in the test facility under constant temperature conditions (20 +/- 1 °C) at a 16 : 8 hour light-dark photoperiod (light intensity: < 20 μE x m-2 x s-1). The culture water (so-called 'M4 medium') was partly renewed once a week. The Daphnia were exclusively fed unicellular green algae (Desmodesmus subspicatus) 'ad libitum'. Mortalities of parent Daphnia during the culture period were recorded daily in a semiquantitative way. The neonates were separated from their parent Daphnia by filtration prior to the acute test.
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
21 d
Hardness:
ranged from 14.5 °dH to 14.9 °dH (= 259 - 266 mg/L CaCO3) during the test
Test temperature:
18 - 22°C (with a maximum temperature fluctuation of +/- 1.4 °C)
pH:
7.9 - 8.1
Dissolved oxygen:
8.6 - 9.0 mg/L = 95 - 100 % O2
Nominal and measured concentrations:
Test item concentration/s: 0.01, 0.04, 0.13 and 0.4 mg/L (nominal)
Details on test conditions:
Exposure conditions:
- Test vessels : 150 mL glass beakers holding 1 neonate in 100 mL of test medium
- Experimental design : 4 concentrations plus 1 control / 1 neonate per vessel, 10 replicates per concentration/control / Semi static system (renewal of the test media on Monday, Wednesday and Friday)
- Method of initiation : neonates were placed in prepared media
- Photoperiod : 16 h light: 8 h dark
- Light intensity : not exceeding 20 μE x m-2 x s-1
- Temperature of incubation unit : 20.1 to 20.5 °C
- Aeration : none
- Food source and feeding rate: Desmodesmus subspicatus: day 0-7: 0.1 mg C / Daphnia/day /day 8-21: 0.2 mg C / Daphnia/day
- Criteria of effects : The criterion of adverse effects used in this study was the item-induced inhibitory effect on the parthenogenetic reproduction rate and the mobility behaviour/mortality rate of parent Daphnia, all effects being assessed at least three times a week.
Reference substance (positive control):
no
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.035 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
0.103 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.103 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
mortality
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
0.372 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
mortality
Details on results:
The results are expressed in terms of time-weighted mean measured concentrations. Effective concentrations ranged from 75.38 % to 97.00 % of the nominal values in the freshly prepared media and from 73.85 % to 96.25 % in the media after 48 hours, or 72 hours of exposure.

Immobilisation/mortality rate and mean reproduction rate of parent Daphnia

 Test item concentration  Mean measured concentration  Immobilisation/mortality rate of parent Daphnia  Mean reproduction rate of parent Daphnia
[mg/L]   [mg/L]  absolute  %  absolute  %
 Control  ----  1  10  79.44 [n = 9]  100
 0.01  0.0086  0  0  83.60 [n = 10]  105.24
 0.04  0.0346  2  20  72.50 [n = 8]  91.26
 0.13  0.1035  1  10  60.11 [n = 9]  75.67
 0.4  0.3725  4  40  57.00 [n = 6)  71.75

[n] = number of parent Daphnia alive at the end of the test

Validity criteria fulfilled:
yes
Remarks:
The mortality rate in the controls did not exceed 20 % by the end of the test. The dissolved oxygen concentration remained above 3 mg/L throughout the exposure period.
Conclusions:
After 21 days of exposure a NOEC (reproduction) of 0.0346 mg/L (measured) and a LOEC (reproduction) of 0.1035 mg/L (measured) for 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (MB2) was determined.
Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Study period:
2013
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The QSAR program is validated for the substance type (organosulphur).
Justification for type of information:
QSAR prediction: migrated from IUCLID 5.6
Guideline:
other: REACH guidance on QSARs R.6, May/June 2008
Principles of method if other than guideline:
Toxicity estimated using ECOSAR class (Thioureas) and Neutral Organic SAR (Baseline Toxicity).
Dose descriptor:
other: Chronic Value (ChV)
Effect conc.:
0.09 mg/L
Remarks on result:
other: ECOSAR Class method (Thioureas). The toxicity value was determined from a predicted SAR using established acute-to chronic ratios and ECOSAR regression techniques which are documented in the supporting Technical Reference Manual.
Dose descriptor:
other: Chronic Value (ChV)
Effect conc.:
6.779 mg/L
Remarks on result:
other: Neutral Organic SAR method (Baseline Toxicity).
Details on results:
Thioureas :

For Fish and Daphnid Acute Toxicity Values: If the log Kow of the chemical is greater than 5.0, or if the compound is solid and the LC50 exceeds the water solubility by 10X, no effects at saturation are predicted for these endpoints.

For Green Algae Acute Toxicity Values: If the log Kow of the chemical is greater than 6.4, or if the compound is solid and the EC50 exceeds the water solubility by 10X, no effects at saturation are predicted for these endpoints.

For All Chronic Toxicity Values: If the log Kow of the chemical is greater than 8.0, or if the compound is solid and the ChV exceeds the water solubility by 10X, no effects at saturation are predicted for these endpoints.
Validity criteria fulfilled:
yes
Remarks:
QSAR validated for substance type (organosulphur)
Conclusions:
1,1,3-dihydro-5-methyl-2H-benzimidazole-2-thione was estimated to have a Chronic Value (ChV) to Daphnia of 0.09 mg/l using the ECOSAR Class (Thioureas) method and a ChV to Daphnia of 6.778 mg/l using the Neutral Organic SAR (Baseline Toxicity) method.

Description of key information

Key Study:

Long-term toxicity to aquatic invertebrates (Daphnia magna) 21 NOECreproduction = 0.0346 mg/L; OECD 202; Safepharm (2003) (data from read-across substance 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, used in a one-to-one approach).

Supporting studies:

Long-term toxicity to aquatic invertebrates (QSAR) chronic toxicity to values (ChV) = 0.079 mg/L; ECOSAR v1.0; ECOSAR (2013)

Long-term toxicity to fish (QSAR) ChV = 0.09 mg/L; ECOSAR v1.0; ECOSAR (2013) (data from read-across substance 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, used in a one-to-one approach)

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
0.035 mg/L

Additional information

Key Study (Read across):

Currenta, 2012 - Daphnia magna were exposed to 4 different concentrations of MB2, 0.01, 0.04, 0.13 and 0.4 mg/L in a 21-day reproductive test (OECD 211, 2008), in a semi-static design with water renewal every 2 -3 days. The concnetrations were made by serially diluting a stock solution of MB2. The stock solution was preared by diluting 4 mg of MB2 into 1 litre of dilution water followed by 1 hour in an ultrasonic bath. Subsequnetly the mixutre was stirred for 24 hours and filtered (0.2 µm). Immobility and reporduction was monitored. The concnetrations were taken in old and new media throughout and the effect levels were based on time-weighted averages. MB2 was found to have a 21 day NOEC (reproduction) value of 0.0346 mg/L (measured TWA) to Daphnia magna (Currenta, 2012).

Supporting studies:

ECOSAR 2013- In accordance with the ECHA Guidance on informtaion requirements and chemical safety assessment - Chapter R.6: QSARs and grouping of chemicals (2008) two studies using QSAR predictions using ECOSAR (v1.0) were available for the derivation of Chronic Values to the invertebrate Daphnia. The results were:

ZMB2 was estimated to have a Chronic Value (ChV) to Daphnia of 0.212 mg/l using the ECOSAR Class (Thioureas) method (ECOSAR, 2013).

The read across substance, MB2, was estimated to have a Chronic Value (ChV) to Daphnia of 0.155 mg/l using the ECOSAR Class (Thioureas) method (ECOSAR, 2013).

Disscussion:

No chronic aquatic invertebrate data are available on the substance ZMB2. However, data from the close structural analog, MB2 (CAS number 53988-10-6) is available and has been used in a direct one-to-one read-across approach to address the endpoint. 

ZMB2 will dissociate at environmentally relevant pHs to form MB2 and zinc salts (LANXESS, 2018 - see Section 13.2 of IUCLID). ZMB2, is therefore, not expected to exist in the environment, or if so only very briefly. Thus, there is no need and little relevance in deriving the long-term toxicity for ZMB2. As such it is appropriate to consider the assessment of these two moieties and their environmental hazard seperately. Based on the aquatic PNECs derived for zinc (ECHA, 2018), it can be seen that basing the PNECs for ZMB2 on the MB2 effects seen in the read-across Daphnia magna reproduction study (Currenta, 2012, OECD 211, 2008), would allow for a conservative and worst-case risk assessment. The PNECs for zinc have been estimated as: PNECfreshwater 20.6 µg/L and PNECmarine 6.1 µg/L. The PNECs for MB2 have been estimated as: PNECfreshwater 1.38 µg/L and PNECmarinewater 0.138 mg/L. It can be seen that the MB2 PNECs are more than 10 -fold lower than those of zinc. Therefore, when using this read-across approach the precuationary principle applies.

Further, supporting data were generated using the United States (US) Environmental Protection Agency (EPA) Ecological Structure Activity Relationships (ECOSAR) v1.0 tool. ECOSAR is validated for organosulphates, a chemical class which includes the read-across substance MB2 (CAS Number 27231-36-3), and is structurally similar to ZMB2 (CAS Number 61617-00-3). It can be seen that the results were similar between the two, ZMB2 ChV = 0.079 mg/L vs MB2 0.09 mg/L, supporting the applicabilitly of read-across from MB2 to ZMB2. Moreover, the predictions for MB2 are comparable to those derived during the live test (Currenta, 2012).

Therefore, the results during the Currenta (2012) study on MB2 will be considered in a read-across approach for the hazard assessment of ZMB2.