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Long-term toxicity to aquatic invertebrates

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Reference
Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
also cited in OECD SIDS
Qualifier:
according to
Guideline:
other: OECD Guide-line 202, part 2 "Daphnia sp., Reproduction Test"
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
Sampling: every second day
Vehicle:
yes
Details on test solutions:
STOCK AND TEST SOLUTION AND THEIR PREPARATION:
Vehicle, solvent: HCO-50 and DMF
Concentration of vehicle/solvent: 30 mg/L

STABILITY OF THE TEST CHEMICAL SOLUTIONS:
The concentration of TBBS in the test solution at the time of preparation of the test solution was 0.019 - 0.304 mg/L (set-up value 0.02 - 0.3 mg/L) and the concentration before the exchange of solution was 0.004 - 0.021 mg/L. In addition the ratios of test material concentration measured to the set-up value in each concentration range were 88 - 135 % at the time of preparation and 5 - 25 % before the exchange.
The concentration of TBBS measured at preparation and before exchange during the exposure period were +/- 20 % of the set-up values, therefore, the measured (time-weighted average) were used.
Test organisms (species):
Daphnia magna
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
21 d
Test temperature:
19.8 - 20.3 °C
pH:
7.3 - 8.1
Dissolved oxygen:
6.7 - 8.5 mg/L
Nominal and measured concentrations:
Concentrations: 0.020, 0.040, 0.080, 0.15 and 0.3 mg/L plus control and vehicle control
Details on test conditions:
TEST SYSTEM:
Test type: Semi-static
Concentrations: Control, vehicle control, 0.020, 0.040, 0.080, 0.15 and 0.3 mg/L
Renewal of test solution: Every two days
Exposure vessel type: 1 L glass beaker
Number of replicates, individuals per replicate: 4 replicates per test concentration, 10 individuals per replicate.
Test temperature: 19.8 - 20.3 °C
Dissolved oxygen: 6.7 - 8.5 mg/L.
pH: 7.3 -8.1
Photoperiod: 16 hours light/ 8 hours dark
Reference substance (positive control):
no
Duration:
21 d
Dose descriptor:
EC50
Effect conc.:
> 0.16 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
> 0.16 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.068 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
other: parental

Number of mortalities and death rate:

Death rates of parent Daphnia in the control and vehicle control were 15 % and 7.5 % respectively by the end of the exposure period. These values fulfilled the standard of less than 20 % which is the requirement of the study.

In the test groups (based on measured concntrations) the death rates were as follows:

0.012 mg/L = 5 %

0.022 mg/L = 2.5 %

0.042 mg/L = 5 %

0.068 mg/L = 5 %

0.16 mg/L = 35 %

Day of first birth: In the control and vehicle control the first day of birth was 7 days after the start of exposure and fulfilled the standard level within 9 days which is the requirement for the study. In the test groups the day of first birth was 7 days for the 0.012, 0.022, 0.042 and 0.068 mg/L dose levels (based on measured test concentrations) and 10 days for the 0.16 dose level.

Mean value of accumulated offspring (based on measured concentrations):

Control group = 82

Vehicle control = 96

0.012 mg/L = 103

0.022 mg/L = 105

0.042 mg/L = 108

0.068 mg/L = 87

0.16 mg/L = 88

Lowest observed effect concentration (LOECr) on accumulated number of born offspring per one parent Daphnia > 0.16 mg/L (measured).

Size and condition of parent: There were no observable differences in the size of parent Daphnia between the control, the vehicle control and the 0.012 and 0.022 mg/L test groups. In comparison to the control group the parent Daphia was small on day 9 in the 0.042 mg/L group, on days 7-15 in the 0.068 mg/L group and on days 7-17 in the 0.16 mg/L group.

Dormant eggs: There were no dormant eggs in any of the groups throughout the study.

Numbers of offspring: Numbers of offspring in the 0.068 and 0.16 mg/L dose groups were inclined to decrease compared with those in the control and vehicle control groups until 14 days after exposure. However, numbers of offspring increased after 14 days in comparison with the other test groups. The numbers exceeded those in the control group and recovered to the level of those in the vehicle control group.

Validity criteria fulfilled:
not applicable
Conclusions:
It was considered that the test material might affect the larva of Daphnia by exposure of 0.068 mg/L or more after 14 days, although recovery in reproduction was observed and there is no significant difference between the 0.160 mg/L and control at 21 days of exposure (end of the test period)
Executive summary:

Regarding the reproduction rate for TBBS the 21day-NOEC for Daphnia magna was > 0.16 mg/L.

Description of key information

Regarding the reproduction rate for TBBS, the 21day-NOEC for Daphnia magna was > 0.16 mg/L.

Key value for chemical safety assessment

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

Additional information

Should read ">0.16 mg/L"

Due to fast hydrolysis of TBBS the observed effect is most probably a combined effect from both, TBBS and MBT. Thus, the value determined on TBBS was chosen as key study. However the effective concentration on invertebrates reported for MBT is less sensitive than the one reported for TBBS on algae, and hence this value was not used in further risk assessment for the PNEC estimation.