Registration Dossier

Administrative data

Endpoint:
fish early-life stage toxicity
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP study, fully adequate for assessment.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1999
Report Date:
1999

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other: ASTM E1241-92
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
Methyl Tertiary-Butyl Ether (MTBE)
Purity: 97.83%
ARCO, Los Angeles, CA

Sampling and analysis

Analytical monitoring:
yes
Details on sampling:
120 ml of test solution was retained from each exposure chamber at test initiation and preserved for analysis. Approximately 180 mL of test solution was drawn from the center of the chamber using three draws of a 60-ml Malgene syringe, and composited in a glass beaker. From there, aliquots of the sample were delivered to three, 40-ml VOA bottles, carefully avoiding the inclusion of any air bubbles, and the bottles were sealed. The samples were refrigerated at 4 °C prior to shipping to Columbia Analytical Services, Inc. (CAS), Kelso, Washington, for analysis. Sampling was repeated each week of the test for all test chambers in all treaments which had surviving organisms at the previous analytical sampling period.

Test solutions

Vehicle:
no
Details on test solutions:
The dilution/control water used in this study was FCETL process water obtained from Horsetooth Reservoir.
A continuous-flow serial diluter with a dilution factor of 0.625 was used for the test. Test solutions were delivered to the test chambers through polyethylene tubing (Nalgene 489). The dilution system delivered five test concentrations and a dilution water control to 24 test chambers.

Test organisms

Test organisms (species):
Pimephales promelas
Details on test organisms:
Fathead minnow (Pimephales promelas) eggs (within 24 hours from fertilization) were used and obtained from ENSR FCETL in-house cultures. Adult fathead minnows are maintained in flowing laboratory process water from Horsetooth Reservoir water (test dilution water). After hatching, organisms were fed 0.5 ml per test chamber brine shrimp nauplii.

Study design

Test type:
flow-through
Water media type:
freshwater
Limit test:
no
Total exposure duration:
31 d
Post exposure observation period:
None

Test conditions

Hardness:
26 - 30 mg/L as CaCO3
Test temperature:
24.7 - 25.4 °C
pH:
7.2 - 7.7
Dissolved oxygen:
5.0 - 6.8 mg O2/L
Nominal and measured concentrations:
Nominal concentrations: 1,400 - 875 - 547 - 342 - 214 mg/l
Measured concentrations: 720 - 450 - 299 - 192 - 110 mg/l

Details on test conditions:
The exposure aquaria were housed in a temperature-controlled water bath that maintained the water temperature 25 ± 1 °C. Lighting was controlled to provide 16 hours of light per 24-hour period; light intensity was low-ambient. The flow rate and exposure chamber volume were selected and adjusted based upon the size of the test organisms in order to provide a loading rate of not more than 0.5 g of biomass per liter of water passing through each chamber in a 24-hour period. Control organisms were weighed upon study termination to determine the loading rate.
The mean weight of the control fish at test termination was 0.0887 g, resulting in loading rates of 0.887 g/l when the test chamber volume was 2 L and 1.774 g/L when the test chamber volume was 1 L.
Reference substance (positive control):
no

Results and discussion

Effect concentrationsopen allclose all
Duration:
31 d
Dose descriptor:
other: IC20
Effect conc.:
279 mg/L
Remarks on result:
other: 95% CI = 238 - 322 mg/L
Duration:
31 d
Dose descriptor:
other: IC25
Effect conc.:
308 mg/L
Remarks on result:
other: 95% CI = 251 - 339 mg/L
Details on results:
GC analysis resulted in average measured concentrations which were 51% to 56% of nominal.

Mortality of fathead minnows in the 720 mg/L treatment started occuring after approximately 5 days of exposure (after the organisms had hatched). Complete mortality was observed in the 720 mg/l treatment on test day 12; no significant organism mortality was observed for the duration of the test in the remaining treatments. Although no terata were observed, fathead minnow growth was reduced (relative to the control) in the 450 mg/L treatment.

Applicant's summary and conclusion