Sodium iodate

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not specified

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

Principles of method if other than guideline:

All fish holding and testing protocols followed the Ontario Ministry of the Environment guidelines (Craig et al. 1983).

GLP compliance:

not specified

Analytical monitoring:

yes

Remarks:

AAS, IC and ICPS

Details on sampling:

Initial chemical analyses for total iodine were performed on a sample aliquot of each test solution.
Upon completion of each toxicity test, the test pails were sampled again for chemical analyses.

Vehicle:

not specified

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM
- Common name: Rainbow trout
- Source: Rainbow trout fry were obtained from certified disease-free commercial hatcheries, transported to the testing facility, and maintained at 6 °C until needed.
The fish were fed a maintenance ration of a commercial pelleted trout food (Martin Feed Mills Limited, Ontario).
- Length at study initiation: 32-56 mm, mean: 44.0 ± 3.0 mm (SD)
- Weight at study initiation: 0.51-0.96 g, mean: 0.78 ± 0.13 g (SD)

ACCLIMATION
- Acclimation period: at least 5 days
Randomly selected fish were acclimated at 15 ± 2 °C. Feeding was suspended 24-h prior to and during the test period.

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Hardness:

7.5 - 222 mg/L (as CaCO3)

Test temperature:

15 ± 2 °C

pH:

6.9 - 8.3

Dissolved oxygen:

near the atmospheric saturation value in all test containers

Conductivity:

19 - 336 µS/cm

Nominal and measured concentrations:

83-199 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: Pails
- No. of organisms per vessel: 10

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: The water supply for the continuous flow-through holding tanks was obtained from the Winnipeg River (in eastern Manitoba, Canada), purified by sand filtration and ultraviolet light sterilisation, and distributed through polyvinylchloride pipes.
To explore the toxicity-modifying role of water chemistry, nine water chemistries were compared. These represented three levels of hardness, chloride, and TOC, respectively.
Bulk quantities of all test waters were prepared five to seven days in advance of each test, and were continuously filtered (through polyester floss) and aerated until used. With each consecutive test, a chemical parameter of the water was modified. A charcoal-filtered sample of Winnipeg River water was selected to be the standard water chemistry. This water is considered soft, with low chloride and TOC concentrations. Hard water (220 mg/L as CaCO3) was obtained from a groundwater spring, and very soft water (7.5 mg/L as CaCO3) was obtained from Lake 625 at the Experimental Lakes Area (ELA) east of Kenora, Ontario, Canada. Higher chloride concentrations (13 and 61 mg/L) were achieved by adding NaCl to the charcoal-filtered Winnipeg River water. A medium TOC concentration (7.8 mg/L) was obtained using the Winnipeg River water without charcoal filtration. A higher natural TOC concentration (28.2 rag/L) was obtained by sampling the Rennie River, a tributary of the Winnipeg River with otherwise similar water chemistry. All dilution waters were sampled prior to use and analysed for total iodine, Na +, K +, Ca 2+, Mg 2+ , CI-, SO4 2-, alkalinity (as CaCO3), pH, hardness (as CaCO3), Cu, Pb, Ni, Cd, Zn, Fe, Mn, electrical conductivity, total organic and inorganic carbon (TOC, TIC), and dissolved oxygen (DO).
- Intervals of water quality measurement: Before the addition of fish to the test solutions, all of the test pails were sampled to measure pH, electrical conductivity, dissolved oxygen, temperature, and total iodine concentrations

OTHER TEST CONDITIONS
- Photoperiod: 16-h light, 8-h dark

EFFECT PARAMETERS MEASURED
The tests were monitored at 0.5 and 4-h, and at each 24-h interval up to the 96-h termination point. At each of these intervals, both the temperatures and mortalities were recorded. Dead fish were removed whenever they were found. At the conclusion of each of the modified test series, all the fish were sacrificed and the control fish were weighed and measured.

TEST CONCENTRATIONS
- Range finding study
- Test concentrations: A control (0 %) and 6 concentration ranges of the test material (1, 3, 10, 30, 60, 100 %) were used.
Preliminary testing determined lethal iodine concentration (LC50) to be 1.0 g I/L as NalO3
- Results used to determine the conditions for the definitive study: yes

Reference substance (positive control):

not specified

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

350 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Remarks on result:

other: Standard Winnipeg River treatment

Details on results:

- Total iodine
The results showed that little or no iodine was lost from solutions during the test period. The mean ratios of total iodine (final) to total iodine (initial) concentration was 1.06 of the initial concentration.

- LC50 values for the various water media:
Standard Winnipeg River treatment: 350 mg/L
Low hardness (7.5 mg/L): 220 mg/L
High hardness (222 mg/L): 280 mg/L
Medium chloride (13 mg/L): 320 mg/L
High chloride (61 mg/L): 340 mg/L
Medium TOC (7.8 mg/L): 420 mg/L
High TOC (28.2 mg/L): 420 mg/L

No effect of hardness on the toxicity of the test material to trout was observed.
Increased chloride concentrations had no effect on the toxicity of the test material to trout.
Similarly, increased TOC concentrations had no effect on the toxicity of the test material to trout.

Reported statistics and error estimates:

The LC50 values for each test series were calculated using a toxicity database system (Toxdata Version 2.0) issued by the Ontario Ministry of the Environment specifically for the calculations and management of toxicity data. Most calculations were completed using the Spearman-Karber method included in the database.

Validity criteria fulfilled:

not specified

Conclusions:

Under the conditions of the study, the 96-hour acute median lethal concentration of the test material to fish was determined to be 350 mg/L when exposed to a standard Winnipeg River water treatment. This medium had medium hardness (45.9 mg/L as CaCO3), low TOC (2.7 mg/L), and low chloride (2.6 mg/L) concentrations.

Executive summary:

The short term toxicity of the test material to fish was investigated in a study which was conducted according to a method similar to that which is outlined in the standardised guideline OECD 203.

During the study, 10 fish were exposed to a range of test concentrations of the test material in test media with three individual concentrations of hardness, total organic carbon, and chloride.

Under the conditions of the study no effect of hardness on the toxicity of the test material to trout was observed. Increased chloride concentrations had no effect on the toxicity of the test material to trout. Similarly, increased TOC concentrations had no effect on the toxicity of the test material to trout.

The 96-hour acute median lethal concentration of the test material to fish was determined to be 350 mg/L when exposed to a standard Winnipeg River water treatment. This medium had medium hardness (45.9 mg/L as CaCO3), low TOC (2.7 mg/L), and low chloride (2.6 mg/L) concentrations.

The mean of individually determined LC50 values, as specified in the literature reference, was ca. 336 mg/L.

Description of key information

Under the conditions of the study, the 96-hour acute median lethal concentration of the test material to fish was determined to be 350 mg/L when exposed to a standard Winnipeg River water treatment. This medium had medium hardness (45.9 mg/L as CaCO3), low TOC (2.7 mg/L), and low chloride (2.6 mg/L) concentrations.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

350 mg/L

Additional information

The short term toxicity of the test material to fish was investigated in a study which was conducted according to a method similar to that which is outlined in the standardised guideline OECD 203.

During the study, 10 fish were exposed to a range of test concentrations of the test material in test media with three individual concentrations of hardness, total organic carbon, and chloride.

Under the conditions of the study no effect of hardness on the toxicity of the test material to trout was observed. Increased chloride concentrations had no effect on the toxicity of the test material to trout. Similarly, increased TOC concentrations had no effect on the toxicity of the test material to trout.

The 96-hour acute median lethal concentration of the test material to fish was determined to be 350 mg/L when exposed to a standard Winnipeg River water treatment. This medium had medium hardness (45.9 mg/L as CaCO3), low TOC (2.7 mg/L), and low chloride (2.6 mg/L) concentrations.

The mean of individually determined LC50 values, as specified in the literature reference, was ca. 336 mg/L.