Sodium iodate

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

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 202 (Daphnia sp. Acute Immobilisation Test)

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 the toxicity tests, the five 30-mL aliquots of each test solution were pooled and subsampled for final chemical analyses. No adjustments were made to replace the loss of iodine from either the trout or the Daphnia test solutions during the test period.
No adjustments were made to replace the loss of iodine from the Daphnia test solutions during the test period.

Vehicle:

not specified

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: water flea
- Age at test initiation: < 24-h old
- Source: Laboratory stock

CULTURE CONDITIONS
Stocks of Daphnia were raised in the laboratory following a minor modification to the Ontario Ministry of the Environment protocol (Poirier et al. 1988). The Daphnia were fed a mixture of two algal species: Selenastrum capricornutum (UTCC #37) and Chlorella emersonii (UTCC #86), both of which were obtained as pure cultures from the University of Toronto Algal Culture Collection of Algae and Cyanobacteria.
The culture water supply was local spring water collected from an artesian aquifer in a glacial moraine, and filtered through activated charcoal, crushed limestone, and polyester floss prior to use.
Daphnia in various stages of growth were maintained to provide healthy populations and a steady supply of neonates.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

7.5 - 222 mg/L (as CaCO3)

Test temperature:

20 ± 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: Test tubes
- Fill volume: 30 mL
- Aeration: Non-aerated
- No. of organisms per vessel: Two Daphnia neonates
- No. of vessels per concentration (replicates): Five test tubes

TEST MEDIUM / WATER PARAMETERS
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: Initial chemical analyses for pH, conductivity, dissolved oxygen, and total iodine were performed on a sample aliquot of each test solution.

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

EFFECT PARAMETERS MEASURED
The tests were monitored at 24 and 48-h. At these same intervals, the mortality in each test solution was monitored. Death was defined as no visible internal movement.

RANGE-FINDING STUDY
- Test concentrations: A control (0%) and 6 concentration ranges of iodine (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:

48 h

Dose descriptor:

LC50

Effect conc.:

58.5 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

mortality

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: 58.5 mg/L
Low hardness (7.5 mg/L): 10.3 mg/L
High hardness (222 mg/L): 54.8 mg/L
Medium chloride (13 mg/L): 58.7 mg/L
High chloride (61 mg/L): 129 mg/L
Medium TOC (7.8 mg/L): 54.8 mg/L
High TOC (28.2 mg/L): 54.9 mg/L


Increased water hardness 7.5 to 45.9 mg/L reduced the toxicity of iodate although a further increase of water hardness to 222 mg/L had no additional effect.
Increased chloride concentrations from 2.6 to 61 mg/L reduced the toxicity of iodate.
High concentrations of total organic carbon had no effect on the toxicity of iodate to daphnia.

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 48-hour acute median lethal concentration of the test material to the aquatic invertebrate, Daphnia magna, was determined to be 58.5 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 the aquatic invertebrate, Daphnia magna, was investigated in a study which was conducted according to a method similar to that which is outlined in the standardised guideline OECD 202.

During the study, 10 daphnia 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.

Increased water hardness 7.5 to 45.9 mg/L reduced the toxicity of iodate although a further increase of water hardness to 222 mg/L had no additional effect.

Increased chloride concentrations from 2.6 to 61 mg/L reduced the toxicity of iodate.

High concentrations of total organic carbon had no effect on the toxicity of iodate to daphnia.

Under the conditions of the study, the 48-hour acute median lethal concentration of the test material to Daphnia magna was determined to be 58.5 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. 60 mg/L.

Description of key information

Under the conditions of the study, the 48-hour acute median lethal concentration of the test material to the aquatic invertebrate, Daphnia magna, was determined to be 58.5 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 invertebrates

Fresh water invertebrates

Effect concentration:

58.5 mg/L

Additional information

The short term toxicity of the test material to the aquatic invertebrate, Daphnia magna, was investigated in a study which was conducted according to a method similar to that which is outlined in the standardised guideline OECD 202.

During the study, 10 daphnia 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.

Increased water hardness 7.5 to 45.9 mg/L reduced the toxicity of iodate although a further increase of water hardness to 222 mg/L had no additional effect.

Increased chloride concentrations from 2.6 to 61 mg/L reduced the toxicity of iodate.

High concentrations of total organic carbon had no effect on the toxicity of iodate to daphnia.

Under the conditions of the study, the 48-hour acute median lethal concentration of the test material to Daphnia magna was determined to be 58.5 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. 60 mg/L.