Iodine

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

96 hours

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

The methodology and results presented below for iodine (I2) have been included as part of a well documented publication that investigated the toxicity of iodine to Daphnia magna and Rainbow Trout (Oncorhynchus mykiss ). The testing protocol follow the Ontario Ministry of the Environment testing guidelines (attached below). The information from this publication and the guidelines followed have been compared with OECD Guideline 203 to further assess the reliability and validity of this study. In comparison with OECD Guideline 203 (Fish, acute toxicity test), a number of variables are compliant with this guideline: - The fish were obtained from certified disease-free commercial hatcheries. - Mortalities were recorded at 24, 48, 72 and 96 hours. - The deviation between the initial concentration and the final concentration of iodine is less than 20%. - The 96-h static tests were conducted at 15°C (±2°C) in a temperature and photoperiod (16-h light, 8-h dark) controlled facility as recommended in OECD 203. - The water hardness in the Standard Winnipeg River Treatment was 45.9 ± 0.5 CaCO3 mg/L, and the pH 8.1 adhere to the ranges in OECD 203. - The mean fish length for the rainbow trout was 44.0 ± 3.0 mm (S.D.) which falls with the recommended total lengths of test fish in OECD 203. - The Ontario Ministry of the Environment testing guidelines state that the test is rendered invalid if more than 10% of the fish in the control test solution die within 96 hours - this is consistent with the validity criteria in OECD Guideline 203. Although mortalities in the publication are not reported it is assumed that either no or less than 10% fish died in the control group, otherwise the test in this publication would have been rendered invalid. - In this static test, constant conditions were maintained. This is based on measurements of temperature, dissolved oxygen, pH, and electrical conductivity which indicated that the test conditions changed minimally during the experiment. However, there are also areas in this study which do not appear to adhere to OECD 203, though some of these factors may be due to lack of information in the publication: - Compliance to GLP is not stated in the publication although it is possible that this study was conducted according GLP principles as a suitable test guideline was adhered to. - Detailed information on the test substance such as impurities were not provided. - The test concentrations exceed a minimum of 5 concentrations but are not in a geometric series with a factor preferably not exceeding 2.2. - Measurement of pH, dissolved oxygen and temperature was not carried out daily - these factors [and also electrical conductivity and total iodine (ITOT) concentrations] were conducted before the start of the test and the end of the test. - The number of fish at each test concentration was not specified in the publication - at least 7 fish must be used at each test concentration according to OECD Guideline 203. However, based on the information in Ontario Ministry of the Environment Guidelines (Craig et al. 1983), a minimum of six fish per concentration is required for a test to be valid. It is unknown whether this study used 6 fish per concentration, or 7 (or more) fish per concentration. - The raw data is not presented (which would not be expected in a publication). The validity criteria specified in OECD Guideline 203 (mortality of controls should not exceed 10%, static conditions maintained throughout the study, and the deviation between the initial and final concentrations less than 20%) have all been met. It is also reported in this publication that dissolved oxygen concentrations were routinely near the atmospheric saturation value in all test containers. The dissolved oxygen validity criteria in OECD Guideline 203 states that "the dissolved oxygen concentration must have been at least 60 per cent of the air saturation value throughout the test". Whilst a specific percentage of air saturation value is not reported in this publication, it is assumed that the statement "dissolved oxygen concentrations were routinely near the atmospheric saturation value in all test containers" adheres to the OECD guideline validity criteria for dissolved oxygen. In summary, whilst there are some deficiencies in the study and the information reported, these are not considered to significantly affect the overall reliability or validity of this study which is broadly comparable with OECD Guideline 203: Fish, acute toxicity test. An overall reliability score of 2 (reliable with restrictions) is considered appropriate.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: Ontario Ministry of the Environment Testing Guidelines. Craig G, Flood K, Lee J, Thomson M (1983) Protocol to determine the acute lethality of liquid effluents to fish. Ontario Ministry of the Environment, Toronto, Ontario, Canada.

GLP compliance:

not specified

Remarks:

No data has been selected as the publication does not state GLP compliance. However, it is possible that this study was conducted according to the principles of GLP as a suitable test guideline was adhered to.

Analytical monitoring:

yes

Details on sampling:

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 (ITOT) concentrations. Following the completion of each of the toxicity tests, the test pails were sampled again for the above chemical analyses. No adjustments were made to replace the loss of iodine from the trout test solutions during the test period. The measurement of pH, dissolved oxygen and temperature was not carried out daily, a requirement under OECD Guideline 203 - these factors [and also electrical conductivity and total iodine (ITOT) concentrations] were conducted before the start of the test and the end of the test.

As part of the publication, nine water varieties were compared to explore the toxicity modifying role of water chemistry. All dilution waters were sampled prior to use and analyzed for total iodine (ITOT), Na+, K+,Ca2+, Mg2+ , CI-, SO4 2 -, alkalinity (as CaCO3), pH, hardness (as CaCO3), CuTOT, PbTOT, NiTOT, CdTOT, ZnTOT, FeTOT, MnTOT, electrical conductivity, total organic and inorganic carbon (TOC, TIC), and dissolved oxygen (D.O.).

Vehicle:

yes

Details on test solutions:

The iodine test solutions were prepared from elemental iodine I2 (99%, Sigma, St Louis, MO).
Preliminary testing determined that the lethal (LC50) iodine concentrations was 10.0 mg I/L as elemental iodine (I2). A control (0%) and six concentrations of iodine (1, 3, 10, 30, 60, 100% of the preliminary lethal concentrations) were used for each test. The test concentrations are not in a geometric series with a factor preferably not exceeding 2.2 which is a requirement under OECD Guideline 203.

For each iodine concentration, the test volume was 20 L of solution in a polyethylene pail lined with a food-grade polyethylene bag. Ten trout were added to each pail. A stock solution (20 g I/L) was prepared by dissolving 2.0 g of elemental iodine into 100 mL of ethyl alcohol (Ethanol, 99.9%, J.T.Baker, Winnipeg, MB). A measured volume of this stock solution was added to each of the I2 pails to obtain the desired test concentration. The remainder of the stock solution was stored at room temperature, in the dark. Preliminary testing exposed trout to equivalent concentration ranges of ethanol to confirm that toxicity was attributable to iodine. The maximum concentration of ethanol to which the trout were exposed was 0.005 %. This maximum concentration was also non-lethal.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

Rainbow trout fry were obtained from certified disease-free commercial hatcheries (this is compliant with OECD Guideline 203). The rainbow trout fry were transported to the test laboratory, 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).

A total of 1990 fish were used in this study. The lengths of the trout varied from 32-56 mm, and their weights varied from 0.51-0.96 g. The mean fish length was 44.0 ± 3.0 mm (S.D.); the mean fish weight was 0.78 ± 0.13 g. The age of the fish was not specified in the publication.

The mean fish length adheres to the length range for rainbow trout as specified in OECD Guideline 203. The number of fish at each test concentration was not specified in the publication - at least 7 fish must be used at each test concentration according to OECD Guideline 203. However, based on the information in Ontario Ministry of the Environment Guidelines (Craig et al. 1983), a minimum of six fish per concentration is required for a test to
be valid. It is unknown whether this study used 6 fish per concentration, or 7 (or more) fish per concentration.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Post exposure observation period:

There was no post exposure observation period. At the conclusion of the test, all the fish were sacrificed and the control fish were weighed and measured.

Hardness:

Refer to Table 2 for a summary of the water chemistry used in the toxicity tests in this publication (this is the table number in the publication and is also included further below in this endpoint study record). The hardness for the standard water sample (Winnipeg River treatment) is 45.9 ± 0.5 mg/L. The water hardness adheres to the range specified in OECD Guideline 203.

Test temperature:

The 96-h static tests were aerated and conducted at 15°C (±2°C). The temperature adheres to the range specified in OECD Guideline 203 for rainbow trout.

pH:

Refer to Table 2 for a summary of the water chemistry used in the toxicity tests in this publication. The pH for the standard water sample (Winnipeg River treatment) is 8.1 ± 0.1. The pH adheres to OECD Guideline 203.

Dissolved oxygen:

Refer to Table 2 for a summary of the water chemistry used in the toxicity tests in this publication. The dissolved oxygen content for the standard water sample (Winnipeg River treatment) is 10.1 mg/L. This value is greater than 7.0 mg/L which is specified in the Ontario Ministry of the Environment testing guidelines.

It is also reported in this publication that dissolved oxygen concentrations were routinely near the atmospheric saturation value in all test containers. One of the validity criteria in OECD Guideline 203 states that "the dissolved oxygen concentration must have been at least 60 per cent of the air saturation value throughout the test". Whilst a specific percentage of air saturation value is not reported in this publication, it is assumed that the statement "dissolved oxygen concentrations were routinely near the atmospheric saturation value in all test containers" adheres to the OECD guideline validity criteria for dissolved oxygen.

Salinity:

Refer to Table 2 for a summary of the water chemistry used in the toxicity tests in this publication. The chloride content for the standard water sample (Winnipeg River treatment) is 2.60 ± 0.13 mg/L.

Nominal and measured concentrations:

The concentrations (nominal) used in this study were 0 (control), 1, 3, 10, 30, 60, 100% of the preliminary lethal concentrations, where the lethal (LC50) iodine concentration for elemental iodine (I2) was 10.0 mg I/L. These nominal concentrations correspond to 0.1, 0.3, 1, 3, 6 and 10 mg I/L.

For NaI, these nominal concentrations correspond to 0.1, 0.3, 1, 3, 6 and 10 g I/L. For NaIO3 these nominal concentrations correspond to 0.01, 0.03, 0.1, 0.3, 0.6 and 1 g I/L.

The measured (initial) iodine concentrations were compared to the expected concentrations, and similarly, the final ITOT concentrations were compared with the initial concentrations. The results showed that little iodine was lost from solutions during the test period. The mean ratio of the final ITOT to the initial ITOT concentrations was 0.94, 0.99 and 1.06 of the initial concentrations for I2, I- and IO3-. The deviation between the initial and final concentration is less than 20% which adheres to OECD Guideline 203.

Details on test conditions:

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. The recording of mortalities at each 24 hour interval adheres with OECD Guideline 203.

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 sterilization, and distributed through polyvinylchloride pipes. Randomly selected fish were acclimated at I5°C (-2°C) for a period of >/5 days prior to testing. Feeding was suspended 24-h prior to and during the test period. The 96-h static tests were aerated and conducted at 15°C (±2°C) in a temperature and photoperiod (16-h light, 8-h dark) controlled facility. All fish holding and testing protocols followed the Ontario Ministry of the Environment guidelines (Craig et al. 1983). The temperature and photoperiod also adhere to OECD Guideline 203.

Reference substance (positive control):

not required

Remarks:

A positive control is not required in OECD Guideline 203

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

1.67 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Remarks on result:

other: Iodine data. The 95% confidence range for this LC50 ranged between 1.51- 1.84 mg/L. This LC50 value was for the Standard Winnipeg sample.

Details on results:

The most sensitive and relevant data endpoints have been included in the effect concentrations section above. The full results table from the publication is included in the "Any other information on results incl. tables section" below.

As stated under the "nominal and measured concentrations" field, little iodine was lost from solutions during the test period. The mean ratio of the final ITOT to the initial ITOT concentrations was 0.94 for I2. Routine measurements of temperature, dissolved oxygen, pH, and electrical conductivity also indicated that the test conditions changed minimally during the experiment. The temperature remained within the specifications of 15 ± 2°C in this study.

The raw data is not presented, although this information would not be expected in a publication. Results on mortalities observed in the control group were not specified. However, the Ontario Ministry of the Environment Guidelines (which this study was conducted to) state that the test is rendered invalid if more than 10% of the fish in the control test solution die within 96 hours - this is consistent with the validity criteria in OECD Guideline 203. It is therefore assumed that either no or less than 10% fish died in the control group, otherwise the test in this publication would have been rendered invalid.

The chemical toxicity of I2 to trout in the standard Winnipeg River treatment were calculated for each observation interval during the test period, although data for each interval were not presented in the publication. Detailed information on observations (number of dead fish, abnormal appearance and behaviour) were not presented. The study authors stated that for I2 a threshold level appeared to be reached within 24 hours.

In the standard Winnipeg River Treatment, the toxicity (96 hour LC50) was 1.67 mg/L (95% confidence range: 1.51 - 1.84 mg/L) for I2.

Increased water hardness increased the toxicity of I2 (96 hour LC50 0.53 mg/L). Increased Cl- concentrations had no effect on the toxicity of I2 to trout. Increased TOC concentrations reduced the toxicity of I2 to trout from 1.67 to >10 mg/L.

Results with reference substance (positive control):

A positive control is not required in OECD Guideline 203

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. Most calculations were completed using the Spearman-Karber method included in this database. A further description of this method is unavailable, and the raw data and calculations for deriving the LC50 are not available in the publication. This method is a non parametric statistical procedure for estimating the LC50 and the associated 95% confidence interval.
(United States Environmental Protection Agency, 2009: Short-Term Methods For Estimating the Chronic Toxicity of Effluents and Receiving Water to Marine and Estuarine Organisms- Appendix I Spearman-Karber Method. URL: http://www.epa.gov/waterscience/methods/wet/disk1/ctmapg-l.pdf)

Sublethal observations / clinical signs:

The most sensitive and relevant data endpoint for iodine has been included in the effect concentrations section above. The full results table from the publication is included below.

Median lethal toxic concentration (LC₅₀) of iodine to rainbow trout. All LC₅₀values were calculated using the Spearman-Karber method (table adapted from publication)

 

Iodine Species	Standard Winnipeg River treatment (a)	Hardness (b)		Chloride (c)		Total organic carbon (c)
		Low (7.5)	High (222)	Medium (13)	High (61)	Medium (7.8)	High (28.2)
I2(mg/L)	1.67 (1.51 – 1.84) (d)	4.19 (4.02 – 4.37)	0.53 (0.48-0.58)	1.73 (1.0-3.0)	1.73 (1.0-3.0)	4.2 (3.0 – 6.0)	>10 (non-lethal)

 

(a) Standard Winnipeg River treatment (charcoal filtered) had medium hardness (45.9 mg/L as CaCO₃), low TOC (2.7 mg/L), and low chloride (2.6 mg/L) concentrations

(b) mg/L as CaCO₃

(c) mg/L

(d) 95% confidence ranges

Validity criteria fulfilled:

yes

Remarks:

The information from this publication (conducted to the Ontario Ministry of the Environment testing guidelines) has been compared with OECD Guideline 203. Refer to field "Rationale for reliability including deficiencies" for further details.

Conclusions:

The 96 hour LC50 for I2 (elemental iodine) is 1.67 mg/L and is considered to be relevant for this endpoint.

Executive summary:

The publication by Laverock, MJ Stephenson, M and Macdonald CR (1995) investigated the toxicity of iodine to Daphnia magna and Rainbow Trout (Oncorhynchus mykiss).

This endpoint study record reviews the short term toxicity test (rainbow trout) using iodine. Rainbow trout were exposed to nominal concentrations of iodine at the concentrations 0.1, 0.3, 1, 3, 6 and 10 mg I/L for 96 hours under static conditions. The study also investigated whether the chemistry of the water used in the studies affected the toxicity results.The test guidelines cited for the conduct of the study (Ontario Ministry of the Environment Guidelines (Craig et al. 1983) are broadly comparable to OECD Guideline 203 (Fish, Acute Toxicity Test) with a few deficiencies that are not considered to significantly affect the overall reliability or validity of this study (reliability score 2 - reliable with restrictions).

The study authors noted that for I2 a threshold level appeared to be reached within 24 hours. In the standard Winnipeg

River Treatment, the toxicity (96 hour LC50) was 1.67 mg/L. Increased water hardness increased the toxicity of I2 (96 hour LC50 0.53 mg/L). Increased Cl- concentrations had no effect on the toxicity of I2 to trout. Increased TOC concentrations reduced the toxicity of I2 to trout from 1.67 to >10 mg/L.

In terms of the validity of the study, static conditions were maintained throughout the test and the deviation between the

initial and final iodine concentrations was less than 20%. It is also reported in this publication that dissolved oxygen concentrations were routinely near the atmospheric saturation value in all test containers. The validity criteria for dissolved oxygen in OECD Guideline 203 states that "the dissolved oxygen concentration must have been at least 60 per cent of the air saturation value throughout the test". Whilst a specific percentage of air saturation value is not reported in this publication, it is assumed that the statement "dissolved oxygen concentrations were routinely near the atmospheric saturation value in all test containers" adheres to the OECD guideline validity criteria for dissolved oxygen. The results for elemental iodine are therefore considered to be valid.

The 96 hour LC50 for I2 (elemental iodine) is 1.67 mg/L and is considered to be relevant for this endpoint.

Reference 2

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Remarks:

short exposure time compare with OECD Guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

Deviations:

yes

Remarks:

Exposure time is shorten than OECD guideline stated

GLP compliance:

not specified

Specific details on test material used for the study:

iodine crystals (analytical reagent grade)

Analytical monitoring:

yes

Vehicle:

yes

Details on test solutions:

Stock solutions of toxicant were made as needed by dissolving 1 g of iodine crystals (analytical reagent grade) in 1 liter of distilled water at 60℃. This yielded typical stock concentrations of 0.72 to 1.00 mg/mL. Stock preparations were wrapped in aluminum foil and stored in the dark to limit photodecomposition.

Test organisms (species):

Ictalurus punctatus

Details on test organisms:

Channel catfish fingerlings were obtained from the Kansas Fish and Game Commission and held in 150-Liter stainless steel flow-through troughs at a temperature of 18 ℃. The test fish were 60 to 100 mm total length and 2.0 to 7.3 g total weight.
Channel catfish were acclimated for at least two hours prior to introduction of the iodine.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

24 h

Test temperature:

20.2 to 22.4 ℃

pH:

7.2 to 7.6

Dissolved oxygen:

7.5-9.0 mg/L

Details on test conditions:

Preliminary bioassays of iodine against channel catfish were carried out in 4-liter glass aquaria to delimit a range of concentrations giving between 10 and 90 percent mortality. Final bioassays were run in 60-liter glass aquaria for intervals of 1, 2, 10, and 24 hours. The test water was dechlorinated tap water with total alkalinity of 62.7 to 72.0 mg/liter, pH of 7.2 to 7.6, and temperature of 20.2 to 22.4℃
Fish loading rates did not exceed 1 g/liter of water. All test fish were starved for 72 hours prior to and during any bioassay to lessen metabolites in solution. At the end of each test, viable fish were placed in 30-liter glass recovery aquaria and observed for 48 hours. A negative control, consisting of the same test water, conditions, and organisms, but containing no iodine, was maintained concurrently with each exposure. Generally, iodine concentrations in the 1-hour assays remained constant. In all other tests iodine concentration was monitored at one hour intervals and extra chemical was introduced to adjust for loss of iodine, presumably due to photodecomposition and organic matter. These periodic adjustments undoubtedly introduced some imprecision into the experiment.

Reference substance (positive control):

no

Duration:

24 h

Dose descriptor:

LC50

Effect conc.:

0.44 mg/L

Nominal / measured:

not specified

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Details on results:

The toxicity of iodine to channel catfish varied with the exposure period. Concentrations as low as 0.72 mg/liter resulted in 100 percent mortality during the 24-hour exposure period. A much higher concentration (7.22 mg/liter) was necessary for complete mortality during a short exposure period (1 hour). Concentrations causing no mortality ranged from 0.10 to 1.50 mg/liter for the 24- and 1-hour tests, respectively. No-mortality levels were roughly one-half of the LC50 value. Mortality was absent in the control groups and water chemistry parameters were similar in both experimental and control groups over the exposure period.
Inactivity, loss of equilibrium, color fading, "piping," massive gill damage, and hemorrhaging at the base of the fins were symptomatic of iodine poisoning. In all toxicity tests channel catfish never recovered after loss of equilibrium and most fish died within 30 minutes of equilibrium loss. Gill damage consisted of severe hemorrhaging and "clubbing" in the gill filaments, sloughing of gill epithelium and production of large amounts of mucous.

Reported statistics and error estimates:

Percent mortality versus iodine concentration was plotted on log-probability paper. Median lethal concentration (LC) 50 values (with 95 percent confidence intervals) were determined using the graphical techniques of LITCHFIELD AND WILCOXON (1949). Their method was also used to transform no and 100 percent mortality data, to test for goodness of fit for the lines drawn, and to determine the slope function of the lines.

Sublethal observations / clinical signs:

The acute toxicity of iodine to channel catfish:

Duration of Test (hours)	No. tested	No mortality(mg/liter)	100% mortality(mg/liter)	LC50 (mg/Liter) (95% confidence interval)	Slope function
1	60	1.50	7.22	3.00 (2.22-4.05)	2.21
2	40	1.20	4.30	2.10 (1.63-2.71)	1.76
10	48	0.50	1.52	0.98 (0.89-1.07)	1.42
24	50	0.10	0.72	0.44 (0.40-0.49)	1.44

Validity criteria fulfilled:

not specified

Conclusions:

The 24h-LC50 to channel catfish was determined to be 0.44 mg/L.

Executive summary:

The acute toxicity of diatomic iodine (I2) to channel catfish (Ictalurus punctatus) was determine in a static test.

The toxicity of iodine to channel catfish varied with the exposure period. Concentrations as low as 0.72 mg/liter resulted in 100 percent mortality during the 24-hour exposure period. A much higher concentration (7.22 mg/liter) was necessary for complete mortality during a short exposure period (1 hour). Concentrations causing no mortality ranged from 0.10 to 1.50 mg/liter for the 24- and 1-hour tests, respectively. No-mortality levels were roughly one-half of the LC50 value.

The 24h-LC50 was determined to be 0.44 mg/L. Iodine is very toxic to channel catfish and mortality is apparently due to asphyxiation caused, at least initially, by severe gill damage.

Description of key information

Short term toxicity to fish:

LC50 (96 hours): 1.67 mg/L Oncorhynchus mykiss (rainbow trout)

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

1.67 mg/L

Additional information

Two short term toxicity to fish studies have been identified for iodine:

- An 96 hour acute study under static conditions that investigated the toxicity of iodine to Rainbow Trout (Oncorhynchus mykiss) (toxicity to Daphnia magna was also investigated) [Laverock MJ, Stephenson M, and Macdonald CR (1995)]. This study is attached under the endpoint study record for section 6.1.1 - short term toxicity to fish.

- An acute study (in static conditions with exposure durations up to 24 hours) that investigated the acute toxicity of iodine to channel catfish [LeValley MJ (1982)].

The 96 hour acute study in rainbow trout has been selected as the key study and a robust study summary of this publication is included for this endpoint. The selection of this study rather than the 24 hour study in catfish is based on the following rationale:

- The 96 hour acute study was conducted according to the Ontario Ministry of the Environment Guidelines (Craig et al. 1983) that is broadly comparable to OECD Guideline 203 with a few deficiencies that are not considered to significantly affect the overall reliability or validity of this study. The acute toxicity study in catfish was not documented in accordance with any testing guidelines.

- The 96 hour acute study was conducted using rainbow trout, which are one of the fish species recommended for testing in OECD Guideline 203 - Fish, Acute Toxicity. The other acute study was conducted in channel catfish which are not listed as a recommended species. Furthermore, there was no detail in the catfish study about whether the fish were obtained under disease controlled conditions.

- For fish toxicity tests, exposure durations less than 96 hours should be treated with caution as these shorter durations lead to higher effect values [ECHA, 2008]. This means that the 24 hour LC50 value in catfish of 0.44 mg/L cannot be considered as reliable compared with the 96 hour LC50 value of 1.67 mg/L derived from Laverock (1995).

- In the acute catfish study, the author noted that iodine concentrations in the 2 hour, 10 hour and 24 hour tests were monitored at 1 hour intervals and that extra chemical was introduced to adjust for the loss of iodine, which the author presumed to be due to photodecomposition and organic matter. The author further acknowledged that these adjustments "undoubtedly introduced some imprecision into the experiment". This raises a large degree of uncertainty about the actual concentrations of iodine exposure in the catfish. Furthermore, it does not appear that constant conditions were maintained. In the 96 hour study in rainbow trout static conditions were maintained throughout the test and the deviation between the initial and final iodine concentrations was less than 20%.

The overall reliability of the 96 hour acute toxicity study in rainbow trout is reliability score 2 - reliable with restrictions. The reliability of the acute toxicity study in channel catfish is reliability score 3 - not reliable.

 

References:

Craig G, Flood K, Lee J, Thomson M (1983): Protocol to determine the acute lethality of liquid effluents to fish. Environment Ontario.

Laverock MJ, Stephenson M, and Macdonald CR (1995): Toxicity of Iodine, Iodide and Iodate to Daphnia magna and Rainbow Trout (Oncorhynchus mykiss ) Arch. Environ. Contam. Toxicol. 29, 344 -350

LeValley MJ (1982): Acute toxicity of Iodine to Channel Catfish (Ictalurus punctatus). Bull. Environm. Contam. Toxicol. 29, 7 -11

OECD (1992): Fish, Acute Toxicity Test. OECD Guideline 203, Adopted by the Council on 17th July 1992.