Iodine

Toxicity to terrestrial arthropods

Link to relevant study record(s)

Reference

Endpoint:

toxicity to terrestrial arthropods: short-term

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

As this test is a semi-field study, there is no standardised test guideline to compare with this publication. This data which uses KI as the test substance, is considered relevant for read across to iodine as iodide is the major existent species of iodine in soil which is available for interactions with soil components. For further information, refer to the environmental fate section of the dossier. There is a lack of data regarding the control groups in this method, and the exact numbers of arthropods in the control groups. However, the study follows scientific principles and is otherwise well documented, and is therefore considered to meet the criteria of Klimisch score 2 - reliable with restrictions.

Qualifier:

no guideline available

Principles of method if other than guideline:

The method was based on a previous publication by the same study authors:

Sheppard, S.C. and Evenden W.G. (1994). Simple whole-soil bioassay based on microarthropods. Bull. Environ. Contam. Toxicol., 52, 95-101.

This study appears to be a semi-field study in that a few species have been exposed together in 3 soil types with very different properties. There is therefore no standardised test guideline to compare with this publication.

The method is generally well described in the publication. The mesocosms that provided the test populations of microarthropods were large boxes filled with forest litter and soil, and planted with grass. Each box contained 24 subvertical sleeves for inserting 15 cm diameter, 2.5 cm deep plastic petri dishes. The numbers of springtails (Collembola), mites (Acari) and remaining meso fauna were counted at up to 40x maginification, and recorded separately. Log transformed counts of springtails plus mites were used for statistical interpretation.

GLP compliance:

not specified

Application method:

soil

Specific details on test material used for the study:

his data which uses KI as the test substance, is considered relevant for read across to iodine as iodide is the major existent species of iodine in soil which is available for interactions with soil components. For further information, refer to the environmental fate section of the dossier.

Analytical monitoring:

yes

Details on sampling:

The I concentrations were confirmed by neutron activation/gamma spectroscopy (NA/GS).

Vehicle:

yes

Details on preparation and application of test substrate:

Three soils were used by the study authors, due to their "very different properties". The soils are given below:

- SIlty-clay soil: This consisted of 43% clay, pH 7.9, an organic matter content (OMC) of 27 g kg-1 and a cation exchange capacity (CEC) of 18 cmol (NH4) kg-1. The soil shrank when dry to about 80% of its volume when moist.
- Garden soil: This soil had a high humus content, typical of a garden soil. This consisted of 46% clay, pH 7.3, an OMC of 89 g kg-1 and a CEC of 40 cmol (NH4) kg-1.
- Sand: This soil consisted of 3% clay, pH 6.3, negligible OMC and a CEC of 1 cmol (NH4)kg-1.

The soil was treated with I within 14 days of the experiment. The soil was amended with ground alfalfa ay 10% by weight (used as a bait for the microarthropods). The mixture was added to the petri dishes and was moistened to 80% of the moisture holding capacity (MHC).

Animal group:

other: Collembola (soil-dwelling springtail) and Acari (soil-dwelling predatory mite)

Details on test organisms:

The organisms that were investigated were springtails (Collembola), also mites (Acari) and remaining meso fauna. No further details are specified.

Study type:

semi-field study

Limit test:

no

Total exposure duration:

11 d

Post exposure observation period:

None stated

Test temperature:

The extraction funnels were in a constant temperature room at 22 ± 1 degrees C

pH (if soil or dung study):

- SIlty-clay soil: pH 7.9
- Garden soil: pH 7.3
- Sand: pH 6.3

Humidity:

- SIlty-clay soil: Not stated
- Garden soil: Not stated
- Sand: Not stated

Photoperiod and lighting:

The grass added to the soil recieved light from an adjacent window that was supplemented by fluorescent lighting.
Light provided by a bank of fluorescent tubes heated the soil from above and forced the microarthropods to exit the soil through the screen cover on the petri dishes and fall through the funnel into an ethanol trap.

Details on test conditions:

There were triplicates of each treatment. The petri dishes were fastened on and the dishes were inserted into the sleeves. The dishes were modified to have a large screen covered hole. After 11 days, the petri dishes were removed and inverted onto Tullgren-type extraction funnels. The funnels were in a constant temperature room at 22 ± 1 degrees C. Fluorescent light tubes heated the soil from above which forced the arthropods to exit the soil through the screen cover on the petri dishes, and fall through the screen cover into an ethanol trap.

Nominal and measured concentrations:

The concentrations of stable I chosen to study were 0, 10, 22, 46, 100, 220, 460 and 1000 mg I kg -1 soil, applied as KI. The KI was applied in solution to the soils, with several cycles of addition and mixing to achieve uniform distribution.

Reference substance (positive control):

no

Duration:

11 d

Dose descriptor:

LOEC

Effect conc.:

15 mg/kg soil dw

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Basis for effect:

mortality

Remarks:

The basis of the effect is not clearly documented, but is assumed to be mortality as the results graphs compared the control soils with the test soils and investigated counts of microarthropods (log scale) in response to soil I.

Remarks on result:

other: Sandy soil

Duration:

11 d

Dose descriptor:

LC50

Effect conc.:

41 mg/kg soil dw

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Basis for effect:

mortality

Remarks:

The basis of the effect is not clearly documented, but is assumed to be mortality as the results graphs compared the control soils with the test soils and investigated counts of microarthropods (log scale) in response to soil I.

Remarks on result:

other: Sandy soil

Duration:

11 d

Dose descriptor:

NOEC

Effect conc.:

20 mg/kg soil dw

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Basis for effect:

mortality

Remarks:

The basis of the effect is not clearly documented, but is assumed to be mortality as the results graphs compared the control soils with the test soils and investigated counts of microarthropods (log scale) in response to soil I.

Remarks on result:

other: Clay soil

Duration:

11 d

Dose descriptor:

LC50

Effect conc.:

160 mg/kg soil dw

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Basis for effect:

mortality

Remarks:

The basis of the effect is not clearly documented, but is assumed to be mortality as the results graphs compared the control soils with the test soils and investigated counts of microarthropods (log scale) in response to soil I.

Remarks on result:

other: Clay soil

Duration:

11 d

Dose descriptor:

NOEC

Effect conc.:

11 mg/kg soil dw

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Basis for effect:

mortality

Remarks:

The basis of the effect is not clearly documented, but is assumed to be mortality as the results graphs compared the control soils with the test soils and investigated counts of microarthropods (log scale) in response to soil I.

Remarks on result:

other: Garden soil

Duration:

11 d

Dose descriptor:

LC50

Effect conc.:

140 mg/kg soil dw

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Basis for effect:

mortality

Remarks:

The basis of the effect is not clearly documented, but is assumed to be mortality as the results graphs compared the control soils with the test soils and investigated counts of microarthropods (log scale) in response to soil I.

Remarks on result:

other: Garden soil

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

The general linear model and non-linear regression routines of were used. Significance was assigned to the 0.05 probability level. The statistical contrasts with controls were performed by single degree of freedom, two-tailed tests. Where statistically significant effects were determined, a segmented regression was fit iteratively to the data. This allowed for the determination of the No-Observed-Effect-Level (NOEL) and the concentration that reduced the performance to 50% of that of the controls (EC50 or LC50). The regression displayed the response as a constant value at I concentrations below the NOEL, and as linearly decreasing values at soil concentrations above the NOEL.

Validity criteria fulfilled:

not applicable

Remarks:

Not applicable as the method used is a semi-field study and there is no standard guideline available.

Conclusions:

Under the protocol used in this study the NOEC ranged between 11 - 20 mg I kg -1 soil in three soil types. As this test is a semi-field study, there is no standardised test guideline to compare with this publication.

The use of Collembolans in this study is considered to be acceptable as these organisms are the most numerous and widely occurring insects in terrestrial ecosystems, according to ECHA guidance. This organisms are therefore widely used as bioindicators in the environment.
There is a lack of data regarding the control groups in this method, and the exact numbers of arthropods in the control groups. Although the control groups are not described in the method, the information from the statistics used states that the test organisms were compared with controls to determine the statistical significance.

The use of three soils with different properties, gave a useful indication on the influence of soil type where the microarthropods appeared to be most sensitive to the sandy soil, although garden soil showed a slightly lower NOEC. The soil concentrations have also been confirmed by chemical analysis and KI was added in solution with several cycles of addition to achieve uniform distribution. It is not known whether the sorption of iodide had reached a steady state, however the toxicity of I was noted to be reduced in previous work by the study author when a steady state is reached, typically after 20 days. As the soils were treated within 14 days this could have resulted in higher toxicity and more conservative values NOEC and EC50 values.

In conclusion, despite the points raised above, the study follows scientific principles and is otherwise well documented and the effect concentrations are considered to be supportable. This study is therefore considered to meet the criteria of Klimisch score 2 - reliable with restrictions.

Executive summary:

This semi-field study investigated the toxicity of inorganic iodine (applied as KI) to microarthropods, which included investigating the effects in springtails (Collembola), also mites (Acari) and remaining meso fauna. This uses of KI as the test substance, is considered relevant for read across to iodine as iodide is the major existent species of iodine in soil which is available for interactions with soil components. As this test is a semi-field study, there is no standardised test guideline to compare with this publication. There is a lack of data regarding the control groups in this method, and the exact numbers of arthropods in the control groups. However, the study follows scientific principles and is otherwise well documented, and is therefore considered to meet the criteria of Klimisch score 2 - reliable with restrictions.

Under the protocol used in this study the NOEC ranged between 11 - 20 mg I kg -1 soil in three soil types.

Description of key information

11 day study (microarthropods) NOEC: 11 mg/kg soil (garden soil)

11 day study (microarthropods) LC50: 41 mg/kg soil (sandy soil)

Key value for chemical safety assessment

Short-term EC50 or LC50 for soil dwelling arthropods:

41 mg/kg soil dw

Additional information

The reviewed semi-field study investigated the toxicity of inorganic iodine (applied as KI) to microarthropods, which included investigating the effects in springtails (Collembola), also mites (Acari) and remaining meso fauna. This uses of KI as the test substance, is considered relevant for read across to iodine as iodide is the major existent species of iodine in soil which is available for interactions with soil components. As this test is a semi-field study, there is no standardised test guideline to compare with this publication. There is a lack of data regarding the control groups in this method, and the exact numbers of arthropods in the control groups. However, the study follows scientific principles and is otherwise well documented, and is therefore considered to meet the criteria of Klimisch score 2 - reliable with restrictions. Under the protocol used in this study the NOEC ranged between 11 - 20 mg/ kg soil in three soil types.

Refer to the attached endpoint study record for further details.