Iodine

Toxicity to soil macroorganisms except arthropods

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil macroorganisms except 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:

The methodology and results presented below have been included as part of a well documented publication that investigated the toxicity of inorganic iodine (I) when applied as KI to terrestrial biota, which included investigating the effects on earthworms. 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. The protocol is not based on standard guidelines (e.g. OECD Guidelines) but follows scientific principles which support the conclusion below.

Qualifier:

no guideline followed

Principles of method if other than guideline:

The protocol used in this study was developed by the study authors in previous publications:

- Sheppard, SC & Evenden, W.G. (1992) Optimised design for earthworm survival tests in soil. Bull. Environ. Contam. Toxicol., 49, 648-55
- Sheppard, S.C., Evenden, W.G., Abboud, S.A. & Stephenson, M. (1993). A plant life-cycle bioassay for contaminated soil, with comparison to other bioassays: Mercury and Zinc. Arch. Environ. Contam. Toxicol., 25, 27-35

Three soil types (see details of the soils below) were treated within 14 days of this experiment. The treated soils were subdivided into 40 cm3 aliquots and placed in small plastic bags. To allow air flow, each of the bags had been perforated with a needle. There were 30 replicates of each of the contaminated soils and 50 replicates of controls. One mature earthworm (Lumbricus terrestris) was placed into each bag. The earthworms were from an allotment recently obtained from a commercial bait supplier. The bags were sealed and incubated at 15 degrees C for 30 days. In the sandy soil type, the earthworm survival was slightly less than in other soils. Therefore, dead worms were counted and removed at 14 days in this soil only. After 30 days, the worms in all of the remaining bags were scored dead or alive.

GLP compliance:

not specified

Specific details on test material used for the study:

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.

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.

All of the soils were air-dried to a workable moisture content and sieved to pass a 5 mm mesh and stored in sealed buckets. The moisture-holding capacity (MHC) was determined for each soil and container size by filling the container with soil, wetting to excess and allowing to drain for 24 hours.

Test organisms (species):

Lumbricus sp.

Animal group:

annelids

Details on test organisms:

Mature earthworms (Lumbricus terrestris). There were 30 replicates of each of the three contaminated soils and 50 replicates of controls. One mature earthworm (Lumbricus terrestris) was placed into each bag. The age and mass of the earthworms is not stated.

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

30 d

Remarks:

14 day exposure duration for sandy soil due to the earthworm survival being less in this soil type.

Post exposure observation period:

None stated

Test temperature:

The bags were sealed and incubated at 15 degrees C for 30 days.

pH:

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

Moisture:

- SIlty-clay soil: The soil shrank when dry to about 80% of its volume when moist.
- Garden soil: Not stated
- Sand: Not stated

Details on test conditions:

See above text.

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:

30 d

Dose descriptor:

NOEC

Effect conc.:

1 000 other: mg I kg -1 soil

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Basis for effect:

mortality

Remarks on result:

other: Garden soil

Duration:

30 d

Dose descriptor:

NOEC

Effect conc.:

1 000 other: mg I kg-1 soil

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Basis for effect:

mortality

Remarks on result:

other: SIlty-clay soil

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

1 000 other: mg I kg-1 soil

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Basis for effect:

mortality

Remarks on result:

other: Sandy soil

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

The general linear model and non-linear regression routines 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 specified

Conclusions:

Under the protocol followed in this study, the NOEC was 1000 mg I kg -1 for the test substance (I) in all three soil types. The 67% survival rate in sand is probably due to the negligible organic matter content. The survival rate is given as an overall value for the soils (rather than separating out the survival rates at each concentration). The survival in the control soils is also not provided. However, the overall 87% survival rate in the other soils (garden soil and silty-clay soil) was presumably sufficient to determine whether iodine had a statistically significant effect on earthworm survival - the study author concluded that there were no significant trends related to I treatments among the data.

The study differs to standard guidelines (e.g. OECD Guideline 207) when considering a number of factors:

- Duration of exposure: The exposure duration in OECD Guideline 207 is 14 days. In this study dead worms were counted after 14 days in the sand soil, and after 30 days in the other soil types.
- OECD Guideline 207 recommends 5 test concentrations in a geometric series - this study used 8 concentrations with some concentrations in a geometric series.
- Test species: The recommended test species is Eisenia spp. This study used mature earthworms (Lumbricus terrestris), although this species is still considered to be relevant as it is a common earthworm species found in garden and agricultural soils and has an important role in decomposition.
- Soil composition: In OECD 207 one articificial composition is specified, whereas this study investigated three soils with different properties.
- Replicates: Four replicates of each treatment (5 treatments) are used in OECD Guideline 207, in this study 30 replicates per soil were used. The amount of replicates per treatment is not known. In terms of controls OECD Guideline 207 recommends four dishes, each containing 10 worms. This study used 50 replicates of controls.
- OECD Guideline 207 recommends that mortality in the controls should not exceed 10% - in this study the survival in the control soils is not provided

However, this study does investigate the effects of a common earthworm species in more soil types than recommended in standard guidelines, and also investigates the effects using more test concentrations. 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 I 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, but the results still produced a NOEC of 1000 mg I kg -1.

In conclusion, although the protocol is not based on standard guidelines (e.g. OECD Guideline 207), the NOEC of 1000 mg I kg -1 is considered to be supportable as this study follows scientific principles and is well documented. This study is considered to meet the criteria of Klimisch score 2 - reliable with restrictions.

Executive summary:

This study investigated the toxicity of inorganic iodine (applied as KI) to terrestrial biota, which included investigating the effects on earthworms. This use 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. The protocol is not based on standard guidelines (e.g. OECD Guidelines) but follows scientific principles and is well documented, supporting a Klimisch score of 2 - reliable with restrictions. The study author concluded that there were no significant trends related to I treatments among the data. Under the protocol followed in this study, the NOEC was 1000 mg I kg -1 for the test substance (I) in all three soil types.

Reference 2

Endpoint:

toxicity to soil macroorganisms except arthropods: long-term

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Description of key information

Short term:

30 day study (Lumbricus terrestris - mature earthworms)  NOEC: 1000 mg I kg-1 soil (garden soil and silty clay soil)

14 day study  (Lumbricus terrestris - mature earthworms)  NOEC: 1000 mg I kg-1 soil (sandy soil)

Long term:

A long term toxicity test on terrestrial invertebrates is not required as the results from the chemical safety assessment do not indicate a risk to these organisms.

Key value for chemical safety assessment

Short-term EC50 or LC50 for soil macroorganisms:

1 000 mg/kg soil dw

Additional information

The reviewed study investigated the toxicity of inorganic iodine (applied as KI) to terrestrial biota, which included investigating the effects on earthworms. This use 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. The protocol is not based on standard guidelines (e.g. OECD Guidelines) but follows scientific principles and is well documented, supporting a Klimisch score of 2 - reliable with restrictions. The study author concluded that there were no significant trends related to I treatments among the data. Under the protocol followed in this study, the NOEC was 1000 mg I kg -1 for the test substance (I) in all three soil types. Refer to the attached endpoint study record for further details.