Sodium dichromate

Toxicity to soil macroorganisms except arthropods

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil macroorganisms except arthropods: long-term

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

other:

Remarks:

Well performed with its methodology very close to OECD 220 (Enchytraeid Reproduction Test). However, as artificial soils per se do not reflect a realistic exposure scenario for hazard assessment, the study is considered not reliable.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 220 (Enchytraeid Reproduction Test)

Deviations:

yes

Remarks:

Performed according to the enchytraeid reproduction test (Römbke and Moser, 1999) and modified to account for smaller size and shorter lifecycle of E. coronatus. OECD 220 validity criteria fulfilled.

Principles of method if other than guideline:

The study investigated the chronic effects of three chemicals including potassium dichromate on the survival and reproduction of the oligochaete worm Enchytraeus coronatus using artificial soils as presented in OECD 220 (Enchytraeid Reproduction Test)

GLP compliance:

not specified

Analytical monitoring:

not specified

Test organisms (species):

Enchytraeus sp.

Animal group:

annelids

Details on test organisms:

Enchytraeus coronatus individuals were isolated from E. albidus soil cultures provided by ECT Oekotoxicologie GmbH (Germany)

Pre-Culture of test organisms:
The sterile culture substrate contained 1.5% agar in a solution of 1 g Ca(NO3)2/L, 0.25 g/L MgSO4, 0.25 g/L KNO3 and 0.25 g/L KH2PO4 in distilled water in petri dishes. Incubations were carried out in the dark (20°C, ambient humidity (90%)) in a Sanyo MLR-350 H incubator. 30 mg of autoclaved, ground outs were added in each petri dish as supplementary food.

Study type:

laboratory study

Remarks:

Sanyo MLR-350 H incubator

Substrate type:

artificial soil

Remarks:

according to OECD 220

Total exposure duration:

3 wk

Test temperature:

see below

pH:

see below

Moisture:

see below

Details on test conditions:

The quantity of soil per replicate and exposure time according to OECD 220 (Enchytraeid Reproduction Test), however slightly modified to account for the shorter life cycle of E. coronatus.
Artificial soil was prepared and pH-equilibrated according to OECD 220, distributed into 50 mL glass beakers (15g soil d.w. each) with 5 mg of autoclaved oats added.
7 to 9-week-old worms were used for the test, selected from the agar plates and subsequently used for the toxicity tests. Testing was performed for 3 weeks in the dark at 20°C and 90% humidity in a Sanyo MLR-350 H incubator. Water loss was compensated for by weighing.
Controls included soils without worms to control soil pH and moisture (pH 5.3-5.8, moisture 38.5%-44%)

Nominal and measured concentrations:

Test concentrations: 10, 31.6, 100, 316.2 and 1000 mg K2Cr2O7/kg d.w., corresponding to Cr(VI) concentrations of 3.53, 11.17, 35.35, 111.77 and 353.49 mg Cr(VI)/ kg soil d.w.

Reference substance (positive control):

yes

Remarks:

The toxic effects of carbendazim were also assessed at concentrations of 3.22, 10.17, 32.18, 101.75 and 321.8 mg/kg soil.

Duration:

3 wk

Dose descriptor:

NOEC

Effect conc.:

35.35 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr(VI)

Basis for effect:

reproduction

Remarks on result:

other:

Remarks:

Corresponding to 100 mg K2Cr2O7/kg soil

Duration:

3 wk

Dose descriptor:

LC50

Effect conc.:

198.77 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr(VI)

Basis for effect:

mortality

Remarks on result:

other:

Remarks:

Corresponding to 562.3 mg K2Cr2O7/kg soil

Duration:

3 wk

Dose descriptor:

EC10

Effect conc.:

27.18 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr(VI)

Basis for effect:

reproduction

Remarks on result:

other:

Remarks:

Corresponding to 76.9 mg K2Cr2O7/kg soil

Duration:

3 wk

Dose descriptor:

EC50

Effect conc.:

115.66 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr(VI)

Basis for effect:

reproduction

Remarks on result:

other:

Remarks:

Corresponding to 327.2 mg K2Cr2O7/kg soil

Details on results:

Regarding the calculation of the EC10 and EC50 (RI), the chi-square test for heterogeneity demonstrated a good adjustment of the data to the Probit model (P<0.05). The 3-week LC50 of 562.3 mg K2Cr2O7/kg (corresponding to 198.77 mg Cr(VI)/kg soil d.w.) was estimated as the geometric mean of the 316.2 and 1000 mg K2Cr2O7/kg soil d.w. treatments.

Results with reference substance (positive control):

Carbendazim LC50 > 321.8 mg/kg; NOEC(juvenile/adults) = 10.17 mg/kg; EC10 (reproductive inhibition) = 4.28 mg/kg; EC50 (reproductive inhibition) = 14.09 mg/kg

Reported statistics and error estimates:

NOEC concentrations were determined using the Dunnett test (one-tailed test, alpha=0.05). Normality and homocedasticity of the data were demonstrated by the Kolmogoroff-Smirnov and Bartletts test. In case homocedasticity or normality could not be shown, the non-parametric Bonferri-Holm U test was applied. LC50 values were calculated according to the trimmed Spearman-Karber method. Confidence intervals were given for alpha = 0.05. The mean number of juveniles per concentration was expressed as the percentage relative to the control (= reproductive inhibition).

EC10 and EC50 concentrations for reproductive inhibition were calculated by the Probit method.

Validity criteria fulfilled:

yes

Conclusions:

The laboratory study is well performed, with its methodology besides minor adaptions to account for the E. coronate life cycle very close to OECD 220 (Enchytraeid Reproduction Test). Testing was performed on artificial soils as described in the guideline. Based on the amount of hatched juveniles per adult, a NOEC of 35.35 mg Cr(VI)/kg soil d.w. was derived. In addition, EC10 and EC50 values of 27.18 and 115.66 mg Cr(VI)/kg soil d.w. were determined based on the percentage of reproductive inhibition observed over 3 weeks. Further, the LC50 for Enchytraeus coronatus was determined with 198.77 mg Cr(VI)/kg soil d.w. based on adult mortality. However, as artificial soils per se do not reflect a realistic exposure scenario for hazard assessment, the study is considered not reliable.

Reference 2

Endpoint:

toxicity to soil macroorganisms except arthropods: short-term

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

other: See 'Remarks'

Remarks:

Comparable to guideline study with acceptable restrictions. However, results of the chronic endpoint (reproduction) for the test substance potassium diichromate are not reported. Furthermore, the study was conducted in artifical soil which is considered not relevant for the hazard assessment of metals in soil.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 220 (Enchytraeid Reproduction Test)

Deviations:

yes

Remarks:

Exposure duration increased (4 wk for adult exposure; 4 wk for offspring exposure)

GLP compliance:

no

Analytical monitoring:

no

Vehicle:

no

Details on preparation and application of test substrate:

Homogenous mixtures of 10 g artificial soil and the test substance were prepared.

Test organisms (species):

Enchytraeus albidus

Animal group:

annelids

Details on test organisms:

TEST ORGANISM
- Common name: white worm
- Source: laboratory culture
- Age at test initiation: adult

ACCLIMATION
- Acclimation conditions: culture conditions same as test conditions

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

8 wk

Test temperature:

12 °C

pH:

6.5 ± 0.5

Moisture:

35%

Details on test conditions:

TEST SYSTEM
- Test container (material, size): plastic boxes (8.4 x 8.4 x 4.5 cm)
- Amount of soil or substrate: 10 g
- No. of organisms per container (treatment): 10
- No. of replicates per treatment group: not clear
- No. of replicates per control: not clear

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Composition (if artificial substrate): 10% sphagnum peat, 20% kaolin, 70% quartz sand

OTHER TEST CONDITIONS
- Photoperiod: darkness

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- mortality (once per week, for 4 weeks)
- reproduction (number of the offspring, after 8 weeks)

Nominal and measured concentrations:

Not reported.

Reference substance (positive control):

no

Duration:

28 d

Dose descriptor:

LC50

Effect conc.:

148 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

mortality

Duration:

28 d

Dose descriptor:

LC50

Effect conc.:

417 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

K2Cr2O7

Basis for effect:

mortality

Validity criteria fulfilled:

not specified

Remarks:

Results are nor shown for the test with potassium dichromate.

Conclusions:

A toxicity test similar to OECD 220 was carried out, exposing adult Enchytraeus albidus for 4 weeks to potassium dichromate in artificial soil. After an additional four weeks, the number of offspring, hatched from the cocoons produced by the adults, was determined. While a LC50 of 148 mg Cr/kg soil dw was derived for adult mortality after 4 weeks exposure, results on the reproduction of E. albidus exposed to potassium dichromate are not presented in the study. Therefore, no conclusions can be drawn regarding the chronic toxicity of potassium dichromate to soil invertebrates.

Description of key information

Two toxicity studies equivalent or similar to OECD TG 220 (Enchytraeid reproduction test) on two enchytraeid species, i.e. E. albidus and E. coronatus, are available for potassium dichromate. Arrate et al. (2001) derived a 21 d NOEC of 35.35 mg Cr(VI)/kg soil d.w. based on the number of hatched juveniles per adult, whereas the percentage of reproductive inhibition observed after three weeks results in 21 d EC10 and 21 d EC50 values of 27.18 and 115.66 mg Cr(VI)/kg soil d.w., respectively. Römbke (1989) reports a 28 d LC50 value of 148 mg Cr(VI)/kg soil d.w. in a study with E. albidus and potassium dichromate. Although performed in accordance with OECD TG, the studies are considered of limited relevance for the hazard assessment of chromium (VI) substances in soil due to the use of artificial substrate, which is not considered representative for soil. However, in absence of a comprehensive dataset on the terrestrial toxicity of chromium (VI) substances to soil invertebrates, the lowest effect concentrations observed are considered to support available data from a reliable study on the soil arthropod species Folsomia candida (Lin et al., 2019, Klimisch 2). Please refer to the summary “Toxicity to terrestrial arthropods” for further information.