Chromium trioxide

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:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

see read-across statement section 13

Reason / purpose for cross-reference:

read-across source

Duration:

14 d

Dose descriptor:

LC50

Effect conc.:

>= 1 656 - <= 1 902 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

chromium(III)

Basis for effect:

mortality

Details on results:

The LC50 values of Cr(III) in all soils ranged from 1656 mg/kg (S8) to 1902 mg/kg.
The LC50 values of Cr(III) was 1635 mg/kg in the organic substrate.

Results with reference substance (positive control):

No data

Reported statistics and error estimates:

The data were analyzed using probit analysis to determine the concentration at which 50% mortality occurred. Correlation analysis was performed to assess the nature of the relationship between the LC50 value of Cr(III)and different soil parameters. Stepwise multiple regression analysis was performed to determine the soil variables that significantly influence the LC50 of Cr(III).

Validity criteria fulfilled:

not specified

Conclusions:

The 14-day median lethal concentrations (LC50) of Cr(III) for earthworm range from 1656 to 1902 mg Cr/L in soil. In the organic substrate, the LC50 values of Cr(III) awas 1635 mg Cr/kg soil dw, which is equivalent to an LC50 value of 4979 mg/kg soil dw based on chromium trichloride.

Executive summary:

The study was conducted to evaluate the effects of Cr(III) on the survival, behavior, and morphology of the earthworm, Eisenia fetida, in water at pH 6, 7, and 8 and their toxicity in 10 different soils and an organic substrate. Six concentrations of 500, 1000, 1500, 2000, 2500, and 3000 mg Cr/kg were applied to the test animals in the definitive test. The 14-day LC50 values of Cr(III) in all soils ranged from 1656 mg/kg to 1902 mg/kg at pH 6, 7 and 8. The LC50 values of Cr(III) was 1635 mg/kg in the organic substrate. Changes were not observed in the morphology of earthworms and in their burrowing behavior in both soil and organic media at all test concentrations. The soil variables that showed significant correlations with LC50 values were considered in the development of regression equations. The equations showed that clay alone accounted for 92% of the variation in the toxicity (LC50 values) of Cr(III).

Reference 2

Endpoint:

toxicity to soil macroorganisms except arthropods: long-term

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

From 1981 to 1993

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

The EU RAR summarises the results of a number of studies which, individually, have limitations regarding study design and reliability. However, the results of these studies when taken as a whole, provide an adequate assessment of toxicity to soil macro-organisms (except arthropods).

Qualifier:

no guideline followed

Guideline:

other: range of studies included

Principles of method if other than guideline:

Several studies, collectively, provide a weight-of-evidence to support acute and long-term toxicity

GLP compliance:

no

Analytical monitoring:

yes

Details on sampling:

Various sampling methods employed.

Vehicle:

not specified

Details on preparation and application of test substrate:

None provided.

Test organisms (species):

other: Pheretima posthuma, Enchytraeus albidus, Eisenia foetida, Eisenia andrei

Animal group:

annelids

Details on test organisms:

No other details than presented in the results section.

Study type:

other: range of test designs used

Substrate type:

other: range of substrates used (see results section)

Limit test:

no

Remarks:

range used

Post exposure observation period:

No

Test temperature:

Not stated

pH:

Not stated

Moisture:

Range stated (see results section)

Details on test conditions:

Those stated are presented in the results section

Nominal and measured concentrations:

Range used (see results section)

Reference substance (positive control):

no

Duration:

28 d

Dose descriptor:

LC50

Effect conc.:

146 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr(VI)

Basis for effect:

other: mortality and biomass production

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

792 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr(VI)

Basis for effect:

mortality

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

32 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr(III)

Basis for effect:

other: reproduction, mortality

Details on results:

Soni and Abbasi (1981) studied the effects of chromium (VI) (as potassium dichromate) on the mortality of earthworms (Pheretima posthuma).
Adult earthworms were kept in beakers containing paddy-field soil treated with chromium (VI). Three sets of experiments were carried out starting in May (Set I), June (Set II) and July (Set III), with the soil being renewed every three weeks. Although the results were found to be variable, the time
required for 100% mortality was found to decrease with increasing chromium concentration. The overall estimated times for 100% mortality were 56-116 days at 10 mg Cr/kg soil, 27-109 days at 20 mg Cr/kg soil, 27 to 85 days at 40 mg Cr/kg soil, 27-78 days at 60 mg Cr/kg soil, 6-56 days
at 80 mg Cr/kg soil and 5 days at 100 mg Cr/kg soil. Mortalities in the controls were 1.25-2.5% after 61 days.

A toxicity test has been carried out with chromium (VI) (as potassium dichromate) using the terrestrial annelid Enchytraeus albidus. An artificial
soil was used in the test (10% sphagnum moss, 20% kaolin, 70% quartz; pH 6.5, moisture content 35%). The endpoints monitored included mortality and biomass production. The 28-day LC50 determined in the test was 146 mg Cr (VI)/kg dry soil (Roembke, 1989; Roembke and Knacker, 1989).
Roembke (1989) also reported the results of an OECD207 earthworm, acute toxicity test carried out by Cabridenc (1984) using Eisenia fetida and
potassium dichromate. The 14-day EC50 was determined as 792 mg Cr (VI)/kg dry soil.

Van Gestel et al. (1993) carried out an OECD 21-day earthworm reproduction test using Eisenia andrei in artificial soil at 20°C. The source of
chromium used in the experiment was chromium(III) nitrate. Reproduction was found to be significantly reduced at chromium concentrations of
100 mg Cr/kg dry soil and above, while growth was significantly reduced only at a concentration of 1,000 mg Cr/kg dry soil. The NOEC from the
study was 32 mg/kg dry soil. At the end of the three week exposure period, the earthworms were placed in clean soil for a further 21 days. At
the end of this period, the reproduction of the earthworms had virtually recovered to that of the control organisms.

Reported statistics and error estimates:

None reported.

For Cr(VI) LC50 and EC50 values were 146 and 792 mg Cr(VI)/kg dry soil. An NOEC value of 32 mg Cr(III)/kg dry soil was observed.

Validity criteria fulfilled:

yes

Conclusions:

Based on a review of existing data on annelids from the EU RAR, an acceptable assessment of acute and long-term toxicity was achieved.

Executive summary:

Once released into soil, it is likely that much of the chromium (VI) present will be reduced to chromium (III). Toxicity data are available for chromium (VI) in soil, but it is also likely that in these experiments the majority of the chromium present will be converted to chromium (III) during the test. Hence, data on chromium (III) nitrate is also presented.

Chromium (III) has generally been shown to be less toxic than chromium (VI) to soil organisms. For Cr(VI) LC50 and EC50 values were 146 and 792 mg Cr(VI)/kg dry soil. An NOEC value of 32 mg Cr(III)/kg dry soil was observed.

Description of key information

The study of Sivakumar (2005) was conducted to evaluate the effects of Cr(VI) on the survival, behavior, and morphology of the earthworm, Eisenia fetida, in water at pH 6, 7, and 8 and their toxicity in 10 different soils and an organic substrate. Six concentrations of 100, 150, 200, 250, 300, and 350 mg Cr/kg were applied to the test animals in the definitive test. The 14-day LC50 values of Cr(VI) in all soils ranged from 222 mg/kg to 257 mg/kg at pH 6, 7 and 8. The LC50 values of Cr(VI) was 219 mg/kg in the organic substrate. Changes were not observed in the morphology of earthworms and in their burrowing behavior in both soil and organic media at all test concentrations. The soil variables that showed significant correlations with LC50 values were considered in the development of regression equations. The equations showed that clay alone accounted for 92% of the variation in the toxicity (LC50 values) of Cr(VI).

Further, Cr(VI) availability in soils may also be reduced because of its reduction to Cr(III) in the presence of reducing agents and the higher affinity of the latter (30- to 300 - fold) to soil clay minerals than Cr(VI).

The toxicity of Cr(VI) was four and seven times greater than that of Cr(III) in water and soil, respectively. Stepwise multiple regression analysis predicted that the clay content of soils accounted for 92% and 88% of the variation in the LC50 values of Cr(III) and Cr(VI), respectively.

Several studies, collectively, provide a weight-of-evidence to support the acute and long-term toxicity to soil macro-organisms are reported in the EU RAR.

Key value for chemical safety assessment

Short-term EC50 or LC50 for soil macroorganisms:

222 mg/kg soil dw

Additional information

Once released into soil, it is likely that much of the chromium (VI) present will be reduced to chromium (III). Toxicity data are available for chromium (VI) in soil, but it is also likely that in these experiments the majority of the chromium present will be converted to chromium (III) during the test. Chromium (III) has generally been shown to be less toxic than chromium (VI) to soil organisms. For Cr(VI) LC50 and EC50 values were 146 and 792 mg Cr(VI)/kg dry soil. An NOEC value of 32 mg Cr(III)/kg dry soil was observed.