Chromium trioxide

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1968 to 1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

The EU RAR summarises the results from a number of higher plant studies which, individually, may have limitations regarding study design and reliability. However, the results of these studies when taken as a whole, provide an adequate assessment of the effects of Cr(VI) to higher plants.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Range of methods used in the review

GLP compliance:

no

Analytical monitoring:

not specified

Species:

other: see results section

Plant group:

other: Monocots and dicots included

Test type:

other: range reported

Study type:

other: range of study types reported

Substrate type:

other: range of substrate types, see results section

Limit test:

no

Remarks:

range

Test temperature:

Range reported

pH:

Range reported

Moisture:

Range reported

Details on test conditions:

See results section

Nominal and measured concentrations:

See Results section

Details on results:

Miller et al. (1980) studied the effects of sodium dichromate on germination and growth of green beans (Phaseolus vulgaris) and sweetcorn (Zea mays) in greenhouse studies. The soil used in the study was a silt loam (organic carbon content 8.1%, pH 6.0-6.2) and 1.8 kg of soil was placed into a pot and planted with 8 seeds. These seedlings were thinned to 6 per pot after germination and the plants grown on for 56 days. At the end of the period, the dry weight yields of crop were determined and compared with that obtained with controls. Two concentrations of Na2Cr2O7 were used in the study, 2.05 g/1.8 kg of dry soil and 12.3 g/1.8 kg dry soil. These concentrations are equivalent to total chromium concentrations of 452 mg Cr/kg dry soil and 2,710 mg Cr/kg dry soil respectively. At the higher exposure concentration, the growth of the crops was severely reduced (10% of controls for beans and 4% of controls for sweetcorn). At the lower exposure concentration, crop growth (yield) was slightly reduced from that of controls (80% of control for beans and 85% of control for sweetcorn; reduction in growth only statistically significant (p=0.01) for beans), and so the exposure concentration of 452 mg Cr/kg dry soil can be considered as a LOEC for beans and a NOEC for sweetcorn. The authors postulated that at least some of the effects seen may have been due to a “salt” effect, due to the high concentrations of sodium also present, but that chromium itself was also toxic to the plants. The effects seen in the study included slowed germination, bluish curled bean leaves and red-tinted and white tipped corn leaves.

Pestemer et al. (1987) reported the results of the OECD Terrestrial Plant Growth Test for potassium dichromate and compared these to results obtained from field studies. The soil used in the laboratory test was a sandy soil of pH 6 and organic carbon content 1.5%. In all 15 plant species were used in the test (Sinapis alba L., Brassica napus L. ssp. napus, Brassica rapa ssp rapa, Brassica chinensis, Raphanus sativus L., Vicia sativa L., Phaseolus aureus Roxb. vigna radiata L., Trifolium pratense L., Trigonella meliotus-coerulea L., Lolium perenne L., Avena sativa L., Triticum aestivum L., Sorghum vulgare Pers., Lepidium sativum L. and Lactuca sativa L.). The EC50 values determined for potassium dichromate were either 100 mg/kg soil (for 9 species) or 10 mg/kg soil (for 6 species). On a total chromium basis, these EC50 values are equivalent to 35.3 mg Cr/kg soil or 3.53 mg/kg soil. The NOEL for the laboratory studies was determined as 0.35-3.53 mg Cr/kg soil. In field studies using the same plant species, stimulation of plant growth or no effects were generally seen at concentrations of 10 and 100 mg/kg of potassium dichromate over the cropping period of the plant. The exception to this was that a slight decrease in growth (<30% effect) was seen at 3.53 mg Cr/kg soil with Sinapis alba L., Brassica napus L, and Raphanus sativus L, but at higher concentrations of 35.3 mg Cr/kg soil, growth stimulation was seen with these species.

10-14 days to chromium (VI) (as potassium dichromate) in a sandy loam soil. The following results were reported for chromium (VI): Avena sativa 14d-EC50 = 30 mg Cr/kg dry soil for growth; Brassica rapa 10d-EC50 = 8.25 mg Cr/kg dry soil for growth (the 10d-EC50 for this species was 4.96 mg Cr/kg dry weight when grown in vermiculite); Lepidum sativum 3d-EC50 = 30 mg Cr/kg soil for germination. Otabbong (1990) reported that a soil concentration of 50 mg Cr (VI)/kg dry soil (as chromium trioxide), caused a slight to moderate inhibition of growth of ryegrass (Lolium perenne) over 30 days.
Adema and Henzen (1989) carried out studies on seed germination and growth (OECD 208) using chromium (VI) (as potassium dichromate) in nutrient solution, a loam soil (1.4% organic matter, pH 7.5) and humic sand (3.7% organic matter, pH 5.1). The species tested included lettuce (Lactuca sativa), tomato (Lycopersicum esulentum) and oats (Avena sativa). The test was carried out from planting the seeds until 14-days after germination occurred. The results of the study are shown in Table 3.60.
Dua and Sawhney (1991) found that chromium (VI) (as potassium dichromate), when added to growth media at a concentration of 52 mg/l, caused the depression in activity of several enzymes associated with germination in seeds of pea (Pisum sativum).

Roy and Mukherji (1982) investigated the effects of chromium (VI) (as potassium dichromate) on the germination of mungbean Phaseolus aureus. A chromium (VI) concentration of 208 mg Cr/l in the growth medium was found to give a reduction in hypocotyl length, root length, wet weight and dry weight after 5 days of germination. Stimulation of enzyme activity was seen at concentrations up to 624 mg Cr/l. Chromium (III) (as chromic sulphate) was also tested under the same conditions and this was shown to be slightly less toxic than chromium (VI), although the reduction in root length seen was similar to that found with chromium (VI).

Turner and Rust (1971) studied the effects of chromium (VI) (as potassium dichromate) on growth of two soybeans (Glycine max L. Merr.) both in nutrient media and soil. In the nutrient media studies, 9-day old plants grown in nutrient solution (pH 6) containing chromium (VI) at concentrations of 0.05-5 mg Cr (VI)/l. After 5 days the plants were assessed for symptoms of toxicity and analysed for the presence of 10 essential elements. A slight, but not statistically significant (p=0.05) increase in the yield of tops was seen at 0.05-0.1 mg Cr (VI)/l, while concentrations of 0.5 mg Cr (VI)/l and above caused a significant reduction in yield of tops and concentrations of 1.0 mg Cr (VI)/l and above caused a significant reduction in yield of roots. A similar pattern was seen in the concentrations of Ca, K, P, Fe, Mn, and Mg found in the plants.
The visual symptoms of toxicity seen in the experiment were wilting of the plants at high doses, and interveinal chlorosis in older leaves. In the soil experiments, potassium dichromate was added to 15-day old plants grown in pots of soil (loam) at doses of 5, 10, 30 and 60 mg Cr (VI)/kg soil. Three days after treatment, the yields of tops and roots were determined. Plants receiving 10 mg Cr (VI)/kg soil showed severe wilting similar to seen in the nutrient solution experiments, and plants receiving 30 and 60 mg Cr (VI)/kg soil died. All treatments significantly reduced the yield of tops.

The ability of chromium (VI) (as chromium trioxide) and chromium (III) (as chromic chloride) to induce stress in barley (Hordeum vulgare) and rape (Brassica napus) has been studied in nutrient culture. The plants (2 week old for barley; 3 week old for rape) were grown in a mineral solution (solution pH=5.0) containing chromium (concentration 10, 30, 50 or 100 mg Cr/l) for between 1 and 14 days. After the exposure period, plants were harvested and inspected for signs of stress. Green leaf material was analysed for the presence of polyamines (produced by the plant when under stress). The growth of plants was found to be significantly reduced at chromium (VI) concentrations of 50 mg/l and above for barley and 30 mg/l and above for rape. No reduction in growth was seen at any of the lower concentrations. In contrast to this, on exposure to chromium (III), growth was significantly reduced only in barley exposed to 100 mg/l. Root length was found to be significantly reduced in all chromium (VI) treatments, whereas chromium (III) caused a significant decrease in root length in barley only at concentrations of 30 mg/l and above. Stress of the plants, as measured by polyamine production and by visual inspection, followed a similar concentration related pattern as the growth parameters. The effects seen were consistent with the toxic effect of chromium (VI) being connected with disturbance of the normal function of the root (Hauschild, 1993).

Liu et al. (1992) studied the effects of chromium (VI) (as potassium dichromate) and chromium (III) (as chromic nitrate) on root growth, cell division and chromosome morphology of Allium cepa grown in nutrient media for 96 hours. A chromium (VI) concentration of 208 mg Cr/l was found to cause an almost complete inhibition in root growth over the 96 hour test period. Chromium (III) was found to be of similar toxicity to root growth as chromium (VI). A small reduction in growth (the significance of which is unknown) was also seen at the lowest concentration of chromium (VI) tested (0.021 mg/l). Miotic irregularities were also seen in the test.

Results of OECD 208 plant growth test (Adema and Henzen, 1989)

Species	Exposure medium	Effect concentration (as Cr(VII))
Avena sativa	Nutrient solution	NOEC = 0.12 mg/L
		EC50 = 1.4 mg/L
	Loam soil	NOEC = 3.5 mg/kg dry weight
		EC50 = 7.4 mg/kg dry weight
	Humic sand	NOEC = 11 mg/kg dry weight
		EC50 = 31 mg/kg dry weight
Lactuca sativa	Nutrient solution	NOEC = 0.04 mg/L
		EC50 = 0.16 mg/L
	Loam soil	NOEC = 0.35 mg/kg dry weight
		EC50 = 1.8 mg/kg dry weight
	Humic sand	NOEC = > 11 mg/kg dry weight
		EC50 = > 11 mg/kg dry weight
Lycopersicon esculentum	Nutrient solution	NOEC = 0.11 mg/L
		EC50 = 0.29 mg/L
	Loam soil	NOEC = 3.2 mg/kg dry weight
		EC50 = 6.8 mg/kg dry weight
	Humic sand	NOEC = 10 mg/kg dry weight
		EC50 = 21 mg/kg dry weight

Validity criteria fulfilled:

yes

Conclusions:

Based on a review of higher plants studies with Cr(VI) and Cr(III) substances, an acceptable assessment of effects on higher plants was achieved. The lowest NOEC from these studies is around 0.35 mg Cr(VI)/kg dry weight of soil.

Executive summary:

Coleman (1988) reported that the amount of chromium 'available' to plants and other soil flora is usually low (e.g. 0.1-1% of the total). This means that in terms of determining a PNEC for the chromium (VI) species of interest, the background concentration of total chromium in soil can be ignored as this is likely to make only a minor contribution to the toxicity seen. 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.

From the EU RAR, a review of the effects of a range of Cr(VI) and Cr(III) substances was carried out. A range of plants species, endpoints, exposure durations and study designs were used to provide a reasonable assessment of toxicological hazard. The lowest NOEC was 0.35 mg Cr(VI)/kg dry weight soil.

It should be noted that studies involving exposure through nutrient solution are included in this section, especially for plants, as they allow exposure to chromium (VI) to be performed. However these studies are not representative of exposure in the environment and are not used in deriving a PNEC.

Reference 2

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

OECD Guideline 208 (Terrestrial Plants Test: Seedling Emergence and Seedling Growth Test)

Version / remarks:

valid version in 1989

GLP compliance:

not specified

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Purity, including information on contaminants, isomers, etc.: >98%

Analytical monitoring:

yes

Details on sampling:

- Concentrations: two or three dose levels in the soils and nutrient solution at start and end of the test
- Sampling method: not specified

Vehicle:

no

Details on preparation and application of test substrate:

- Method of application to soil surface (if used): The test material was added as concentrated solution in water to the soil, such that the desired final concentrations of test material and water in the soil were achieved.
- Controls: yes, but not further specified

Species:

Lactuca sativa

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: lettuce
- Plant family: Asteraceae
- Variety: Ravel RZ

Species:

Lycopersicon esculentum

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: tomato plant
- Plant family: Solanaceae
- Variety: Bellina RZ

Species:

Avena sativa

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: Oat
- Plant family: Poaceae

Test type:

seedling emergence and seedling growth test

Study type:

laboratory study

Substrate type:

natural soil

Limit test:

no

Total exposure duration:

21 d

Test temperature:

25+/-2°C room temperature

pH:

measured at start and end, always in the range of the control; results not given

Moisture:

29.5-30.4% based on dry soil

Details on test conditions:

TEST SYSTEM
- Test container (type, material, size): disposable plastic, diameter 8 cm, height 6 cm
- No. of seeds per container: 10
- No. of plants (retained after thinning): 5
- No. of replicates per treatment group: 5 (one used for chemical analysis only, four with seeds)
- No. of replicates per control: 5

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Soil texture (if natural soil)
- % sand: 90.5% (humic sand) and 71.7% (loam)
- % silt: 5.8% (humic sand) and 17.1% (loam)
- % organic matter: 3.7% (humic sand) and 1.4% (loam)
- pH: 5.1 (humic sand) and 7.5 (loam)

GROWTH CONDITIONS
- Light source: fluorescent tubes (color 57)
- Light intensity and quality: 6500 lux
- Day/night temperatures: 25+/-2°C
- Relative humidity (%): 65%
- Watering regime and schedules: evaporation of water was accurately compensated daily by addition of distilled water
- Water source/type: distilled water
- Volume applied: not specified

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
wet weight (two weeks after germination)

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3.2
- Test concentrations: not specified

Key result

Species:

Lactuca sativa

Duration:

14 d

Dose descriptor:

NOEC

Remarks:

humic sand

Effect conc.:

> 11 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Lactuca sativa

Duration:

14 d

Dose descriptor:

NOEC

Remarks:

loam

Effect conc.:

0.35 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Lactuca sativa

Duration:

14 d

Dose descriptor:

EC50

Remarks:

humic sand

Effect conc.:

> 11 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Lactuca sativa

Duration:

14 d

Dose descriptor:

EC50

Remarks:

loam

Effect conc.:

1.8 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Lycopersicon esculentum

Duration:

14 d

Dose descriptor:

NOEC

Remarks:

humic sand

Effect conc.:

10 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Lycopersicon esculentum

Duration:

14 d

Dose descriptor:

NOEC

Remarks:

loam

Effect conc.:

3.2 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Lycopersicon esculentum

Duration:

14 d

Dose descriptor:

EC50

Remarks:

humic sand

Effect conc.:

21 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Lycopersicon esculentum

Duration:

14 d

Dose descriptor:

EC50

Remarks:

loam

Effect conc.:

6.8 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Avena sativa

Duration:

14 d

Dose descriptor:

NOEC

Remarks:

humic sand

Effect conc.:

11 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Avena sativa

Duration:

14 d

Dose descriptor:

NOEC

Remarks:

loam

Effect conc.:

3.5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Avena sativa

Duration:

14 d

Dose descriptor:

EC50

Remarks:

humic sand

Effect conc.:

31 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Key result

Species:

Avena sativa

Duration:

14 d

Dose descriptor:

EC50

Remarks:

loam

Effect conc.:

7.4 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

Cr

Basis for effect:

growth

Reported statistics and error estimates:

The highest concentration tested that did not cause a plant weight significantly different from the control weight was determined with the Student t-test at a 5% level of significance and is indicated as no observed effect concentration (NOEC).
A curve of the average wet weight per plant with its standard deviation after 2 weeks of growth vs. the concentration of the test material was constructed and from this relation the EC50 and its confidence limits was calculated.

Conclusions:

The EC50 values in humic sand were higher (3-10 times) than those in loam, indicating less adsorption of to loam. This is in agreement with the higher content of organic matter of humic sand. Lettuce was more sensitive than tomato and oats whereby the difference was greater in loam than in humic sand.

Executive summary:

The toxicity of chromium to three types of plants was determined according to OECD Guideline 208. Apart from two types of soil (humic sand and loam), soilless culture was used in the test. It was found that in soilless culture the EC₅₀ values obtained were much lower than those in soil culture. It is concluded that adsorption of the chemical to soil particles is the main factor governing the results. As compound used in the tests potassium bichromate was taken with a purity >98%. The concentrations of Cr in both soils, at the start and end of the test, were-when corrected for the background values-about equal (within 15%) to the nominal values. The background concentrations were about 20 (loam) or 10 (humic sand) mg Cr per kilogram dry soil. 

Description of key information

1) Key_Toxicity to terrestrial plants by summary of data from European Union Risk Assessment Report: chromium trioxide, sodium chromate, sodium dichromate, ammonium dichromate and potassium dichromate; 3rd. Priority List; Volume 53: lowest NOEC: 0.35 mg Cr(VI)/kg dry weight soil for several species from various studies with different test durations

2) Key_Toxicity to terrestrial plants: 14d-EC50: 11-31 mg Cr/kg dry weight soil (humic sand), 1.8-7.4 mg Cr/kg dry weight soil (loam); 14d-NOEC: 10->11 mg Cr/kg dry weight soil (humic sand), 0.35-3.5 mg Cr/kg dry soil weight (loam) for the parameter growth of three species (Lactuca sativa, Avena sativa, Lycopersicon esculentum) exposed to potassium dichromate according to OECD TG 208

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for terrestrial plants:

0.35 mg/kg soil dw

Additional information

1) The EU RAR summarises the results from a number of higher plant studies which, individually, may have limitations regarding study design and reliability. However, the results of these studies when taken as a whole, provide an adequate assessment of the effects of Cr(VI) to higher plants. The lowest NOEC was 0.35 mg Cr(VI)/kg dry weight soil.

2) The toxicity of chromium to three types of plants was determined according to OECD TG 208. Two types of soil (humic sand and loam) and potassium bichromate  as test material were used. The concentrations of Cr in both soils, at the start and end of the test, were-when corrected for the background values-about equal (within 15%) to the nominal values. The background concentrations were about 20 (loam) or 10 (humic sand) mg Cr per kilogram dry soil.