Diquat dibromide

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

28 Feb 2005 to 11 Apr 2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2000

Deviations:

yes

Remarks:

See 'Deviations from the study plan' in 'Any other information on materials and methods incl. tables'

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Samples collected on 28 Feb 2005 to verify the test substance concentrations in soil. Immediately after mixing the the substance with soil and before dilution or application, triplicate samples of 100 g each were collected from the concentrations of 3 and 100 mg ai/ kg dry soil on the day of preparation, and single samples were collected from the control and all other concentrations. Samples were shipped on 07 March 2005 with dry ice for residue analysis. The samples arrived on 08 March 2005 deep frozen with dry ice remaining.

Vehicle:

no

Details on preparation and application of test substrate:

Soil of all species was treated on 28 February 2005. First a stock solution of the highest concentration was prepared by dissolving 59.289 g test item in 100 mL water. The lower concentrations were obtained by diluting an aliquot of the stock solution (19.44, 6.48, 1.944, 0.648, 0.1944 and 0.0648 ml made up to 64.8 mL, respectively) in water. Application and incorporation of the control started at 15:30 h, continued by ascending concentrations with the highest rate applied at 17:50 h.
Application was performed by distributing the prepared spray solution on the soil (saturated to approx. 50 % of the water holding capacity) with a hand atomiser while mixing the soil with a kitchen stirrer until all spray solution prepared was applied. After a 7 day lasting aging period in 5 cm high trays (40 cm x 55 cm x 5 cm) covered with a transparent plastic film a total of 6 or 10 pots per species and concentration were prepared afterwards by filling them with the treated soil.

Species:

Brassica napus

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Oilseed rape
- Plant family: Brassicaceae
- Variety: Talent
- Prior seed treatment: None
- Seed depth: 1.5 cm

Species:

Helianthus annuus

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Sunflower
- Plant family: Asteraceae
- Variety: Peredovick
- Prior seed treatment: None
- Seed depth: 1.5 cm

Species:

Triticum aestivum

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: Wheat
- Plant family: Poaceae
- Variety: Estero
- Prior seed treatment: None
- Seed depth: 1 cm

Species:

Zea mays

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: Corn
- Plant family: Poaceae
- Variety: Golden Bantan
- Prior seed treatment: None
- Seed depth: 1 cm

Test type:

seedling emergence and seedling growth test

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

28 d

Test temperature:

16.5 - 21.5°C

Moisture:

45 - 95 %

Details on test conditions:

TEST SYSTEM
- Testing facility: A polycarbonate greenhouse (with a floor area of 400 m2).
- Test container: Plastic pots approximately 16 cm in diameter and 12 cm in depth.
- Randomisation: Pots were moved at random at the 7 and 14 day (all species) and 20 days (for Helianthus annuus only) assessment to compensate potential non-homogeneous conditions in the greenhouse.

An overview of the experimental set-up was provided in Table 1 in 'Any other information on materials and methods inlc. tables'.
- No. of seeds per container: 5 - 7
- No. of replicates per treatment group: 6 - 10
- No. of replicates per control: 6 -10

SOURCE AND PROPERTIES OF SUBSTRATE
- Soil type: Artificial soil substrate (sterilised soil mixed with sand and bentonite and adjusted to the pH)
- Pesticide use history: Soil, clay and sand had not been subjected to any pesticide or organic fertiliser treatment for at least 3 years prior to collection and until use by the test facility.
- Soil classfication: Clay sand (according to German classficiation)
- % sand: 82%
- % silt: 5%
- % clay: 13%
- WHC: 18.8%
- pH (CaCl2): 7.3
- Organic carbon (%): 1.74%
- Pretreatment of soil: The soil was sieved to a particle size of 5 mm after slightly drying. A sample of soil representative of that used in this
study was sent to the soil analytical laboratory for characterization
- Storage: After mixing and sieving the soil was stored dry in the greenhouse until use.

GROWTH CONDITIONS
- Photoperiod: 16 hours light and 8 hours darkness
- Light intensity: 5000-30000 Lux

EFFECT PARAMETERS MEASURED
Observations were made during the test to document plant condition and growth. The condition of test plants was assessed weekly after 50 % emergence in control. A total of 3 - 4 assessments of phytotoxicity (stunted growth, wilting, discoloration, necrosis) were performed (at 7, 14 and 20 (all species) and 28 days ( Helianthus annuus) after 50 % emergence in the control). The assessments were done according the EPPO guideline 1/135(2). After approval of study director and sponsor the trial was prolonged from 21 to 28 days in order to check for a recovery of Helianthus annuus.
At the final assessment the shoot fresh weight was determined for all plants of one replicate as a batch sample. The plants were clipped at soil level and each replicate was weighed immediately afterwards to avoid losses of plant fresh weight. After determination of the fresh weight plants were dried for approx. 12 h at 80 °C in an aerated drying oven and weighed again to determine the dry weight.

Nominal and measured concentrations:

- Nominal concentration: 0 (negative control), 0.1, 0.3, 1.0, 3.0, 10, 30 and 100 mg a.i. (as cation)/kg soil dw
- Measured concetration: 0 (negative control), 0.084, 0.257, 0.825, 2.77, 9.70, 27.4 and 91.1 mg a.i.(as cation)/kg soil dw (see Table 2 in 'Any other information on materials and methods incl. tables')

Reference substance (positive control):

no

Key result

Species:

Zea mays

Duration:

20 d

Dose descriptor:

NOEC

Effect conc.:

5.6 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

seedling emergence

Remarks on result:

other: Recalculated value, expressed as pure substance, see ‘Any other information on results incl. tables’ for respective calculation

Key result

Species:

Helianthus annuus

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

> 186.8 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: Seedling emergence and dry weight

Remarks on result:

other: Recalculated value, expressed as pure substance, see ‘Any other information on results incl. tables’ for respective calculation

Key result

Species:

other: Brassica napus and Triticum aestivum

Duration:

20 d

Dose descriptor:

EC50

Effect conc.:

> 186.8 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

other: Seedling emergence and dry weight

Remarks on result:

other: Recalculated value, expressed as pure substance, see ‘Any other information on results incl. tables’ for respective calculation

Details on results:

An overview of the results is provided in Table 3 – Table 5 in ‘Any other information on results incl. tables’.

- Seedling Emergence: No effects were observed on Brassica napus or Triticum aestivum. A very slight effect on the emergence was noted for Helianthus annuus at a soil concentration of 10 -100 mg a.i./kg oven-dried soil, but the responses were not continuous with ascending concentrations. A statistically significant reduction of 23 - 30 % in emergence of Zea mays from soil concentrations of 30.0 and 100.0 mg a.i. (as cation)/kg oven-dried soil was observed.
- Phytotoxicity: Apart from Brassica napus, visual phytotoxicity symptoms that increased with higher dosage rate were observed for all species tested.
- Biomass: The higher concentrations of the test item reduced the dry biomass of all tested species, with maximum reductions of 12 - 34% seen at 100 mg/kg for the 4 species. Lower reductions in dry weight were seen at lower rates. Statistically significant reductions of up to 16-17 % in dry weight of Zea mays from soil concentrations of 10.0 and 30.0 mg a.i./kg oven-dried soil were observed. At 100 mg a.i.(as cation)/kg oven-dried soil statistically significant reductions were observed for all species with a maximum of 34 % for Zea mays.

Reported statistics and error estimates:

See Statistics in 'Any other information on materials and methods incl. tables'.

Table 3. Effects on seedling emergence (Number of emerged plants) caused by pre-seeding application followed by a 7 day aging period of the test substance (dosage in mg a.i.(as cation)/kg oven-dried soil).

Species	Brassica napus
Parameter	Means, significance			Standard Deviations			Inhibitions  (% compared to control)
Time	day 7	day 14	day 20	day 7	day 14	day 20	day 7	day 14	day20
Dosage
0.0	3.80	3.80	3.80	0.79	0.79	0.79	-	-	-
0.1	380	3.80	3.80	0.63	0.63	0.63	0.00	0.00	0.00
0.3	3.80	3.80	3.80	0.92	0.92	0.92	0.00	000	0.00
1.0	3.70	3.70	3.70	0.95	0.95	0.95	2.63	2.63	2.63
3.0	3.50	3.50	3.50	0.71	0.71	0.71	7.89	7.89	7.89
10.0	3.90	3.90	3.90	0.99	0.99	0.99	-2.63	-2.63	-2.63
30.0	3.90	3.90	3.90	0.88	0.88	0.88	-2.63	-2.63	-2.63
100.0	3.80	3.80	3.80	0.79	0.79	0.79	0.00	0.00	0.00
Species	Helianthus annuus
Parameter	Means,significance			Standard Deviations			Inhibitions (% compared to control)
Time	day 7	day 14	day 20/28	day 7	day 14	day 20/28	day 7	day 14	day 20/28
Dosage
0.0	4.20	4.20	4.20	0.42	0.42	0.42	-	-	-
0.1	3.90	3.90	3.90	0.74	0.74	0.74	7.14	7.14	7.14
0.3	4.20	4.20	4.20	0.92	0.92	0.92	0.00	0.00	0.00
1.0	3.80	3.80	3.80	0.92	0.92	0.92	9.52	9.52	9.52
3.0	4.00	4.00	4.00	0.67	0.67	0.67	4.76	4.76	4.76
10.0	3.70	3.70	3.70	0.67	0.67	0.67	11.90	11.90	11.90
30.0	3.60	3.60	3.60	0.84	0.84	0.84	14.29	14.29	14.29
100.0	3.70	3.70	3.70	0.82	0.82	0.82	11.90	11.90	11.90
Species	Triticum aestivum
Parameter	Means,significance			Standard Deviations			Inhibitions (% comPared to control)
Time	day 7	day 14	day 20	day 7	day 14	day 20	day 7	day 14	day 20
Dosage
0.0	6.00	6.00	6.00	0.63	0.63	0.63	-	-	-
0.1	5.83	5.83	5.83	0.75	0.75	0.75	2.78	2.78	2.78
0.3	6.00	6.00	6.00	0.63	0.63	0.63	0.00	0.00	0.00
1.0	6.17	6.17	6.17	0.75	0.75	0.75	-2.78	-2.78	-2.78
3.0	5.83	5.83	5.83	0.41	0.41	0.41	2.78	2.78	2.78
10.0	5.83	5.83	5.83	0.75	0.75	0.75	2.78	2.78	2.78
30.0	5.50	5.67	5.67	0.84	0.52	0.52	8.33	5.56	5.56
100.0	5.33	5.50	5.50	0.82	0.55	0.55	11.11	8.33	8.33
Species	Zea mays
Parameter	Means, significance			Standard Deviations			Inhibitions (% comnared to control)
Time	day 7	day 14	day 20	day 7	day 14	day 20	day7	day 14	day20
Dosage
0.0	4.40	4.40	4.40	0.70	0.70	0.70	-	-	-
0.1	4.30	4.30	4.30	0.67	0.67	0.67	2.27	2.27	2.27
0.3	4.20	4.20	4.20	0.79	0.79	0.79	4.55	4.55	4.55
1.0	3.90	3.90	3.90	0.74	0.74	0.74	11.36	11.36	11.36
3.0	3.80	3.80	3.80	0.92	0.92	0.92	13.64	13.64	13.64
10.0	3.60	3.60	3.60	0.97	0.97	0.97	18.18	18.18	18.18
30.0	3.40	3.40	3.40*	0.70	0.70	0.70	22.73	22.73	22.73
100.0	3.10	3.10	3.10**	0.74	0.74	0.74	29.55	29.55	29.55

  * significant difference compared to the water control (p < 0.05, Wilcoxon rank-sum test and Bonferroni-adjustment)

** significant difference compared to the water control (p < 0.01, Wilcoxon rank-sum test and Bonferroniadjustment). Significances are only given if the mean is in fact smaller than the control mean.

 

Table 4. Phytotoxicity symptoms (% compared to control ) caused by preseeding application followed by a 7 day aging period of the test substance (dosage in mg a.i.(as cation)/kg oven-dried soil).

Species Brassica napus Parameter Means Standard Deviations Time day 7 day 14 day 20 day 7 day 14 day 20 Dosage             0.0 - - - - - - 0.1 0.00 0.00 0.00 0.00 0.00 0.00 0.3 0.00 0.00 0.00 0.00 0.00 0.00 1.0 0.00 0.00 0.00 0.00 0.00 0.00 3.0 0.00 0.00 0.00 0.00 0.00 0.00 10.0 0.00 0.00 0.00 0.00 0.00 0.00 30.0 0.00 0.00 0.00 0.00 0.00 0.00 100.0 0.00 0.00 0.00 0.00 0.00 0.00 Species Helianthus annuus Parameter Means Standard Deviations Time day 7 day 14 day20 Day28 day 7 day 14 day 21 Day28 Dosage                 0.0 - - - - - - - - 0.1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.0 0.00 0.00 0.00 0.00 0 00 0.00 0.00 0.00 3.0 0.00 5.50 3.50 8.00 0.00 0.00 0.00 6.75 10.0 0.00 5.50 3.00 7.00 0.00 1.58 3.37 5.87 30.0 0.00 7.00 5.00 7.00 0.00 1.58 2.58 7.89 100.0 6.50 11.50 12.00 17.00 0.00 2.58 4.08 4.83 Species Triticum aestivum Parameter Means Standard Deviations Time day 7 day 14 day 20 day 7 day 14 day20 Dosage             0.0 - - - - - - 0.1 0.00 0.00 0.00 0.00 0.00 0.00 0.3 0.00 0.00 0.00 0.00 0.00 0.00 1.0 0.00 0.00 0.00 0.00 0.00 0.00 3.0 0.00 0.00 0.00 0.00 0.00 0.00 10.0 0.00 0.00 5.00 000 0.00 4.47 30.0 0.00 0.00 13.33 0.00 0.00 6.06 100.0 0.00 0.00 36.67 0.00 0.00 5.16 Species Zea mays Parameter Means Standard Deviations Time day 7 day 14 day 20 day 7 day 14 day 20 Dosage             0.0 - - - - - - 0.1 0.00 0.00 0.00 0.00 0.00 0.00 0.3 0.00 0.00 0.00 0.00 0.00 000 1.0 0.00 0.00 0.00 0.00 0.00 0.00 3.0 000 0.00 0.00 0.00 0.00 0.00 10.0 0.00 1.50 1.00 0.00 3.37 2.1 I 30.0 0.00 0.50 2.00 0.00 1.58 3.50 100.0 1.00 9.50 12.00 2.11 5.99 6.75

Table 5. Biomass (fresh and dry weight of plants (g)) after a pre-seeding application followed by a 7 day aging period of the test substance (dosage in mg a.i.(as cation)/kg oven-dried soil)

 

FRESH WEIGHT
Species	Brassica napus			Helianthus annuus
Parameter Dosage	Means	Standard Deviations	Inhibitions (¾comp. to control)	Means	Standard Deviations	Inhibitions (¾comp. to control)
0.0	15.36	1.41	-	40.04	4.28	-
0.1	15.23	1.16	0.84	39.91	4.54	0.33
0.3	14.92	0.77	2.88	39.17	2.05	2.18
1.0	14.72	1.10	4.17	38.33	2.31	4.29
3.0	14.53	0.78	5.39	39.13	4.01	2.28
10.0	14.10	1.47	8.18	38.76	3.96	3.21
30.0	14.08	1.63	8.32	32.93	2.99	17.78
100.0	14.11	1.07	8.13	28.44	5.04	28.97
Species	Triticum aestivum			Zea mays
Parameter Dosage	Means	Standard Deviations	Inhibitions (%comp.to control)	Means	Standard Deviations	Inhibitions (¾comp. to control)
0.0	7.39	0.71	-	10.44	1.33	-
0.1	7.63	0.28	-3.34	10.20	1.65	2.31
0.3	7.10	0.57	3.90	10.57	0.74	-1.24
1.0	6.98	0.84	5.55	10.47	1.72	-0.24
3.0	6.79	1.26	8.12	9.51	1.47	8.93
10.0	6.56	1.07	11.17	9.39	2.22	10.09
30.0	6.76	0.40	8.46	9.00	1.45	13.84
100.0	5.47	0.82	26.00	7.26	2.02	30.46
DRY WEIGHT
Species	Brassica napus			Helianthus annuus
Parameter Dosage	Means, signif.	Standard Deviations	Inhibitions (%comp.to control)	Means, signif.	Standard Deviations	Inhibitions (%comp.to control)
0.0	1.80	0.28	-	4.17	0.48	-
0.1	1.77	0.27	1.45	4.14	0.43	0.58
0.3	1.71	0.11	5.06	4.02	0.22	3.41
1.0	1.74	0.19	3.45	3.87	0.22	7.11
3.0	1.71	0.12	4.89	3.87	0.37	7.11
10.0	1.63	0.20	9.56	3.82	0.41	8.36
30.0	1.64	0.24	8.89	3.17**	0.32	23.84
100.0	1.58*	0.17	12.45	2.78**	0.54	33.25
Species	Triticum aestivum			Zea mavs
Parameter Dosage	Means, signif.	Standard Deviations	Inhibitions (¾comp. to control)	Means, signif.	Standard Deviations	Inhibitions (¾comp. to control)
0.0	1.19	0.11	-	0.97	0.10	-
0.1	1.22	0.09	-2.66	0.94	0.15	3.59
0.3	1.18	0.06	1.26	0.95	0.06	2.67
1.0	1.08	0.10	9.09	0.90	0.16	7.80
3.0	1.06	0.21	11.19	0.85	0.12	12.94
10.0	1.03	0.15	13.85	0.82*	0.19	16.22
30.0	1.09	0.06	8.67	0.81*	0.12	16.63
100.0	0.97*	0.09	18.46	0.65**	0.17	33.57

signif.=significance;

* significant difference compared to the control (p < 0.05);

** significant difference compared to the control (p < 0.0 I)

Dunnett's test was used forBrassica napusandZea mays, Wilcoxon rank-sum test (U-test) followed by a step down­ Bonferroni adjustment forTriticum aestivumandHelianthus annuus.Statistical anlalysis was only done on dry biomass.

 

Calculation of key results

The original effect levels were expressed as cation species of the test substance. The key effect levels are re-calculated and corrected to include the counterion species by multiplying with 1.868 (344.0 g/mol molecular weight of test substance divided by 184.2 g/mol molecular weight of cation species).:

NOEC: 1.868 x 3 mg a.i. (as cation)/kg soil dw = 5.6 mg pure test substance/kg soil dw

EC50: 1.868 x 100 mg a.i. (as cation)/kg soil dw = 186.8 mg pure test substance/kg solil dw

Validity criteria fulfilled:

yes

Conclusions:

The EC50 for seedling emergence and dry weight of all four species was determined to be >100 mg cation/kg soil dw. The NOEC for growth (dry weight) of Zea mays was determined to be 3 mg cation/kg soil dw.

Executive summary:

A greenhouse toxicity study was performed to determine the effects of the test substance on the seedling emergence of Oilseed rape (Brassica napus), sunflower (Helianthus cinnuus), wheat (Triticum aestivum) and Corn (Zea mays). This study followed OECD TG 208 and compliant with GLP criteria. Seven test concentrations (0.1, 0.3, 1.0, 3.0, 10.0, 30.0 and 100 mg cation/kg oven-dried soil of the test substance and a negative (deionised water) control were tested. The spray solutions were applied to the soil with a hand atomiser while mixing the soil with a kitchen stirrer to simulate soil incorporation. After 7 days of aging seeds of two monocot species (Triticum aestivum, Zea mays) and two dicot species (Brassica napus, Helianthus annuus) were planted. Each treatment group consisted of 6 - 10 replicates, with each pot containing 5 - 7 planted seeds of one species. The test duration was 21 (Triticum aestivum, Zea mays, Brassica napus) or 28 days (Helianthus annuus) after 50% emergence in the control. The number of emerged seedlings, number of surviving seedlings and phytotoxicity were assessed 7, 14 and 20 (Triticum aestivum, Zea mays,Brassica napus) or 28 (Helianthus annuus) days after 50% emergence in the control. The seedling weight was determined at test termination 21 days after 50% emergence in the control only. The study was carried in 16.5 – 21.5 °C and with 45-95% humidity. The plants received 5000 - 30000 lux of light intensity (16 hours light and 8 hours darkness per day).

Seedling emergence:

No statistically significant effects were observed on Brassica napus, Triticum aestivum or Helianthus animus. Significant effects on Zea mays from a soil concentration of 30.0 mg cation/kg oven-dried soil were observed. Statistically significant reductions of 23 - 30% in emergence of Zea mays from soil concentrations of 30.0 and 100.0 mg cation/kg oven-dried soil were observed. Visual phytotoxicity symptoms were less than 14% for all species tested at rates up to 30 mg cation/kg oven dried soil.Triticum aestivumwas the most sensitive species with 37% damage recorded at the highest rate (100 mg cation/ kg soil dw).

Biomass (dry weight):

The higher concentrations of the test item reduced the biomass of all tested species. The maximum reductions seen at 100 mg cation/kg oven-dried soil were 12 - 34% for the 4 species. Lower

reductions in dry weight were seen at lower rates. Statistically significant reductions of up to 16 - 17% in dry weight of Zea mays from soil concentrations of 10.0 and 30.0 mg cation/kg oven-dried soil were observed. At 100 mg cation/kg oven-dried soil statistically significant reductions were observed for all species with a maximum of 34% for Zea mays.

 

Based on the findings, the EC50 for seedling emergence and dry weight of all four species was determined to be >100 mg cation/kg soil dw. The NOEC for growth (dry weight) of Zea mays was determined to be 3 mg cation/kg soil dw.

 

Description of key information

20-d EC50 >186.8 mg pure test substance/kg soil dw, seedling emergence and growth (dry weight), Brassica napus, Triticum aestivum and Zea mays, OECD TG 208, Balluff 2006

28-d EC50 >186.8 mg pure substance/kg soil dw, seedling emergence and growth (dry weight), Helianthus cinnuus, OECD TG 208, Balluff 2006

20-d NOEC = 5.6 mg pure test substance/kg soil dw, growth (dry weight), Zea mays, OECD TG 208, Balluff 2006

Key value for chemical safety assessment

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

5.6 mg/kg soil dw

Additional information

A greenhouse toxicity study was performed to determine the effects of the test substance on the seedling emergence of Oilseed rape (Brassica napus), sunflower (Helianthus cinnuus), wheat (Triticum aestivum) and Corn (Zea mays) under GLP to OECD TG 208. Test concentrations of 0.1, 0.3, 1.0, 3.0, 10.0, 30.0 and 100 mg cation/kg oven-dried soil were tested in parallel to a solvent control (deionised water). After 7 days of aging following the appliction of test substance to the soil, seeds of two monocot species (wheat and corn) and two dicot species (rape and sunflower) were planted. Each treatment group consisted of 6 - 10 replicates, with each pot containing 5 - 7 planted seeds of one species. The test duration was 21 or 28 days after 50% emergence in the control. The study was carried at 16.5 – 21.5 °C and with 45 to 95% humidity. The plants received 5000 - 30000 lux of light intensity (16 hours light and 8 hours darkness per day).

Seedling emergence: No statistically significant effects were observed on rape, sunflower and wheat. Significant effects on corn were seen from a soil concentration of 30.0 mg cation/kg soil dw, with reductions of 23-30% in emergence of corn seeds at 30.0 and 100.0 mg cation/kg soil dw. Visual phytotoxicity symptoms were less than 14% for all species tested at rates up to 30 mg cation/kg soil dw. Wheat was the most sensitive species with 37% damage recorded at 100 mg cation/kg soil dw.

Biomass (dry weight): Statistically significant reductions of up to 16-17% in dry weight of corn at soil concentrations of 10.0 and 30.0 mg cation/kg soil dw were observed. At 100 mg cation/kg soil dw, statistically significant reductions were observed for all four species with a maximum of 34% for corn.

Based on the findings, the EC50 for seedling emergence and dry weight of all four species was determined to be >100 mg cation/kg soil dw (equivalent to >186.8 mg registered substance/kg soil dw. The NOEC for growth (dry weight) of corn was determined to be 3 mg cation/kg soil dw (equivalent to 5.6 mg registered substance/kg soil dw).