Paraquat-dichloride

Toxicity to aquatic plants other than algae

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic plants other than algae

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

07 May 1992 to 21 May 1992

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: US EPA Pesticide Assessment Guidelines, Subdivision J, Hazard Evaluation: Non target plants EPA 540/09-86-134

Version / remarks:

1986

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

The test concentration were analytically determined on day 8 and 14.

Vehicle:

no

Details on test solutions:

A 1000 mL stock solution (nominal concentration 51200 μg/L) was prepared by the direct addition of the test substance to sterile culture medium. The three highest nominal concentration test solutions were prepared, using sterile medium, by the addition of an aliquot of this stock. All lower test_concentrations were similarly prepared, using aliquots of the nominal 512 μg/L test solution. The control consisted of culture medium only. All final solution volumes were 1000 mL and contained nutrients (Hoagland's M-Medium).

Test organisms (species):

Lemna gibba

Details on test organisms:

TEST ORGANISM
- Common name: Duckweed
- Strain: G3
- Source: University of Waterloo, Canada.
- Method of cultivation: The cultures were grown in the medium, and under the environmental conditions, described for the test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

14 d

Test temperature:

24.9 - 25.4 °C

pH:

- New solutions: 4.5 - 4.9
- Old solutions: 4.8 - 5.6

Nominal and measured concentrations:

- Nominal concentrations: 0 (control), 4.0, 8.0, 16, 32, 64, 128, 256 and 512 μg/L
- Mean measured concentrations:

Details on test conditions:

TEST SYSTEM
- Incubation chamber used: Yes; The cultures were incubated at 25 ± 1 °C in a Gallankamp INR-401 type incubator
- Test vessel: The test vessels were borosilicate glass cylindrical dishes of 400 mL nominal capacity
- Type: Closed
- Fill volume: 160 mL
- Type of cover: Loose-fitting lids
- Aeration: No
- No. of colonies per vessel: 3
- No. of fronds per colony: 4
- No. of vessels per concentration: 3
- No. of vessels per control: 3

GROWTH MEDIUM
- Standard medium used: The culture medium used for the test, and for the maintenance of cultures of the duckweed used as inoculum for the test was that described by Hillman, and known as M-Hoagland's M-medium.

OTHER TEST CONDITIONS
- Photoperiod: Continuous
- Light intensity and quality: Approximately 5000 lux; the cultures were illuminated using "warm-white" lights.

WATER QAULITY PARAMETERS
- pH: The pH of each newly prepared ("on") test solution was measured on days 0, 4, 8 and 11, using the excess remaining after filling the test vessels. The pH of 2 replicates of replaced ("old") test solutions were similarly measured, after plant transfer, on days 4, 8, 11 and 14. The measurements were made using a Coming Model 240 pH meter.
- Temperature: The temperature of the incubator was measured daily by thermometer and at hourly intervals using an automatic recording system. The light intensity was measured once during each week of the study, using a Skye Instruments photometer.

EFFECT PARAMETERS MEASURED: plant number, frond number, symptoms of toxicity, dry weight
On days 1, 4, 6, 8, 11 and 14 the number of plants and the number of fronds were counted and recorded for each test vessel. All fronds which visibly projected beyond the edge of the parent frond were counted. Any other symptoms of toxicity were recorded. At the end of the test (14 days) the duckweed from each vessel was rinsed briefly in distilled water and dried to constant weight at 60°C. The dry weight of the tissue was determined.

Reference substance (positive control):

no

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

52.3 µg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

frond number

Remarks on result:

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

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

113 µg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

frond number

Remarks on result:

other: 95% C.I.: 101 - 127 µg/L

Remarks:

Original value as presented in the study report

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

29.6 µg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

frond number

Remarks on result:

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

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

64 µg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

frond number

Remarks on result:

other: Original value as presented in the study report

Details on results:

The results are presented in 'Any other information on results incl. tables'
- Frond growth: No significant inhibition of frond growth was identified at nominal concentrations of 64 μg/L and below. Significant inhibition was observed in the three higher concentration treatments in a dose-dependent matter.
- Dry weight: No significant effect on dry weight increase was noted in nominal concentrations of 64 μg/L and below. Significant decrease in dry weights was observed in the three higher concentration treatments in a dose-dependent matter.
- Symptoms of toxicity: From day 4 onwards, plants in the 128, 256 and 512 μg/L test concentrations started to exhibit progressively more marked visible effects, including paler frond colouration and small size, less root growth, abnormal colony configurations and flotation patterns. A similar pattern was visible in the 64 μg/L test concentration from day 6 onwards. On day 14, the plants in the 32 μg/L test replicates were recorded as having pale colouration in some fronds and visibly reduced root growth. With the exception of the observation that plants in one replicate of the 8.0 μg/L test concentration appeared to have a smaller colony size and less root growth on day 11 only, there were no observed symptoms at, or below, the nominal 16 μg/L test concentration when compared to the control. Therefore, the transient variation in growth at the 8.0 μg/L test concentration was considered not to have been due to any effect by the test substance.

Reported statistics and error estimates:

The data for increase in number of fronds were examined by one-sided analysis of variance, and Dunnett's procedure was used to identify significant inhibition (P=0.05, one-sided) compared with the control. The data for weight increase were analysed as described for frond increase, to identify significant inhibition (P=0.05) compared with the control.

Table: Frond and plant numbers

Nominal concentration of technical test material   (µg/L)	Replicate	Number of fronds (Number of plants)
		Day 1		Day 4		Day 6		Day 8		Day 11		Day 14
Control	A B C Mean	14 13 13 13	(4) (3) (3)	44 33 40 39	(8) (6) (6)	66 49 62 59	(11) (9) (10)	103 89 103 98	(18) (15) (19)	186 157 168 170	(42) (33) (40)	280 230 271 260	(66) (51) (62)
4.0	A B C Mean	13 14 13 13	(4) (4) (4)	37 38 37 37	(5) (6) (6)	53 51 60 55	(12) (11) (12)	97 91 95 94	(14) (15) (19)	178 162 162 167	(38) (34) (35)	259 248 306 271	(60) (60) (60)
8.0	A B C Mean	13 15 13 14	(4) (3) (3)	35 35 36 35	(6) (6) (6)	53 55 56 55	(10) (11) (11)	89 92 92 91	(16) (18) (17)	170 117 163 150	(34) (43) (35)	256 214 270 247	(91) (53) (66)
16	A B C Mean	12 14 14 13	(4) (4) (4)	34 39 36 36	(6) (6) (6)	49 64 57 57	(11) (12) (11)	88 97 93 93	(17) (21) (19)	174 194 196 188	(33) (43) (35)	289 343 284 305	(73) (86) (79)
32	A B C Mean	13 13 13 13	(4) (3) (3)	33 42 30 35	(6) (6) (6)	56 61 46 54	(9) (12) (9)	95 104 83 94	(16) (22) (12)	193 205 168 189	(41) (47) (34)	292 344 298 311	(79) (84) (72)
64	A B C Mean	13 15 14 14	(4) (3) (3)	33 39 34 35	(6) (6) (6)	45 49 48 47	(9) (10) (9)	61 75 72 69	(12) (12) (12)	118 147 145 137	(20) (24) (23)	206 212 231 216	(37) (47) (46)
128	A B C Mean	12 18 13 14	(3) (4) (3)	25 24 26 25	(3) (5) (5)	33 42 36 37	(5) (5) (5)	48 51 44 48	(7) (7) (6)	61 71 68 67	(16) (12) (11)	71 81 75 76	(32) (42) (32)
256	A B C Mean	14 14 15 14	(3) (3) (4)	24· 24 23 24	(6) (5) (6)	26 26 24 25	(6) (6) (6)	27 26 25 26	(6) (6) (6)	32 30 28 30	(11) (10) (9)	33 32 29 31	(12) (13) (11)
512	A B C Mean	12 13 12 12	(3) (3) (3)	20 21 19 20	(4) (4) (3)	21 22 21 21	(5) (5) (6)	23 22 22 22	(7) (9) (10)	23 22 20 22	(14) (12) (12)	23 22 21 22	(14) (15) (13)

 

Table: Increase in number of fronds

Nominal concentration of technical test material (µg/L)	Increase in number of fronds (Days 0-14) #				% Inhibition
	Rep A	Rep B	Rep C	Mean
Control	268	218	259	248
4	247	236	294	259	0
8	244	202	258	235	0
16	277	331	272	293	0
32	280	332	286	299	0
64	194	200	219	204	18
128	59	69	63	64	74*
256	21	20	17	19	92*
512	11	10	9	10	96*

#Increase = (No. of fronds at day 14 - No. of fronds (12) at day 0)

*Significant inhibition (P=0.05, one-sided) compared with the control

 

Table: Dry weights

Nominal concentration of technical test material (µg/L)	Tissue dry weight (Day 14) (mg)				Mean increase# (Days 0-14) (mg)	% Inhibition
	Rep A	Rep B	Rep C	Mean
Control	31.4	28.2	32.3	30.6	29.2
4	31.6	29.8	37.2	32.9	31.5	0
8	32.4	23.6	32.3	29.4	28	4
16	35.8	45	34.3	38.4	37	0
32	31.6	36.1	31.9	33.2	31.8	0
64	31.3	28.2	36.9	32.1	30.7	0
128	12.1	12.3	13	12.5	11.1	62*
256	3.8	3.7	3	3.5	2.1	93*
512	2	1.9	1.9	1.9	0.5	98*

#Increase = (Dry weight at day 14 - estimated day 0 dry weight).

Dry weight at day 0 estimated from control dry weight to be 1.4 mg per 12 fronds. (Calculated from 781 fronds weighing 91.9 mg on day 14)

*Significant inhibition (P=0.05, one-sided) compared with the control

Calculation of key result

The doses of the test substance were expressed in technical test material, which relates to an aqueous solution of the registered substance. The effect values are calculated by correction for the amount of water in the test item:

- EC50: 0.463 x 113 µg technical test material/L = 52.3 µg pure test substance/L.

- NOEC: 0.463 x 64 µg technical test material = 29.6 µg pure test substance/L.

Validity criteria fulfilled:

not specified

Conclusions:

The 14-d EC50 and 14-d NOEC values in freshwater duckweed (Lemna gibba) are 113 and 64 µg technical test material/L, respectively. These values correspond to recalculated values of 52.3 and 29.6 µg pure substance/L, respectively.

Executive summary:

The toxicity to aquatic plants other than algae was determined in a study according to EPA 540/09-86-134 and in compliance with GLP criteria. In this study, 3 replicates of 3 uniform, healthy-looking duckweed (L. gibba), with 4 fronds each, were introduced in medium in test vessels containing the test substance at the following nominal concentrations: 0 (control), 4.0, 8.0, 16, 32, 64, 128, 256 and 512 μg/L. The mean measured concentrations were analytically determined to be <LOQ (control), <LOQ, <LOQ, <LOQ, <LOQ, 48, 120, 240 and 460 µg/L. As the analyses available were limited, the results have been calculated on the basis of nominal concentrations. The plants were exposed for 14 days under semi-static conditions. On days 1, 4, 6, 8, 11 and 14 the number of plants and the number of fronds were counted and recorded for each test vessel. All fronds which visibly projected beyond the edge of the parent frond were counted. Any other symptoms of toxicity were recorded. At the end of the test (14 days), dry weight of the plants was determined.

No significant inhibition of frond growth was identified at nominal concentrations of 64 μg/L and below. Significant inhibition was observed in the three higher concentration treatments in a dose-dependent matter. No significant effect on dry weight increase was noted in nominal concentrations of 64 μg/L and below. Significant decrease in dry weights was observed in the three higher concentration treatments in a dose-dependent matter. From day 4 onwards, plants in the 128, 256 and 512 μg/L test concentrations started to exhibit progressively more marked visible effects, including paler frond colouration and small size, less root growth, abnormal colony configurations and flotation patterns. A similar pattern was visible in the 64 μg/L test concentration from day 6 onwards. On day 14, the plants in the 32 μg/L test replicates were recorded as having pale colouration in some fronds and visibly reduced root growth. With the exception of the observation that plants in one replicate of the 8.0 μg/L test concentration appeared to have a smaller colony size and less root growth on day 11 only, there were no observed symptoms at, or below, the nominal 16 μg/L test concentration when compared to the control. Therefore, the transient variation in growth at the 8.0 μg/L test concentration was considered not to have been due to any effect by the test substance. Based on these findings, the 14-d EC50 and 14-d NOEC values were determined to be 113 and 64 µg technical test material/L. These values correspond to recalculated values of 52.3 and 29.6 µg pure substance/L.

Description of key information

The 14-d EC50 and 14-d NOEC values in freshwater duckweed (Lemna gibba) are 113 and 64 µg technical test material/L, respectively. These values correspond to recalculated values of 52.3 and 29.6 µg pure substance/L, respectively.

Key value for chemical safety assessment

EC50 for freshwater plants:

52.3 µg/L

EC10 or NOEC for freshwater plants:

29.6 µg/L