Dichlobenil

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:

key study

Study period:

08 July 1987 to 20 July 1988

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: EPA Guideline 123-2

Deviations:

yes

Remarks:

See principles of method if other than guideline

Principles of method if other than guideline:

According to the protocol the light intensity for the 5-day toxicity test with Anabaena flos-aquae should be 2000 lux. Cell biomass of Anabaena flos-aquae increased slowly when cultured under this low light intensity. Therefore, the light intensity was increased during culturing and testing of this species to 5000 and 4500 lux, respectively. It is the opinion of the testing laboratory that this did not affect the results of the study.

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Prepared every 3 days as a stock solution by adding test material to M-Type Hoaglands medium. The stock was ultrasonicated (for 10 minutes) to ensure that the test material dissolved.

Test organisms (species):

Lemna gibba

Details on test organisms:

TEST ORGANISM
- Common name: duckweed
- Strain: Lemna gibba G3

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Key result

Duration:

14 d

Dose descriptor:

EC10

Effect conc.:

19 µg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

frond number

Key result

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

33 µg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

frond number

The results of this test are detailed in Table 1 below.

Table 1: Mean frond production

	Days of exposure
Exposure concentration (µg/L)	3	6	9	12	14
Controls	43	103	211	358	463^h
6.3	43	103	223^g	399	517^h
13	36	114^f	337^g	634^f	875^f
25	24^a	41^f	96^f	154^i	266^i
50	20^b,c	18^d	23^e	22^e,j	23^e
100	16	15^d	15^e	16^e	16^e
EC50	48	30	36	33	33

^aAll fronds slightly yellow; ^bAll fronds mostly brown; ^cMany small individual fronds; ^dSome fronds brown, individual; ^eFronds brown, individual; ^fFronds small, some are yellow; ^gFronds smaller than controls; ^hFew yellow fronds; ⁱFew fronds same size as controls, most are very small, few roots observed; ^jRoots are brown

The EC₁₀, EC₅₀ and EC₉₀ values and their 95% confidence limits were determined by linear regression of the response (percent reduction of frond production, as compared with controls) versus nominal exposure concentration over the range of test concentrations where a clear exposure-response relationship was observed. They are presented in Table 2 below.

Table 2: EC₁₀, EC₅₀ and EC₉₀ values

Exposure duration	EC10 (µg/L) (95% C.I.)	EC50 (µg/L) (95% C.I.)	EC90 (µg/L) (95% C.I.)
3 days	8.6 (4.6 -15)	48 (27 -87)	270 (140 -550)
6 days	10 (3.0 -31)	30 (9.7 -95)	85 (28 -310)
9 days	19 (7.4 -47)	36 (14 -92)	71 (29 -200)
12 days	18 (7.2 -44)	33 (14 -82)	63 (26 -170)
14 days	19 (8.2 -41)	33 (15 -75)	63 (29 -150)

Validity criteria fulfilled:

not specified

Conclusions:

Under the conditions of the test, the 14 day EC50 for inhibition of growth (frond production) of Lemna gibba G3 was determined to be 33 µg/L (95 % C.I. 15-75 µg/L).

Executive summary:

In a GLP compliant effects on aquatic plants study conducted in line with standardised guideline EPA Guideline 123 -2, the effects of the test material on aquatic plants was determined. Aquatic plants were exposed to the test material at nominal test concentrations of 0, 6.3, 13, 25, 50 and 100 µg/L. Under the conditions of the test, the 14 day EC₅₀ for inhibition of growth (frond production) was determined to be 33 µg/L.

Description of key information

The EC50 of the test material was determined to be 33 µg/L according to a study performed in line with EPA Guideline 123-2.

Key value for chemical safety assessment

EC50 for freshwater plants:

33 µg/L

EC10 or NOEC for freshwater plants:

19 µg/L

Additional information

In a GLP compliant effects on aquatic plants study conducted in line with standardised guideline EPA Guideline 123-2, the effects of the test material on aquatic plants was determined. Aquatic plants were exposed to the test material at nominal test concentrations of 0, 6.3, 13, 25, 50 and 100 µg/L. Under the conditions of the test, the 14 day EC₅₀ for inhibition of growth (frond production) was determined to be 33 µg/L.