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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Acutely very  toxic for aquatic organisms

Key value for chemical safety assessment

Additional information

Several tests on the toxicity of Triclosan to different algae species are available. In a study on freshwater algae Desmodesmus subspicatus the growth inhibition after 96 hours was tested. The test followed US EPA guideline OTS 797.1050. After 96 hours of exposure a NOEC of 0.69 µg/l (EC50 1.61 µg/l) based on the growth rate was determined (Ciba-Geigy 1997). The result is supported by several other studies on different freshwater and marine algae species. Two further studies on Scenedesmus subspicatus (new name: Desmodesmus subspicatus) detected a comparable inhibition of algal growth. A NOEC of 0.5 µg/l (EC50 2.8 µg/l) based on the growth rate was determined after 72 hours in a study following OECD guideline 201 (Ciba-Geigy 1995). In a study conducted in compliance with EPA OPPTS 850.5400 the effect of Triclosan on Desmodesmus subspicatus in presence and absence of humic acid was tested. Algae were exposed for 96 hours. Based on the algal growth rate a NOEC of 0.742 µg/l (EC50: 2.25 µg/l) without humic acid and a NOEC of 2.38 μg/l (EC50: 4.6 μg/l) with humic acid was detected (Colgate-Palmolive Company 1999). In a study on Anabaena flos-aquae exposed for 96 hours to Triclosan according to EPA OPPTS 850.5400 a NOEC of 0.81 µg/l (EC50 1.6 µg/l) based on growth rate was recorded (Ciba Specicialty Chemicals 1998). The results of freshwater algae are confirmed by a further study focusing on the effect of Triclosan to Selenastrum capricornutum, Anabaena flos-aquae and Navicula pelliculosa. Algal growth was within 96 hours of exposure to Triclosan was determined and an EC50 of 13.7 µg/l for Pseudokirchneriella subcapitata (reported as: S. capricornutum), of 1.36 µg/l for A. flos-aquae and of 0.44µg/l was determined. Furthermore effects of the substance on growth of the marine species Skeletonema costatum were investigated. Skeletonema costatum was slightly less sensitive. An EC50 > 66µg/l was determined (Ciba-Geigy Corporation 1997).

The study by Ciba-Geigy (1997) using Desmodesmus subspicatus as test species was selected as key study (96 -h ErC50 = 1.61 µg/L; 96 -h NOErC = 0.69µg/L). This study was preferred over the others since NaOH was used as solvent. The other studies resulting in lower effect values used acetone as solvent. Acetone can lead to an overestimation of the toxicity of triclosan due to the possibility of acetone inducing formation of free radicals by photolysis.

The toxic effect of the transformation product methyltriclosan (CAS 4640 -01 -1) was studied in a growth inhibition test according to OECD 201 (Ciba, 2006). The 72 -h ErC50 was 0.17 mg/L, the 72 -h NOEC was 0.040 mg/L.

The available data on algalo toxicity of triclosan and methyltriclosan are summarised in the table below.

Reference

RL

Species

Exp.

Effect

 level

Value

(µg/L)

Nom./

meas.

Fw/

Mar.

Triclosan

Acute effect data

Ciba Specialty Chemicals (1998). Rep. No. 437A-101

2

Anabaena flos-aquae

72 h

EC50

5.01

meas.

fw

Ciba-Geigy Corp. (1997) Rep. No. 21-02-1

2

Anabaena flos-aquae

96 h

EC50

1.08

nom.

fw

Ciba Specialty Chemicals (1995). Rep. No. 385837

2

Desmodesmus

subspicatus

72 h

EC50

1.99

meas.

fw

Ciba-Geigy Corp. (1997). Rep. No. 43118

2

Desmodesmus

subspicatus

72 h

EC50

1.89

meas.

fw

Colgate-Palmolive (1999). Rep. No. 362A-105, without humic acid

2

Desmodesmus

subspicatus

72 h

EC50

1.89

meas.

fw

De Lorenzo et al. (2008)

2

Dunaliella

tertiolecta

96 h

EC50

3.55

meas.

mar.

Ciba-Geigy Corp. (1997) Rep. No. 21-02-1

2

Navicula

pelliculosa

96 h

EC50

55.96

nom.

fw

Ciba-Geigy Corp. (1997) Rep. No. 21-02-1

2

Pseudokirchneriella

subcapitata

96 h

EC50

15.84

nom.

fw

Tamura et al. (2012)

2

Pseudokirchneriella

subcapitata

72 h

EC50

5.1

meas.

fw

Tatarazako et al. (2004)

2

Pseudokirchneriella

subcapitata

72 h

EC50

4.7

nom.

fw

Ciba-Geigy Corp. (1997) Rep. No. 21-02-1

2

Skeletonema

costatum

96 h

EC50

> 66

nom.

mar.

Longterm effect data

Ciba Specialty Chemicals (1998). Rep. No. 437A-101

2

Anabaena flos-aquae

72 h

EC10

1.98

meas.

fw

Ciba-Geigy Corp. (1997) Rep. No. 21-02-1

2

Anabaena flos-aquae

96 h

EC10

0.42

nom.

fw

Ciba Specialty Chemicals (1995). Rep. No. 385837

2

Desmodesmus

subspicatus

72 h

EC10

0.46

meas.

fw

Ciba-Geigy Corp. (1997). Rep. No. 43118

2

Desmodesmus

subspicatus

72 h

EC10

1.03

meas.

fw

Colgate-Palmolive (1999). Rep. No. 362A-105, without humic acid

2

Desmodesmus

subspicatus

72 h

EC10

1.03

meas.

fw

Ciba-Geigy Corp. (1997) Rep. No. 21-02-1

2

Navicula pelliculosa

96 h

EC10

12.66

nom.

fw

Ciba-Geigy Corp. (1997) Rep. No. 21-02-1

2

Pseudokirchneriella

subcapitata

96 h

EC10

1.81

nom.

fw

Tatarazako et al. (2004)

2

Pseudokirchneriella

subcapitata

72 h

EC10

2.7

nom.

fw

Ciba-Geigy Corp. (1997) Rep. No. 21-02-1

2

Skeletonema

costatum

96 h

EC10

> 66

nom.

mar.

De Lorenzo et al. (2008)

2

Dunaliella tertiolecta

96 h

NOEC

1.6

meas.

mar.

Tamura et al. (2012)

2

Pseudokirchneriella

subcapitata

72 h

NOEC

0.53

meas.

fw

Methyl-Triclosan

Ciba Specialty Chem. (2006). Rep. No.A34918

1

Desmodesmus

subspicatus

72 h

EC10

0.076

meas.

fw

Ciba Specialty Chem. (2006). Rep. No.A34918

1

Desmodesmus

subspicatus

72 h

EC50

0.17

meas.

fw

Exp.: exposure duration; Fw.: freshwater; Mar.: marine water; Meas.: measured; Nom.: nominal; RL: Reliability