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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

 A key study is presented which determines the growth inhibition of 2,4-dichlorophenol to the algal Pseudokirchnerella subcapitata over a 72 hour exposure period. The EC50 was determined to be 3.44 mg/l and the No Observed Effect Concentration was observed as 0.7 mg/l. The SIDS dossier references 11 sources of information on toxicity to aquatic plants in support of the key study. Those with a reliability of 2 (valid with restrictions) are described in the 6.1.5 endpoints (001-004). The lowest LC50 from those sources with a reliability of 2 was 1.5 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
3.44 mg/L
EC10 or NOEC for freshwater algae:
0.7 mg/L

Additional information

In a key study a growth inhibition study of 2,4-dichlorophenol to the alga Pseudokirchnerella subcapitata over a 72 hour exposure period has been performed. The study was conducted according to OECD guideline 201 (2006), Alga Growth Inhibition Test, Annex V EEC C3, Algal Inhibition Test and it was performed to GLP. The study is reported as having been conducted without any deviations from the protocol. The ECx values were measured (where x = 10, 20 and 50) at 0-48 hours and 0-72 hours both by yield and by growth rate. The EC50 (72 hours at 23 degrees C) [by growth rate] was determined to be 3.44 mg/l and the NOEC (0 -72 hours at 23 degrees C) [by growth rate] was observed to be 0.7 mg/l.

In addition, in support of the key study the SIDS dossier describes the toxicity to aquatic plants in 11 references, three were assessed validity 2, seven validity 3.

Two valid test were carried out on green algae. A study on Chlorella pyrenoidosa led to an EC0 value of 8 mg/L and an EC100 value of 10 mg/L (growth rate). Exposure duration was 12 days instead of the usual period of 72 hours. The NOEC obtained on Scenedesmus quadricauda (endpoint: biomass, exposure duration: 7 days) is 3.6 mg/L. All these tests are considerably longer than the standard time, and no information is given concerning the growth of the control algae.

One other valid study was realised on the aquatic plant Lemna gibba and yielded a 7d-EC10, considered as a NOEC, of 0.41 mg/l.

Given that a key modern day guideline study has been performed the EC50 [72 hours] (growth rate) is concluded to be 3.44 mg/l.