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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The Scholz (1989) study was selected as a key study because it provides both an EC50 (1.3 mg nonylphenol/L) and EC10 (0.5 mg nonylphenol/L) concentration for growth inhibition for a common algal test species Desmodesmus subspicatus.

Ward and Boeri (1990) was also selected as a key study because it provides EC50 toxicity information for the preferred algal test organism Pseudokirchneriella subcapitata and of the marine algae Skeletonema costatum, determining 96 h EC50s were of 0.41 mg/L and 0.027 mg nonylphenol/L, respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.41 mg/L
EC50 for marine water algae:
0.027 mg/L
EC10 or NOEC for freshwater algae:
0.5 mg/L
EC10 or NOEC for marine water algae:
0.5 mg/L

Additional information

The Scholz (1989) study was selected as a key study because it provides both an EC50 (1.3 mg nonylphenol/L) and EC10 (0.5 mg nonylphenol/L) concentration for growth inhibition for a common algal test species Desmodesmus subspicatus. Ward and Boeri (1990) was also selected as a key study because it provides EC50 toxicity information for the preferred algal test organism Pseudokirchneriella subcapitata. In addition, the results of the Ward and Boeri (1990) study combined with the supporting results of Brooke (1993) and Graff et al (2003) suggest the preferred test algae P. subcapitata to be more sensitive than D. subspicatus to effects of nonylphenol on growth inhibition. The growth inhibition EC50 for the preferred test species P. subcapitata ranged from 0.41 to 0.53 mg nonylphenol/L. Reliable marine algae test results with nonylphenol were limited to a single study with Skeletonema costatum (Ward and Boeri 1990) which showed growth inhibition at 96 hr to be 0.027 mg nonylphenol/L, an order of magnitude lower than for the freshwater algae P. subcapitata. 

A number of other species assessed the toxicity for a large number of different algal species, many non-standard test species. Nonylphenol exposure studies with algae ranged from 72-96 hr and 14 days duration and reliable data included nine studies representing a wide range of freshwater algae and one study with the marine diatom taxon S. costatum (Bacillariophyta) (Ward and Boeri, 1990).

Long-term (14 days) test results reported as NOEC based on growth rate ranged from 0.14 mg/l for Nodularia spumigena, to 0.2 mg/l for Microcystis aeruginosa 972, to 0.25 mg/l Aphanizomenon flos-aquae, to 0.3mg/l for Anabaena variabilis, to 0.4 mg/l for Oscillatoria agardhii, to 0.6mg/l for Oocystis parva and 0.65 mg/L for Scenedesmus quadricauda (Zaytseva et al, 2015). 14 days exposure of the cyanobacterial strain P. agardhii 1113 to NP resulted in a NOEC of 0.4 mg/L based on the growth rate (Medvedeva et al 2017).

Long term test results for the same species reported as LC50’s based on growth rate were 0.45 mg/l for Microcystis aeruginosa 972, to 0.55 mg/l for Anabaena variabilis 972, Aphanizomenon flos-aquae and Nodularia spumigena, 1mg/l for Oscillatoria agardhii, 2.2mg/l for Oocystis parva and 2.45mg/l for Scenedesmus quadricauda.

Short-term (72 to 96 and 120 hr) test results were reported as EC50 values based on cell growth or growth rate and ranged from 0.4 mg nonylphenol/L for P. subcapitata at 96 hr (Ward and Beori 1990) to 1.3 mg nonylphenol/L at 72 hr for D. subspicatus (Scholz 1989). An EC50 concentration of 0.027 mg nonylphenol/L was reported by Ward and Boeri (1990) for cell growth of the marine diatom S. costatum. The available EC50 concentration data for cell growth indicates that for the algae tested the preferred freshwater test species P. subcapitata was more sensitive to nonylphenol exposure than D.subspicatus, but the marine diatom S. costatum was the most sensitive to effects of nonylphenol. 

The study by Zaytseva (2015) determined a lower NOEC for the blue-green algal species, Nodularia spumigena, of 0.14 mg/l (nominal), than was determined in the key studies by Scholz (1989) and Ward & Boeri (1990), but the reliable studies Scholz 1989 and Ward & Boeri 1990 are preferred as key studies because of their use of standard test organisms and measured concentrations.