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Ecotoxicological information

Short-term toxicity to fish

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Description of key information

Using a reliable QSAR model, Ecological Structure Activity Relationships (ECOSAR) Class Program was used to estimate the 96hr LC50 for fish to be 2.682 mg/L. 

Key value for chemical safety assessment

Fresh water fish

Fresh water fish
Effect concentration:
2.682 mg/L

Additional information

Reliable (Klimisch 1 or 2) measured and modeled short-term toxicity studies in fish have been conducted for o-tert-butylphenol and are included in this dossier.  These studies are summarized below.  Additionally, reliable toxicity studies with fish with the structural analogue, o -sec-butylphenol, have been included for supporting evidence. 


Sasol (2013) provided a reliable (Klimisch 2) study for o-tert-butylphenol using the QSAR model, Ecological Structure Activity Relationships (ECOSAR) Class Program to estimate short-term toxicity to fish. The ECOSAR model estimates aquatic toxicity based on the structural similarity to chemicals for which aquatic studies are available.In addition, the log Kow and molecular weight of o-tert-butylphenol are within the criteria (max log Kow = 7 for acute, 8 for chronic and max molecular weight = 1000) and domain of the model. The measured log Kow of 3.3 was used in the model. Model results indicate a 96 hr LC50 to be 2.682 mg/L for phenol. The baseline 96 hr LC50 was 8.391 mg/L.

To evaluate model results for short-term toxicity to fish, measured toxicity data for other aquatic organisms were compared to modeled results. Below is a comparison of measured data and modeled data for the invertebrate, Daphnia, and algae for both the baseline case and for the phenol class. Comparisons indicate that modeled data, in general, are slightly lower and more conservative than the measured data. Therefore, use of the modeled data for fulfilling the requirement for short-term toxicity to fish is a conservative approach. Since o-tert-butylphenol is in the class of phenols, the result for phenol will be used as key for short-term toxicity to fish.

    ECOSAR 1.10
(w/ measured log Kow)
Measured Values
 96 hr Fish LC50   Phenol: 2.682 mg/L
Baseline: 8.391 mg/L
 >0.1 mg/L
 48 hr Daphnia EC50   Phenol: 1.441 mg/L
Baseline: 5.681 mg/L
 3.4 mg/L
 72/96 hr Algae EC50   Phenol: 5.839 mg/L
Baseline: 5.309 mg/L
6.5 mg/L 
 72/96 hr Algae ChV   Phenol: 2.698 mg/L
Baseline: 2.249 mg/L
  EC10 = 2.0 mg/L
NOEC = <1.2 mg/L

In a reliable (Klimisch 2) 96-h acute toxicity study by Wetton (1991), rainbow trout (Oncorhynchus mykiss) were exposed to o-tert-butylphenol at nominal concentrations of 0 and 0.1mg/L under semi-static conditions.  The 96-h LC50 was >0.1 mg/L as no mortality was observed during the test. Although this is considered a reliable study, the study results are based on a limit test, where only one test concentration was tested. Due to test performance, a definitive result was not possible. Since reliable modeled data and measured data on the analogue are available, this study is used as supporting evidence.

In a 96-h acute toxicity study conducted by Japan MOE (1999) and presented in the SIDS Initial Assessment Report For CoCAM2 (2012) , medaka, (Oryzias latipes) were exposed to o-sec-butylphenol at measured concentrations of 0 ,1.0, 1.8, 3.2, 5.6, and 10 mg/L under semi-static conditions.  The 96-h LC50 was 6 mg/L, based on mortality. 

Reliable (Klimisch 1 or 2) measured and modeled short-term toxicity studies with fish have been conducted for o-tert-butylphenol and the structural analogue, o-sec-butylphenol and are included in this dossier. The key study,Sasol (2013), provides a 96-hr LC50 of 2.682 mg/L for fish for o-tert-butylphenol. Consequently this value will be taken as the short-term toxicity in fish endpoint for o-tert butylphenol. Although the study by Wetton (1991) shows a 96 -h LC50 result of >0.1 mg/L, study results with the analogue provide evidence and support that the modeled data are likely more representative of the short-term toxicity of o-tert-butylphenol to fish.