4-(1,1,3,3-tetramethylbutyl)phenol

Endpoint summary

Additional information

Read-Across

A read-across approach was used to meet minimum data requirements (>10 families of aquatic organisms) to calculate predicted no effect concentrations (PNEC_aquatic) using species sensitivity distribution; a statistical rather than an assessment factor approach.   It has been determined according to this information that read-across from nonylphenol to octylphenol for toxicity to aquatic organisms can be used for four reasons; (i) the two substances are considered analogue substances, (ii) the toxicities of the substances are similar, and (iii) the information is reliable and (iv) the substances tested were without impurities.

Structure

A structural analogue is a source chemical whose physico-chemical and toxicological properties are likely to be similar to the target chemical as a result of structural similarity. The structural similarity and similar properties between PTOP and NP support consideration of these substances as structural analogues for the purpose of read-across. Thus, endpoint information is read-across between structural analogues.

The similarity between PTOP and NP is based on their structural likeness (→similar chain length: eight and nine C-atoms for PTOP and NP, respectively) and their common functional group (→phenol group). PTOP and NP display very similar physico-chemical properties that determine environmental distribution and fate (e.g. molecular weight, partition coefficients such as log Kow, water solubility) and ecotoxic effects.

Toxicity

The aquatic toxicity of the two substances is comparable as summarized in the table below:

A Comparison of Ecotoxicity Data for the Same Aquatic Species (where available) Exposed to NP and PTOP
Species               and Type of Test	NP Toxicity Range (mg/L)	PTOP Toxicity Range (mg/L)
Ceriodaphnia sp. 48 hr L(E)C50	0.02 to 0.47	0.07 to 0.28
Americamysis bahia 96 hr LC50	0.043 to 0.06	0.048 to 0.113
Oncorhynchus mykiss    96 hr LC50	0.11 to 0.22	>0.1
Fundulus heteroclitus     96 hr LC50	0.26 to 5.44	0.29 to 3.86
Daphnia magna               21-d NOEC	0.013 to 0.116	0.03
Fish        NOEC	>0.0019 to 0.078	0.012 to 0.035

 

The data for both short- and long-term toxicity for each type of organism in the table above are within the same orders of magnitude with comparable ranges of toxicity when a like-for-like comparison is made. The short-term toxicity of NP and PTOP for other aquatic freshwater and saltwater invertebrates and fish species (used in the CSR but not presented in the table above) are also in agreement with each other when similar toxicity endpoints are compared. For example exposure to nonylphenol resulted in similar LC₅₀concentrations of 0.31 and 1.72 mg/L for the fish species Cyprinodon variegates and Puntius conchonius. Fish data relating to octylphenol exposure resulted in toxicities of >0.1 and 0.26 mg/L for Oncorhynchus mykiss and Leuciscus idus melanotus, respectively. Long-term data for different species and similar endpoints are also in agreement. Based on this evidence it can be stated that PTOP and NP have similar degrees of toxicity to the aquatic organisms for which there are reliable data. Therefore, the reliable NP (source chemical) aquatic toxicity data can be used to fill the data gaps for PTOP (target chemical) aquatic toxicity in accordance with ECHA guidance set out in Chapter R. 6: QSARs and Grouping of Chemicals.

Reliability, Adequacy and Accuracy of the Source Studies

All of the ecotoxicity studies used in the CSR were carried out in accordance with OECD or similar guidelines and scored a Klimisch I or II. In particular, the studies represented in the table above showed consistent results indicating that octylphenol is ecotoxic to aquatic organisms. These studies are considered to be reliable for use in read-across between NP and PTOP.

Evaluation of the purity and impurity profiles of the Test Substance

The purity of PTOP used in the key studies for ecotoxicological endpoints ranged from 98.97 to 100%. The purity of NP used in key studies was 85 to 100%, with all but one study being ≥90% purity. Impurities were not reported these ecotoxicity studies evaluated for the CSR. Because of the high purity of the test substance, impurities probably do have a negligible or no impact on the ecotoxicity of PTOP.

In summary, NP and PTOP are similar in structural composition and both exert similar short- and long-term toxic effects to aquatic organisms. The studies used to make these comparisons are highly reliable (Klimisch I or II) and the NP or PTOP test substance in toxicity studies were of high purity. Therefore, it is considered scientifically for toxicity data relating to NP studies to be read-across to PTOP endpoints and used in PNEC_aquaticderivation.

Discussion

A review of the toxicity test results for exposure of aquatic organisms resulted in reliable data from studies that included freshwater species and saltwater species representing fish, invertebrates, algae, and a snail. Short-term (acute) exposures of octylphenol to freshwater and marine invertebrates ranged from 0.019 to 0.11 mg octylphenol/L and suggested the freshwater test organism (Gammarus pulex) may be more sensitive to effects on immobility and survival than the marine organism tested (Mysidopsis bahia). Long-term octylphenol exposure tests indicated a NOEC on inhibition of reproduction on the preferred invertebrate test species Daphnia magna to be 0.03 mg octylphenol/L. Fish species were generally found to be less sensitive to short-term octylphenol exposure than invertebrate organisms. Short-term survival LC₅₀ values were >0.1 mg octylphenol/L for both fresh and saltwater test species. However, effects on reproduction and survival from long-term octylphenol exposure to freshwater were at equivalent concentration to that reported for invertebrates. Other organisms tested included short-term octylphenol exposure to algae (Pseudokirchneriella subcapitata formerly Selenastrum capricornutum) and a mixed culture of microorganisms from activated sludge, both of which were markedly less sensitive to toxic effects of octylphenol than all other species tested.