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

Endpoint summary

Additional information

Read Across

Reliable studies regarding toxicity of nonylphenol to terrestrial organisms were used according to a read-across approach to fill data requirements for octylphenol for these endpoints. Argumentations based on the structure of the substances, purity and reliability of studies were the same as for aquatic organisms. It is reasonable to assume that the trends in toxicity between NP and PTOP seen in aquatic organisms will be reflected in the toxicities between NP and PTOP in terrestrial organisms.  The approach is considered scientifically justified and appropriately conservative.

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

In the absence of reliable toxicity data for sediment organisms, the aquatic toxicity of the two substances was compared (data are summarised in the table below). The data for both short- and long-term toxicity are within the same orders of magnitude with comparable ranges of toxicity. It would be reasonable to assume that comparable ranges of toxicity between NP and PTOP would also be exhibited by sediment organisms. Accordingly, reliable NP sediment toxicity data are used to fill the data gap for PTOP sediment toxicity. Reliable data for nonylphenol toxicity to aquatic organisms is also used in the calculation of the PNEC_soilfor octylphenol.

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

 

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 terrestrial toxicity data relating to NP studies to be read-across to PTOP endpoints and used in PNEC_soilderivation.

 

Terrestrial Toxicity Data

The review of nonylphenol exposure to terrestrial organisms resulted in reliable toxicity test studies by eight authors for a total of eight terrestrial species of soil invertebrates, plants and soil micro-organisms.From the limited reliable data available, soil invertebrates were more sensitive to the toxic effects of nonylphenol than terrestrial plants and micro-oragnsims for acute, short-term exposures and the relative sensitivity between soil invertebrates and plants was an order of magnitude different (L/EC₅₀for earthworm survival and plant growth were 88.6and 559 mg nonylphenol/L, respectively).

 

Toxicity data for long-term exposure to nonylphenol indicated the lowest Key Study NOEC or EC₁₀value of 23 mg nonylphenol/kg soil for reproduction in the Collembolan (Folsomia fimetaria) by Scott-Fordsmandet al., 2004. The lowest Key Study NOEC or EC₁₀for plants based on fresh weight was field mustard (Brassica rapa) of 574.8 mg nonylphenol/kg using artificial soils (Domeneet al, 2009). As in short-term toxicity studies, soil invertebrates were more sensitive than plants to long-term nonylphenol exposures.

A single study was available for avian toxicity where the test substance was octylphenol. No effects were seen in zebra finches (Taeniopygia guttata) for a number of reproductive endpoints at 100 nmol/g body mass per day (Millamet al, 2001).