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Sediment toxicity

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Description of key information

Read-across approach from nonylphenol.
Bettinetti and Provini (2002) provided 28 day EC10 = 231 mg nonylphenol/kg dw based on emergence. This value is the mean of two test results (203 and 259 mg/kg) dw.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:
231 mg/kg sediment dw
EC10, LC10 or NOEC for marine water sediment:
61.5 mg/kg sediment dw

Additional information

Read Across

Studies on the toxicity of nonylphenol were included in using the read-across approach to meet data requirements for the toxicity of octylphenol to sediment organisms. Argumentations based on the structural similarity of the substances, their purity and the reliability of studies are the same as for the aquatic species and are provided below.

It has been determined according to this information that read-across from nonylphenol to octylphenol for toxicity to sediment 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

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 PNECsedimentfor 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 and the same argumentations of consistency and reliability are made for sediment data.

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

Summary of the ecotoxicity data

A review of reports for nonylphenol exposure to sediment organisms resulted in selection of two reliable studies that included two freshwater organisms and one marine organism.  The study of nonylphenol exposure to Chironomus riparius andTubifix tubifix in spiked sediment tests by Bettinetti and Provini (2002) was selected as the key study because it provided calculated EC10concentrations for endpoints derived from duplicate tests for more than one sediment organism. The EC10concentration is accepted as an equivalent substitute for the NOEC value, and has the added benefit of being a calculated response-based concentration rather than an estimate derived from the treatment dilution series. The average EC10concentration reported in the key study for inhibition of Chironomus riparius emergence was 231 nonylphenol/Kg dw, which was comparable to an average EC10concentration of 360 and 359 mg nonylphenol/Kg dw for production of cocoons and production of young worms, respectively, for Tubifix tubifix (Bettinetti and Provini 2002).  

 

In supporting documents, the 28 -day NOEC for Leptocheirus plumulosus, a marine benthic crustacean, survival and reproduction from exposure to nonylphenol was reported by Zulkosky et al. (2002) to be >61.5 mg nonylphenol/Kg dw for both endpoints.

 

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