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Toxicity to aquatic algae and cyanobacteria

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Description of key information

No data on acute and chronic toxicity to aquatic algae is available for HiMO LAB.  Data from LAB (CAS no: 67774-74-7) and HAB (CAS No: 84961-70-6) as structural analogues were used to understand the acute /chronic  toxicity profile of substance to Scenedesmus subspicatus . The 72-hr ErC50 and NOECr values were >100 ug/L and >= 50ug/L  for LAB, and > 2.08 mg/L  and , >= 2.08 mg/L for HAB, respectively. As a consequence,  the acute and chronic toxicity of HiMo LAB is considered to be greater than the water solubility  (<0.1 mg/L).

Key value for chemical safety assessment

Additional information

Benzene, C16-24 alkyl derivatives are also known as High Molecular Weight Linear Alkylbenzenes (HiMo LAB).  The substance is a UVCB. Because of their high molecular weight, they are very similar in composition and properties to the heavy alkylate bottoms (HAB). Based on these structural and functional similarities, data on LAB (CAS no: 67774-74-7) being registered under REACH, LAB Alkylate Bottoms (CAS no: 85117-41-5) described in OECD SIDS dossier, and HAB (CAS no: 84961-70-6) being registered under REACH are suitable as supporting studies in case where specific data on the HiMo LAB is lacking. 

To assess the acute toxicity profile of the substance to aquatic algae, structral analogue approach was used from LAB (CAS no: 67774-74-7) and HAB (CAS no: 84961-70-6). These studies examined the toxicity of linear alkyl benzenes to aquatic algae according to OECD 201

Scenedesmus subspicatus was exposed to concentrations of 25, 50 and 100 ug/L of LAB for 72 hrs. During this time, readings of the growth rate were taken. Tests were also done on C10, C12, and C14 linear alkyl benzenes in addition to commercial LAB. The 72 -hr ErC50 values for all substances were >100 ug/L and NOECr values were >= 50ug/L, which is higher than the solubility limit for these substances (measured solubility limit for C12 LAB = 37.6 ug/l).

Algae of the species Scenedesmus subspicatus were exposed to concentrations of 0, 0.23, 0.39, 0.69, 1.16 and 2.08 mg/L of HAB. The 2.08 mg/L concentration represents the solubility limit of the test substance. Algae were exposed for 72 hrs. Observations for biomass and growth rate were made at 24, 48, and 72 hrs after start of exposure. No reduction in either of these parameters as compared to controls was seen. The 72 -hr ErC50 and EbC50 was > 2.08 mg/L of test substance. The NOEC was >= 2.08 mg/L of test substance. The 72-hr ErC50 and EbC50 are therefore greater than the solubility limit of the test substance.

The EPISUITE QSAR modelling was used to predict the acute and chronic toxicity profile of HiMo LAB. Modelled toxicity values for HiMo LAB (C20 and C24 alkyl derv.) confirmed that the aquatic acute and chronic toxicity value exceeds (i) the predicted water solubility, indicating the substance is not soluble enough to measure the predicted effect and (ii) the log Kow cutoff value of 6.4 and 8.0 for acute and chronic toxicity to green algae, respectively.

According to data from analogue substances and QSAR modelling of HiMo LAB, the substance does not demonstrate acute and chronic aquatic toxicity at water soluble concentrations.