Benzene, C20-24 (even numbered) sec-alkyl derivs.

Short-term toxicity to aquatic invertebrates

Description of key information

No data on acute toxicity to aquatic invertebrates 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 toxicity profile of substance to daphnia. The 48-hr EC50 values were  >0.041 mg/L for LAB, and > 1.4 mg/L for HAB. As a consequence, due to the extremely low water solubility,  the acute toxicity is above the water solubility (<0.1 mg/L).

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 daphnia, structral analogue approach was used from LAB. Daphnids were exposed to concentrations of 0, 12.5%, 25%, 50%, 75%, and 100% saturated test solution for 48 hrs. At the end of this period, the daphnids were observed for mobility. Though immobilized daphnids were seen at 4 test concentrations, there was no dose-related increase in immobilization, nor was the number of immobilized daphnids significantly increased over negative controls. The 48-hr EC50 is >0.041 mg/L, this is greater than the water solubility for the test substance.

The acute toxicity to daphnia of supporting substance; HAB was determined in OECD 202 guideline study. Groups of 20 daphnids were exposed to concentrations of 0, 0.35, 0.49, 0.70, 0.98, or 1.40 mg/L of test substance. The daphnids were then observed at 24 and 48 hrs after start of exposure for immobilization. At the 24 hr observation, one daphnid at the 0.98 mg/L concentration was immobilized. At the 48-hr observation one daphnid at the 0.70, 0.98, and 1.40 mg/L concentrations was immobilized. The 48-hr EC50 was > 1.4 mg/L test substance, which is greater than the water solubility of the test substance. Concentrations refer to TOC. No effect at saturated solutions (1.4 mg/L).

The EPISUITE QSAR modelling was used to predict the acute toxicity profile of HiMo LAB. Modelled toxicity values for HiMo LAB (C20 and C24 alkyl derv.) confirmed that the aquatic acute 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 5.0 for acute toxicity to daphnia.

 

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