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

Short-term toxicity to fish

Description of key information

No data on acute toxicity to fish is available for HiMO LAB.  Data from LAB and LAB Alkylate bottoms were used to understand the acute toxicity profile of substance to fish. The toxicity of the substances has been measured experimentally with freshwater fish.  As a consequence, 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. 

There is no acute fish study available with HiMo LAB. The studies from Benzene, C10-13-alkyl derivs. (LAB, CAS No 67774-74-7) and Benzene, mono-C12-14-alkyl derivatives, fractionation bottoms (LAB Alkylate bottoms, CAS No 68515-32-2) as structural analogues were used to cover this endpoint.

The toxicity of LAB to fish was determined in an extended acute study according to OECD 204. Fish were exposed for 14 days to a water accommodated fraction of 0, 5, 6.5, and 10 µg/L of test substance. The test medium was renewed daily. Fish were monitored daily for toxicity during the study for swimming behaviour, reaction to stimuli, discoloration, food intake, and mortality. All fish were weighed and measured before the test and survivors were weighed at test termination. No adverse effects were observed for the concentrations tested during the study period. A decrease in the test substance concentration was observed within 24 hours (day 1 and day 14), but the daily renewal of test solutions maintained the exposure to the test substance. Both the LOEC and NOEC were higher than the solubility concentration of >10 ug/L.

The acute toxicity to fish of substance; LAB Alkylate bottoms was determined in ASTM guideline study. Duplicate groups of 10 fish were exposed to concentrations of 0, 12.5, 25, 50, 100 % water accommodated fraction (WAF) of test substance. Fish were exposed for 96 hrs, with the renewal of the test solution at 48 hrs. Fish were observed at 24, 48, 72, and 96 hrs for mortality. One fish in the 25% WAF exposure group died during renewal of the test solution. This death was not considered treatment related. All other fish in the exposure groups survived. The 96-hr LC50 is > 100% WAF.

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 fish.

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