2-methylpropan-2-ol

Long-term toxicity to fish

Description of key information

Effect of short-term exposure on the hatch rate and development of the African catfish, Clarias Gariepinus

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

332 mg/L

Additional information

A study of toxicity to the sensitive early life stages (from eggs, through hatching to the sac-fry stage) of the African catfish Clarias gariepinus is available. The methods employed are comparable to those set out in OECD guideline 212 (Short-term Toxicity Test on Embryo and Sac-Fry Stages), with some variations: OECD 212 studies are recognised as acceptable to address long-term toxicity to fish for substances with log Kow <4 (REACH guidance R.7B). Although C. gariepinus is not listed as a recommended test species in OECD 212, use of other species is not precluded in that guideline and the authors of this published paper state that C. gariepinus is a suitable model for investigation of early life stage toxicity in fish, with a short embryo-larval period of 4-5 days after egg fertilisation. Adequate sensitivity of C. gariepinus to chemical toxicity is demonstrated by the observation that methyl tertiary butyl ether concentrations above 50 mg/l significantly increased larval deformations: the 31-day methyl tertiary butyl ether IC20 value of 279 mg/l reported for of toxicity to eggs, larvae and fry of P. promelas in the EC RAR indicates lesser (or at least no greater) sensitivity of this OECD 212 recommended species. OECD 212 specifies “As larvae are not fed during the exposure period, the test should be terminated just before the yolk sac of any larvae in any of the test chambers has been completely absorbed or before mortalities by starvation start in controls. Test duration will depend upon the species used”: while the report of the C. gariepinus study does not specifically justify the exposure period employed (24h egg plus 96h larval exposure) it seems highly probable that yolk sac absorption was near completion when exposure finished (5 days post-fertilisation). Omission of daily larval hatch counts and length/weight measurements of survivors represent deviations from OECD 212, but are considered of little importance since test versus control group comparisons were made for the major parameters of total numbers of unhatched eggs, dead larvae and surviving larvae with three separate categories of malformation. Only non-viable egg numbers increased significantly following (high concentration) exposure to tertiary butyl alcohol: no NOEC was specified in the paper, but based on the highest level at which no significant effect was noted between control and exposure groups a NOEC value of 332 mg/l can be concluded.