Hexyl chloroformate

Short-term toxicity to fish

Description of key information

The 96-h LC50 is 15 mg/L in fish (D. rerio).

Additional information

Data on the acute toxicity of hexyl chloroformate to fish (D. rerio) is available from a study performed according to guideline OECD 203 and in compliance with GLP criteria (BASF, 2008). From this study the 96 -h LC50 value was determined to be 15 mg/L. As the substance is expected to rapidly hydrolyse in contact with water to form hexanol (CAS 111 -27 -3), hydrogen chloride (CAS 7647-01-0) and carbon dioxide (CAS 124-38-9) in addition, a screening study with hexyl chloroformate was performed to determine the effect of hydrolysis time on fish toxicity. In this study a test solution of 100 mg/L hexyl chloroformate and a control were allowed to hydrolyse (under continuous homogenisation) for 0, 1, 4, 12 or 24 hours prior to exposure of fish. The aqueous phase of the test batches was clear. Undissolved test substance was visible at the bottom of the test vessels throughout the exposure time. For the first 12 hours additionally undissolved test substance was visible at the water surface in all test batches. From this study a 96 -h EC100 value of <100 mg/L was determined for all test solutions hydrolised for 12 hours or less whereas the test solution that hydrolised for 24 hours gave a 96 -h EC0 value of >100 mg/L.

Key information on the hydrolysis products was gathered also.

For the hydrolysis product hexanol a short-term fish study was conducted by Veith et al. (1983) in order to describe the relationship between experimentally determined 96 -h LC50 values and substances log Kow values. For hexanol a 96 -h LC50 value of 97.2 mg/L was determined in fish (P. promelas).

For the hydrolysis product hydrogen chloride a short-term study in fish (C. carpio) according to OECD guideline 203 is available (OECD SIDS, 2002).The 96-h LC50 was 4.92 mg/L (acid equivalent to pH 4.3).

For the hydrolysis product carbon dioxide no fish toxicity data are available.

In the study with the parent substance (BASF, 2008), no test substance was detected in the samples taken from any of the tested concentrations (limit of quantification 8.1 mg/L for hexyl chloroformate). The analytical values for the degradation product 1 -hexanol were also below the limit of quantification (9.0 mg/L). Undissolved test substance was still visible in the higher test concentrations. In the preliminary study no toxicity was seen at 100 mg/L after stirring a hexyl chloroformate test solution for 24 hours before fish were inserted (BASF, 2007). It was therefore concluded that toxicity is likely to be related to the high reactivity of unhydrolyzed hexyl chloroformate in the early phase of the test rather than to exposure to the hydrolysis product hexanol. The 96 -h LC50 of 97.2 mg/L determined for hexanol further strengthens this conclusion. Toxicity related to a pH effect due to hydrolytical formation of HCl can be ruled out based on pH values determined regularly throughout the study (all pH values within OECD preferences). Despite these considerations, the 96 -LC50 value of 15 mg/L as determined with the parent substance is used for assessment as a worst case approach.