1-butyl-1,2-dihydro-6-hydroxy-4-methyl-2-oxonicotinonitrile

Endpoint summary

Description of key information

Short-term aquatic toxicity to aquatic invertebrates

The 48-h EC50 value is >120 mg/L (nominal) in aquatic invertebrates (D. magna).

Toxicity to microorganisms

Based on data available for the close structural analogue 1-Ethyl-2-hydroxy-3-cyan-4-methylpyridon-6 (CAS 28141-13-1), the 30-min EC50 and EC10 values are >372 mg/L (nominal; based on a.i.) in activated sludge.

Additional information

Discussion

Apart of a short-term toxicity test with Daphnia magna (BASF SE, 2017), no experimental ecotoxicity data are available for the substance itself. Therefore, the ecotoxicological potential is assessed based on data available for the close structural analogue 1-Ethyl-2-hydroxy-3-cyan-4-methylpyridon-6 (CAS 28141-13-1). This analogue differs from the substance only in that it has an ethyl- instead of a butyl-chain attached to the nitrogen atom in the pyridine ring. The available data for read-across purpose are tabulated below.

Overview of aquatic toxicity data available for the read-across substance 1-Ethyl-2-hydroxy-3-cyan-4-methylpyridon-6 (CAS 28141-13-1):

Study	Species	Guideline	Endpoint	Effect value
Short-term toxicity to fish	No data available	-	-	-
Long-term toxicity to fish	No data available	-	-	-
Short-term toxicity to aquatic invertebrates	D. magna	OECD 202	48-h EC50	>120 mg/L (nominal)
Long-term toxicity to aquatic invertebrates	No data available	-	-	-
Toxicity to aquatic algae	No data available	-	-	-
Toxicity to microorganisms	Activated sludge (domestic/synthetic)	OECD 209	30 -min EC50 30 -min EC10	>372 mg/L (nominal, a.i.) >372 mg/L (nominal, a.i.)

As no effects were observed up to the highest concentration tested, effect values are not corrected for molecular weight. As the target chemical has a slightly higher molecular weight, this may be considered a worst case approach.

Short-term toxicity to aquatic invertebrates

The acute immobilisation of the test substance to Daphnia magna (STRAUS) was determined under GLP conditions according to OECD Guideline 202 (BASF SE, 2017). The test was performed in a static and closed system as a limit-test over a duration of 48 hours with the only nominal test concentration of 120 mg/L (based on range finding information; measured mean concentration during the test: 108 mg/L), along with a laboratory negative control (0 mg/L). Four replicates with five daphnids each for the test concentration and the negative controls were used. Mobility of daphnids was recorded after 24 and 48 hours of exposure. Based on the nominal concentrations of the test substance the 48-h EC50 was determined to be >120 mg/L.

For the close structural analogue 1-Ethyl-2-hydroxy-3-cyan-4-methylpyridon-6 (CAS 28141-13 -1) the acute toxicity to aquatic invertebrates was determined in a study according to OECD guideline No 202 and in compliance with GLP criteria (BASF AG, 1999). In this study daphnids (D. magna, 20 per concentration) were exposed to nominal test substance concentrations of 0 (control), 12.5, 25, 50 and 100 mg/L for 48 hours under static conditions. Analytical confirmation of the nominal test concentrations of 12.5 and 100 mg/L at the start and the end of the test showed that test concentrations remained well within ±20% of nominal concentrations. Therefore, effect concentrations are expressed as nominal. Mobility of daphnids was recorded after 24 and 48 hours exposure. No immobilization of daphnids was observed in any of the concentrations tested. Based on these findings the 48-h EC50 value is >100 mg/L (nominal). Based on a test substance purity of 37.2%, this value is recalculated at >37.2 mg/L for the active ingredient. As the structural analogue differs from the target substance only in that it has an ethyl- instead of a butyl-chain attached to the nitrogen atom in the pyridine ring, it may be considered likely that this 48-h EC50 value applies also to the test substance 1-butyl-1,2-dihydro-6-hydroxy-4-methyl-2-oxonicotinonitrile.

Based on the results of the Acute Immobilisation Test with Daphnia magna (BASF SE, 2017), the test substance is considered to be not toxic to aquatic invertebrates since no aquatic toxicity was observed at 120 mg/L. This result is supported by the results for the structural analogue 1-Ethyl-2-hydroxy-3-cyan-4-methylpyridon-6 (CAS 28141-13 -1) as no effects were observed up to the highest concentration tested.

Toxicity to microorganisms

The toxicity of the structural analogue 1-Ethyl-2-hydroxy-3-cyan-4-methylpyridon-6 (CAS 28141-13-1) to microorganisms was investigated in an activated sludge respiration inhibition study according to OECD guideline No 209 and in compliance with GLP criteria (BASF AG, 1999). In this limit test activated sludge from laboratory wastewater plants treating municipal and synthetic sewage was exposed to nominal test substance concentrations of 0 (control) and 1000 mg/L (based on test substance) for 30 minutes. Test concentrations were not analytically verified. After the 30 minutes incubation period, the change in oxygen consumption rate compared with the blank control was 0%. Based on these findings, the 30-min EC50 and EC10 values are determined at >372 mg/L (nominal, a.i.).

Based on the results with the structural analogue, the test substance is considered to be not toxic to aquatic microorganisms as the 30-min EC50 and EC10 values are determined at >372 mg/L (nominal, a.i.).