6-cyclohexyl-1-hydroxy-4-methylpyridin-2(1H)-one, compound with 2-aminoethanol (1:1)

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Principles of method if other than guideline:

Data published on toxicity studies to aquatic algae for 2-aminoethanol, neutral form of ethanolaminium cation.

GLP compliance:

not specified

Remarks:

Data published. No detailed information about GLP compliance.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

2.8 mg/L

Nominal / measured:

nominal

Conclusions:

In water at environmentally relevant pH, 2-aminoethanol will exist as ethanolaminium cation. (CAS number: 141-43-5). For 2-aminoethanol, the neutral form of ethanolaminium cation, the lowest reliable toxicity value to aquatic algae is ECr50 (72h) = 2.8 mg/L (nominal; pH 8.0-9.7; Pseudokirchneriella subcapitata).

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Qualifier:

according to guideline

Guideline:

other: OECD 201

GLP compliance:

not specified

Remarks:

Data published. No detailed information about GLP compliance.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.063 mg/L

Nominal / measured:

not specified

Conclusions:

Within the environmentally relevant pH range, a substantial fraction of 6-cyclohexyl-4-methyl-2-oxopyridin-2(1H)-olate anion will be in the neutral form (6-cyclohexyl-1-hydroxy-4-methylpyridin-2-one (Ciclopirox); CAS 29342-05-0; pKa (estimated) = 6.84 (ChemAxon)).
For Ciclopirox, the neutral form of 6-cyclohexyl-4-methyl-2-oxopyridin-2(1H)-olate anion, NOEC (72h) is 0.063 mg/l .

Description of key information

Since Ciclopirox olamine is an organic salt, it is expected to dissociate upon its release in the environment and to dissolve in water into 6-cyclohexyl-4-methyl-2-oxopyridin-2(1H)-olate anion and ethanolaminium cation. Because of this dissociation behaviour, the assessment of Ciclopirox olamine toxicity to aquatic algae was focused on the dissociation products.

For 2-aminoethanol, the neutral form of ethanolaminium cation, the lowest reliable toxicity value to aquatic algae is ECr50 (72h) = 2.8 mg/L (nominal; pH 8.0-9.7; Pseudokirchneriella subcapitata). In water at environmentally relevant pH, 2-aminoethanol will exist as ethanolaminium cation. (CAS number:141-43-5).

For Ciclopirox, the neutral form of 6-cyclohexyl-4-methyl-2-oxopyridin-2(1H)-olate anion, NOEC (72h) is 0.063 mg/l (OECD 201; Pseudokirchneriella subcapitata). Within the environmentally relevant pH range, a substantial fraction of 6-cyclohexyl-4-methyl-2-oxopyridin-2(1H)-olate anion will be in the neutral form (6-cyclohexyl-1-hydroxy-4-methylpyridin-2-one (Ciclopirox); CAS 29342-05-0; pKa (estimated) = 6.84 (ChemAxon)).

Based on experimental data on toxicity to aquatic algae of dissociation products, Ciclopirox olamine is regarded as hazardous for aquatic organisms.