Methenamine

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1980

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: non GLP, US EPA (Algal assay procedure: bottle test) guideline for a 14 day algae test

Qualifier:

according to guideline

Guideline:

other: National Environmental Research Center, 1971: Algal assay procedure: bottle test. US EPA Corvallis, Oregon

Deviations:

yes

Remarks:

other growth media used: Bold's mineral salts media

GLP compliance:

no

Analytical monitoring:

no

Details on sampling:

no sampling

Vehicle:

no

Details on test solutions:

Growth medium used: Bold's mineral alsts media

Test organisms (species):

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

Details on test organisms:

concentration of algae: 10E03 cells/ml

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

14 d

Post exposure observation period:

no post exposure period

Hardness:

not indicated

Test temperature:

not indicated

pH:

7.5

Dissolved oxygen:

not indicated

Salinity:

freshwater used

Nominal and measured concentrations:

nominal: 0, 1000, 2500 and 5000 mg/L

Details on test conditions:

Selenastrum capricornutum was exposed in a 14 d growth inhibition test following U.S. EPA (AAP: BT) guidelines. Bold's mineral salts medium was slightly modified by adding tris buffer and NaHCO3 and an illumination regime of 12 h light/12 h dark was applied. The pH of the medium was 7.5. The maximum specific growth rates for 1, 2.5 and 5 g methenamine/l (dosed as flo-powder) were determined on the basis of cell counts (initial algal concentration approximately 10E03 cells/ml).

Reference substance (positive control):

yes

Remarks:

Phenol

Key result

Duration:

14 d

Dose descriptor:

EC50

Effect conc.:

ca. 3 g/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: estimated from the growth curves

Key result

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

1.5 g/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

A value of 1.5 g/L was estimated as concentration not resulting in a significant growth rate reduction. Here, the rising impact of turbidity on the results with increasing methenamine concentrations was taken into account, although this impact is not exactly quantifiable. Hence, the test is is considered not fully in line with OECD requirements. However, taking the findings of the other tests into account, the result is reliable and conservative enough for a risk assessment. The 14 day EC50 estimated from the growth curves is 3 g/L.

Results with reference substance (positive control):

Parallel test were conducted with phenol to give perspective as to the sensitivity of the assay procedure. These test gave positive results, as expected and demonstrated the sensitivity of the test system.

Reported statistics and error estimates:

Since all tests were run in triplicate, the values were averaged and expressed as log(10) numbers.

Validity criteria fulfilled:

yes

Conclusions:

The LC50 of methenamine in Selenastrum capricornutum (freshwater) was determined to be about 3 g/L.

Executive summary:

Selenastrum capricornutum was exposed in a 14 d growth inhibition test following U.S. EPA (AAP: BT) guidelines. Bold's mineral salts medium was slightly modified by adding tris buffer and NaHCO3 and an illumination regime of 12 h light/12 h dark was applied. The pH of the medium was 7.5. The maximum specific growth rates for 1, 2.5 and 5 g methenamine/l were determined on the basis of cell counts (initial algal concentration approximately 10E03 cells/mL).

A value of 1.5 g/L was estimated as concentration not resulting in a significant growth rate reduction. Here, the rising impact of turbidity on the results with increasing methenamine concentrations was taken into account, although this impact is not exactly quantifiable. Hence, the test is is considered not fully in line with OECD requirements. However, taking the findings of the other tests into account, the result is reliable and conservative enough for a risk assessment. The 14 day EC50 estimated from the growth curves is 3 g/L.

Description of key information

The LC50 of methenamine in Selenastrum capricornutum(freshwater) was determined to be about 3 g/L.

Key value for chemical safety assessment

EC50 for freshwater algae:

3 000 mg/L

EC10 or NOEC for freshwater algae:

1 500 mg/L

Additional information

Selenastrum capricornutum was exposed in a 14 d growth inhibition test following U.S. EPA (AAP: BT) guidelines. Bold's mineral salts medium was slightly modified by adding tris buffer and NaHCO3 and an illumination regime of 12 h light/12 h dark was applied. The pH of the medium was 7.5. The maximum specific growth rates for 1, 2.5 and 5 g methenamine/l (dosed as flo-powder) were determined on the basis of cell counts (initial algal concentration approximately 10E03 cells/mL).

A value of 1.5 g/L was estimated as concentration not resulting in a significant growth rate reduction. The rising impact of turbidity on the results with increasing methenamine concentrations was taken into account, although this impact is not exactly quantifiable. Hence, the test is is considered not fully in line with OECD requirements. However, taking the findings of the other tests into account, the result is reliable and conservative enough for a risk assessment. The 14 day EC50 estimated from the growth curves is 3 g/L.

Based on the available data, no toxicity towards two algae species even at concentrations > 1500 mg/L, which by far exceeded the recommended limit concentration of OECD guidelines (100 mg/L) clearly indicate, that methenamine is not toxic at all towords algae.