6-hydroxy-1H-pyrimidin-4-one

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1996-01-31 to 1996-03-04

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Valid and conclusive study under GLP , similar to guideline but deficiencies in reporting and no analytical dose verification

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

Version / remarks:

92/69/EWG

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Version / remarks:

1984

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

yes

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test item was dissolved in synthetic freshwater.
- Concentration of vehicle in test medium (stock solution and final test solution): stock solution: 1 g/L, final test solutions: 60, 100, 170, 300, 500, 900 mg/L

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Strain: clone 5
- Source: in-house breeding
- Age at study initiation (mean and range, SD): < 24h
- Method of breeding: in 1L beakers in M4 medium, feeding with alge (Scenedesmus subspicatus) daily

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Post exposure observation period:

No post-observation performed

Test temperature:

20 ± 1°C

pH:

4.3-7.7, dependent on concentration of the test item which shows acidic behavior.

Dissolved oxygen:

7.8-8.1 mg/L

Nominal and measured concentrations:

nominal concentrations: 60, 100, 170, 300, 500, 900 mg/L
No analytical determination of test item concentrations were performed during the test.

Details on test conditions:

TEST SYSTEM
- Test vessel: round-bottom glasses
- Material, size, headspace, fill volume: glass, fill volume 10 mL
- Aeration: none
- No. of organisms per vessel: 5 animals/vessel
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4
- Biomass loading rate: 1 animal per 2 mL

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: synthetic freshwater: CaCl2*2 H2O: 294 mg/L, MgSO4*7H2O: 123 mg/L, NaHCO3: 63 mg/L, KCl: 5.5 mg/L
- Ca/Mg ratio: 4:1
- Culture medium different from test medium: yes

OTHER TEST CONDITIONS
- Adjustment of pH: not specified
- Photoperiod: not specified
- Light intensity: not specified

EFFECT PARAMETERS MEASURED: immobilisation

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.67-1.8
- Test concentrations: nominal concentrations: 60, 100, 170, 300, 500, 900 mg/L

Reference substance (positive control):

yes

Remarks:

potassium dichromate (CAS 7778-50-9 )

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

104 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 95% CL: 83-130

Duration:

48 h

Dose descriptor:

EC100

Effect conc.:

300 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

168 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 95% CL: 123 - 230

Duration:

48 h

Dose descriptor:

EC10

Effect conc.:

> 60 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 5% immobility at 60 mg/L

Details on results:

Results are displayed in table 2.
The EC50 value after 48h incubation, based on immobilisation, is 104 mg/L. The highest concentration at which no immobilisation (< 10%) was observed was 60 mg/L.

Results with reference substance (positive control):

For potassium chromate, the following results were determined after 24h incubation:
concentration 1 mg/L: 25% immobilisation
concentration 2 mg/L: 100% immobilisation

Assuming linear dose-response, the 24h EC50 can be determined from these two measurements to be 1.33 mg/L. As this is in the required EC50 range of 0.6-2.1 mg/L for potassium dichromate, the test system is valid.

Table 2: Cumulated number of immobilized daphnia after incubation with the test item 4,6-dihydroxypyrimidine

Concentration [mg/L]	after 24 h			after 48 h
	number		% immobile	number		% immobile
	mobile	immobile		mobile	immobile
0 (control)	20	0	0	20	0	0
60	19	1	5	19	1	5
100	13	7	35	10	10	50
170	9	11	55	2	18	90
300	8	12	60	0	20	100
500	0	20	100	0	20	100
900	0	20	100	0	20	100

Validity criteria fulfilled:

yes

Conclusions:

The test item 4,6-dihydroxypyrimidin (CAS 1193-24-4) was found not acute toxic to daphnids.

Executive summary:

Acute aquatic toxicity of 4,6-dihydroxypyrimidin (CAS 1193-24-4) was tested under GLP with an Daphnia immobilisation assay similar to EU Method C.2 and OECD Guideline 202. Briefly, daphnids (4 replicas with 5 animals each per concentration) were incubated with the test item dissolved in freshwater. After 24 and 48 h the number of immobile daphnids were counted. The concentrations tested were 60, 100, 170, 300, 500, and 900 mg/L (nominal concentrations). No analytical verification of test item concentrations was performed during the test but stability was assessed in a pre-test over 72 h without daphnia.

The test item 4.6-dihydroxypyrimidine caused distinct immobilisation of daphnids with clear concentration-response data. The 48 h EC50 was 104 mg/L.

Description of key information

EC50 = 104 mg/L, 48h, Daphnia Magna, similar to EU Method C.2 and OECD Guideline 202, Scholz 1996

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

104 mg/L

Additional information

The study report for the determination of the Acute Toxicity to Daphnia magna conducted under GLP (Scholz 1996) shows deficiencies in reporting and no analytical dose verification, however it is considered to be relevant and adequate for the purposes of risk assessment, classification and labeling.

Several other studies were available from the literature, but none were suitable for regulatory use.

In the Kaiser et al (2001) publication, four QSAR models for the acute toxicity (as LC50 value) of chemicals to daphnids (Daphnia magna) using probabilistic neural networks were developed and reported, however not all validity criteria for regulatory purposes were met. Thus the estimation method is scientifically invalid and not usable for regulatory purposes.

In the context of the Kaiser et al (2001) publication, reference values taken from the TerraTox database (http://www.terrabase-inc.com/) were cited. The publication gives no information for the original source of this value but it is possibly that measured by Chen et al (1996 & 1997). It should be noted that Chen at al (1996 & 1997) tested according to APHA (American Public Health Association) standards, where EC50 rather than LC50 is measured, immobility is considered without agitation of the test vessel.

In the Chen (1996 & 1997) publication, the effect of 24 h exposure of no further specified daphnids (Daphnia sp.) to 4,6-dihydroxypyrimidine was tested according to American Public Health Association (1985) standards. The authors use the results for QSAR considerations in two different publications (1996 & 1997). However the validity criteria of the method used has significant methodological deficiencies compared to current standards (no standardized test animals, different effect definition for immobility, and evaluation after 24 h) and the detail level of the documentation is poor. A daphnid was counted as immobile when it swam a distance less than its length in 15 s without foregoing agitation of the test vessel as required by OECD 202 (2004). Consequently, the EC50 may be determined to be at a lower concentration compared to the OECD standard and accordingly the results are considered not reliable and discarded.