Naphthenic acids, zinc salts

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:

06 April 2018 - 30 May 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Version / remarks:

Adopted April 13, 2004.

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Guidance document on aquatic toxicity testing of difficult substances and mixtures

Version / remarks:

OECD series on testing and assessment number 23, 2000.

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

- Source and lot/batch No.of test material: A036/99 (Supplier batch number: SCC-1709-0300)
- Expiration date of the lot/batch: 31 August 2018
- Storage condition of test material: At room temperature protected light.
- Treatment of test material prior to testing: None

Analytical monitoring:

yes

Details on sampling:

ZINC ANALYSIS
- Concentrations: Samples for possible analysis were taken from all test concentrations and the control.
- Frequency: 0 and 96 hours.
- Sampling method: Duplicate 4.8 mL from the approximate centre of the test vessels. At the end of the exposure period, the replicates were pooled at each concentration before sampling.
- Sample storage conditions before analysis: Samples were stored in a freezer (≤-15°C) until analysis.

TOC ANALYSIS
- Concentrations: Samples for possible analysis were taken from all test concentrations and the control.
- Frequency: 0 and 96 hours.
- Sampling method: Duplicate 40 mL.
- Sample storage conditions before analysis: Samples were stored in a refrigerator (2-8°C) until analysis.

Vehicle:

no

Details on test solutions:

- Test solution preparation: The test item was added to media at the relevant concentrations (1.0, 10 and 100 mg/L for the combined limit/range-finding test and at 10, 18, 32, 56 and 100 mg/L for the final test) then stirred for 2 days, followed by 1 day settling. WAFs were collected by siphoning and used directly as test concentrations.
- Solution appearance: All test solutions were clear and colorless at the end of the preparation procedure.
- Test media: Adjusted ISO medium.
- Vehicle: None
- Control: Test medium without test item or other additives.

Test organisms (species):

Daphnia magna

Details on test organisms:

- Common name: Giant water flea
- Strain/clone: Straus, 1820
- Source: In-house laboratory culture with a known history.
- Parental daphnids: 2nd to 5th brood originating from healthly stock, more than 2 weeks old and showed no signs of stress.
- Age: < 24 hours
- Feeding during test: No feeding

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Hardness:

- Breeding media: 180 mg/L expressed as CaCO3

Test temperature:

20-21°C

pH:

- Test start: 7.6-7.8
- Test end: 7.8-8.2

Dissolved oxygen:

- Test start: 9.5-9.7
- Test end: 8.7-8.9

Salinity:

Not applicable

Conductivity:

Not specified

Nominal and measured concentrations:

- WAF loading rates: 10, 18, 32, 56 and 100 mg/L

Details on test conditions:

- Test vessel: 60 mL, all glass, containing 50 mL solution
- Aeration: No
- No. of organisms per vessel: 5
- No. of vessels per concentration: 4
- No. of vessels per control: 4
- Biomass loading rate: 5 per vessel containing 50 mL of test solution
- Composition of medium: Adjusted ISO medium, prepared in Reverse Osmosis tap water
- Intervals of water quality measurement: pH and dissolved oxygen were measured at the beginning and at the end of the test, for all concentrations and the control. Temperature of medium was measured continuously in a temperature control vessel.
- Adjustment of pH: No
- Photoperiod: 16 hours photoperiod daily
- Effect parameters: Immobility (including mortality) at 24 hours and at 48 hours

RANGE-FINDING STUDY
- Test concentrations: 1, 10 and 100 mg/L
- Results used to determine the conditions for the definitive study: Yes

Reference substance (positive control):

no

Key result

Duration:

48 h

Dose descriptor:

EL50

Effect conc.:

35 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Details on results:

ACCEPTABILITY
- Effects in control: No daphnids in the control became immobilised or showed other signs of disease or stress, for example discoloration or unusual behaviour such as trapping at the surface of the medium.
- Dissolved oxygen: The oxygen concentration at the end of the test was ≥3 mg/L in control and test vessels.

ANALYTICAL RESULTS
- Zinc: Analysis of the samples taken at the start of the final test showed measured zinc concentrations of 0.49, 0.71, 1.4, 1.7 and 2.9 mg/L in the WAFs at 10, 18, 32, 56 and 100 mg/L, respectively. All zinc concentrations remained stable during the test period and ranged between 94 and 98% of initial at the end of the test.
- TOC: An increase with the loading rate at the start of the test was observed and carbon concentrations slightly decreased during the test period, i.e. to 68-92% of initial. It should be noted that concentrations below 1.0 mg TOC/L are only indicative.

EFFECT RESULTS
- Immobility: After 48 hours of exposure, ≥65% of the daphnids exposed to WAFs prepared at loading rates of 32 mg/L and higher were immobilized. No immobility was observed in the WAFs up to and including 18 mg/L and in the control during the 48-hour test period.
- Conclusion: The 48h-EL50 for Daphnia magna was 35 mg/L based on loading rates (95% confidence interval between 29 and 41 mg/L based on loading rates).

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

The 48h-EL50-value was calculated using the Spearman-Karber method (without trim) on the percentages of affected daphnids and the logarithms of the corresponding test item loading rates.

Measured TOC Concentrations during the Final Test

 

Naphthenic acids, zinc salts Loading rate^1(mg/L)	Measured concentrations (mg TOC/L)				Relative to initial (%)
	As measured		Corrected^2
	t=0h	t=48h	t=0h	t=48h
Control	0.40	0.61
10	3.1	2.5	2.7	1.9	68
18	4.1	3.3	3.7	2.7	74
32	7.0	6.0	6.6	5.3	81
56	8.5	7.4	8.1	6.8	84
100	14	13	13	12	92

¹WAF prepared at the given loading rate
²Corrected for the control treatment

Measured zinc concentrations during the Final Test

 

Naphthenic acids, zinc salts Loading rate^1(mg/L)	Concentration dissolved Zn analysed (mg Zn/L)		Relative to initial (%)
	t=0h	t=48h
Control	<0.001^2	<0.001^2	n.a.
10	0.487	0.459	94
18	0.709	0.665	94
32	1.36	1.30	95
56	1.70	1.64	96
100	2.92	2.87	98

¹WAF prepared at the given loading rate. Samples were stored in the freezer (≤ -15°C) until the day of analysis.
²A small response was measured. Concentration was below that of the lowest calibration solution and therefore reported to be < 0.001 mg/L.

n.a. Not applicable.

Number of Introduced Daphnids and Incidence of Immobility in the Final Test

Time (h)	Replicate	Naphthenic acids, zinc salts; Loading rate^1(mg/L)
		Control	10	18	32	56	100
0	A	5	5	5	5	5	5
	B	5	5	5	5	5	5
	C	5	5	5	5	5	5
	D	5	5	5	5	5	5
	Total introduced	20	20	20	20	20	20
24	A	0	0	0	0	1	0
	B	0	0	0	0	0	0
	C	0	0	0	0	0	0
	D	0	0	0	0	0	0
	Total immobilised	0	0	0	0	1	0
	Effect %	0	0	0	0	5	0
48	A	0	0	0	4	4	5
	B	0	0	0	4^#	3	5
	C	0	0	0	2	3	5
	D	0	0	0	3	4	5
	Total immobilised	0	0	0	13	14	20
	Effect %	0	0	0	65	70	100

¹WAF prepared at the given loading rate

^#Microscopic observation revealed no test item attached to the daphnids

Validity criteria fulfilled:

yes

Conclusions:

The 48h-EL50 for Daphnia magna exposed to Naphthenic acids, zinc salts was 35 mg/L based on loading rates (95% confidence interval between 29 and 41 mg/L based on loading rates).

Executive summary:

The acute toxicity of naphthenic acids, zinc salts to Daphnia magna was determined to give a 48 -hour EL50 of 35 mg/L based on a water accommodated fraction loading rate (WAF). The acute toxicity of naphthenic acids, zinc salts to Daphnia magna was determined in a GLP-compliant test (Charles River 2018) following OECD guideline 202. The results are considered to be reliable for use.

Description of key information

The 48h-EL50 for Daphnia magna exposed to Naphthenic acids, zinc salts was 35 mg/L based on loading rates (95% confidence interval between 29 and 41 mg/L based on loading rates).

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

35 mg/L

Additional information

The acute toxicity of naphthenic acids, zinc salts to Daphnia magna was determined to give a 48 -hour EL50 of 35 mg/L based on a water accommodated fraction loading rate (WAF). The acute toxicity of naphthenic acids, zinc salts to Daphnia magna was determined in a GLP-compliant test (Charles River 2018) following OECD guideline 202. The results are considered to be reliable for use.