3,5,5-trimethylhexanoic acid

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1999-04-19 to 1999-07-15

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

, but performed to an older version of the guideline.

Qualifier:

according to guideline

Guideline:

other: "Bioaccumulation test of chemical substance in fish and shellfish" in Prescribing the Items of the Test Relating to the New Chemical Substance (1974, Order of the Prime Minister of Health and Welfare, MITI No.1). This guideline corresponds to OECD 305 C.

Qualifier:

according to guideline

Guideline:

OECD Guideline 305 C (Bioaccumulation: Test for the Degree of Bioconcentration in Fish)

Version / remarks:

adopted 12 May 1981

Deviations:

yes

Remarks:

a lower number of fish was used per exposure group. However, the number of fish analysed per time point was according to OECD 305.

GLP compliance:

yes

Radiolabelling:

no

Details on sampling:

- Sampling intervals/frequency for test organisms: after two, three, four and six weeks (n = 2 per exposure concentration)
- Sampling intervals/frequency for test medium samples: 2x/week (n = 1)
- The controls were analysed before initiation and termination of exposure (n = 2).

Vehicle:

yes

Remarks:

HCO-40; - 1 mg/L nominal concentration: 10 mg/L HCO-40; - 0.1 mg/L nominal concentration: 1 mg/L HCO-40;

Test organisms (species):

Cyprinus carpio

Details on test organisms:

TEST ORGANISM
- Common name: carp
- Source: Sugishima fish farm (Japan)
- Length at study initiation (mean): 10.3 cm
- Weight at study initiation (mean): 26.1 g
- Health status: fish showing visible abnormal signs were removed before and during acclimation
- Description of housing/holding area: flow-through system
- Feeding during test
- Food type: pelleted feed for carp
- Amount: ca. 2 % of body weight
- Frequency: 2x/day


ACCLIMATION
- Acclimation period: 28 d
- Acclimation conditions (same as test or not): yes
- Type and amount of food: pelleted feed for carp, ca. 2 % of body weight
- Feeding frequency: 2x/day

Route of exposure:

aqueous

Justification for method:

aqueous exposure method used for following reason: According to ECHA guidance document R.7c (2017) preferred route of exposure for substaces with acceptable water solubility (>0.1 mg/L - test item: 0.7 g/L) and moderate log Kow (below 6 - test item: 3.2)

Test type:

flow-through

Water / sediment media type:

natural water: freshwater

Total exposure / uptake duration:

6 wk

Test temperature:

25 +/- 2 °C

pH:

7 +/- 1

Dissolved oxygen:

7.4-8.1 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Material, size, headspace, fill volume: 100-L glass tank
- Renewal rate of test solution (frequency/flow rate): 800 mL/min
- exposure groups (nominal): 1 mg/L; 0.1 mg/L; control group;
- No. of organisms per vessel: 11 fish/concentration; 5 control fish
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1 (blank without test substance), 1 (recovery test)

TEST MEDIUM / WATER PARAMETERS
- Intervals of water quality measurement: 2x/week

RANGE-FINDING / PRELIMINARY STUDY
- Results used to determine the conditions for the definitive study: 48-h LC50 (Oryzias latipes): 160 mg/L

Nominal and measured concentrations:

nominal: 0.1 and 1.0 mg/L

Reference substance (positive control):

not specified

Details on estimation of bioconcentration:

- observations/measurements: weight, length, lipid content (at test start);
- test item analyses:
test water (2x/week), test fish (after 2, 3, 4, and 6 weeks; 2 fish per concentration level), control fish before initiation and termination of exposure (2 fish, each).
- BCF = concentration of test substance in fish (based on whole fish wet weight)/concentration of test substance in water

Lipid content:

3.5 %

Time point:

start of exposure

Conc. / dose:

>= 0.932 - <= 0.936 mg/L

Temp.:

25 °C

pH:

7

Type:

BCF

Value:

>= 0.5 - <= 1.7 L/kg

Basis:

whole body w.w.

Remarks:

based on individual concentration results for fish (n= 2 at each time point)

Time of plateau:

2 wk

Calculation basis:

steady state

Remarks on result:

other: based on arithmetic mean values for each time point, steady state was reached between 2 and 3 weeks.

Remarks:

Nominal exposure concentration: 1 mg/L

Key result

Conc. / dose:

>= 0.092 - <= 0.094 mg/L

Temp.:

25 °C

pH:

7

Type:

BCF

Value:

>= 4.1 - <= 7 L/kg

Basis:

whole body w.w.

Remarks:

based on individual concentration results for fish (n= 2 at each time point)

Time of plateau:

4 wk

Calculation basis:

steady state

Remarks on result:

other: based on arithmetic mean values for each time point, steady state was reached between 3 and 4 weeks.

Remarks:

Nominal exposure concentration: 0.1 mg/L

Details on kinetic parameters:

No kinetic parameters determined.

Metabolites:

No metablites detected.

Results with reference substance (positive control):

No positive control

Details on results:

Test fish did not show any abnormal appearance at both test item concentrations applied.

Details on results:

Weeks		2	3	4	6
1st Concentration (1 mg/L nominal)	Test substance concentration (mg/L)	0.935	0.935	0.932	0.936
	Bioconcentration factor (L/kg)	1.6	0.6	1.7	0.6
		1.7	1.3	1.4	0.5
2nd Concentration (0.1 mg/L nominal)	Test substance concentration (mg/L)	0.0932	0.0925	0.0930	0.0943
	Bioconcentration factor (L/kg)	< 3.1	7.0	5.7	4.8
		< 3.1	< 3.1	4.1	4.9

Validity criteria fulfilled:

yes

Conclusions:

No significant bioaccumulation potential is to be expected for 3,5,5-trimethylhexanoic acid based on the measured BCF of <= 7.0 (steady state) determined according to the MITI protocol, which corresponds to OECD 305 C.

Executive summary:

To determine any potential for aquatic bioaccumulation of the submission substance, the bioconcentration factor for fresh water fish was determined using carp (Cyprinus carpio). The valid test was performed compliant with GLP according to OECD 305C (1981), following the steady state method. Based on preliminary acute toxicity testing (LC50 (Oryzias latipes; 48 h) = 160 mg/L), two exposure concentrations of 1.0 and 0.10 mg/L had been applied in a flow through system using glass aquaria (25 °C).

Aquatic test item concentrations were determined 2 times a week, and concentrations in fish were determined after two, three, four and six weeks. At each time point 2 fish per concentration level were used and extracted separately after weighing (wet weight). A mean lipid content of 3.5% had been determined at the start of exposure for the fish used.

Steady state (plateau) was reached between 2 and 3 weeks for 1 mg/L nominal concentration (>= 0.932 mg/L <= 0.936 mg/L measured) and between 3 and 4 weeks for 0.1 mg/L nominal concentration (>= 0.0925 mg/L <= 0.0943 mg/L measured). The highest BCF determined based on individual concentration results for fish (n= 2 at each time point) was 7.0 L/kg (whole body wet weight).

Concluding, these valid results convincingly demonstrate that there is no relevant aquatic bioaccumulation potential for 3,5,5-trimethylhexanoic acid (NITE, 2000).

Description of key information

No significant bioaccumulation potential is expected for 3,5,5-trimethylhexanoic acid based on a measured BCF according to the MITI protocol, which corresponds to OECD 305 C (NITE, 2008). The BCF at the lower test concentration (0.1 mg/L) was < 3.1-7.0, while the BCF at the higher test concentration (1 mg/L) was lower (0.5-1.7).

Key value for chemical safety assessment

BCF (aquatic species):

7 L/kg ww

Additional information

To determine any potential for aquatic bioaccumulation of the submission substance, the bioconcentration factor for fresh water fish was determined using carp (Cyprinus carpio). The valid test was performed compliant with GLP according to OECD 305C (1981), following the steady state method. Based on preliminary acute toxicity testing (LC50 (Oryzias latipes; 48 h) = 160 mg/L), two exposure concentrations of 1.0 and 0.10 mg/L had been applied in a flow through system using glass aquaria (25 °C).

Aquatic test item concentrations were determined 2 times a week, and concentrations in fish were determined after two, three, four and six weeks. At each time point 2 fish per concentration level were used and extracted separately after weighing (wet weight). A mean lipid content of 3.5% had been determined at the start of exposure for the fish used.

Steady state (plateau) was reached between 2 and 3 weeks for 1 mg/L nominal concentration (>= 0.932 mg/L <= 0.936 mg/L measured) and between 3 and 4 weeks for 0.1 mg/L nominal concentration (>= 0.0925 mg/L <= 0.0943 mg/L measured). The highest BCF determined based on individual concentration results for fish (n= 2 at each time point) was 7.0 L/kg (whole body wet weight).

Concluding, these valid results convincingly demonstrate that there is no relevant aquatic bioaccumulation potential for 3,5,5-trimethylhexanoic acid (NITE, 2000).

A supporting QSAR study is available (ECT, 2008). The log BCF of 3,5,5-trimethylhexanoic acid was estimated to be 0.5 (BCF 3.2 L/kg ww) by using the BCFWIN program (v2.17) as part of US EPA EPI Suite(TM). This fits very well to the experimentally determined data and further corroborates that the submission substance will not bioaccumulate.