2,6-diisopropylnaphthalene

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

OECD Guideline 305 (Bioconcentration: Flow-through Fish Test)

Deviations:

no

GLP compliance:

yes

Radiolabelling:

no

Details on sampling:

- Sampling intervals/frequency for test organisms: at day 7, 14, 21, 35, 46, and 60 of exposure period and at day 0.5, 1, 3, and 4 (test group 1)
or 6 (test group 2) of depuration period
- Sampling intervals/frequency for test medium samples: at day 1, 7, 14, 21, 35, 46, and 60 of exposure period
- Details on sampling and analysis of test organisms and test media samples (e.g. sample preparation, analytical methods):
For each sampling intervall, 4 test fish were used. Two fish were pooled for work up and analysis yielding in two results (group a and b)
for each sampling period.
Test fish were cut in pieces and fragmented. A 3 to 5 g aliquot was homogenized in 15 mL acetonitrile and centrifuged at 5000 x g for 5 min.
The supernatant was filtrated and a 5 mL aliquot of a total of 25 ml purified over a SepPack Alumina B column (elution with acetonitril).
The column eluate was analyzed by GC-MS.
After addition of sodium chloride, test water samples were extracted with choroform and the organic phase was filtrated over filter paper.
The filtrate adjusted to 5 mL with cloroform was used for GC-MS analysis.

Vehicle:

yes

Details on preparation of test solutions, spiked fish food or sediment:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: DMSO was used as dispersing agent: 10 g TS/L DMSO was diluted with DMSO to prepare two stock solutions:
These were prepared by dissolving test substance in the vehicle at a concentration of 200 mg/L and 20.0 mg/l for group 1
and group 2 respectively; test solutions were generated by supplying 0.04 mL/min of stock solution using a micro metering pump
and 1600 mL/min of dilution water to the flow-through test system (total of 2304 L/day).
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): DMSO
- Concentration of vehicle in test medium (test groups and controls): 25 ppm
- Evidence of undissolved material (e.g. precipitate, surface film, etc): no data

Test organisms (species):

Cyprinus carpio

Details on test organisms:

TEST ORGANISM
- Common name: common carp
- Source: Yabegawa Fishery Cooperative Association, Fukuoka, Japan
- Age at study initiation (mean and range, SD): yearling
- Length at study initiation: 6.3 - 10 cm
- Health status: healthy
- Description of housing/holding area: aquatron room of the test facility
- Feeding during test
- Food type: young carp formula feed, Nippon Formula Feed Mfg Co., Ltd.
- Amount: ca. 2% if fish body weight
- Frequency: twice per day

ACCLIMATION
- Acclimation period: 24 d
- Acclimation conditions (same as test or not): yes
- Type and amount of food: young carp formula feed, Nippon Formula Feed Mfg Co., Ltd.
- Feeding frequency: twice per day
- Health during acclimation (any mortality observed): no data

Route of exposure:

aqueous

Test type:

flow-through

Water / sediment media type:

natural water: freshwater

Total exposure / uptake duration:

60 d

Total depuration duration:

>= 4 - <= 6 d

Hardness:

77.5 mg/L (Ca, Mg; analytic value of dilution water)

Test temperature:

25 °C

pH:

7.7 - 8.1

Dissolved oxygen:

7.2 - 8.1 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): flow through system for volatile matter
- Material, size, headspace, fill volume: 100 L glas tank
- Aeration: no data
- Type of flow-through (e.g. peristaltic or proportional diluter):
- Renewal rate of test solution (frequency/flow rate): flow rate 96 L/h (1600 mL/min)
- No. of organisms per vessel: 46 (test groups), 12 (vehicle contol)
- No. of vessels per concentration (replicates): 1
- No. of vessels per control / vehicle control (replicates): 1
- Biomass loading rate: no data

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: ground water from the site of the laboratory (water quality according to OECD TG 305)
- Particulate matter: < 1 mg/L
- Metals:
- Pesticides: < 0.0001 mg/L
- Chlorine: < 0.01 mg/L
- Alkalinity: 158 mg/L
- Ca/mg ratio:
- Conductance: 493 µS/cm
- Holding medium different from test medium: no
- Intervals of water quality measurement: once every 6 month
- Intervals of test medium replacement: flow-through test

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 14 h light / 10 h dark (white fluorescent lamp)
- Light intensity: no data

RANGE-FINDING / PRELIMINARY STUDY
- Test concentrations: 0.953, 1.71, 3.09, 5.56, and 10.0 mg/L
- Results used to determine the conditions for the definitive study: 96-h LC50 of 2.44 mg/L (test species Oryzias latipes)

Nominal and measured concentrations:

Nominal concentrations
Group 1: 5 µg/l ; Group 2: 0.5 µg/L
Measured concentrations (mean over exposure period and 7 peaks)
Group 1: 4.78 µg/L; Group 2: 0.47 µg/L

Lipid content:

ca. 4.1 %

Time point:

end of exposure

Remarks on result:

other: control group

Type:

BCF

Value:

ca. 1 800 - ca. 6 400

Basis:

whole body w.w.

Time of plateau:

35 d

Calculation basis:

steady state

Remarks on result:

other: BCF range for peak A to G (individual values see table below)

Remarks:

Conc.in environment / dose:4.85 µg/L (measured, mean of plateau)

Type:

BCF

Value:

770 - 2 400

Basis:

whole body w.w.

Time of plateau:

35 d

Calculation basis:

steady state

Remarks on result:

other: BCF range for peak A to F (individual values see table below)

Remarks:

Conc.in environment / dose:0.47 µg/L (measured, mean of plateau)

Elimination:

yes

Details on results:

- Mortality of test organisms: no
- Behavioural abnormalities: no
- Observations on body length and weight: no data
- Other biological observations: no abnormalities observed
- Organ specific bioaccumulation: highest acculmulation of test substance in head and viscera, lowest acculmulation in the edible portion of the fish
- Mortality and/or behavioural abnormalities of control: only vehicle controls
- Results with vehicle control: no abnormalities observed

1. BIOCONCENTRATION

 

Steady state could be established for peak A of group 1 and peaks B to F of group 1 and 2 using whole body BCF. For the other groups steady state was determined using BCF based on average lipid content (see below).

Steady state BCF values (BCFss, based on total body weight) were as follows (Section 5.3):

 

Peak	Group 1 (5 µg/L)	Group 2 (0.5 µg/L)
A	6100	2400
B	2200	1100
C	3600	1200
D	1800	770
E	2600	940
F	6400	2200
G	3000	~ 2000

 

 

The bioaccumulation potential for the isomer peak A and F of diisopropylnaphthalene was found to be much higher than for the other isomers as indicated by their BCF.

 

Steady states were reached after 21 days (group 1) and 7 days (group 2) (see Tables 12 + 13 / Fig. 1 and 2 and Section 6(5), p. 38).

 

Total-body values were converted to the BCF values relating to average lipid content to minimize the range of fluctuation of individual measurements.

 

Tissue distribution of BCFs was determined for four body regions (integument, head, viscera, edible portion, see above under materials and methods). Head and viscera showed the highest regional BCF values. They were significantly above the average overall BCFs. The edible fraction showed the lowest BCFs considerable below the average overall BCFs (Section 5.5, Tables 6-1 to 6-4).

 

2. ELIMINATION (half-lives) (Section 5.4 and Fig-Series 13)

 

Following depuration for 6 and 4 days (group 1 and 2 respectively, 4 samples each), half-life for individual peaks was determined from the resulting depuration curves.

 

 

Peak	Group 1 (5 µg/L)		Group 2 (0.5 µg/L)
	half-life [d]	body residue day 6 [%]	half-life [d]	body residue day 4 [%]
A	3.9	46	1.7	17
B	1.9	11	1.6	22
C	2.3	19	1.8	28.5
D	2.0	11.5	1.8	28
E	2.0	11.5	1.7	24.5
F	3.2	26.5	1.9	33
G	5.0	36	1.8	25.5

 

Validity criteria fulfilled:

yes

Conclusions:

1. The extent of bioaccumulation is dependent on individual components.
2. The extent of bioaccumulation is dependent on the exposure concentration. At the low concentration (group 2), the BCF was significantly lower (highest value 2400) compared to the high concentration (group 1, highest value 6400) (see table under Remarks on results).
3. The elimination rate appears to be dependent on exposure concentration. At the lower concentration, somewhat shorter half-lifes were observed. The higher depuration at the lower body burden may be explained by limitations/saturation of metabolism and excretion mechanisms at higher exposure.
4. Irrespective of the exposure concentration, elimination from the organism proved to be very high.
5. The relative high accumulation of the viscera suggests active metabolism and elimination.
6. 2,6-DIPN showed the lowest BCF values of the position isomers examined.

Reference 2

Endpoint:

bioaccumulation in aquatic species, other

Type of information:

other: Expert statement

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Qualifier:

no guideline required

Principles of method if other than guideline:

Expert statement

GLP compliance:

no

Remarks:

Expert statement

Remarks on result:

not measured/tested

Reference 3

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

Refer to analogue justification provided in IUCLID section 13

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Conc. / dose:

4.85 µg/L

Type:

BCF

Value:

2 200 dimensionless

Basis:

normalised lipid fraction

Time of plateau:

35 d

Calculation basis:

steady state

Conc. / dose:

0.47 µg/L

Type:

BCF

Value:

810 dimensionless

Basis:

normalised lipid fraction

Time of plateau:

35 d

Calculation basis:

steady state

Description of key information

No bioaccumulation study concerning only 2,6-diisopropylnaphthalene (CAS 24157-81-1; 2,6-DIPN) was available. But a GLP study according to OECD 305 examining the bioaccumulative potential of Bis(isopropyl)naphthalene (DIPN), an isomeric mixture which consist of seven isomers (1,3-, 1,4-, 1,5-, 1,6-, 2,6- and 2,7-DIPN) is available and used in a read-across approach. In this study the BCF values of the seven isomers was determined individually for each isomer. The determined BCF values differed strongly between the isomers.

According to the recent OECD 305 (2012) as well as the ECHA Guidance Document R.11 (v2.0; ECHA, 2014), the BCF values should be expressed based on a 5% lipid content. In the original study report the BCF data were not lipid-normalised. Therefore, in an expert statement by ECT Oekotoxikologie GmbH (ECT, 2017) a lipid-normalisation was performed using the data (BCF and lipid content) available in the original study report.

For 2,6-DIPN the lipid normalized BCF values were determined as 810 (low dose group; 0.47 µg/L) and 2200 (high dose group; 4.85 µg/L), respectively. Hence, 2,6-DIPN fulfils the criterion of being bioaccumulative (BCF > 2000). Although the environmental relevance of the results from the high exposure concentration is questionable (see expert statement ECT, 2017) the highest measured BCF value of 2200 was used as a worst case assumption for the bioaccumulation assessment. Therefore, 2,6-DIPN was assessed as bioaccumulative (B) under environmental conditions.

Key value for chemical safety assessment

BCF (aquatic species):

2 200 dimensionless

Additional information

No bioaccumulation study concerning only 2,6-diisopropylnaphthalene (CAS 24157-81-1; 2,6-DIPN)  was available. Therefore a bioaccumulation study using Bis(isopropyl)naphthalene (DIPN) was used in a read-across approach for assessment of the bioaccumulation potential of 2,6-DIPN.

Bis(isopropyl)naphthalene (DIPN) is an isomeric mixture, which consists of seven isomers (1,3-, 1,4-, 1,5-, 1,6-, 2,6- and 2,7-DIPN). Bioaccumulation potential differs between the isomers.

Kikushima et al. (2003) performed a study of the bioconcentration of DIPN in fish according to OECD 305 (1996) and under GLP conditions. Fish were exposed for 60 days to two concentrations of DIPN (4.85 and 0.47 µg/L). The seven individual isomers of DIPN could be separated and quantified by GC-MS in order to calculate the BCF for 2,6-DIPN individually. Steady state conditions were reached after 21 days and after 7 days (high dose group and low dose group respectively).

The BCF values for 2,6-DIPN were determined to be 1800 (high dose group) 770 (low dose group) for individual isomers. After lipid normalisation (5% lipid) according to the current OECD 305 and the REACH Guidance Document R.11 (v2.0; ECHA, 2014), the BCF ranges changed to 810 and 2200, respectively. Depuration was fast after cessation of exposure with half-lives of 2.0 days for high dose and 1.8 days for low dose species.

The study is valid and reliable, as no major deviations from the guideline and methodological deficiencies were noted. However, the exposure was performed at concentrations significantly higher than currently observed in the environment. The upper exposure level of DIPN is about 240 times the median concentration of the River Rhine and still 42 times its highest concentration. Therefore, the environmental relevance of the results from this high exposure is questionable (Expert statement evaluating the available information on bioaccumulation authored by ECT, 2017).

Although the environmental relevance of the results from the high exposure concentration is questionable, the highest measured BCF value for 2,6-DIPN of 2200 was used as an worst case assumption for the bioaccumulation assessment. Therefore, 2,6-DIPN was assessed as bioaccumulative (B) under environmental conditions.