Bis(isopropyl)naphthalene

Endpoint summary

Additional information

Stability

Hydrolysis

Due to its chemical structure, diisopropylnaphthalene (DIPN) cannot be hydrolyzed. The structure of the molecule does not contain hydrolysable groups.

Phototransformation in air

No data available (not required for REACH)

Phototransformation in water

Photolytic half-life of 2,6-DIPN (used as supporting substance) in distilled water was 16 h using a high pressure mercury lamp as irradiation source. For 2,7-DIPN, a half-life of 6.4 h was determined. In salt water, phototransformation was accelerated (half-life of 2,6 DIPN in 0.5 M NaCl < 4 h).

Phototransformation in soil

No data available (not required for REACH)

Biodegradation

Biodegradation in water: screening tests

Results on biodegradation of DIPN are ambiguous. In concentrations below solubility in water, DIPN seems to be readily biodegradable (Yoshida 1978_301 B, dissolved substrate). At higher concentrations, inherent biodegradability has been demonstrated (Yoshida 1978_301 B, not dissolved substrate). In a MITI II test, no biodegradation was observed (CERI 1977/CITI1992). In a sealed vessel CO2 head space test (OECD TG 310) using 14C ring labelled diisopropylnaphthalene, no significant ultimate biodegradation could be demonstrated (LAUS 2010a). Analysing DIPN content by GC in the test medium, primary biodegradation of approx. 20 - 30 % and total degradation of approx. 50 % was observed after 56 days (LAUS 2010b).

Biodegradation in surface water, sediment and soil: simulation tests

Tests on aerobic mineralisation in surface water according to OECD 309 were performed for the isomers 1,3-DIPN and 1,4-DIPN, which were shown on screening test level to be less degradable. Since only a negligible amount of CO2 (0 – 0.1% AR) was formed and no metabolites occurred both isomers can be considered as stable under the OECD 309 test condition (Eurofins, 2020). However, based on volatility the dissipation time from water phase was very short. The determined DisT50 values were below 2 days indicating a rapid evaporation from the water phase, which means that the results of the OECD 309 studies are not sufficient for a final persistence assessment. Therefore, QSAR estimates for the degradation in the compartments sediment and soil were considered additionally in a weight of evidence approach. For degradation in sediment the QSAR prediction is persistent (P) and/or very persistent (vP). For the soil compartment the QSAR prediction leads to a “borderline result” with a DT50 close to the P threshold of 120 days. Both QSARs can be considered as reliable since the substance is in the applicability domain of the model. Based on study results and QSAR estimates, it can be assumed that bis(isopropyl)naphthalene (CAS 38640-62-9) contains persistent and/or very persistent isomers. Therefore, the isomeric mixture bis(isopropyl)naphthalene (CAS 38640-62-9) needs to be assessed as potentially persistent (P) and/or very persistent (vP). No substantial new findings can be expected from further simulation tests with DIPN isomers. Therefore, further testing is not intended.

Mode of degradation in actual use

No data available (not required for REACH)

Bioaccumulation

Bioaccumulation: aquatic / sediment

Bis(isopropyl)naphthalene (DIPN) is an isomeric mixture, which consist of seven isomers (1,3-, 1,4-, 1,5-, 1,6-, 2,6- and 2,7-DIPN). Bioaccumulation potential differs between the isomers. According to OECD 305 the lipid normalized BCF values were determined to range between 810 -2500 (low dose group; 0.47 µg/L) and 2200-7800 (high dose group; 4.85 µg/L), respectively. Hence, some isomers of bis(isopropy)naphthalene fulfil the criterion of being bioaccumualtive (BCF > 200). Although the environmental relevance of the results from the high exposure concentration is questionable (see expert statement ETC, 2017) the highest measured BCF value of 7800 was used as an worst case assumption for the bioaccumulation assessment. Therefore, the isomer mixture bis(isopropyl)naphthalene (CAS 38640-62-9) was assessed as bioaccumulative (B) and potentially very bioaccumulative (vB) under environmental conditions.

Bioaccumulation: terrestrial

No data available (not required for REACH)

Transport and distribution

Adsorption/Desorption

Based on Koc values of 33,108 or 188,973 (log Koc 4.5576 or 5.2764) calculated using two different methods, DIPN is expected to have a low mobility and high accumulation potential in soil (MWC, 2009).

Henry’s Law constant

Using the method of bond contribution and group contribution, Henry's Law constants of 202 and 197 Pa*m³/mol were determined, indicating quite rapid volatilization of DIPN from water into air.

Environmental data

Monitoring data

In Japan, bis(isopropyl)naphthalene DIPN was detected in environmental samples from two locations. In sea mud from the mouth of a river (Osaka Bay), 0.019 to 0.16 ppm (n = 5) of DIPN were analyzed and in sea fish (Yokkaichi Bay), levels of ca. 0.003 ppm (n = 7) were found (Sumino 1977).

Close to a paper recycling plant, DIPN concentrations in river sediment were found to be 0.3 - 23.0 µg/g (Sato 1980). At the wastewater discharge of another plant, 2200 µg/g were analyzed but 100 m downstream, only concentrations of 8.5 µg/g were detected (Haga et al.1984).

Surveys of the Environmental Agency of Japan published environmental monitoring data in surface water, sediment and fish of the years 1975, 1977, 1980 and 2005/2006/2007 (see Summary in the table below):

 

-      DIPN was detectable in 10 out of 400 water samples with a maximum of 0.0044 µg/L.

-      DIPN was positive in 35 out of 358 sediment samples (10 %) with a maximum (2005) of 7500 µg/kg dry weight

-      DIPN was positive in 41 out of 349 fish samples (12 %) with a maximum (1975) of 48 µg/kg wet weight.

Overview of monitoring data 1975 - 2005/2007 (follow-up 2009 and 2010, see below addendum Suzuki et al. 2012) [Chemical Risk Information Platform (CHRIP) 2010 / (Environment Agency, Japan, 1998)]:

Compartment	Fiscal Year	Number of detection A/B	Concentration [µg/L (water), µg/g dwt (sediment), µg/g wwt (fish)]
			Range of detection	Limit of detection
Water	1975	0/100	---	70 - 5,000*
	1977	0/117	---	0.01 – 10
	1980	0/120	---	0.01 - 20
	2006	0/12	---	0.0004
	2007	10/51	0.0044	0.00071 – 0.0015
Sediment	1975	9/100	0.061 - 0.19	0.03 - 0.25
	1977	6/117	0.0019 - 0.1	0.00074 - 0.6
	1980	3/120	0.049 - 0.064	0.01 - 1.0
	2005	17/21	0.0037 – 7.5	0.002
Fish	1975	2/94	0.028 -0.048	0.025 - 0.25
	1977	7/93	0.00052 - 0.0017	0.0002 - 0.5
	1980	3/108	0.006 - 0.025	0.002 – 2.5
	2005	29/54	0.00019 – 0.027	0.00019

*(no reliable data)

In 2009 and 2010 (Suzuki et al. 2012), sampling was continued in the Southern Hyogo prefecture, which embraced 41 sampling points in the Osaka bay and the Seto Inland Sea:

- Seawater: <1.9 - 9.8 ng/L DIPN was found.

- Sediment: <1.1 - 100 μg/kg dw (30 points in 2009), the highest solitary contamination of 4400 μg/kg dw was detected in a river sediment of a river without a relevant industrial source.

- Fish tissue (Japanese sea perches: Lateolabrax japonicus): 1.2 - 3.4 μg/kg ww (five samples). There was no difference in the levels of DIPN in males and females; however, the isomers 1,3- and 1,4 -DIPN were more pronounced in female perch.