Bis(isopropyl)naphthalene

Endpoint summary

Additional information

Short-term toxicity to fish

Five studies on short-term toxicity to fish have been identified. All of them have shortcomings. Only two of the reports present a LC50 which can be considered to be reliable (Kikushima 2003, Handley 2003)). But also for these studies, not all validity criteria are fulfilled (use of vehicle, test concentrations above or just above the water solubility of DIPN, no analytical measurement of test concentration by Kikushima 2003). Overall, LC50 values range from > 0.5 to > 1000 mg/L.

For only one study the concentration used is in the range of the maximum water solubility of DIPN (Handley/Safepharm, 2003). This study has been selected as key study. It is a limit test with a concentration (0.5 mg/L) slightly above the water solubility of DIPN. Test substance concentrations were measured and demonstrated to decrease within the renewal periods (24 h) to about 0.098 to 0.135 mg/L which corresponds to the approximate level of water solubility (ca. 0.122 mg/L). There was no mortality observed at this concentration. Thus the LC0 is ca. 0.24 mg/L (averaged geometric means of concentrations at the start and the end of renewal solutions from different time points). The LC50 is reported as > 0.5 mg/L.

There were no effects observed at concentrations within the water solubility of DIPN.

Long-term toxicity to fish

A new study is considered scientifically unjustified. Long-term toxicity testing of fish does not appear scientifically necessary as data for a more sensitive species of a different trophic level is available. For regulatory purposes as well as for environmental risk assessment, only the lowest toxicity value in species from three trophic levels is considered relevant (see Guidance on information requirements and chemical safety assessment, chapter R.7b: Endpoint specific guidance, section 7.8.5, p. 41 - Threshold approach for toxicity testing in fish).

Short-term toxicity tests with diisopropylnaphthalene, available for species of three trophic levels (invertebrates, aquatic algae, and fish), show that Daphnia magna is the most sensitive species (EC0 values being lower by a factor of 2 to 3 compared to the LC0 values in fish (EC/LC50 was not reached within the water solubility of diisopropylnaphthalene)).

Since aquatic invertebrates turned out being the most sensitive species in short-term studies, long-term studies were considered necessary for evaluation of chronic hazards of the substance. Long-term toxicity tests are available for Daphnia magna (fresh water) and Acartia tonsa (marine water). Based on the higher sensitivity observed in short-term tests, it is assumed that in long-term tests Daphnia will also be the most sensitive species. Thus, classification and derivation of PNECs will be based on long-term NOEC obtained in invertebrate tests and no additional chronic study with fish is considered necessary.

Short term toxicity to aquatic invertebrates

For assessment of the short-term toxicity to aquatic invertebrates, in addition to two older tests, a most recent test with Daphnia magna is available (STZ 2012). The test was conducted under strictly closed conditions, taking the volatility of the substance into account. Water accommodated fractions were prepared from different loadings of the poorly water soluble multi constituent compound, likewise under closed conditions. This test resulted in an effect loading EL50 (48 h) of 1.7 mg/L.

Among the older studies, only one valid study is available (WaBoLu/BGA, 1990, key study). In a second study (Shigeoka/MITES, 1982), a vehicle was used to solubilise the test substance and the exposure period is only 24 h.

In the first of these studies, only slight effects on mobility of Daphnia magna were observed within the range of water solubility of diisopropylnaphthalene (0.1 to 0.2 mg/L). The LC0 was determined as 0.066 mg/L and EC50 (48 h) was > 0.16 mg/L (highest concentration tested).

In the study of Shigeoka, Tween 80 in DMSO was used as vehicle. The EC50 (24 h) was determined to be 2.3 mg/L. The EC0 (24 h) was 0.4 mg/L.

In conclusion within the range of water solubility of DIPN, no or only slight effects on the mobility of Daphnids were observed.

Long term toxicity to aquatic invertebrates

Four tests on long-term toxicity of the isomeric mixture bis(isopropyl)naphthalene (CAS 38640-62-9) to aquatic invertebrates are available, two with the freshwater standard species Daphnia magna (WaBoLu/BGA, 1990 & Laus 2017) and two with the marine copepods Acartia tonsa (TNO, 1998a & 1998b). The two reproduction tests with Daphnia magna leads to no observed effect concentrations of 0.0118 mg/L (measured, TWA) and 0.013 mg/L (nominal) after 21 d. The NOEC values for the marine copepods are approx. 0.05 mg/L (measured) and 0.02 mg/L (measured), respectively. In all four studies a decrease of test item was noted, which might lead to an underestimation of the toxicity. Considering that the results of the two Daphnia reproduction studies with the isomeric mixture bis(isopropyl)naphthalene are on the borderline of meeting the T-criterion, two further Daphnia reproduction tests in a closed system under flow-through conditions were requested by ECHA, for the most critical isomers of the isomeric mixture (1,3-DIPN and 1,4-DIPN) with respect to PBT properties. In the OECD 211 test with 1,3-DIPN the number of alive offspring produced by adults did not show any statistically significant decrease of reproduction up to the highest test concentration of 40 µg/L (Eurofins, 2020). Therefore, the NOEC (21 d) was set to be ≥ 40.0 µg/L (nominal) equivalent to ≥ 24.4 µg/L (measured), including mortality of adults, reproduction and body length.

In the second test with 1,4-DIPN the number of alive offspring produced by adults alive from test start showed statistically significant decrease of reproduction in the highest test item concentration of 125 µg/L (nominal) equivalent to 38.8 µg/L (measured) compared to the solvent control (Eurofins, 2020b). This study was performed in a flow-through design as well. The NOEC (21 d) was calculated to be 62.5 µg/L (nominal) equivalent to 28.1 µg/L (measured) based on reproduction. Statistically significant effects for mortality were observed at 62.5 and 125 µg/L, therefor the NOEC (21 d) for mortality was calculated to be 31.3 µg/L (nominal) equivalent to 16.3 µg/L (measured).

Toxicity to aquatic algae and cyanobacteria

For assessment of the toxicity to aquatic algae and cyanobacteria, one valid study is available (Vogel/WaBoLU, 1999).In a freshwater algal growth inhibition test according to DIN 38412 part 9, no growth inhibition effect was observed up to DIPN test concentration close to its maximum water solubility (ca. 0.15 to 0.19 mg/L). The NOEC (72 h) was ca 0.15 mg/L (measured).

Toxicity to microorganisms

For assessment of the toxicity to microorganisms, three studies are available. Due to limited reporting (secondary literature or short communication in tabular form), the reliability is 4. As results are very similar, they are used in a weight of evidence approach.

In two tests (UBA/KBwS 1999a, Yoshioka 1985), fresh water single species have been used (Pseudomonas putida, Tetrahymena pyriformis) in a static test. EC10 and EC0 (growth inhibition) after 24 h were > 0.16 mg/L and >0.15 mg/L, respectively.

The third test used Vibrio fischeri in marine water measuring luminescence inhibition. The EC50 was > 0.1 mg/L.

Diisopropylnaphthalene did not exhibit inhibitory effects on the microorganism tested within its range of water solubility (0.1 to 0.2 mg/L).