1,4-diisopropylbenzene

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

effects on growth of green algae

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
In this justification, the read-across (bridging) concept is applied. Please refer to a full version of Read-across statement attached in the section 13 "Assessment reports".

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The underlying hypothesis for the read-across is that the target and the source substance have similar toxicological properties (including the same target organs) due to their structural similarity, resemblance to their chemical reactivity, and therefore a similar mode of action.
The source substance ‘Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene' is a mixture of structural isomers, 1,3- diisopropylbenzene and 1,4-diisopropylbenzene (target substance). The physico-chemical properties are highly equivalent based on the high structural similarity. As a conclusion, it is scientifically justified to address the endpoint Toxicity to aquatic algae and cyanobacteria with data on this mixture of isomers.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source substance: Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene (Diisopropylbenzene), CAS no. 25321-09-9
structural formula: C12H18
Smiles: CC(C)C1=CC=CC=C1C(C)C
Molecular weight: 162 g/mol
CAS 25321-09-9
EC No 246-835-6
purity: not specified

target substance: 1.4-diisopropylbenzene (or p-DIPB)
structural formula: C12H18
Smiles: CC(C)c1ccc(cc1)C(C)C
Molecular weight: 162 g/mol
CAS 100-18-5
EC No 202-826-9
purity: not specified

No additional information is available on purity of the source and the target substances. Both substances are normally of high purity, containing only minor amounts of impurities that do not influence the read-across validity.

3. ANALOGUE APPROACH JUSTIFICATION
Please refer to the full version of the read-across statement.

4. DATA MATRIX
Please refer to the full version of the read-across statement attached in the section 13 "Assessment reports".

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

1.37 mg/L

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

5.44 mg/L

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

3.12 mg/L

95% CI:

>= 1.77 - <= 5.44

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.615 mg/L

Conc. based on:

test mat.

Basis for effect:

biomass

Details on results:

Concentration of test substance in test solution
The concentration of the test substance in the test solution was measured at the beginning of the test and after 72 hours.
Because there were analytical results in which the concentration at the start of the test exceeded ± 20 % of the set concentration, the measured values were used for the calculation of each effect concentration below.
The concentrations of the test substance at 72 hours of exposure ranged from 0.034 to 4.57 mg/L, and the percentage of the set value ranged from 17 to 23 %. Since the test substance is insoluble in water and has a low boiling point, volatilization and transfer to the algae seemed to be the main causes of the decrease in concentration.

Growth curve

The cell concentrations in the control and the control-agent-control areas increased an average of 44-fold and 56-fold, respectively, during 72 hours of incubation, indicating normal growth under the test conditions (sealed conditions). Cell concentrations in each concentration tended to decrease (in a dose-dependent manner) with increasing concentration.

 

50 % growth inhibition concentration (EC50) and maximum no-effect concentration (NOEC)

The growth inhibition rate at each concentration is shown in Table 3, the 50 % growth inhibition concentration (EC50) and the maximum no-effect concentration (NOEC) in Table 4, and the concentration-1 inhibition rate curves in Figures 2 and 3. From these results, the following conclusions were drawn.

 

1) Inhibition concentration by comparison of area under the growth curve

　EbC50 (0-72): 3.12 mg/L (95% confidence interval: 1.77-5.44 mg/L)

　NOECb (0-72) ： 0.615 mg/L

 

(2) Inhibition concentration by comparison of growth rate

　ErC50 (24-48): 6.05 mg/L (95% confidence interval: 3.32-11.0 mg/L)

　NOECr (24-48) : 1.37 mg/L

　ErC50 (24-72): 5.44 mg/L (95% confidence interval: calculate not available)

   NOECr (24-72) ： 1.37 mg/L)

 

Temperature and pH

The temperature was within the set range (23 ± 2 °C). The pH of the test solution ranged from 7.8 to 8.1 at the beginning of the exposure and from 8.1 to 10.6 at the end of the test. If carbonic acid assimilation is active and algal growth rates are high, the pH may increase by more than 1. In the present study, the pH of the control, the control with the aid, and the control with 4.31 mg/L or less were all higher than the pH of the control.

The pH increased by more than 1 in the test section.

Validity criteria fulfilled:

yes

Conclusions:

Green algae was exposed to test item for 72 hours. it was determined that EC50 (72h): 5.44 mg/L and NOEC (72h) value: 1.37 mg/L.

Executive summary:

The toxicity to aquatic algae and cyanobacteria study was performed according to OECD guideline 201 under GLP compliance. The purpose of the test: Growth inhibition test of the test substance on algae (Selenastrum capricornutum) was conducted for 72 hours. The 50 % growth inhibition concentration (EC50) and the maximum No observed Effect concentration (NOEC) were determined. Green algae was exposed to test item for 72 hours. it was determined that EC50 (72h): 5.44 mg/L and NOEC (72h) value: 1.37 mg/L.

Based on the arguments presented in the Read Across statement attached in IUCLID Section 13, it is clear that the source substance, which consists only of the target substance and its structural isomer, shows an identical toxicokinetic pattern. As such, the data presented here could be used to fulfil lthe information requirements for the target substance 1.4-diisopropylbenzene.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
In this justification, the read-across (bridging) concept is applied. Please refer to a full version of Read-across statement attached in the section 13 "Assessment reports".

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The underlying hypothesis for the read-across is that the target and the source substance have similar toxicological properties (including the same target organs) due to their structural similarity, resemblance to their chemical reactivity, and therefore a similar mode of action.
The source substance ‘Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene' is a mixture of structural isomers, 1,3- diisopropylbenzene and 1,4-diisopropylbenzene (target substance). The physico-chemical properties are highly equivalent based on the high structural similarity. As a conclusion, it is scientifically justified to address the endpoint Toxicity to aquatic algae and cyanobacteria with data on this mixture of isomers.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source substance: Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene (Diisopropylbenzene), CAS no. 25321-09-9
structural formula: C12H18
Smiles: CC(C)C1=CC=CC=C1C(C)C
Molecular weight: 162 g/mol
CAS 25321-09-9
EC No 246-835-6
purity: not specified

target substance: 1.4-diisopropylbenzene (or p-DIPB)
structural formula: C12H18
Smiles: CC(C)c1ccc(cc1)C(C)C
Molecular weight: 162 g/mol
CAS 100-18-5
EC No 202-826-9
purity: not specified

No additional information is available on purity of the source and the target substances. Both substances are normally of high purity, containing only minor amounts of impurities that do not influence the read-across validity.

3. ANALOGUE APPROACH JUSTIFICATION
Please refer to the full version of the read-across statement.

4. DATA MATRIX
Please refer to the full version of the read-across statement attached in the section 13 "Assessment reports".

Reason / purpose for cross-reference:

read-across source

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

1.6 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.31 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

biomass

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

2.7 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.69 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

Statistical Method:

a) Data Analysis: The EC50 values and associated 95 % confidence limits were determined by least squares linear regression analysis of the logarithm of measured test concentration against percent growth inhibition relative to the solvent control. The NOEC values were determined by analysis of variance (ANOVA), Dunnet test, subsequent to Bartlett test for homogeneity of variances.

b) Method of Calculating Mean Measured Concentrations (i.e. arithmetic mean, geometric mean, etc.): Geometric mean of measured concentrations at 0 hr and at 72 hr were used for calculation.

Effect Data:
Area Method
EbC50(0-72hr) = 1.6 mg/L (mc)
NOEC (0-72hr) = 0.31 mg/L (mc)

Measured Concentrations :
The tested concentrations were measured at the start and the 72nd hour. The concentrations of 72 hours after were low. Those percent of nominal were 17 - 23 %. The test substance seemed to be incorporated into cell slightly.

Nominal Measured Conc. mg/L			Percent of nominal
	0 Hour	72 Hour	0 Hour	72 Hour	Mean*conc. mg/L
Control	<0.002	<0.002	-	-	-
Solvent Control	<0.002	<0.002	-	-	-
0.200	0.138	0.034	69	17	0.068
0.430	0.291	0.076	68	18	0.15
0.930	0.615	0.158	66	17	0.31
2.00	1.37	0.345	69	17	0.69
4.31	2.98	0.762	69	18	1.51
9.28	6.25	1.90	70	20	3.45
20.0	14.8	4.57	74	23	8.22
* Geometric mean

Percent Growth Inhibition of Selenastrum capricornutum 

Measured Conc. mg/L	Area under the growth curves (Average)
	Area A (0-72hr)	Inhibition (%) *1 (0-72hr)
Control	7,934,000	---
Solvent Control	10,816,000	---
0.068	10,995,000	-1.7
0.15	10,629,000	1.7
0.31	9,770,000	9.7
0.69	9,170,000	15.2*
1.51	6,651,000	38.5**
3.45	1,638,000	84.9**
8.22	397,000	96.3**

   

Growth rates and percent inhibition (Average)
Measured Conc. mg/L	Rate	Inhibition(%) *1	Rate	Inhibition(%)*1
	u (24-48 hrs)	Im(24-48hr)	u (24-72 hrs)	Im(24-72hr)
Gontrol	0.0684	---	0.0629	---
Solvent Control	0.0680	---	0.0593	---
0.068	0.0691	-1.6	0.0599	-1.0
0.15	0.0691	-1.6	0.0591	0.3
0.31	0.0661	2.8	0.0582	1.9
0.69	0.0648	4.7	0.0570	3.9
1.51	0.0552	18.8**	0.0526	11.3**
3.45	0.0300	55.9**	0.0227	61.7**
8.22	0.0094	86.2**	0.0057	90.4**
*1：Values are the percent inhibition relative to the control
*: Indicates a significant difference (alpha=0.05) from the solvent control
					**: Indicates a significant difference (alpha=0.01) from the solvent control

 

Water chemistry (pH) in test:
pH was measured for control and each concentration at the start and end of test.
pH: 8.1 - 10.

Calculation of toxicity values: The calculation of toxicity values was the mean measured concentrations.
The reason is that some of the error ranges of measured concentration were not less than +/- 20 % of nominal concentration.

Growth Curves: Log phase during the test period

NOEC = 0.69 mg/L (growth rate), = 0.31 mg/L (biomass)
EC50 = 2.7 mg/L (growth rate), = 1.6 mg/L (biomass)

Rate Method
ErC50(24-48hr) >= 3.05 mg/L (mc) (95% C.I.: 1.65-5.5 mg/L)
NOErC(24-48hr) = 0.69 mg/L (mc)
ErC50(24-72hr) >= 2.7 mg/L (mc)
NOErC = 0.69 mg/L (mc)
mc: based on mean measured concentration

Validity criteria fulfilled:

not specified

Conclusions:

The 72 h EbC50 and NOEC were determined to be 1.6 mg/L and 0.31 mg/L (measured concentrations) and in respect to growth rate the 72 h ErC50 and NOEC were found to be 2.7 mg/L and 0.69 mg/L (measured concentrations), respectively.

Executive summary:

In a study conducted according to OECD Guideline 201 (Alga, Growth Inhibition Test), Selenastrum capricornutum were exposed to diisopropylbenzene concentrations (a mixture of m-DIPB and p-DIPB, with o-DIPB as an impurity) for 72 h in closed system and EC50 and NOEC in respect to biomass and growth rate determined. The test was conducted using solvent (mixture of a dispersant of HCO40 and DMF) and the estimated values were higher than water solubility, however, analytical monitoring was done. In this test, it could not be separated the true toxicity of the test substance from the physical effect of non-dissolving substance. In respect to biomass the 72 h EbC50 and NOEC were determined to be 1.6 mg/L and 0.31 mg/L (measured concentrations) and in respect to growth rate the 72 h ErC50 and NOEC were found to be 2.7 mg/L and 0.69 mg/L (measured concentrations), respectively.

Based on the arguments presented in the Read Across statement attached in IUCLID Section 13, it is clear that the source substance, which consists only of the target substance and its structural isomer, shows an identical toxicokinetic pattern. As such, the data presented here could be used to fulfil lthe information requirements for the target substance 1.4-diisopropylbenzene.

Description of key information

- 2 OECD 201 studies are available using the mixed isomers (m- and p-) of diisopropylbenzene.

 

a) MOE, 2000g

EC50 (72h): 5.44 mg/L

NOEC (72h) value: 1.37 mg/L.

 

b) SIDS, 2002
EC 50: 2.7 mg/L
EC 10 or NOEC: 0.69 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:

2.7 mg/L

EC10 or NOEC for freshwater algae:

0.69 mg/L

Additional information

The toxicity to aquatic algae and cyanobacteria study (MOE, 2000g) was performed according to OECD guideline 201 under GLP compliance (reliability 1 -  reliable without restriction). The purpose of the test: Growth inhibition test of the test substance (diisopropylbenzene - a mixture of the meta and para isomers) on algae (Selenastrum capricornutum) was conducted for 72 hours. The 50 % growth inhibition concentration (EC50) and the maximum No observed Effect concentration (NOEC) were determined. Green algae were exposed to test item for 72 hours. it was determined that EC50 (72h): 5.44mg/L and NOEC (72h) value: 1.37mg/L.

 

In a study conducted according to OECD Guideline 201 (Alga, Growth Inhibition Test; reliability 2, reliable with restrictions as original data not available), Selenastrum capricornutum were exposed to diisopropylbenzene concentrations (a mixture of m-DIPB and p-DIPB, with o-DIPB as an impurity) for 72 h in closed system and EC50 and NOEC in respect to biomass and growth rate determined. The test was conducted using solvent (mixture of a dispersant of HCO40 and DMF) and the estimated values were higher than water solubility, however, analytical monitoring was done. In respect to biomass the 72 h EbC50 and NOEC were determined to be 1.6 mg/L and 0.31 mg/L (measured concentrations) and in respect to growth rate the 72 h ErC50 and NOEC were found to be 2.7 mg/L and 0.69 mg/L (measured concentrations), respectively. The EC50 and NOEC values are higher than the water solubility of DIPB thereby indicating that the substance is not toxic at the limit of water solubility.

 

Based on the arguments presented in the Read Across statement attached in IUCLID Section 13, it is clear that the source substance, which consists only of the target substance and its structural isomer, shows an identical toxicokinetic pattern. As such, the data presented here could be used to fulfill the information requirements for the target substance 1.4-diisopropylbenzene.

 

As key values - despite the lower reliability score of the underlying study entry - the lowest available EC50 value of 0.69 mg/L and the lowest available NOEC value of 2.7 mg/L were included in a worst case approach.