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Vapour pressure

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Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
2f: accepted calculation method Based on measured data in saturation chamber, Weschler calculated the vapor pressure but details on the calculation are not described. However this data is obtained in good conditions and Clausen cite this calculated value in his following article in 2004 (Environ. Sci. Technol., 38, 2531 -2537).
Qualifier:
no guideline followed
Principles of method if other than guideline:
An open beaker containing 50mL of pure DEHP was placed in a clean CLIMPAQ chamber at 22°C and under air flow of ca 9L/min. The vial was heated to ca. 150°C for 2 hours (saturation of the chamber including all sinks). After the beaker was cooled, air was sampled 3 times from the outlet of the chamber (on days 1, 21 and 25).
GLP compliance:
not specified
Type of method:
gas saturation method
Remarks:
CLIMPAQ test chamber
Temp.:
25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: saturated vapor pressure calculated by Weschler et al. 2008 based on Clausen et al. 2001 data.

Clausen et al. 2001 reports the following measurements of the dynamic equilibrium concentration of DEHP in the CLIMPAQ chamber:

-day 1: 30 µg/m³

-day 21: 3.7 µg/m³

-day 25: 3.4 µg/m³

Based on this value, Weschler calculated the vapor pressure but details on the calculation are not described. However this data is obtained in good conditions and Clausen cite this calculated value in his following article in 2004 (Environ. Sci. Technol., 38, 2531 -2537).

Conclusions:
In the test conditions, the saturated vapor pressure of DEHP was estimated to 30 µg/m³ 1 day after. The consecutive vapor pressure was calculated to be 1.9x10E-5 Pa at 25°C.
Executive summary:

Clausen et al. (2002) have measured the saturated concentration in DEHP a clean CLIMPAQ chamber at 22°C. For this, an open beaker containing 50mL of pure DEHP was placed in and under air flow of ca 9L/min. The vial was heated to ca. 150°C for 2 hours (saturation of the chamber including all sinks). After the beaker was cooled, air was sampled 3 times from the outlet of the chamber (on days 1, 21 and 25).

The concentration obtained were 30 µg/m³, 3.7 µg/m³ and 3.4 µg/m³ respectively.

Based on this value, Weschler calculated the vapor pressure

VP at 25°C= 1.9x10E-5 Pa but details on the calculation are not described. However this data is obtained in good scientific conditions and Clausen cite this calculated value in his following article in 2004 (Environ. Sci. Technol., 38, 2531 -2537). Moreover as data at very low pressure are difficult to obtain and are subject to greater variability.

Therefore, this data is considered as reliable with acceptable restrictions.

Endpoint:
vapour pressure
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
2f: acceptable calculation method According to authors, the regression for predicting solubilities in water and vapour pressure can be used for phthalate esters with alkyl chain lengths from 1 to 13. (note that DEHP as 2 alkyl chains of 8 carbons) and points corresponding to high molar volume (>450cm³/mol) are considered as unreliable on graphical representation. However the data are in good agreement with recent and reliable measured data.
Justification for type of information:
QSAR prediction: migrated from IUCLID 5.6
Principles of method if other than guideline:
development of a model based on the three solubilities measurements (in air, octanol and water) of 22 phthalate esters.
GLP compliance:
no
Type of method:
other: Quantitative structure-property relationship
Temp.:
ca. 25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: 2.52x10E-5 Pa

Linear regression between the 3 solubilities and the Le Bas molar volume are presented in attachement.

These regressions showed good correlation (99.9%) for low molecular volume phthalate esters.

On these figures we can see that some point corresponding to high molar volume (>450cm³/mol) are considered by authors as unreliable.

Authors also indicate that the regression for predicting solubilities in water and vapour pressure can be used for phthalate esters with alkyl chain lengths from 1 to 13. Authors do not indicate if it is per alkyl chain or for the total of carbon in all alkyl chains of the molecule

(note that DEHP as 2 alkyl chains of 8 carbons).

Conclusions:
According to the model based on the 'three solubility approach' and the molar volume of phthalate esters, DEHP show a calculated vapor pressure of 2.52x10E-5 Pa at 25°C. This calculated value is in accordance with recently measured ones.
Executive summary:

The quantitative structure-property relationship method for the correlation of physical-chemical properties and partition coefficients, namely the 'three solubility' approach, is described by Cousin and Mackay (2000) to a group of 22 phthalate esters.

The model is based on apparent solubilities collected from the literature and were correlated with the Bas molecular volume in the three primary media (air, water and octanol).

Kaw, Kow and Koa can be deduced as the ratio of the 3 solubilities correlations. The data used in this study were extracted from the literature (excluding data not assignable data due to unknown primary literature or because the value were clearly inconsistent with the other data). The endpoints are: water solubility, vapor pressure (assimilated to its solubility in air on basis of the gas law), octanol solubility (estimated as the product of solubility in water and the octanol-water partition coefficient). The values used in this study are reported in table 1 (in attachement).

These data were correlated with the Bas molar volume at the normal boiling point as estimated by the Le Bas method (Reid et al. 1987). This common molecular descriptor is based on the summation of atomic volumes with adjustement for the volume decrease arising from ring formation. DEHP Bas molar volume is : 520.4 cm³/mol). 

With the relationships obtained, authors have estimated the vapor pressure, the solubility in water and the three partition coefficients.

DEHP show a calculated vapor pressure of 2.52x10E-5 Pa at 25°C. This calculated value is in accordance with recently measured ones.

Linear regression between the 3 solubilities and the Le Bas molar volume are presented in attachement. These regressions showed good correlation (99.9%) for low molecular volume phthalate esters. On these figures we can see that some point corresponding to high molar volume (>450cm³/mol) are considered by authors as unreliable.

Authors also indicate that the regression for predicting solubilities in water and vapour pressure can be used for phthalate esters with alkyl chain lengths from 1 to 13. Authors do not indicate if it is per alkyl chain or for the total of carbon in all alkyl chains of the molecule

(note that DEHP as 2 alkyl chains of 8 carbons).

However the data are in good agreement with recent and reliable measured data.

Endpoint:
vapour pressure
Type of information:
other: literature review
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: 2g: Data from reliable literature review . The original study report was not checked considering that these values were validated by swedish comptetent authorities and used in previous risk assessment report, RAR, 2008.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Value selected in RAR, 2008 was reported from an experimental result from Hüls AG, 1997. Vapour pressure at 20°C was extrapolated from measurements with 99.5% pure DEHP.
GLP compliance:
not specified
Type of method:
other: no data
Temp.:
20 °C
Vapour pressure:
0 Pa
Remarks on result:
other: data selected for risk assessment (EUSES / fugacity) in RAR, 2008.

RAR reports: "A large range of values on the vapour pressure is available in the literature (0.00000004 - 0.0014 Pa, Staple et al. 1997b). However, recent studies have shown that many of these values probably are overestimations due to interference from impurities (Rippen 1992). In a newly made measurement with 99.5% pure DEHP, the vapour pressure was estimated to 0.000034 Pa at 20°C (See Table below) (Hüls AG 1997). This value is used for assessing the environmental fate."

 Temperature (°C)  Pressure (Pa)  Comment

 10

 0.000010*  
15  0.000023   
20  0.000034*  used in EUSES/fugacity 
30 0.00013*   
40  0.00047*   
50  0.0016*   
60  0.0057   
70  0.011  max.indoor car (BUA 1986) 
80  0.039   
90  0.10   
100  0.29   
110  0.76   
120  1.09  
140 4.5*   
160 2.4*  injection moulding, PVC 
180  80*   
203  287  
210 389   
216  511   

Conclusions:
In the test conditions, the vapor pressure of DEHP was extrapolated to 0.000034 Pa at 20°C.
Executive summary:

Data for vapour pressure of DEHP are cited in Risk Assessement report, 2008 validated from Swedish competent authorities.

Vapour pressure for temperatures from 10 to 216°C are reported.

At ambient temperature the data from Hüls AG, 1997 was selected for the environmental risk assessment:

VP =0.000034 Pa at 20°C.

This value was considered as reliable because extrapolated on basis of measurements with 99.5% pure DEHP.

The original study report was not checked considering that these values were validated by swedish comptetent authorities and used in previous risk assessment report, RAR, 2008.

Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: 2g: Data from handbook.
Principles of method if other than guideline:
No data
GLP compliance:
not specified
Temp.:
ca. 25 °C
Vapour pressure:
ca. 0 Pa
Remarks on result:
other: 30x10E-6 Pa
Temp.:
ca. 20 °C
Vapour pressure:
ca. 0 Pa
Remarks on result:
other: 18.1x10E-6 Pa
Conclusions:
In this handbook, the values reported for DEHP vapour pressure are average of literature review: 18.1x10E-6 Pa at 20 °C and 30x10E-6 Pa at 25 °C.
Authors considered this value as overestimated
Executive summary:

Data from handbook.

Description of key information

Vapour pressure: very low pressure (below 10E-4 Pa) are difficult to measure therefore a weight of evidence is chosen in the case of DEHP. Based on measured, calculated and handbook values vapour pressure of DEHP is estimated between 1.8x10E-5 and 3.4x10E-5 Pa at room temperature (20 - 25°C).

Key value for chemical safety assessment

Vapour pressure:
0 Pa
at the temperature of:
20 °C

Additional information

The EU Risk Assessment Report 2008, validated by Swedish authorities used the value from Hüls AG (1997) for assessing the environmental fate.

This study has not been re-evaluated and considered as reliable. A literature average, and two recent studies are in accordance with this value. Therefore, the weight of evidence is based on the following data:

_0.000034 Pa et 20°C (Hüls AG, 1997 in RAR, 2008)

_0.000019 Pa 25°C, saturation chamber, (Clausen, 2002).

_0.0000252 Pa at 25°C, where a QSAR relationship between water, octanol and air solubilities are correlated to the molar volume of phthalate esters (Cousins, 2000).

_0.0000181 Pa at 20 °C, literature average in reference handbook (Rippen, 2000),

A large range of values is observed and may be due to methodological difficulties to obtain precise measures of very low pressure and many values are overestimations due to interference from impurities (Rippen, 2000). Nonetheless, other data at ambient temperature are also recorded at ambient temperature (20, 25°C) supporting this range of very low vapour pressure for DEHP:

_0.0000133322 Pa at 25°C, is an average from literature review (Staples, 1997)

_0.00001 Pa at 20-25°C, another average value from selected data from a literature review (Tukker, 1998).

_0.0000006 Pa at 20°C, ASTM E1782 (CCRA, 2008),

_0.00086 (+/-0,00066) Pa at 25°C, US EPA Proposed rules, saturation method, 1980 (Howard, 1985),

At least, RAR (2008) and Hoyer, (1958) give values of vapour pressure at higher and lower temperature (from 10 to 216°C). These data were validated in the risk assessment and some were extrapolated. In Hoyer 1958, the value is considered as unreliable because extrapolated outside the range of measured temperatures. However, these data are consistent and show an augmentation of vapour pressure with the temperature. Therefore these values were kept as supportive as it may give information on the substance behaviour at higher temperatures.