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Physical & Chemical properties

Water solubility

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Reference
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 105 (Water Solubility)
Version / remarks:
Adopted by the Council on 27th July 1995
Deviations:
no
GLP compliance:
no
Other quality assurance:
ISO/IEC 17025 (General requirements for the competence of testing and calibration laboratories)
Type of method:
flask method
Key result
Water solubility:
ca. 86 µg/L
Conc. based on:
test mat.
Temp.:
25 °C
pH:
>= 6.24 - <= 6.42

Results:

No. Solubility at 25 °C Unit pH

1 67 mg.l-1 6.42

2 101 mg.l-1 6.24

3 89 mg.l-1 6.35

Standard deviation: 17 mg.l-1

Average solubility: 86 ± 17 mg.l-1 at 25 °C

Conclusions:
Average solubility: 86 ± 17 mg.l-1 at 25 °C

Note: DEHP easily forms more or less colloidal dispersions in water, which increase the amount DEHP in the water phase (Lundberg and Nilsson 1994). The colloidal formation can influence results of determination.

Description of key information

Key value for chemical safety assessment

Water solubility:
0.003 mg/L
at the temperature of:
20 °C

Additional information

A large range of values on the water solubility is available in the literature (0.003-1.3 mg/l at 20-25°C)

Available studies clearly show considerable difficulties in estimating relevant water solubility. As reported by Cousins et al. 2003, and in OECD guideline standard method can be undertaken for compounds with solubilities greater than 1 mg/L. Below this limit problems occurs.

In the case of DEHP, a probable explanation of this is that DEHP easily forms more or less colloidal dispersions in water due to flask shaking, which increase the amount DEHP in the water phase (Staples et al. 1997). The colloidal formation might be of relevance in understanding laboratory studies in aquatic media. A colloidal water solubility of about 0.34 mg/l (Howard et al., 1985) is assumed in the Risk Assessment Report 2008.

Thomsen et al. 2001, to avoid this problem, measured the unimeric solubility of DEHP via surface tension measurements. Although lower value was demonstrated (17 µg/L), this measure as it is an indirect method and may be affected by impurities present in the test sample, this result will not be considered for the assessment.

The "true" water solubility value validated and used in the previous RAR, 2008 was the one proposed by Staples et al. 1997:

water solubility = 0.003 mg/L at ambient temperature (20 -25°C).

This value, considered as the key value, is today supported by 3 new studies:

- Turner & Rawling 2000, estimated the DEHP water solubility in a experiment using slow stirring technique to avoid colloid formation(radiolabelled DEHP followed by Liquid Scintillation Counting after 16h equilibration period on a lateral shaker). In addition, authors took particular cares to avoid contaminations and losses due to adsorption. The water solubility was thus estimated to be in a few µg/L range.

- Ellington and Floyd, 1996, using SPARC calculation model estimated the water solubility of DEHP at 0.0026 mg/L. In 2009 the updated version 4.5 of the model gives a value at 0.00362 mg/L.

- Cousins and Mackay, 2000 used the "three solubilities" approach to determine solubilities and partition coefficients of phthalate esters. In their model, authors have shown correlation between "apparent" solubilities in air, water and octanol, and the Le Bas molar volume as molecular descriptor (i.e. sum of atomic volumes with adjustement of the volume decrease arising from ring formation). With this approach authors hightlighted the measurement errors from water solubility data available in the literature. Althought authors, due to this variability, excluded data for substances of high molar volume (like DEHP) the water solubility calculated with this model was 2.49 µg/L. This value is consistent other value previously validated in experimatal and calculation model studies.

Therefore, the based on these studies, the true solubility of DEHP is considered to be at 0.003 mg/l at 20°C and will be used in the current risk assessment.