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Environmental fate & pathways

Henry's Law constant

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Reference
Endpoint:
Henry's law constant
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Study period:
2018-01-08
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Qualifier:
no guideline available
Principles of method if other than guideline:
Henry's Law constant was calculated based on the measured vapour pressure (Tremain, 2017a) and the water solubility (Fox, 2017b).
GLP compliance:
no
Key result
H:
40.11 Pa m³/mol
Conclusions:
The calculated Henry's Law constant of magnesium metaborate is 40.11 Pa m3/mol.
Executive summary:

Henry's Law constant of magnesium metaborate was calculated based on the measured vapour pressure and water solubility. It is 40.11 Pa m3/mol.

Description of key information

Henry's Law constant of magnesium metaborate was calculated based on the measured vapour pressure and water solubility. It is 40.11 Pa m3/mol.

Key value for chemical safety assessment

Henry's law constant (H) (in Pa m³/mol):
40.11

Additional information

Boric acid as well as other simple boron compounds will predominantly exist as undissociated boric acid in aqueous solutions in acidic milieu with pH <7, whereas at about pH 10 the metaborate anion (B(OH)4-) becomes the main species in solution (WHO, 1998).

It is therefore conclusive that in the plasma of mammals and in the environment the main species is undissociated boric acid.

Since other borates like magnesium mentaborate dissociate to form boric acid in aqueous solutions, they too can be considered to exist as undissociated boric acid under the same conditions.

The vapour pressure for boric acid is extremely low so volatilization is expected to be minimal. The same can be expected for magnesium metaborate with a tested vapor pressure of 0.0365 Pa at 25°C (Tremain, 2017a)