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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The key values are based on data from a reliable study with application of the batch equilibrium method. For filing in IUCLID5, the various soils were divided into 5 groups according to soil characterization by OECD guideline test n°106. Characteristics of the soils (e.g. clay, organic matter and pH) strongly influencedthe Kp for lead. Hence, the key value is replaced by the following regression equations:
log Kp = 1.79 - 0.20 * pH(CaCl2)(with CaCl2 extraction)
log Kp = -0.13 + 0.48*pH(CaCl2) + 0.16*log Fraction + 0.73 log*Al-ox(with aqua-regia digestion)
log Kp = -0.35 + 0.50*pH(CaCl2) + 0.86*log Al-ox(with HNO3digestion)
where Al-ox is the amount of Al-/oxyhydroxide (mmol.kg-1) and Fraction defined as the available metal fraction is the percentage of the total metal concentration (aqua regia digestion and HNO3digestion) that is extractable by means of 0.01M CaCl2extraction.

Key value for chemical safety assessment

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
1.07

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
4.22

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
4.28

Additional information

In a study comparable to OECD guideline test n°106 with some exceptions, the partition coefficient and soil characteristics were identified. Pb concentrations and partition coefficient were identified by three ways: HNO3digestion; aqua-regia digestion and CaCl2extraction with respect to soil characteristics. Studies were performed on soils which already contain metals (including lead) and on OECD soil to which further metals were added.

The average values of log Kp soil found by De Groot et al. were at 4.28 (Aqua regia extraction); 4.22 (HNO3 digestion) and 1.07 (CaCl2 extraction) and they were used as imput values for the exposure modelling.

Kp values strongly depended on soil characteristics: clay, organic matter, pH and dissolved organics carbon (DOC). The regression equation obtained for describing the quantitative relationship between partition coefficient and soil/pore water characteristics (pH CaCl2) appears to be dependent of the digestion and extraction methods.

Addition of metal salts to one of the soils led to a decrease in the magnitude of the partition coefficients implying an increase of bio-availability of the metal salts added for soils organisms whose dominant uptake route is via the pore water.