Reaction mass of [[(2-hydroxyethyl)imino]bis(methylene)]bisphosphonic acid and Phosphonic acid, P-[(tetrahydro-2-hydroxy-2-oxido-4H-1,4,2-oxazaphosphorin-4-yl)methyl]-

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil: simulation testing

Data waiving:

other justification

Justification for data waiving:

other:

Transformation products:

not measured

Description of key information

No data are available on the biodegradation of HEBMP-H in soil. In accordance with Column 2 of REACH Annex IX, the simulation test on soil or the identification of degradation products do not need to be conducted as the chemical safety assessment conducted according to Annex I indicates that they are not necessary. Furthermore, simulation tests (soil) are not considered necessary because the risk characterisation ratios (RCRs) for the terrestrial compartment, even with the realistic assumption that the parent substance is not biodegradable, are <1.

Although biodegradation in soil has not been demonstrated for HEBMP-H and its salts, the role of abiotic removal processes is significant for analogous phosphonate complexing agents. The key data for soil adsorption for the HEBMP category are from the study by Noack (Goller, 2014) (refer to Section 5.4.1 for further information about this test). Adsorption of the linear form was rapid with high Kd values, particularly under conditions where calcium concentrations in the aqueous phase and clay content in the soil phase were both high. Phosphonates were not extracted from the solid phase. The cyclic form shows much lower adsorption constants (Goller, 2014), but the continuous processes of re-establishment of the cyclic/linear equilibrium means that adsorption and binding phenomena can still be expected to continue to deplete the available HEBMP (of both cyclic and linear forms).

In general for the phosphonate complexing agents effectively irreversible binding is consistent with the known behaviour of complexation and binding within crystal lattices. The high levels of adsorption which occur are therefore treated as a form of removal from the environment. For analogous phosphonate complexing agents, after approximately 40-50 days, the phosphonate is >95% bound to sediment with only 5% extractable by ultrasonication and use of 0.25N HCl-xylene solvent (based on radiolabelling) in river and lake water microcosms (Gledhill and Feijtal, 1992). 66-80% removal (binding) was seen after 11 days in the same test.

In the context of the exposure assessment, largely irreversible binding is interpreted as a removal process; 5% remaining after 40 - 50 days is equivalent to a half-life of 10 days, which is significant for the environmental exposure assessment in the regional and continental scales. This abiotic removal rate is used as the half-life for soil in the chemical safety assessment of HEBMP-H and its salts.

Gledhill W.E. and Feijtel T.C.J (1992) Environmental Properties and Safety Assessment of Organic Phosphonates used for Detergent and Water Treatment Applications. The Handbook of Environmental Chemistry 3 (F), 261-285.

Key value for chemical safety assessment

Half-life in soil:

10 d

at the temperature of:

12 °C