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Environmental fate & pathways

Biodegradation in soil

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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 REACH Annex I, it is not necessary to conduct the simulation test on ultimate degradation in soil, or to identify degradation products. 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 HEBMP 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 K 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 (Saeger, 1979). 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 in the chemical safety assessment of HEBMP-H and its salts.

Key value for chemical safety assessment

Half-life in soil:
10 d
at the temperature of:
12 °C

Additional information