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]-

Endpoint summary

Description of key information

Due to its high adsorption and low toxicity to aquatic organisms, HEBMP was assigned to soil hazard category 3 and a PNECscreen was conducted, based on the equilibrium partitioning method (PEC * 10 / PNECscreen). Testing for toxicity to terrestrial organisms has been commissioned with two taxonomic groups and representing two trophic levels (decomposers and consumers): earthworms (OECD 222) and soil microorganisms (OECD 216).

The results from the OECD 216 toxicity to soil microorganisms study indicate no effects of HEBMP-xNa to soil microorganisms, based on nitrate formation rate (NOEC ≥ 1000 mg active acid/kg soil dry weight). However, the OECD 222 toxicity to soil macroorganisms except arthropods study (conducted with HEBMP-H) is not available for the present update. Therefore, the current PNECsoil has not been updated and is derived by the equilibrium partitioning method. The PNECsoil and environmental exposure assessment will be updated with both terrestrial toxicity results once the OECD 222 study becomes available. Currently, the terrestrial RCRs based on the PNECsoil derived by the equilibrium partitioning method are < 1, therefore no further toxicity testing of soil organisms is currently considered to be necessary. The need for additional testing will be reviewed once the results from the OECD 222 study become available.

Additional information

The acid and sodium salts in the HEBMP category are freely soluble in water. The HEBMP anion can be considered fully dissociated from its sodium cation when in dilute solution. Under any given conditions, the degree of ionisation of the HEBMP species is determined by the pH of the solution. At a specific pH, the degree of ionisation is the same regardless of whether the starting material was HEBMP-H, HEBMP-xNa, or another salt of HEBMP.

 

Therefore, when a salt of HEBMP is introduced into test media or the environment, the following is present (separately):

1. HEBMP is present as HEBMP-H or one of its ionised forms. The degree of ionisation depends upon the pH in vivo and not whether HEBMP-xNa salt, HEBMP-H (acid form), or another salt was used for dosing.
2. Disassociated sodium cations. The amount of sodium present depends on which salt was dosed.
3. It should also be noted that divalent and trivalent cations would preferentially replace the potassium ions. These would include calcium (Ca²⁺), magnesium (Mg²⁺) and iron (Fe³⁺).

The terrestrial environment is exposed to HEBMP predominantly via application of WWTP sludge, and as such this phenomenon also directly affects soil in the receiving environment.