(1-hydroxyethylidene)bisphosphonic acid, potassium salt

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Endpoint:

toxicity to terrestrial plants: short-term (with study design considered suitable for long-term assessment)

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Additional information

Two reliability 4 studies are available for HEDP (2-3Na) that indicate low toxicity to plants. Minimum toxicity was observed in a range of weeds and crops at application rates ranging from 3 -30 kg/ha and 1 -100 mg/L for tomato, cucumber and radish plants (Gledhill and Feijtel, 1992). A 14-day NOEC value of ≥960 mg active acid/kg soil dry weight was determined for the effects of HEDP (2-3Na) on Avena sativa (Henkel, 1984).

The acid, sodium and potassium salts in the HEDP category are freely soluble in water and, therefore, the HEDP anion is fully dissociated from its sodium or potassium cations when in solution. Under any given conditions, the degree of ionisation of the HEDP 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 HEDP-H, HEDP (1-2Na), HEDP (2-3Na), HEDP-4Na, HEDP-xK or another salt of HEDP.

 

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

1. HEDP is present as HEDP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the system and not whether HEDP (1-2Na), HEDP (2-3Na), HEDP-4Na, HEDP-xK salts, HEDP-H or another salt was added.
2. Disassociated sodium/potassium cations. The amount of sodium/potassium present depends on which salt was added.
3. Divalent and trivalent cations have much higher stability constants for binding with HEDP than the sodium or potassium ions, so would preferentially replace them. These ions include calcium (Ca²⁺), magnesium (Mg²⁺) and iron (Fe³⁺). Therefore, the presence of these in the environment or in biological fluids or from dietary sources would result in the formation of HEDP-dication (e.g. HEDP-Ca, HEDP-Mg) and HEDP-trication (e.g. HEDP-Fe) complexes in solution, irrespective of the starting substance/test material.

In this context, for the purpose of this assessment, read-across of data within the HEDP Category is considered to be valid.

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in terrestrial plant study because, as indicated in REACH guidance R7c Section R.7.11.6 (ECHA 2017), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1, therefore the risk is already adequately controlled and further testing is not justifiable.   The substance is involatile and highly adsorbing and low toxicity was observed in short and long-term aquatic tests, and there is no reason to expect effects in the terrestrial compartment that were not expressed in the aquatic compartment.   Based on the long-term aquatic data set, the most sensitive trophic level is invertebrates. Due to its high adsorption and low toxicity to aquatic organisms, HEDP-xK was assigned to soil hazard category 3 (R.7c Section R.7.11.6, ECHA 2017) and a screening assessment was conducted, based on the equilibrium partitioning method (PEC * 10 / PNECscreen). In accordance with Table R.7.11 -2 of R.7c Section R.7.11.6, confirmatory testing for long-term toxicity to terrestrial organisms has been carried out with one trophic level, earthworms (consumers). PNECsoil has been derived using both the equilibrium partitioning method and measured terrestrial ecotoxicity data and the most conservative value (PNECsoil based on measured terrestrial ecotoxicity data) has been used for PNECsoil. As the terrestrial RCRs based on this PNEC are < 1, no further toxicity testing of soil organisms is currently considered to be necessary. Additionally, supporting data from terrestrial plants and short-term earthworm studies indicate low toxicity (no effects observed to Eisenia fetida or Avena sativa after 14-days exposure, up to concentrations of 1000 mg active acid/kg soil dry weight). The phosphonate ligand binds strongly and irreversibly to various minerals present in soil and so bioavailability to soil organisms is extremely limited. Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively.