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EC number: 267-956-0
CAS number: 67953-76-8
Due to its high adsorption and low toxicity to aquatic organisms,
HEDP 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) (see IUCLID section 6.3.1) for
the read-across substance, HEDP-H. 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 in the
chemical safety assessment. As the terrestrial RCRs based on this PNEC
are < 1, no further toxicity testing of soil organisms is currently
considered to be necessary.
A long-term toxicity to soil macroorganisms except arthropods
study with HEDP-H is available, which reported a 56-day NOEC value of
472.5 mg active acid/kg soil dry weight, based on reproduction, for Eisenia
fetida (Noack, 2014). This is supported by two (short-term) 14-day LC50
values of >960 mg active acid/kg soil dry weight and >1000 mg active
acid/kg soil dry weight for the effects of HEDP (2-3Na) and HEDP-H on Eisenia
fetida (Henkel, 1984 and Springborn Laboratories, 1990,
Additionally, two supporting studies are available for HEDP (2-3Na) that
indicate low toxicity to plants (short-term studies). 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).
HEDP and its salts are highly adsorbing to soil and soil mineral
substrates. The nature of the adsorption is believed to be
primarily due to interaction with inorganic substrate or generalised
surface interactions. High adsorption is consistent with similar
behaviour seen across other phosphonates, and other common complexing
agents such as EDTA. By reference to findings with other similar
substances, the binding occurs very rapidly and is effectively
irreversible. For environmental fate purposes in exposure assessment
this is assessed as a removal process and for hazard assessment of the
soil compartment, this demonstrates low bioavailability to soil
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):
In this context, for the purpose of this assessment, read-across of data
within the HEDP Category is considered to be valid.
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