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EC number: 267-956-0
CAS number: 67953-76-8
HEDP acid and its salts are phosphonic acid substances of very high
water solubility and low octanol-water partition coefficient. The
phosphonic acid groups are multiply ionised at pH values relevant to
biological and environmental systems. Ionisation gives them the ability
to form stable complexes with metal ions, particularly polyvalent
ones. Phosphonates are found to adsorb strongly to inorganic matrices,
and hence they adsorb strongly to sewage sludge and to soil. They will
be removed to a high extent in biological waste water treatment by
The toxicity of HEDP and its salts to environmental species is
presented and interpreted in terms of the concentration of active HEDP
acid in the test media. As such, the results of tests conducted on HEDP
and its salts are directly comparable, because the ionisation state will
depend only on the pH of the test medium. Section 1 of the CSR and
IUCLID Section 4.21 describe the pKa values for the ionisation of HEDP. Four
pKa values of 1.7, 2.47, 7.28, 10.29 are reported in the key study at
25°C (Martell 1968). At environmentally-relevant pH
values HEDP will be ionised typically around two to three times, and
will form stable complexes with metal ions.
HEDP acid and its salts have the potential to cause effects on
aquatic plants as a consequence of nutrient limitation caused by
complexation of trace metals. As complexing agents, these substances
could remobilise metals in the environment; however, their high degree
of adsorption to sediments suggests that this is unlikely to occur. The
substances are acids and when present at high concentration they have
the potential to cause local effects on aquatic organisms as a
consequence of lowered pH.
Effects on aquatic organisms arising from exposure to the acid
form of the substance are thought to result from a reduction in the pH
of the ambient environment (arising from an increase in the H+ concentration)
to a level below their tolerable range. It is not considered appropriate
or useful to derive a PNEC with studies in which pH deviations may have
been attributable to the cause of effects seen because any effects will
not be a consequence of true chemical toxicity and will be a function
of, and dependent on, the buffering capacity of the environment.
Open sea PNEC
HEDP acid and its salts are used in some scenarios (offshore
oilfield) in open sea. The methodology of CHARM (2005) has been used to
derive the PNEC for risk characterisation in this setting. These can be
found in Section 7.6 of the CSR.
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.
Please refer to IUCLID Section 13 and Annexes 3 and 4 of the CSR for
justification of read-across within the HEDP category, and read-across
from the ATMP and DTPMP categories for the long-term fish endpoint.
CHARM (2005) CHARM Chemical Hazard Assessment and Risk Management for
the use and discharge of chemicals used offshore. User Guide Version 1.4.
There are long-term data available for three trophic levels: fish (Oncorhynchus
mykiss), invertebrates (Daphnia magna) and algae (Pseudokirchneriella
subcapitata). HEDP-xK is not readily biodegradable and has a low log
Kow value. Therefore, it is not classified according to
Regulation (EC) No 1272/2008, based on the following:
Hazards to the aquatic environment (acute/short-term): not
classified on the basis of the lowest E(L)C50 in short-term
test results in fish, invertebrates and algae being >10 mg active acid/L.
Hazards to the aquatic environment (long-term): not classified on
the basis of the lowest NOEC or E(L)C10 in long-term test
results in fish, invertebrates and algae being ≥1 mg active acid/L.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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