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EC number: 267-956-0
CAS number: 67953-76-8
ANALYSIS: Analysis was performed on days 0, 1, 2, 4 and 8.
The concentration of the test substance in water was
determined by liquid scintillation counting. The
concentration in sediment was then calculated by difference,
based on the assumption that any reduction in water
concentration was due to adsorption to sediment. Due to the
high level of adsorption significant change in aqueous
concentration occurred, and therefore analysis of the soil
was not essential.
values are expressed in litres/kilogram for soft water
values are expressed in litres/kilogram for hard water
The 5.0 ppm test concentration may not have reached
equilibrium over the test period due to saturation of some
of the sediment adsorption sites. Therefore, a mean value
applicable to soft water is 1900 l/kg, and to hard water,
HEDP-H and its salts are
expected to adsorb significantly to sediment, soil and sludge substrates
based on the available study data. It is believed that the binding to
organic carbon is not predominant, however it is useful for context to
note that the Kd values derived from the key study appear consistent
with a log Koc (equivalent) value of approximately 4.2.
HEDP-H and its salts are mineral-binding and complexing agent,
with unusual chemical properties. HEDP-H and its salts adsorb strongly
to inorganic surfaces, soils and sediments, in model systems and
mesocosms, despite the very low log Kow; this has
implications for the approach to environmental fate modelling. High
adsorption is consistent with similar behaviour seen for structural
analogues, and other common complexing agents such as EDTA.
Studies on analogous phosphonate complexing agents have revealed
that adsorption is correlated with concentration in the aqueous phase
and also relates significantly to the type and nature of inorganic
content in the substrate (Gledhill and Feijtel, 1992).
The normal approach to modelling binding behaviour in
environmental exposure assessment assumes that the substance is binding
only to the organic carbon present in soils, sediments, and WWTP
sludges. This assumption does not apply to HEDP-H and its salts. The
extent of binding to substrates is fundamental to understanding and
modelling of environmental exposure, for substances like this.
Therefore, adsorption / desorption data, required in Section 9.3.1 of
REACH Annex IX, is an extremely important part of the data set for
HEDP-H and its salts.
The nature of the adsorption of HEDP-H and its salts is believed
to be primarily due to interaction with inorganic substrate or
generalised surface interactions. While Koc is the
conventional indicator for adsorption, the interaction with organic
carbon present in the substrate may be exceeded by these other
interactions in the case of HEDP-H and its salts, meaning that Koc as
such is not a meaningful parameter. It is convenient for comparison
purposes to determine the value of log Koc that is consistent
with/equivalent to the degree of sediment or soil binding exhibited by
Thus, a log Koc (equivalent) value of 4.22 was obtained
by evaluating Kp (sediment-water) data in a reliable study
with HEDP-H conducted according to generally accepted scientific
principles (Michael, 1979). In this study, river sediments were
analysed by using liquid scintillation on day 0, 1, 2, 4, 8. Methods and
sample data were represented clearly and the test substance was being
described adequately. The result is considered as reliable and has been
assigned as key study.
Adsorption coefficient values of 0.91-0.98 for the adsorption of
HEDP (2-3Na) to activated sludge and primary sludge are reported in a
literature paper (Steber and Wierich, 1986a). Freundlich isotherm
constants values of ca. 2600-13000 for HEDP (2-3Na) were determined in
this study however it was assigned reliability 4 due to insufficient
documentation (Steber and Wierich, 1986a). A second literature paper
(Jaworska, 2002) reports partitioning for water-sediment, water-active
sludge and water-soil studies for HEDP-H. Kd ranges of ≥920 - ≤1300, ≥20
-<-190 and ≥2600 - ≤12700 for sediment, soil and activated sludge were
reported, but assigned reliability 4 due to the information being
secondary literature. Another study (Stone, Knight and Nowack, 2002)
reported that iron, copper and zinc have no discernible effect on
adsorption of HEDP-H using activated sludge as the testing medium,
however this study was also secondary literature and was assigned
Adsorption data for soils (Kd (soil-water) values of 182 (silt
loam), 6.15 (sand) and 129 (silty clay loam); and Koc values of 51600
(silt loam), 653 (sand) and 6260 (silty clay loam)) for HEDP-H were
derived in an OECD 106 study using radiochemical analysis (Springborn
Laboratories, 1991, reliability 2) and further values for adsorption to
soil are reported in literature for HEDP (2-3Na) (Steber and Wierich,
1986b and c; reliability 4 - documentation insufficient for assessment).
The Kd values from the Springborn Laboratories (1991) and Steber and
Wierich (1986b and c) studies are consistent(Kd 6.15 -182 l/kg in both
tests). The log Koc (equivalent values) of 3.8-4.7 from the silty soils
and 2.8 from the sands reported in the Springborn Laboratories (1991)
study are consistent with the log Koc (equivalent) value of 4.22 derived
from the key sediment adsorption study (Michael, 1979). In further
studies (Nowack and Stone, 1999b; reliability 4 - secondary literature),
goethite (an iron-based mineral commonly found in soil) was used as a
testing substrate. High levels of adsorption of HEDP-H were reported. A
study by Fischer (1991) reports Freundlich constants of 46 -2378 for
clay minerals for HEDP (2-3Na) and a Kd adsorption constant of 2042
(dimensionless) for Neckar sediments with overlying Neckar water for
HEDP (2-3Na) (Fischer, 1993 - reliability 2).
A screening study using the conventional HPLC method (OECD 121) to
estimate the value of Koc (organic carbon-water partition
coefficient) is considered not appropriate. Adsorption behaviour onto
the normal aminopropyl column used in OECD 121 would not necessarily
follow the pattern of adsorption onto substrates that are of importance
in the environment. Understanding of sludge binding is informative, but
much less significant in the chemical safety assessment than binding to
matrices with a higher inorganic content or high surface area. It is
important to understand Kd directly, and preferably as a
function of variables such as solid phase composition and
characteristics, water hardness, dilutions, and phase ratios.
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
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.
Gledhill and Feijtel (1992) Environmental properties and safety
assessment of organic phosphonates used for detergent and water
treatment applications. The Handbook of Environmental Chemistry, Vol. 3,
Part F, (Ed.: Hutzinger, O.), Springer-Verlag, Berlin.
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