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EC number: 223-267-7
CAS number: 3794-83-0
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,
The substance adsorbs
significantly to sediment, soil and sludge substrates based on the
available study data. While the binding is not necessarily to organic
carbon, Kd values appear consistent with a log Koc (equivalent) value of
This substance is a
mineral-binding and complexing agent, with unusual chemical properties.
HEDP 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
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 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 Annex IX, is an extremely important part of the data set for
HEDP and its salts.
The nature of the
adsorption is believed to be primarily due to interaction with inorganic
substrate or generalised surface interactions. While Kocis
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 and its salts, meaning that Kocas
such is not a meaningful parameter.It
is convenient for comparison purposes to determine the value of log Kocthat
is consistent/equivalent to the degree of sediment or soil binding
exhibited by the substance.
Thus, a log Koc(equivalent)
value of 4.22 was obtained by evaluating Kp(sediment-water)data
in a reliable study conducted according to generally accepted scientific
principles (Michael, 1979). 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.
From other various
sources, an adsorption coefficient value of 0.91-0.98 is reported in
reviewed literature paper (Steber and Wierich, 1987). The Freundlich
isotherm constants values of ca. 2600-13000 for HEDP were determined by
following the EPA test guide method in an activated sludge. A paper
(Jaworska, 2002) supported the measured data for water sediment and
water active sludge studies. Another study (Nowack, 2002) has reported
the same phenomena using active sludge as testing medium.
Adsorption data for
soils were derived in an OECD 106 study using radiochemical analysis
(Springborn Laboratories, undated) and further values are reported in
literature (Steber and Wierich, 1987). The adsorption values determined
(Kd~10 - ~200 l/kg in both tests) are consistent with a log Koc(equivalent)
value of 3.8-4.7 from the silty soils and 2.8 from the sands, consistent
with the log Koc(equivalent) derived from the key
sediment study. In further studies (Nowack and Stone1999), goethite (an
iron-based mineral commonly found in soil) was used as a testing
substrate. High levels of adsorption were reported. A study by Fischer
(1991) resulted in Freundlich constants 50 – 2400 for relevant soil
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 Kddirectly,
and preferably as a function of variables such as solid phase
composition and characteristics, water hardness, dilutions, and phase
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