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EC number: 281-897-8
CAS number: 84057-80-7
- Soil B (the calcareous soil) had more affinity for Zr than soil A (the
acidic soil) and sorption also occurred faster in soil B. This may be
explained by the fact that the H+ ions present in the acidic soil enter
in competition with Zr ions for adsorption to available sites on the
- The very low soil:solution ratio used in this study was necessary
because at higher ratios the concentrations of Zr in solution would be
below the detection limit of the available method of analysis. However,
such low soil:solution ratios favor adsorption and therefore the Kp
values may have been affected by these experimental conditions.
- The method of Kp determination does not allow to distinguish between
the different solid forms of Zr in the experiment (adsorbed to iron
oxides, adsorbed to organic matter, precipitated as hydroxydes or
carbonates). According to formerly obtained results, the authors mention
that adsorption to iron oxides may be the predominant process in soil.
- The desorption experiments indicate that the concentrations of Zr in
soil remain largely unaffected, suggesting that non-reversible processes
are involved such as inner sphere complexation or surface precipitation.
of this endpoint and derivation of adsorption coefficients are
element-based (i.e., not substance-based). A total of five studies was
used in a weight of evidence approach to cover the endpoint. Reliable
data were available for soil, suspended matter, and sediment. The
following final key values were retained: a log Kp of 5.00 for suspended
matter-water, a log Kp of 5.47 for sediment-water, and a log Kp of 4.13
for soil-water. Adsorption of
sediment and suspended matter appears to be slightly more pronounced
than for soil.
Adsorption of zirconium compounds (as such)
to particles of suspended matter, sediment, or soil, is not expected to
occur. It is rather the zirconium cation (or potentially other cationic
zirconium species) that will adsorb to particulate matter. Therefore,
the assessment of adsorption capacity and the derivation of adsorption
coefficients is element-based (and not substance-based).
In total, five reliable studies were
identified containing relevant information on adsorption of zirconium to
particulate matter. Data were available for soil, sediment, and
suspended matter and will be further discussed below.
For suspended matter, two studies were
identified as useful. Veselý et al. (2001) reported a median log Kp of
3.23 for a series of samplings along Czech rivers. Gobeil et al. (2005)
analysed samples from several locations along the St. Lawrence river, at
one location river water was sampled and at the other location effluent
of the Montreal waste water treatment plant was sampled. Based on
average concentrations of zirconium in filtered water and suspended
particulate matter, log Kp values of 6.26 and 5.51 were calculated for
these locations. Because there is a limited amount of values available,
the average log Kp (arithmetic mean) of 5.00 for these two studies is
selected as key value for characterising distribution between suspended
matter and water.
For sediment, only one reliable study is
available (Klimisch score of 2). In this study, zirconium concentrations
were determined in paired samples of filtered water and sediment from 20
sites along the Blesbokspruit, South Africa. Based on data from this
study (Roychoudhury and Starke, 2006) an average log Kp value
(arithmetic mean) of 5.47 was calculated, the range being 5.12-5.92.
For soil, two reliable studies were retained
for the determination of the key value. Ferrand (2005) (see also Ferrand
et al., 2006) conducted batch equilibrium experiments with ZrOCl2
solutions and two different soils (acidic sandy clayey loamy soil and a
clayey calcareous soil). The Kp values resulting from this study were
6,000 L/kg (dw) (or log Kp of 3.78) for the acidic soil and 30,000 L/kg
(dw) for the calcareous soil (or log Kp of 4.48). The average log Kp
value (arithmetic mean) of 4.13 was taken as key log Kp for soil.
Overall, strong adsorption of zirconium to
particulate matter is observed, whether soil, sediment, or suspended
For adsorption to occur however, zirconium
has to end up in the aqueous phase of the environmental compartment
under consideration (water column, or pore water in sediment/soil).
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