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EC number: 204-694-8
CAS number: 124-28-7
isotherms and desorption kinetics
was measured in the supernatant (SN) and in the methanol washings of the
glass container walls. Subtraction of these two values from the total
applied activity should give the activity that had adsorbed to the test
system. For one sample per test system (spiked with treatment solution
2) the activity adsorbed to the test system was determined by combustion
and a mass balance was calculated. The results are presented in Table 3.
As can be seen, mass balances were all >90%,
as specified by the guideline, hence proving the validity of the method
used and indicating that calculating the activity that had adsorbed to
the test system from the other experimentally determined values (total
activity in supernatant, on glass and initially applied) was correct.
Total activity in SN 1)
Total activity on glass 1)
Total activity on test system (calculated) 1)
Total activity on test system (combustion) 1)
Mass balance (%)
1) In dpm. Total activity applied: 981580 dpm.
various total activities that were measured and calculated the
concentrations of octadecylamine adsorbed on test system and in solution
were calculated. The mean value of the two replicates was then further
used for calculation of the Freundlich adsorption parameters. These are
presented in Table 4. Based on the classification given by Mensink and
the values for the Kom
from the adsorption isotherm, octadecylamine can be considered immobile
in all test systems investigated. The fitted Freundlich isotherms appear
to have a convex shape, whereas usually such isotherms are concave. The
reason for this difference is that, because of its typical surfactant
structure, the adsorption of the test substance need not be limited to
adsorption of a monolayer. Multilayer adsorption is a well-known
phenomenon for surfactants and octadecylamine may also be expected to
show multilayer (i.e. bilayer) adsorption.
K (F) ads [µg^(1 -1/n)(cm³)^(1/n) g^(-1)]
K (F, om) ads [µg^(1 -1/n)(cm³)^(1/n) g^(-1)]
solution (B) and treatment solutions 2, 3 and 4, although of high
radiochemical purity, still showed the presence of two metabolites at a Rf
of 0 and 0.9, respectively, and these metabolites were again encountered
in several isotherm samples. The metabolite at Rf
was encountered in all test system extracts, as well as in the
supernatant and container wall extract of sludge DB1, thus confirming
its high adsorptivity. Purity of octadecylamine extracted from the test
system was high for the two Cranfield soils and the sediment (93-96%)
and moderate (62%) for the sludge DB1. In the container wall extracts of
the two Cranfield soils and the sediment OVP only octadecylamine was
found, whereas the sludge DB1 container wall extract contained 90%
octadecylamine and 10% of metabolite Rf
Finally, the supernatant chromatograms for the two Cranfield soils and
the OVP sediment appeared to indicate instability of the test substance,
but as the amount of activity present in the sample was low, these
values were treated as unreliable. The DB1 supernatant contained 79%
octadecylamine as well as 4% of metabolite Rf0
and 17% of metabolite Rf0.9.
The reason for the decrease in purity of the test substance is not
clear. Biodegradation is unlikely as the test systems had been
irradiated prior to testing and the decrease was also observed for a
test substance solution not in contact with any test system. The
guideline recommends that under these circumstances both phases (soil
and solution) are to be analysed. This has been done.
the limited number of samples available for the desorption kinetics
experiment after the adsorption isotherm experiment, and the fact that
each vial could be sampled only once (total supernatant, removal of test
system, washing of the container walls) a limited number of samplings
could be performed in the desorption kinetics experiment. For results
see Table 5.
Table 5: Desorption kinetics:
% desorption after 47 hours
% desorped after 166 hours
Sludge DB 1
The result clearly show that octadecylamine desorption occurs to a
lesser extent than adsorption and is slower than adsorption for all test
objective of this study was to obtain information on the
adsorption/desorption behaviour of octadecylamine on soil, sediment and
sludge. Adsorption parameters were determined compliant to GLP using the
batch equilibrium method according to OECD 106 (reliability category 1)
in two soils which represent major agricultural areas in Europe and
North America, one sediment and one sewage sludge:
164 soil [21.8% clay, 6.6% organic matter, silt loam], Cranfield 266
soil [50.2% clay, 2.6% organic matter, clay], Oostvaardersplassen
sediment [18.7% clay, 4.1% organic matter, silt loam] and sewage sludge
DB1 [45.9% clay, 51.9 % organic matter, silty clay]. These test systems
encompass a range of % clay and % organic material.
of the strong adsorption of octadecylamine on the container materials,
an alternative set-up for performance of the study was developed. In
this method, activity was determined in the supernatant and on the
container walls. Activity adsorbed to the test system was calculated
from these results and the initial activity applied. Adsorption and
desorption kinetics were determined at an initial concentration of
approximately 1 μg/mL.
Adsorption isotherms were determined over a concentration range from
approximately 0.04 to 5 μg/mL.
All adsorption-desorption experiments were carried out at 20°C ±2°C.
balances thus obtained for the adsorption isotherm experiment were all >90%,
indicating the validity of the test set-up.
can be considered immobile in Cranfield 164 silt loam soil, Cranfield
266 clay soil, Oostvaardersplassen sediment silt loam and sewage sludge
DB1 silty clay.
obtained from the Freundlich adsorption isotherm, were
Cranfield 164 silt loam, 1/n = 1.5384,
Cranfield 266 clay, 1/n = 1.8897,
Oostvaardersplassen sediment silt loam, 1/n = 1.4478 and
sewage sludge DB1 silty clay, 1/n = 1.0322.
For all test systems r2> 0.96.
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