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EC number: 240-521-2
CAS number: 16470-24-9
1. ANALITICAL METHODS
1.1 Extraction of FWA from Sludges
Liquid Extraction (LE)
Bases are believed to promote extraction
by increasing the negative surface charge of the sludge matrix. With
ion-pairing reagents, FWAs form strong lipophilic ion-pairs that
partition more readily into organic solvents. The influence of
increasing TBA concentration on the extraction efficiency was
investigated using methanol as a solvent. A TBA concentration of 0.03 M
was selected for subsequent experiments since no further increase in
extraction efficiency was observed at higher concentrations. The use of
TBA in methanol is less laborious as only dilution prior to HPLC
analysis is necessary, rather than the evaporation and re-dissolution
required when using basic extractants.
Supercritical Fluid Extraction (SFE)
FWA recovery in SFE, as well as in LE,
largely depends on the type of sludge sample. Extraction of FWAs is less
efficient from raw than from anaerobically digested sludge probably due
to the much higher content of organic matter in raw sludge. Thus, the
number ot extractions required tor quantitative recovery depends on the
sludge type. Two consecutive SFE extractions were required to
quantitatively extract FWAs from raw sludge samples while only a single
extraction was required for digested sludge.
Results obtained by SFE and LE extraction
procedures are in good agreement, the differences of FWA concentrations
being well within the relative standard deviation (RSD) of each method.
The higher RSD's obtained by SFE may, in part, be due to the smaller
sample sizes (100 mg) used in SFE compared to 500 mg used in LE.
1.2 Enrichment ot FWA from Aqueous
To determine the precision of the method,
replicate sample extractions were performed using samples of raw sewage,
primary effluent, secondary effluent and river water from the
Zürich-Glatt sewage treatment plant and from Glatt river 1 km downstream
of the plant. For the determination of FWA recovery, the samples were
spiked with different amounts. Recovery rates were determined after an
equilibration time of 15 h, to allow for partitioning of FWA between
water and suspended particles.
Recovery rate was good for the test item:
Reproducibility of test substance
determination and recovery from water samples
*Samples trom Zürich-Glatt municipal
sewage treatment plant and trom Glatt river 1 km downstream ot the
**Relative standard deviation ot 4
***Spiked with 5-15 µl of standard
solution and equilibrated tor 15 h.
****Average of six determinations.
1.3 Extraction of FWA from Lake
Lake sediments were extracted in the same
way as sludge samples using LE with methanol containing 0.03 M TBA. The
extraction of sediment samples was exhaustive, e.g. no FWA was found
upon re-extraction and analysis ot pre-extracted samples. In order to
lower the detection limit compared to sludge analysis, the extracts were
evaporated and the residue was redissolved in DMF:H2O (1:1). Assuming
similar behaviour of FWA in sediment extracts as in elutes from Empore
disks, evaporation of solvent and re-dissolution should not affect the
recovery values. Assuming that recovery values will be less than 100%,
the reported FWA levels in sediments from lake Biel should be treated as
1.4 Chromatographic separation and detection
The combination of post-column irradiation
and fluorescence detection provides the possibility to determine not
only the total concentration of FWA in environmental matrices but also
its isomeric composition. This is necessary to assess the environmental
behaviour of FWAs, since different isomers behave differently. The
sensitivity and selectivity of the method are adequate for the
determination of FWAs in extracts of sewage wastewaters and sludges as well
as in extracts of river water and lake sediment.
2. SOLID/WATER PARTITIONING
2.1 Octanol-Water partitioning
Hydrophobic interactions between natural
organic matter and FWA were expected to be a significant contribution to
the binding of FWA to suspended solids.
If more than one species contributes to
the overall partitioning of a compound, as is the case with organic
acids and bases, an octanol-water distribution ratio, Dow, is used
instead of Kow. Hydrophobic organic acids may partition into octanol in
their protonated or deprotonated form. The partition coefficients of the
anions are usually more than 2 orders of magnitude smaller than of the
neutral species. In addition, formation of ion-pairs of anions with
cations such as Na+, K+, Mg2+, and Ca2+ has been
found to promote partitioning into octanol[1 -2]. Thus,
partitioning of organic acids (and bases) is strongly dependent on pH
and ionic strength. Sulfonic acids usually have pKa values below 2.
Therefore, only anions have to be considered at pH 6-8. Ion-pair
formation, however, might influence the partitioning behaviour of sulphonates,
as was shown for linear alkyl benzene sulphonates (LAS).
Octanol·water distribution ratios for all
photoisomers of test substance were determined with aqueous phases
containing different Ca2 + concentrations in large excess
compared to FWA concentrations. Very low Dow value for test item was
obtained in the absence of calcium ions in the aqueous phase, indicating
that the sulphonated item is too hydrophilic to partition readily into
octanol. The large increase of Dow in the presence of calcium ions
indeed strongly supported the assumed ion·pair formation.
Octanol-water distribution ratios of
test item isomers at different calcium concentrations ([CA2+])
in the aqueous phase.
Kow of (E)-isomers is greater than of
(Z)-isomers. This is in agreement with the general finding, that
hydrophobic molecules are more compatible with the aqueous phase, when
their volume is smaller. (Z)·Stilbenes are more flexible than the
corresponding (E)-stilbenes with its rigid conjugated π-system and may
fold to yield smaller molecular volumes in aqueous solution.
Good agreement of experimental data and
model calculation was found for both isomers of test item. The Kow of
the FWA ion-pairs obtained by the model is more than 2 orders of
magnitude higher than Kow for the native FWA. The two sulphonate
moieties of the test substance are close together and it could even
serve as a bidentate ligand. This might explain the relatively high
conditional stability constant for the formation of ion-pairs obtained
by the model calculation.
2.2 Sorption to River Sediment
Sorption equilibria were achieved within
20 h. Initially, both adsorption and desorption processes are fast,
followed by a considerably slower step. In the desorption experiments,
even a slight decrease in the amount of dissolved FWA was found after 6
h. This decrease was attributed to the fact that dry sediment was added
to the river water in the beginning ol the experiment and that some
swelling of the particles might have occurred.
In analogy to the Kow data, different
distribution coefficients were obtained for different isomers.
Distribution coefficient of (Z)-isomer was generally higher than of
Dow values for a Ca2+ concentration of 1
mM were used for the correlation in order to simulate the natural
conditions as well as possible. However other cations such as Na+, K+,
Mg2 +,and NH4+ may further increase Dow. The hydrophobic partitioning is
not the only interaction between
FWA and natural suspended matter. Specific
interactions and ion-exchange interactions between FWA and suspended
solids may contribute strongly to the observed partitioning.
2.3 Photoisomerization and Partitioning
While adsorbed FWAs are relatively stable,
dissolved FWAs readily isomerize in the presence of light.
The constant ratio of (E)- and (Z)·isomers, the so-called
photostationaly state, is achieved within a few minutes of exposure to
direct sunlight. Because different isomers have different UV spectra,
the isomer ratio is dependent on the spectrum of the irradiating light.
The spectrum of the light which actually
reaches the dissolved FWA is altered by UV absorbing co-soIutes, as well
as, in concentrated solutions by the FWA itself. Therefore, the isomer
ratios are dependent also on the concentration of FWA (except for dilute
solutions as sewage and river water samples) and the kind and
concentration of co-solutes.
E/Z-ratios of FWA in the photostationary
state after sunlight and UV Irradiation.
* Left column: aqueous sample was exposed
to sunlight in a glass vial. Right column: isomer ratio in the aqueous
phase of primary and secondary effluent samples taken after sunlight
** Ratio of peaks for (E)-isomers ln HPLC
chromatograms with and without post-column UV-irradiation.
Although the different isomers exhibit
different partitioning characteristics, in a first step it is useful to
treat the FWA as a sum of isomers and examine its average partitioning
behaviour. This picture is then refined in a second step by looking at
the isomeric compositions and the partitioning behaviour of individual
Isomerization of FWA in sewage was found
to be very fast. The isomeric composition of the FWA tested varies
between raw influent, and in primary and secondary effluent,
respectively. This is not simply the result of different irradiation
A simple model was used to simulate the
partitioning of FWA under the influence of sunlight. Irradiation yields
and maintains a constant ratio of (E)- and (Z)-isomers in solution. The
isomers adsorb to the solid phase with their individual distribution
The isomer ratio of the test item is
dependent on the amount of suspended particulate matter. ln solutions
with low particle content, the ratio is dominated by the photochemically
favoured (Z)-isomer. With increasing particle content, the more strongly
adsorbing (E)-isomer is favoured and becomes the dominant species.
Very good agreement between model
calculation and field data is obtained for primary and secondary
effluent. For raw influent the model overestimates the fraction of the
(Z)·isomer, most likely because the sample was not exposed to sunlight
long enough to achieve photostatlonary conditions (one of the model
assumptions). The same is also true for sludges, where the (E)-isomer is
the absolutely dominant (>9O %) specie. Primary sludge is settled before
isomerization can take place. Activated sludge is loaded with (Z)-isomer
only during the day when isomerization takes place. During the night,
this isomer is washed out due to their smaller affinity for suspended
Comparison of measured and predicted
* Model parameters: KEZ (Ratio
(E) (Z) isomer in solution) = 3; KdZ = 2000 l/kg; KdE=
3. OCCURRENCE and BEHAVIOR of FWA in
SEWAGE TREATMENT PLANTS
3.1 Sewage In- and Effluents
Concentrations of test item in 24 h
composite samples of primary and secondary sewage effluent from various
treatment plants in the region of
Zürich, Switzerland are reported in Table.
As these concentrations may vary considerably from day to day, the data
presented should only be seen as first insight into the approximate
range of concentrations at which FWA occur in wastewaters. Note that
sand filtration does not reduce FWA concentrations significantly,
because secondary effluent contains only little suspended solids.
FWA concentrations in wastewater*
*24 h composite sample; **raw influent;
The FWA concentrations in raw sludge were
lower than those in anaerobically digested sludges, indicating that test
item becomes relatively enriched in sludge due to solids reduction
during anaerobic sludge digestion.
FWA concentrations in sewage sludges
3.3 Diurnal and Daily Variations
The efficiency of removal during the
activated sludge treatment increases.
When the FWA levels in primary effluent
are high, the activated sludge is charged with FWA. Conversely, when FWA
levels in primary effluent are low, FWA may be released from the sludge.
The levels of FWA in raw influent va ried
significantly during the day. The effluent levels, however, remained
almost constant and were sometimes higher than the influent levels.
3.4 Elimination of FWA ,During
Activated Sludge Treatment
Biological degradation of FWA would
gradually reduce its concentration in activated sludge. The total
concentration (sum of dissolved and adsorbed fraction) however, remained
constant throughout the residence time of the wastewater in the
activated sludge system, indicating that no detectable biochemical
transformation processes occurred. To verify this result, samples of
activated sludge were taken to the laboratory and aerated for another 48
h. Again no change in FWA concentrations occurred.
FWA concentrations, the fraction in the
dissolved phase gradually decreased during the activated sludge
treatment, and finally reached a value close to the one found in returned
sludge. FWA is indeed removed from wastewater by adsorption to activated
sludge. The differences in mass flows between primary and secondary
effluent (e.g. the amount of FWA eliminated in the activated sludge
treatment) may therefore be attributed to sorption processes and not to
3.5 Mass Flow
During primary clarification,
approximately 69% of the test item in raw sewage was removed associated
with primary sludge. Of the residual FWA in primary effluent, another
65% was removed during activated sludge treatment and secondary
clarification. Residual mass in secondary effluent was 18 g/day (11%) of
the corresponding influent level. As no biodegradation of FWA was
observed during activated sludge treatment, test item removed during
activated sludge treatment was quantitatively recovered in excess
Average FWA mass flows (g/day)
Comparison of the mass flows associated
with raw sludge (e.g. the sum of primary and excess sludge) and with
anaerobically digested sludge yielded very good agreement (89% and 85%).
Good agreement was obtained despite the fact that the
anaerobically-digested sludges sampled in this study do not correlate
with the influents and effluents sampled, because of the lang residence
time of sludge in the digesters. This finding strongly indicates that
FWA is also not biodegraded during anaerobic sludge treatment.
Isomerization in wastewater was found to
be a fast process and photostationary conditions are achieved within a
few minutes of exposure to sunlight. This raises the question, what
impact sunlight has on the elimination of FWA during sewage treatment.
Sunlight will generally reduce the removal
rates of FWA, because photoisomerization leads to isomers which are less
sorptive than the parent isomers. A quantification of this reduction in
removal rates, however, is more difficult since several factors are
limiting the impact of sunlight:
- intense sunlight is only available
during few hours a day
- sunlight only penetrates the top layer
of the water in the settling tanks and in the activated sludge basin
- in the case of the test item
isomerization leads to a significant fraction of the less sorptive
As a result, the fractions of (Z)-test
item in activated sludge and anaerobically digested sludge was far below
the fractions calculated for photostationary conditions. A closer look
should be given to test item: a rough estimate can be made by the
content of the (Z)-isomer in sludge (4.5%) and its adsorption constant
for sludge particles (2000 Ukg). The adsorption constant of (Z)-test
item is very close to the adsorption constant of the isomer of another
FWA tested and a similar elimination rate (50%) may therefore be
assumed. This means that the amount of (Z)-test item released to the
secondary clarifier is approximately equal to the amount in sludge. Thus
the contribution of the (Z)-isomer (or the impact of sunlight) is in the
range of only 10%.
3.6 Discharge of FWA to Surface Water
Estimates of the fractions of FWA entering
the Swiss STPs associated with raw sewage and leaving the STPs
associated with anaerobically digested sewage sludge and sewage
effluents can be made based on the levels of FWA in
anaerobically-digested sludges and the elimination rates of FWA during
sewage treatment. Since sludge is stored in the anaerobic digesters for
several weeks, the FWA levels determined in anaerobically-digested
sludge represent an average value of FWA removed from wastewater during
this time period. Calculation of FWA discharge to surface water based on
FWA levels in sludge and elimination rated as determined in the mass
flow study are therefore more reliable than estimates based on effluent
Estimation of the amounts in raw sewage,
secondary effluents and anaerobically-digested sludge. Numbers in
brackets indicate the fraction in each compartment relative to the
a) Data from Ciba-Geigy AG.
b) Amount in sludge divided by elimination
rate in STP
c) Amount in raw sewage multiplied by
d) Level in sludge multiplied by annua1
sludge production of 260000 t dry mass/y.
A considerable fraction (72 %) of the
consumed test item is lost before the sewage treatment facility. This
may be expected because FWAs are produced and added to detergents in
order to adsorb to the textiles. Approximately 20% is bound to sewage
sludge and another 2% is discharged to surface water.
4. OCCURRENCE of FWA in NATURAL WATERS
and LAKES SEDIMENTS
1.5 % of the test item is finally found in
Levels of FWA in river water samples.
*2-wwek composite samples (November 29 to
December 13, 1993) from automatic sampling stations of ttle
NADUF-program. Samples were stored at 4°C, no preservatives were added.
**Limit o quantification (LOQ = Blank + 10
Mass flow and per capita flow of FWA
calculated from data in the table above.
*Data supplied by Landeshydrologie und
-geologie, Bern, Switzerland.
**Chromatographic signals for test
substance overlapped with signals from an unknown compound.
The history of the application FWA as
detergent ingredients and along, with it the history of FWA inputs into
lake Biel is recorded in the concentration profile of FWA in the
sediment core. Besides the nowadays mainly used the test substance and
another FWA-2 (distyrylbiphenyls type), another more
hydrophobic FWA-6 is found in deeper sections of this core
with a concentration maximum corresponding to the time period tram
1959-69. This FWA-6 has lost its significance as a detergent additive
with the introduction of the test substance and the other FWA-2. This
change in detergent formulation is recorded in the sediment core. The
fact that the levels of the test substance and FWA-2 in the sediment are
almost constant on a depth corresponding to a time period of more than
30 years strongly indicates their persistence under the environmental
conditions of this sediment.
 West all J.C., Leuenberger
C. and Schwarzenbach R.P., 1985. Influence of pH and ionic Strength on
the Aqueous-Nonaqueous Distribution of Chlorinated Phenols.
Environmental Science and Technology, 19, 193-198.
 Jafvert C. T., Westall
J.C., Grieder E. and Schwarzenbach R.P., 1990. Distribution of
Hydrophobic lonogenic Compounds between Octanol and Water: Organic
Acids. Environmental Science and Technology, 24, 1795-1803.
 King JI.F., 1991, Acidity.
In: The Chemistry of Sulfonic Acids, Esters and their Derivatives (eds.
Patai :5. end Rappaport Z.), Wiley, 249-258.
 Brownawell B.J., Chen H.,
Zhang W. and West all J.C., 1991. Adsorption of Surfactants. In: Organic
Substances and Sediments in Water (eds. Baker R. A.), Lewis Publishers,
 Milligs B. and Holt l.A.,
1974. Fluorescent Whitening Agents. I.
Acid: Its Photodecomposition in Solution and on Wool. Aust. J. Chem.,
 Gujer N., 1989. Die
Entwicklung des Klärschlammanfalles in der Schweiz. Mitteilungen der
EAW.A.G, 28, 2-5.
A field study was conducted at a
full-scale mechanical-biological sewage treatment plant at
Zuerich-Glatt, Switzerland. Samples of wastewater (raw sewage, primary
and secondary effluent) and sludge (raw, activated and anaerobically-
digested sludge) were collected during a 10-day period. The test
substance concentrations in water samples were determined using
solid-phase extraction with C18 disks and HPLC. The concentrations of
the test substances in sludge were determined by supercritical fluid
extraction and HPLC.
The method allowed the equally sensitive
determination of the parent FWA as well as the isomers which are formed
upon exposure to sunlight.
The mass flow of FWA was determined in a
field study at the municipal sewage treatment plant Zürich-Glatt,
The analytical methods based on
reversed-phase high-performance liquid chromatography, post-column
irradiation in combination with fluorescence detection provided an
excellent tool for the sensitive and selective determination ot the
(highly fluorescent) parent compounds as well as the (non-fluorescent)
isomers. FWAs were extracted from freezedried sewage sludges using
either liquid extraction (LE) or supercritical fluid extraction (SFE).
Photoisomerization and partitioning
Isomerization of FWA in sewage was found
to be very fast. The isomeric composition of the FWA tested varies
between raw influent, and in primary and secondary effluent,
respectively. A simple model was used to simulate the partitioning of
FWA under the influence of sunlight. ln solutions with low particle
content, the ratio is dominated by the photochemically favoured
(Z)-isomer. With increasing particle content, the more strongly
adsorbing (E)-isomer is favoured and becomes the dominant species. Very
good agreement between model calculation and field data is obtained for
primary and secondary effluent.
Primary sludge is settled before
isomerization can take place.
From field data the following conclusions
concerning the behaviour and fate of FWA in a mechanical sewage
treatment plant can be drawn:
(I) elimination of FWAs from wastewater
occurs during both mechanical and biological treatment.
(II) overall removal rate of 98 % was
(III) elimination is due to adsorption to
primary and activated sewage sludge and the observed elimination, rate
is consistent with the individual sorption behaviour of the FWA as
investigated in laboratory experiments.
(IV) no evidence for biodegradation of FWA
was found during the (aerobic) biological treatment of wastewater with
activated sludge and during anaerobic-mesophilic digestion of raw sewage
(V) the FWA removed during wastewater
treatment is thus quantitatively recovered in anaerobically digested,
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