June 2006
Universiteit van Amsterdam
Susanne Waaijers
Drs. J. Haftka, Dr. J. Parsons
Partitioning of Organic Contaminants to Dissolved Organic Matter
Effect of Solution Composition
Abstract
Organic matter influences binding of contaminants in soil. Therefore, the partitioning of organic
matter from soil to surrounding waters also influences the partitioning of contaminants from soil.
To study the partitioning of contaminants to organic matter, the partitioning of organic matter
itself has to be studied as well.
During this study, the influence of pH on the release of dissolved organic carbon (DOC) from
sediment is examined. DOC is extracted from organic rich sediment with buffered and nonbuffered solutions of varying pH values (pH~5-9). DOC is analysed by measuring the total
organic carbon (TOC) content with a TOC analyser. Furthermore, the influence of the buffered
and non-buffered treatments on the freely dissolved concentration and thus the partitioning
behaviour of PAHs to TOC is examined with solid phase micro extraction (SPME). Phenanthrene,
anthracene and pyrene were chosen as representative model compounds for PAHs.
It was found that with increasing pH the release of TOC from sediment increases as well. For the
buffered extractions the absorption of phenanthrene, anthracene and pyrene by TOC decreased
with increasing pH. For the non-buffered extractions the absorption of phenanthrene and pyrene
by TOC remained more or less constant with increasing pH. For phenanthrene and pyrene, log
KDOC values at pH 6.81 were 4.74 and 5.52, respectively. However anthracene showed
unexpected behaviour for the non-buffered extractions. At increasing pH, freely dissolved
anthracene disappeared completely and binds in totality to TOC. No explanation could be found
for this behaviour and further research needs to be done.
Samenvatting
Als vervuiling in het milieu terechtkomt, is de levensloop afhankelijk van het soort milieu waar het
in terechtkomt en de processen waaraan het onderhevig is. In de grond wordt de mate waarin
vervuilende stoffen binden aan de bodem onder andere bepaald door het organisch materiaal in
de bodem. Dit organisch materiaal kan uit de bodem in porie- en grondwater komen en
beïnvloedt daarmee ook de mate waarin vervuiling in het grond- en poriewater terechtkomt. De
mate waarin organisch materiaal vanuit de bodem in de waterfase terechtkomt is afhankelijk van
het milieu. Om te onderzoeken in welke mate vervuiling aan organisch materiaal in de waterfase
bindt, is het noodzakelijk om te kijken naar de mate waarin organisch materiaal zich tussen de
bodem en het bodem- / poriewater verdeelt.
Als model voor vervuilende stoffen zijn tijdens dit project Polycyclische Aromatische
Koolwaterstoffen gebruikt (PAKs), namelijk phenanthrene, antracene en pyrene.
De invloed van pH op de verdeling van opgelost organisch materiaal (DOC, dissolved organic
carbon) tussen sediment en water is eerst onderzocht. DOC is geëxtraheerd uit organisch rijk
sediment met gebufferde en niet-gebufferde oplossingen met verschillende pH waarden
(oplopend van pH~5-9). DOC is geanalyseerd door de totale hoeveelheid organisch koolstof
(TOC, total organic carbon) te meten met een ‘TOC analyser’.
Vervolgens is gekeken naar de invloed van deze gebufferde en niet-gebufferde extracties op de
vrije concentratie PAKs aanwezig in de waterfase. Deze vrije concentratie werd gemeten met
behulp van ‘solid phase micro extraction’ (SPME). Door dit te doen kon indirect worden gekeken
naar de invloed van de gebufferde en niet-gebufferde extracties op de partitie van PAKs naar
TOC.
Tijdens het project bleek dat een toename van pH tevens zorgt voor een toename van de partitie
van DOC naar de waterfase. Bij de gebufferde extracties nam de opname van phenanthrene,
anthracene en pyrene door TOC af met toenemende pH. Bij de niet-gebufferde extracties bleef
de absorptie van phenanthrene en pyrene door TOC gemiddeld genomen constant bij
toenemende pH. Voor phenanthrene en pyrene waren de log KDOC waarden bij een pH van 6.81
respectievelijk 4.74 en 5.52. Anthracene daarentegen vertoonde onverwacht gedrag bij de nietgebufferde extracties. Bij een toenemende pH verdwijnt de concentratie vrij opgelost anthracene
volledig en bindt het geheel aan TOC. Er werd geen verklaring gevonden voor dit gedrag en om
meer inzicht te krijgen in het afwijkend gedrag van anthracene is verder onderzoek nodig.
Introduction
Dissolved organic carbon (DOC) can be found in all natural waters, soils and sediments as
macromolecular organic compounds1, that can distribute from soil or sediment to the pore water
or surrounding waters. This distribution or sorption-desorption behaviour among the solid and
aqueous environmental compartments depends on the concentration and nature of DOC and the
pH and ionic strength of the surrounding solution composition. The amount and composition of
DOC are dependent on several factors including the microbial activity, the stream and rate of
water movement (flow), sediment composition and climatic conditions. Usually the composition of
DOC consists for a great amount of fulvic and humic acids that are diagenetically and microbially
altered complex macromolecules derived from plant, animal and microbial residues.
DOC plays an important role in the partitioning of all kinds of hydrophobic organic compounds
(HOCs) in surface and pore waters. The association of HOCs to DOC takes place via hydrophobic
interactions. The binding of HOCs to DOC will influence their fate and behaviour in the
environment by increasing the mobility of sorbed HOCs and by rendering them (mostly) less
bioavailable for microbial biodegradation and uptake by invertebrates.2, 3
A specific class of HOCs consists of polycyclic aromatic hydrocarbons (PAHs) and can be found in
soils and sediments mainly originating from petroleum residues and incomplete combustion
products of wood. These compounds have, like many HOCs, a recalcitrant chemical structure, are
hydrophobic, relatively insoluble in water and are semivolatile, which means they have the
potential to bioaccumulate in organic tissues of organisms. Often PAHs tend to be also mutagenic
and/or carcinogenic and are therefore of environmental concern. 4 To be able to predict the
bioremediation potential, the toxicological risk or the likelihood of bioaccumulation from polluted
soil, it is of great importance to study the behaviour of PAHs in the environment. 3, 5 Because of
the hydrophobicity of PAHs they will (ad)sorb to solid organic matter facies and clays, exhibit
slow desorption, dissolve poorly in the aqueous phase and absorb to DOC in natural waters.
Therefore, these compounds, like many HOCs, will be less available for biodegradation and are
able to persist in the environment.
The degree of binding to DOC is reflected by the KDOC, the partition coefficient of HOCs to DOC.
KDOC can differ greatly depending on the properties of DOC, solution composition and properties
of the contaminant.6
The amount of aromatic compounds present in DOC is taken to be a measurement for the
aromaticity of DOC. Recent study showed however that for pyrene K DOC was related to the
aromaticity of DOC only within a narrow pH range. 6
The pH and the presence of ions in natural waters, influence the sorption of hydrophobic organic
contaminants to DOC. At very alkaline pH, functional groups, such as carboxylic acid and phenolic
groups, can deprotonate and because of the increased polarity, the hydrophobic interaction will
decrease. At the same time DOC will expand because of its surface charge and will therefore
provide fewer sorption sites for HOCs.7 In contrary, at lower pH, the functional groups of DOC
will be mostly protonated, the surface charge will decrease and due to hydrophobic interactions
molecules can coil up and form micelle-like conformations, which creates extra sorption sites for
HOCs. 8 Naturally, the polarity or charge of the contaminant will also influence the sorption to
DOC. In addition, the acidity or alkalinity of the environment also influences the solubility of DOC
in natural waters. When adjacent natural water contains a high pH, DOC will partition with
greater ease from soil to the water phase.
During this study, the influence of pH on the release of DOC from sediment is examined. DOC is
extracted from organic rich sediment with buffered and non-buffered solutions of varying pH
values (pH~5-9). The extracted DOC is analysed with UV measurements (280 nm, as an
indication for aromaticity) and TOC measurements. Total organic carbon (TOC) refers to the
organic content of an unfiltered sample. Since organic matter is considered dissolved when it has
passed through a 0.45 m filter (which is an arbitrary definition) 1 and no filtration took place
during this project, from now on the organic carbon in solution is referred to as TOC.
Furthermore, the influence of the buffered and non-buffered treatments on the freely dissolved
concentration and thus the partitioning behaviour of PAHs to TOC is examined with solid phase
micro extraction (SPME). In SPME, fibers coated with PDMS (polydimethylsiloxane) extract an
amount of freely dissolved PAHs (not associated with DOC) from solution. To use this method,
Kfiber has to be taken into account (which is known from recent studies 9). During this study
phenanthrene, anthracene and pyrene (see figure 1) have been used as model compounds for
PAHs to study the pH dependent partitioning behaviour of PAHs and DOC.
Figure 1: Schematic chemical structures for phenanthrene, anthracene and pyrene.
Materials and methods
Sediment sample
For the preparation of DOC samples sediment from lake Kontiolampi in Finland was used (55.3%
OC dw, 96% water content). The collected sediment was sieved (w = 1mm) and stored at
approximately 5°C.
Extraction of DOC
There were two different types of soil extraction performed. One series of sediment samples
were extracted with buffer solutions (pKa = 7.2, [K2HPO4*3H2O] : [NaH2PO4*2H2O] = 0.02) by
increasing the pH -from ~ 5 to 9- and another series were extracted with unbuffered Finnish
medium (FM; both with a sediment to water ratio of 1:2). The Finnish medium has a low salt
content (3.97*10 -4 M CaCl2*2H2O, 9.94*10-5 M MgSO4*7H2O, 1.49*10-4 M NaHCO3 and 2.00*10-5
M KCl) and contained biocide (1.02*10-3 M NaN3) to prevent microbial growth. The buffer
solutions contained only biocide and no other salts as they precipitated with phosphate.
To release DOC from sediment, the samples were shaken horizontally at room temperature for
one hour (200 rpm, Labline Shaker). The sediment suspensions were subsequently centrifuged at
7,400g (Herolab Unicen fr) for 30 minutes to separate the sediment from the aqueous phase.
The supernatant was finally centrifuged at 31,000g (Herolab Unicen fr) for 3 hours to separate
colloidal particles from the DOC solutions. The samples extracted with Finnish medium were
afterwards set at different pH values (pH increasing from ~5 to 9) with diluted NaOH.
Determination of TOC and analysis of DOM
The DOC solutions were analyzed with a TOC-5000 Shimadzu analyzer to determine TOC
concentrations (Total Organic Carbon; calibrated with potassium hydrogen phthalate). TOC
concentrations are calculated by substracting the amount of IC (inorganic carbon) from the
amount of TC (total carbon). The sediment samples extracted with buffer solutions were also
analyzed with UV-vis measurements (252nm, 270nm 280nm and full spectra, UV 500 Unicam)
after diluting the samples 1:1 with Finnish medium. The pH was measured using a Consort
m.p.a. C535 and for the final pH measurements of the samples (containing PAHs) a Mettler
Toledo MP220 was used.
SPME extraction of PAHs
For the determination of freely dissolved PAHs, SPME fibers were used (cut in pieces of 2 cm, ø
110 μm, 28.5 μm PDMS coating (12.4 μl/m)). Before use, the fibers were thermally cleaned at
250 °C for approximately 2 hours under a constant Helium flow (10 ml/min). The DOC solutions,
with a total volume of 50 ml (in duplicate) for each treatment (buffer and FM extracted), were
spiked with 20 μl of a PAH mixture dissolved in acetonitrile, containing phenanthrene (Acros
98+%, 69.5 mg/l), anthracene (Fluka 98+%, 12.3 mg/l) and pyrene (Aldrich 98%, 16.0 mg/l).
For internal calibration standards, fibers were also added to four spiked solutions (FM, not
containing DOC) with different PAH concentrations (see Appendix I).
After 12 hours, the fibers were exposed to the solutions. The samples were shaken (200 rpm,
Gerhardt) for 12 days to reach equilibrium between water and fiber and were kept at a constant
temperature of 20 °C.
Analysis with HPLC and fluorescence detection
After the exposure, the fibers were desorbed in 150 μl acetonitrile (weighed) containing 500 μg/l
benzo(a)anthracene (Acros 99%, injection standard). These samples were analysed with HPLC
(Waters; autosampler 717 plus, controller 600) and fluorescence detection (Waters; scanning
fluorescence detector 474). As external calibration standards, four extra samples with different
PAH concentrations were injected directly (see Appendix I).
The column used for the HPLC analysis was a reversed phase C18 column (125mm length, ø 2.00
mm, particle size: 3 µm, temperature: 36°C, ‘Phenomenex’ Lichrospher RP18) and as eluens a
mixture (already mixed before use) of 45% water (nanopure) and 55% acetonitrile (HPLC grade)
was used. The flow was set at 0.4 ml/min and the injection volume at 2 µl. With fluoresence
detection the samples were measured for phenanthrene (exitation 250 nm, emission 385 nm),
anthracene (exitation 250 nm, emission 385 nm), and pyrene (exitation 335 nm, emission 383
nm), the bandwith was set at 40 nm and the gain at 100 (0.07-0.22 ng injected).
Determination of KDOC
To calculate KDOC, a mass balance equation of the total amount of PAHs distributed over the
freely dissolved amount and the amounts sorbed to the fiber and DOC, is used as follows:
m total  m free  m fiber  mdoc
(1)
And rearranged in the appropriate concentrations and volumes:
c totalVwater  c freeVwater  c fiber Vfiber  c docMdoc
(2)
ctotal = Total PAH concentration in solution
cfree = Freely dissolved PAH concentration
cdoc = PAH concentration sorbed to DOC
Vwater = Total volume of water
Vfiber = Volume of PDMS fiber
Mdoc = Mass of DOC present in solution
Together with Kfiber and KDOC (defined as below), the mass balance can be rewritten as shown in
equation 5:
c
K fiber  fiber
c free
(3)
c
K doc  doc
c free
(4)
c free

c total
(5)
1
Vfiber
1
K fiber  {doc}K doc
Vwater
{doc} = the concentration of DOC in the sample.
From equation 5, KDOC can be calculated provided that all other parameters are known or
calculated.
Results
pH
The pH of the samples was measured (buffer and Finnish medium), before and after the DOC
extraction, as well as after the fiber extraction. Results are given in the table below.
Table 1: pH measurements
Sample
B1
B2
B3
B4
B5
FM
before DOC
extraction
5.17
5.97
6.99
7.96
8.86
7.20
pH
After DOC
extraction
5.08
5.47
6.61
7.20
7.29
→
→
5.19 →
→
→
5.24
6.36
6.90
8.17
9.18
After
fiber
extraction
5.08
5.48
6.63
7.14
7.21
5.35
6.18
6.55
6.70
6.81
TOC & UV-visible spectra
The amount of DOC extracted from the sediment depended on the pH of the solution used and
was determined (in triplicate) by TOC analysis. The DOC extractions were also analysed with UVvis measurements at 280 nm, to examine the aromaticity of DOC. The results are given below in
figure 2.
Figure 2: pH dependence of TOC concentration and UV absorption at 280 nm of phosphate
buffered extracted sediment.
The amount of TOC extracted with Finnish medium (pH 7,20) equals 39.5 mg/l (average of 5, σ
= 6.8). From an initial pH of 5.19, these samples were set at different pH values (see table 1).
After the 12 d equilibration time, final pH values changed -2.37 to 0.14 compared to initial
values. The sediment extractions performed with Finnish medium resulted in a shortage of DOC
solution. Therefore, there was not enough DOC solution of the FM treatment left for TOC
measurements. Because of this, the samples needed for TOC measurements were diluted with
nanopure water (1:1 ratio). Due to the low DOC concentrations, the amounts of DOC in solution
were close to the detection limit of the TOC analyser. During the following calculations, wherever
needed, the concentration of DOC in FM was taken to be the average concentration of DOC in
the FM samples.
KDOC and other determined parameters
After the fiber extraction, the samples were analysed with HPLC. The area of the integrated
peaks were corrected with the area of the injection standard (B aA) and total desorption volume.
By regression of this corrected area with the freely dissolved concentration (c free) from the
internal calibration, cfree (amount of PAHs not absorbed by DOC or fiber), cfiber, cDOC (amount of
PAHs absorbed by DOC) and KDOC could be determined by rearrangement of equations 3 and 5.
With the use of the external calibration regression, Kfiber was calculated and cfiber could be
determined again. The experiment was performed in duplicate and the standard error of mean I
was used to calculate the error interval.
The results are shown in the figures below.
Effect of pH on free and DOC sorbed PAH concentrations in buffered DOC extraction
The influence of pH on the sorption of PAHs to DOC and the amount of freely dissolved PAHs in
solution is shown in figure 3-5 for phenanthrene, anthracene and pyrene, respectively.
CDOC is normalised to the concentration of DOC in solution.
The amount of DOC increases as sediment extracted with higher pH results in higher DOC
concentrations. The amount of free PAHs is influenced by the amount of DOC as well as by the
pH of the solution. After a slight increase in cfree at pH 5.48 for all PAHs, a decrease of cfree is
observed with increasing pH as DOC concentrations are increasing. On the other hand, DOC
sorbed PAHs expressed as cdoc are decreasing due to normalisation to higher DOC concentrations
at higher pH values.
I
SEM = SD/√N, SD=√[∑ (xi -<x>)2 / (N-1)]
Cfree & CDOC Phenanthrene B
7.5
1.0
C free phe (g/l)
Cdoc phe (mg/gC)
0.5
cDOC
cfree
5.0
2.5
0.0
0.0
4
5
6
7
8
pH
Figure 3: cfree and cDOC of phenanthrene versus pH of buffered extraction
Cfree & CDOC Anthracene B
1.00
0.3
C free anth (g/l)
Cdoc anth (mg/gC)
0.2
cDOC
cfre e
0.75
0.50
0.1
0.25
0.00
0.0
4
5
6
7
8
pH
Figure 4: cfree and cDOC of anthracene versus pH of buffered extraction
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
C free pyr (g/l)
Cdoc pyr (mg/gC)
cDOC
cfree
Cfree & CDOC Pyrene B
0.0
4
5
6
7
8
pH
Figure 5: cfree and cDOC of pyrene versus pH of buffered extraction
Effect of pH on free and DOC sorbed PAH concentrations in non-buffered DOC extraction
The amount of DOC remains overall constant in the sediment extraction with FM and the pH was
adjusted afterwards. The amount of PAHs sorbed to DOC (c DOC) is normalised to the average
concentration of DOC in FM solution.
It was expected for cDOC and cfree to be not significantly influenced by the pH of the non-buffered
treatments, which was adjusted afterwards. For phenanthrene and pyrene, c DOC and cfree remain
more or less constant with increasing pH (see Appendix IV). Therefore, these results are not
shown below. However the results for anthracene are unexpected and show quite a different
behaviour compared to the buffered treatments. Freely dissolved anthracene completely
disappears with increasing pH and cDOC slightly increases. These results are given below in figure
6.
Cfree & CDOC Anthracene FM
0.4
0.75
0.3
0.50
0.2
0.25
0.1
0.00
C free anth (g/l)
Cdoc anth (mg/gC)
cDOC
cfree
1.00
0.0
4
5
6
7
8
pH
Figure 6: cfree and cDOC of anthracene versus pH of non-buffered extraction
Effect of pH on the partitioning of PAH to DOC in buffered DOC extraction
KDOC is calculated to examine the influence of pH on the sorption of PAHs to DOC. K DOC is shown
in figure 7-9 for phenanthrene, anthracene and pyrene, respectively . The KDOC is normalised to
the concentration of DOC in solution.
The amount of freely dissolved PAH is influenced by the amount of DOC as well as by the pH of
the solution. After a decrease of KDOC until pH 6.63 for all PAHs, KDOC remains more or less
constant.
Figure 7: KDOC of phenanthrene versus pH of buffered extraction
Figure 8: KDOC of anthracene versus pH of buffered extraction
Figure 9: KDOC of pyrene versus pH of buffered extraction
Effect of pH on the partitioning of PAH to DOC in nonbuffered DOC extraction
Values of KDOC for Phenanthrene and Pyrene remained constant with increasing pH (see Appendix
IV). It was expected for KDOC to be not significantly influenced by the pH of the non-buffered
treatments, which was adjusted afterwards. However the results for Anthracene are unexpected
and show quite a different behaviour than for phenanthrene and pyrene. The K doc values for
anthracene is increasing to very high values as freely dissolved anthracene is disappearing rapidly
and accurate values of Kdoc could not be calculated anymore. The results are given in figure 10
below.
KDOC Anthracene FM
400000
Kdoc anth (l/kg)
KDOC
300000
200000
100000
0
4
5
6
7
8
pH
Figure 10: KDOC of antracene versus pH of non-buffered extraction
Further determined parameters
The influence of TOC on the free concentration of PAH could also be examined and is shown in
Appendix II. cfiber calculated with the use of the internal as well as the external standards is
shown in Appendix III. These results show the same relative decrease with increasing pH in the
buffered extractions and in the non-buffered extraction. The results for phenanthrene and pyrene
in the non-buffered extractions show the same relative stability. However the results of Cfiber
calculated with internal standards do not resemble the results calculated with the external
standards. During this project, no explanation could be found for these differences.
An overview of all the calculated parameters is shown in Appendix IV.
Another finding during this study was the increased inorganic carbon content of TOC with
increasing pH. These results were measured during TOC analysis and are shown in Appendix V.
No further effort was taken to study these results.
Discussion
Results
The influence of pH on the release of TOC from sediment extracted with phosphate buffers was
clear. With increasing pH, the amount of TOC partitioning from sediment to water-phase
increased (see figure 2) due to deprotonation of TOC which increases its polarity and thereby its
solubility in water. These results resemble data published in previous studies. 9, 10
The amount of aromatic compounds in TOC is often taken to be a measure for the aromaticity of
TOC. The buffered sediment extractions showed an increasing amount of aromatic TOC
compounds with increasing pH (see figure 2). These results confirm the findings that with
increasing pH the amount of TOC released from sediment increases as well, given that the
aromacity of TOC is independent on the increase of pH.
The amount of freely dissolved PAH in buffered extraction is fairly dependent on pH.
Phenanthrene, anthracene and pyrene show the same behaviour in the sediment buffered
extractions (see figure 3-5). At higher pH values, the extracted TOC from sediment will have
more deprotonated carboxylic and phenolic groups and therefore TOC will become more polar.
This means that there are fewer sorption sites available for PAH, also due to intramolecular
repulsion there will be less hydrophobic cavities available for PAH.6 In the sediment buffered
extraction, cDOC (normalised to concentration of TOC) decreases with increasing pH. cfree is also
decreasing due to an increased amount of TOC at higher pH, see figure 11 below. This can also
be illustrated by plotting TOC against Cfree and is shown in Appendix II.
Figure 11: Effect of pH on cfree and cDOC of buffered extractions
Above pH 6.63, equilibrium between freely dissolved PAH and TOC absorbed PAH is established.
This is shown by KDOC for phenanthrene, anthracene and pyrene given in figure 7 - 9. KDOC
decreases until pH 6.63 and then reaches equilibrium for the buffered extractions of
phenanthrene, anthracene and pyrene. Apparently above pH 6.63 the polarity of TOC (due to
deprotonation) is at that kind of state at which no further hydrophobic PAH will be absorbed
because of repulsive interactions.
For the non-buffered extractions, increasing pH values did not significantly influence the
partitioning behaviour of phenanthrene and pyrene to TOC; cDOC, cfree and KDOC remained more or
less constant (see Appendix IV). Adjusting the pH after sediment extraction apparently did not
have a significant effect on polarity of TOC to influence sorption of phenanthrene and pyrene.
Anthracene shows however quite a different behaviour in the non-buffered extractions and shows
rather unexpected results compared to buffered extractions. Above pH 6.55, the freely dissolved
concentration completely diminishes and the concentration associated to TOC increases
concomitantly. This means that in contrary to phenanthrene and pyrene the amount of
anthracene associated with TOC (normalised !) increases with increasing pH. In buffered
extraction, anthracene shows no deviating behaviour compared to phenanthrene and pyrene.
Due to the fast decrease of cfree above pH 6.55, the uncertainty in measured cfree at pH 6.55 is
large. Consequently, KDOC calculated at that pH value is subject to large errors. KDOC values for
increasing pH could not be calculated because cfree approaches zero. It is very difficult to
understand why anthracene behaves in this way based on only the results of this study. It could
be possible that the hydroxy groups of sodium hydroxide (which is used to adjust the pH of the
non-buffered extracts) bind to anthracene making it more polar and thereby decreasing its
repulsion towards polar TOC. Additionally, the high symmetry of anthracene would make it
possible to ‘disappear’ into TOC. This would also explain why this behaviour does not occur in the
buffered extraction, since no sodium hydroxide is used for the buffered extraction. These
speculations seem to be inconsistent with the fact that adjusting pH after extraction had no
significant effect on polarity of TOC (for phenanthrene and pyrene). Consequently, TOC would
not be very polar, making the sudden ‘attraction’ between polar anthracene and non polar TOC
not a very logical explanation.
It is clear that further research needs to be done in order to find an explanation for the increased
sorption of anthracene to TOC at increasing pH values of non-buffered extracts.
Log KDOC values calculated at pH 6.81 for non-buffered extraction could be compared with log
KDOC found in a previous study by J. Haftka 11 (determined at pH 7). This comparison is shown in
table 2 below. In both studies, no value for log KDOC for anthracene could be calculated. The log
KDOC values calculated for this study are lower (note: pH is lower as well) in value, but also less
accurate and based on only one experiment. When additional research would be done,
presumably more accurate values for log KDOC would be found.
Table 2: Comparison of log KDOC J. Haftka and S. Waaijers
log KDOC (JH)
pH 7 log KDOC (SW) pH 6.81
Phenanthrene
4.95 (0.01)
4.74 (0.04)
Antracene
Pyrene
5.80 (0.01)
5.52 (0.05)
Method
The concentrations of cfree, cfiber (derived from internal calibration) and cDOC are all corrected for
injection volume (internal standard) and desorption volume of the fiber. Through a second
calibration, the external standards, Cfiber could be determined again and these values are
corrected for desorption volume of the fiber as well. CDOC and KDOC are both normalised to the
amount of TOC in solution. No correction could be made for the length of the fiber (2 cm, which
is cut by hand), the spiking volume (assumed to be 20 µl) and the variation in thickness of the
fiber coating. The first and last can be overcome by cutting longer fibers, which will minimize the
deviation. The variation in spiking volume will be more negligible when it is added to larger
volume samples.
Despite the conventional method of obtaining DOC solution from the sediment via filtration, the
samples were chosen to be centrifuged at high speeds. This was based on the conclusion that
sediment extraction using the filtration method gave irreproducible results. In a previous study, it
was observed that during filtration a fouling occurred on the filter and more aromatic compounds
of DOC seemed to be retained on the filter. 11
To check whether TOC itself does not function as a buffer, small amounts of sodium hydroxide
(100 l, 0.5 M) were added to TOC solution (FM treatment) and pH was measured. With one
drop, the pH increased from approximately 5 to 11.5. From this result, it can be concluded that
TOC itself does not function as a buffer. Further proof could be found in the results of pH
measurements after the sampling equilibrium time. The pH of the non-buffered FM treated
samples did decrease to a much greater extent than the buffer treated samples (see table 1).
A previous published study mentioned the existence of a matrix (macromolecular binding agents)
effect called fiber fouling.12 Fiber fouling refers to the effect of attachment of DOC (matrix) to the
surface of the fiber thereby influencing the measurements. During the experiments performed in
this study, a few light spots were seen on some fibers. There were however no signs that fiber
fouling influenced the experimental results.
cfiber is normalised to the peak area, which was calculated by integration of the HPLC results,
using internal standards. Hereby the results are corrected for desorption volume of the fiber and
for injection volume. Cfiber, calculated by using the external standard, was not corrected for the
injection volume. However, this could be no explanation for the large differences between the
results for cfiber calculated with internal and external standards (see Appendix III). The values for
cfiber calculated with the external standards seem to be larger with a constant value than those for
cfiber calculated with internal standards. No explanation could be found for this constant value. To
understand these differences, further research should be done.
Conclusion
It was found that with increasing pH the release of TOC from sediment increases as well. For the
buffered extractions the absorption of phenanthrene, anthracene and pyrene by TOC decreased
with increasing pH. For the non-buffered extractions the absorption of phenanthrene and pyrene
by TOC remained more or less constant with increasing pH. For phenanthrene and pyrene, log
KDOC values at pH 6.81 were 4.74 and 5.52, respectively. However anthracene showed
unexpected behaviour for the non-buffered extractions. At increasing pH, freely dissolved
anthracene disappeared completely and binds in totality to DOC. No explanation could be found
for this behaviour and further research needs to be done.
Acknowledgements
I would like to thank Dr. John Parsons who made it possible for me to do research at the IBED
department.
Especially I would like to thank Drs. Joris Haftka who proposed this study and supported me
during the experiment despite of his everlasting time shortage. I am very grateful that he was
always available to assist whenever needed and gave helpful comments.
1
J.I. Drever, The Geochemistry of Natural Waters, third ed., 1997, Prentice Hall, Ch. 6
A.V. Ogram, R.E. Jessup, L.T. Lou, P.S.C. Rao, Applied and Environmental Microbiology, 1985,
49, 582-587 (ad 5)
3
B.J. Reid, K.C. Jones, K.T. Semple, Environmental Pollution, 2000, 108, 103-112
4
J.E. Andrews, P. Brimblecombe, T.D. Jickells, P.S. Liss, B.J. Reid , An Introduction to
Environmental Chemistry, second ed., 2004, Blackwell Publishing
5
K.T. Semple, A.W.J. Morriss, G.I. Paton, European Journal of Soil Science, 2003, 53, 809-818
6
B. Marschner, R. Winkler, D. Jödemann, European Journal of Soil Science, 2005, 56, 299-306
7
J.R. Lead, K.J. Wilkinson, V. Starchev, J. Buffle, Environmental Science and Technology, 2000,
34, 1365-1369
(ad 6)
8
C.S. Ragle, R.R. Engebretson, R. von Wandruszka, Soil Science, 1997, 162, 106-114 (ad 6)
9
S.-J. You, Y. Yin, H.E. Allen, The Science of the Total Environment, 1999, 227, 155-160
10
L.A. Oste, E.J.M. Temminghoff, W.H. van Riemsdijk, Environmental Science and Technology,
2002, 36, No. 2, 208-214
11
J. Haftka, Determination of DOC to water partition coefficients with SPME
(article in preparation)
12
M.B. Heringa, J.L.M. Hermens, Trends in Analytical Chemistry, 2003, 22, No. 10
2
Appendix I; Internal and external calibration standards
The calibration slopes were calculated with linear regression and forced through zero. This was
done to be able to calculate the associated concentration of some low value peak areas.
CPAH (µg/l)
int.cal.std 1
int.cal.std 2
int.cal.std 3
int.cal.std 4
slope (y=ax)
phe
6,089293
16,44112
26,73559
36,96946
0.0304 ±
0.00042
anth
1,563677
3,154142
4,662732
6,270797
0.1735 ±
0.002084
pyr
1,909261
3,75626
5,584086
7,405622
0.5001 ±
0.004206
Minj. (ng)
ext.cal.std 1
ext.cal.std 2
ext.cal.std 3
ext.cal.std 4
slope (y=ax)
phe
0,102077
0,179196
0,648903
1,417855
4207000
± 99590
anth
0,018011
0,031619
0,114497
0,250177
20210000
± 493800
pyr
0,023558
0,041357
0,149760
0,327227
20820000
± 498200
Appendix II; Cfree versus TOC
The graphs below (IIa-c) show the influence of TOC on the amount of free PAH, not absorbed by
fiber or DOC.
Due to unequally spread DOC in the Finnish medium extracts (as mentioned before), an average
concentration of DOC was used to calculate Cfree in the Finnish medium solutions. Because of this
no Cfree dependence of TOC could be calculated for the FM solutions.
Cfree is normalised by using an internal standard (Benzo(a)anthracene) and by correcting for
desorption volume of the fiber.
TOC vs Cfree Phenanthrene
7.5
Cfree Phe (µg/l)
Cfree
5.0
2.5
0.0
0
25
50
75
100
TOC (mg/l)
IIa
TOC vs Cfree Anthracene
1.00
Cfree Anth (µg/l)
Cfree
0.75
0.50
0.25
0.00
0
25
50
75
100
TOC (mg/l)
IIb
TOC vs Cfree Pyrene
0.4
Cfree
0.3
Cfree Pyr (µg/l)
0.2
0.1
0.0
0
25
50
TOC (mg/l)
IIc
75
100
Appendix III; Cfiber versus pH
The graphs below (IIIa-f) show the influence of pH on the sorption of PAHs to fiber.
To calculate Cfiber, the internal as well as the external calibration could be used.
The results of these two methods are both given in the graphs below. C fiber derived from the
internal standards regression is normalised by using an internal standard (Benzo(a)Anthracene),
for Cfiber derived from the external standards no internal standard is used. Both concentrations
are corrected for desorption volume of the fiber. The amount of PAHs absorbed by fiber is
influenced by the amount of DOM, as well as the pH of the solution. For the buffers, the amount
of DOC increases as pH rises, for the Finnish medium the overall DOC concentration remains
constant.
Cfiber Phenanthrene B
75
Cfiber phe in(mg/l)
Cfiber phe ex(mg/l)
cfiber
50
25
0
4
5
6
7
8
pH
IIIa
Cfiber Anthracene B
10.0
Cfiber ant in(mg/l)
Cfiber ant ex(mg/l)
cfiber
7.5
5.0
2.5
0.0
4
5
6
pH
IIIb
7
8
Cfiber Pyrene B
10.0
Cfiber pyr in(mg/l)
Cfiber pyr ex(mg/l)
cfiber
7.5
5.0
2.5
0.0
4
5
6
7
8
pH
IIIc
Cfiber Phenanthrene FM
cfiber
60
50
Cfiber phe in(mg/l)
40
Cfiber phe ex(mg/l)
30
20
10
0
4
5
6
pH
IIId
7
8
Cfiber Anthracene FM
10.0
Cfiber ant in(mg/l)
Cfiber ant ex(mg/l)
cfiber
7.5
5.0
2.5
0.0
4
5
6
7
8
pH
IIIe
Cfiber Pyrene FM
10.0
Cfiber pyr in(mg/l)
cfiber
7.5
Cfiber pyr ex(mg/l)
5.0
2.5
0.0
4
5
6
pH
IIIf
7
8
Appendix IV; pH versus TOC, KDOC, Cfree, Cfiber and CDOC
The tables below (IVa-h) show the parameters calculated for the PAHs. All values are calculated
as an average of two (the experiment was done in duplicate), except the TOC concentrations
(see also method description).
IVa
Buffers TOC (mg/l) KDOC
pH
phe
stdev
anth
stdev
pyr
stdev
5.08
27,64
146023
4285
199153
8627
854035
29849
5.48
34,42
99351
4208
136364
3379
616237
15864
6.63
45,14
84288
3218
115610
3201
493282
28981
7.14
49,24
96505
6470
132488
8102
554507
41979
7.21
79,08
87526
15806
119756
20496
531493
62235
IVb
Buffers Cfree (g/l)
PH
phe

5.08
5,480
5.48
6,238
6.63
5,742
7.14
4,808
7.21
3,536
0,128
0,203
0,172
0,264
0,555
anth
pyr


0,749
0,027
0,259
0,009
0,854
0,017
0,287
0,007
0,783
0,018
0,274
0,015
0,649
0,034
0,226
0,016
0,472
0,073
0,150
0,017
IVc
Buffers Cfiber (g/l) –internal calibrationPH
phe
anth


5.08
44284
1033
7893
5.48
50417
1637
9003
6.63
46406
1391
8250
7.14
38859
2138
6837
7.21
28579
4487
4974
pyr
287
182
190
360
766

7807
8640
8261
6806
4502
260
211
462
494
513
IVd
Buffers CDOC (g/mg C)
pH
phe
anth
pyr



5.08
0,800
0,005
0,155
0,009
0,224
0,004
5.48
0,619
0,006
0,121
0,001
0,177
0,000
6.63
0,484
0,004
0,096
0,006
0,135
0,000
7.14
0,463
0,006
0,095
0,007
0,124
0,000
7.21
0,305
0,007
0,062
0,000
0,077
0,000
IVe
FM
PH
TOC (mg/l)

5.35
6.18
6.55
6.70
6.81
IVf
FM
PH
<39,52>
6,825
KDOC
phe

98670
92579
95870
96111
89732
1978
2084
952
1073
8462
anth

140125
150499
294244
-
5.35
6.18
6.55
6.70
6.81
Cfree (g/l)
phe

5,631
5,919
5,759
5,748
6,080
5.35
6.18
6.55
6.70
6.81
Cfiber (g/l) –internal calibrationphe
anth


45506
720
7849
47839
839
7391
46545
362
4171
46453
407
0
49136
3583
0
5.35
6.18
6.55
6.70
6.81
CDOC (g/mg C)
phe
anth
pyr



0,556
0,002
0,104
0,000
0,155
0,000
0,548
0,003
0,105
0,000
0,154
0,000
0,552
0,001
0,114
0,002
0,154
0,000
0,552
0,001
0,124
0,000
0,155
0,000
0,544
0,012
0,124
0,000
0,155
0,001
IVg
FM
PH
IVh
FM
PH
0,089
0,104
0,045
0,050
0,443
anth
pyr


0,745
0,001
0,270
0,008
0,701
0,016
0,277
0,003
0,396
0,083
0,278
0,007
0,000
0,000
0,255
0,006
0,000
0,000
0,248
0,029
pyr
10
164
876
0
0

8120
8334
8353
7681
7463
248
87
199
185
885
211
3927
67406
-
pyr

573118
557408
556206
607416
630500
18372
6125
13978
15316
78198
Appendix V; [IC] versus pH of buffered extraction
Table V below shows the amount of inorganic carbon in buffered extraction with increasing pH,
measured during TOC analysis.
Table V
pH
[IC] (mg/l)
5.08
0,140
5.48
0,198
6.63
1,012
7.14
4,020
7.21
4,424