Mobiliza ion o poly- and pe luo oalkyl subs ances (PFAS) om
he e ogeneous soils: Deso p ion by e hanol/xan han gum mix u e
Ali Ba ikh
a,b,c,*
, S ´
e an Colombano
a
, Maxime Cochennec
a
, Do ian Da a zani
a
,
A naul Pe aul
c
, Julie Lions
a
, Julien G andcl´
emen
c
, Dominique Guyonne
a
, Anne Togola
a
,
Cl´
emen Zo nig
a
, Nicolas De au
a
, Fabien Lion
a
, Ami Alamoo i
a
, S´
ebas ien B is eau
a
,
Mohamed Djemil
a
, E ic D. an Hullebusch
b
a
BRGM (F ench Geological Su ey), 3 A enue Claude Guillemin, O l´
eans 45100, F ance
b
Uni e si ´
e Pa is Ci ´
e, Ins i u de physique du globe de Pa is, CNRS, F-75005 Pa is, F ance
c
COLAS En i onnemen , 91, ue de la Folliouse, 01700 Mi ibel, F ance
HIGHLIGHTS GRAPHICAL ABSTRACT
•E hanol (50 % / ) did no impac he
shea - hinning beha io o xan han gum
solu ions.
•A posi i e co ela ion was obse ed be-
ween PFAS so p ion and oc anol-wa e
coe icien .
•O e shoo in PFAS concen a ions was
obse ed a e lushing wi h e hanol
(50 % / ) and xan han-e hanol mix u e
(in 1D column expe imen s).
•Mo e han 93 % o di e en PFASs we e
eco e ed a e lushing by xan han-
e hanol mix u e.
•Nume ical modeling success ully e-
p oduces b eak h ough cu es.
ARTICLE INFO
Keywo ds:
Poly- and pe luo oalkyl subs ances (PFAS)
Non-New onian luids (NNF)
Deso p ion
Alcohol
He e ogenei y o po ous media
ABSTRACT
Remedia ing soils con amina ed by pe - and poly luo oalkyl subs ances (PFAS) is a challenging ask due o he
unique p ope ies o hese compounds, such as a iable solubili y and esis ance o deg ada ion. In-si u soil
lushing wi h sol en s has been conside ed as a emedia ion echnique o PFAS-con amina ed soils. The use o
non-New onian luids, displaying a iable iscosi y depending on he applied shea a e, can o e ce ain ad-
an ages in imp o ing he e iciency o he p ocess, pa icula ly in he e ogeneous po ous media. In his wo k, he
e icacy o e hanol/xan han mix u e (XE) in he eco e y o a mix u e o pe luo ooc ane sul ona e (PFOS),
pe luo ooc anoic acid (PFOA), pe luo ohexane sul ona e (PFHxS), and pe luo obu ane sul ona e (PFBS) om
soil has been es ed a lab-scale. XE’s non-New onian beha io was examined h ough heological measu emen s,
con i ming ha e hanol did no a ec xan han gum’s (XG) shea - hinning beha io . The eco e y o PFAS in
ba ch-deso p ion exceeded 95 % in e hanol, and 99 % in XE, excep o PFBS which eached 94 %. 1D-column
* Co esponding au ho a : BRGM (F ench Geological Su ey), 3 A enue Claude Guillemin, O l´
eans 45100, F ance.
E-mail add esses: [email p o ec ed], [email p o ec ed] (A. Ba ikh).
Con en s lis s a ailable a ScienceDi ec
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h ps://doi.o g/10.1016/j.jhazma .2024.136496
Recei ed 8 Janua y 2024; Recei ed in e ised o m 3 No embe 2024; Accep ed 11 No embe 2024
Jou nal o Haza dous Ma e ials 481 (2025) 136496
A ailable online 17 No embe 2024
0304-3894/© 2024 The Au ho (s). Published by Else ie B.V. This is an open access a icle unde he CC BY license (
h p://c ea i ecommons.o g/licenses/by/4.0/ ).
expe imen s e ealed o e shoo s in PFAS b eak h ough cu es du ing e hanol and XE injec ion, due o o e -
solubiliza ion. XE, (XG 0.05 % w/w) could eco e 99 % PFOA, 98 % PFBS, 97 % PFHxS, and 92 % PFOS.
Nume ical modeling success ully ep oduces b eak h ough cu es o PFOA, PFHxS, and PFBS wi h he
con ec ion-dispe sion-so p ion equa ion and Langmui so p ion iso he m.
1. In oduc ion
Pe - and poly luo oalkyl (PFAS) subs ances ha e ecen ly a ac ed a
lo o a en ion because o hei ubiqui ous p esence in he en i onmen
and po en ial e ec s on human heal h [1,2]. PFAS a e widely p esen in
he ai , wa e , and soil as a esul o hei widesp ead use in a a ie y o
indus ial and consume i ems, such as wa e - esis an ex iles, aqueous
i e- igh ing oam (AFFF), and non-s ick cookwa e [3]. Thei
luo -ca bon bounds p o ide hem excep ional chemical and he mal
esis ance, as well as a highly s able na u e in he en i onmen [4,5].
PFAS a e cha ac e ized by hei en i onmen al pe sis ence which has
led o he label “Fo e e chemicals”. Conce ns ega ding he long- e m
impac s o PFAS exposu e on human heal h and ecosys ems ha e been
aised due o hei pe sis ence and bio-accumula i e na u e [6,7].
In he cu en decade, concen a ions o a ious PFAS ha e been
de e mined in g oundwa e in he ange o <0.03 ng.L
-1
o 6.75 mg.L
-1
o pe luo ooc anoic acid (PFOA), 0.01 ng.L
-1
o 4.6 mg.L
-1
o pe -
luo ooc ane sul ona e (PFOS), 0.01 ng.L
-1
o 2.38 mg.L
-1
o pe -
luo ohexane sul ona e (PFHxS), and 0.01 ng.L
-1
o 0.822 mg.L
-1
o
pe luo obu ane sul ona e (PFBS) [8], in su ace wa e sys em, eaching
le els o up o 100 ng.L
-1
[9] and in d inking wa e , exceeding. 500 ng.
L
-1
(Dixi e al., 2021). These concen a ions exceed he d inking wa e
h eshold se by he U.S. En i onmen al P o ec ion Agency 4 ng.L
-1
o
PFOS and PFOA and 10 ng.L
-1
o PFHxS [10], and hose se by he
Eu ope Union 100 ng.L
-1
o he sum o 20 PFAS (including PFOA and
PFOS) and 500 ng.L
-1
o all o al PFAS [11], posing subs an ial heal h
isks o humans, including enal oxici y, hepa o oxici y, and ca cino-
genici y [12,13].
Soil has been iden i ied as a p ominen and pe sis en sou ce o PFAS
pollu ion a con amina ed si es [14]. The occu ence o soil and sedi-
men s con amina ed by PFAS esul s om a ious sou ces, such as he
use o bio-solids in ag icul u e (soil amendmen s) [15], leacha es om
land ills [16], discha ges om luo opolyme manu ac u ing plan s
[17], and no ably, he widesp ead use o aqueous i e- igh ing oam
(AFFF) in mili a y si es and ai po s [18,19]. Global soil PFAS concen-
a ions ha e been epo ed in he ange o ens o ng.g
-1
by se e al
s udies in China, he Uni ed S a es, Ko ea, No way, and Belgium
[20-22]. B usseau e al. [23] e ealed ha soils in nume ous mili a y
ins alla ions in he USA con ained signi ican concen a ions o PFOA a
50,000 ng.g
-1
and PFOS a 373,000 ng.g
-1
. In F ance, o ins ance, pe -
luo ina ed ca boxylic acids (PFCA) we e ound in soil sampled om a
luo o- elome e p oduc ion si e a concen a ions o 655 ng.g
-1
[24],
while i e igh e aining si es had a maximum o di e en PFAS com-
pounds (mainly PFOS) o 357.46 ng.g
-1
, acco ding o Dauchy e al. [25].
These alues highligh he wide ange o PFAS con amina ion and i s
possible global en i onmen al impac . Conside ing he ising concen-
a ions o PFAS in soils and he associa ed isks o ecosys ems and
human heal h due o po en ial exposu e h ough g oundwa e , he e is a
c i ical need o de elop e ec i e echnology o he eco e y o PFAS
om soil and g oundwa e sys ems.
Remedia ion o PFAS-con amina ed soils ep esen s a challenging
ask due o he unique chemical p ope ies o hese subs ances [26].
Se e al emedia ion echnologies ha e been es ed o he emedia ion
o PFAS including ex-si u me hods such as bio emedia ion echnology
[27], oxida ion/ educ ion p ocesses [28,29], he mal p ocesses [5], soil
i i ica ion [30] and soil washing me hod using an in-si u app oach
[31] and an ex-si u one [32]. Howe e , hese me hods showed a ious
limi a ions and challenges such as high cos due o exca a ion, ans-
po a ion, and ene gy equi emen s [33,34]. Compa ed o he
p e iously men ioned emedia ion echnologies, he in-si u soil lushing
me hod has become a eliable and e icien me hod o he emedia ion
o soil ha has been con amina ed by o ganic pollu an s such as Poly-
chlo ina ed biphenyl (PCB), Polycyclic A oma ic Hyd oca bons (PAHs),
and di e en chlo ina ed hyd oca bons. This emedia ion echnology
has se e al ad an ages including he emedia ion o a la ge con ami-
na ed zone wi h minimized exca a ion and anspo , negligible
dis u bance o soil s uc u e, a small equi emen o a ea o he
equipmen , and applica ions in bo h he sa u a ed and he unsa u a ed
zones [35]. Di e en addi i es can be injec ed in o he soil, such as
o ganic polyme s [36] and co-sol en s [37].
Sol en s such as alcohol ha e been used o decades as a lushing
solu ion o mobilizing and solubilizing di e en o ganic con aminan s
[38,39]. To da e, sol en s such as me hanol, e hanol, and p opanol ha e
been used in he egene a ion o a ious so ben s con amina ed wi h
PFAS. This applica ion has been in es iga ed in bo h ba ch and column
PFAS egene a ion s udies in ol ing g anula and powde ed ac i a ed
ca bon (GAC, PAC, espec i ely) as well as esin [40-42]. Fo ba ch-scale
in es iga ions, e hanol 50% olume ac ion ( / ) has been consis en ly
con i med o be he bes emo al and egene a o sol en o PFAS, in
pa icula PFOS and PFOA, om soils and so ben ma e ials [43,44].
This choice s ems om i s demons a ed ad an ages, including lowe
oxici y han me hanol [45] and supe io e iciency han p opanol [35].
Mo eo e , column-scale s udies ha e expanded on his by simula ing
mo e ealis ic condi ions, whe e emo al solu ions low h ough he
po ous medium (soil, so ben ma e ials). Si iwa dena e al. [46] con-
duc ed a s udy on he e icacy o e hanol in egene a ing a GAC column,
e ealing a emo al e iciency o 64% o PFOS and 93% o PFOA.
Sene i a hna e al. [35] ca ied ou expe imen s in columns. They e-
po ed emo al o 98% o PFOS a e injec ion o i e bed- olumes o
e hanol (50% / ). Shaikh e al. [47] ound compa able ou comes,
e hanol (50% / ) achie ed a ema kable 89% egene a ion o PFOA
om he ac i a ed ca bon column a e injec ion o eigh bed- olumes.
Despi e e hanol’s ad an age o e PFAS eco e y, he e ogeneous
pe meabili y in subsu ace soil may pose challenges in uni o mly
dis ibu ing emo al solu ions du ing in-si u soil lushing. This is due o
he o ma ion o p e e en ial pa hways, esul ing in signi ican non-
swep a eas wi hin low-pe meabili y laye s. Addi ionally, he pe me-
abili y could be educed esul ing om he educ ion o soil po osi y due
o he so p ion o PFAS o soil pa icles, which could dec ease he
e ec i eness and eliabili y o soil lushing [35]. The use o
non-New onian luid (bio-polyme solu ion) can p esen ad an ages o
imp o ing he homogenei y o he injec ion o addi i es in he e oge-
neous soils. The mos ecen imp o emen s in in-si u soil lushing
echnologies in ol e he injec ion o non-New onian luids such as
polyme (xan han gum, gua gum) [48,49] and oam [50,51]. The shea
hinning beha io o polyme s imp o es he mobili y o lushing solu-
ion and he sweeping in po ous media especially in lowe pe meabili y
zones [52]. Acco ding o Gau hie and Kuepe [53], a lushing solu ion
consis ing o xan han gum and wo dis inc alcohols (e hanol and
n-p opanol) was able o emo e 94% o PolyChlo oBiphenyls om sand
in a 2D ank sys em. O he s udies, demons a ed ha xan han gum
could imp o e he sweeping e iciency in he e ogeneous sandbox ex-
pe imen s [54].
In addi ion, he expe imen al da a a e used o calib a e a nume ical
model o so bed solu e anspo in soil columns. Se e al models ha e
been p oposed and es ed in he li e a u e [55,56]. Mos o hem ocus
on he anspo o dilu ed PFAS in g oundwa e /soil, ei he unde
wa e -sa u a ed o unsa u a ed [57], adose zone condi ions. Fo
A. Ba ikh e al.
Jou nal o Haza dous Ma e ials 481 (2025) 136496
2
sa u a ed soils, he op ions include (1) a con ec ion-dispe sion equa ion
wi h an addi ional equilib ium non-linea e m o adso p ion (e.g.,
Langmui iso he m, o a lumped e m o include di e en so p ion
phenomena), [58], (2) modi ica ion o he con ec ion-dispe sion equa-
ion o include wo adso p ion si es (one ins an aneous and one is
a e-limi ed), namely he wo-si e model (TSM) [59-61] and (3) mo e
complex models ha can ep oduce anomalous anspo (de ia ing
om Fick’s di usion) due o, o example, soil he e ogenei y,
a e-limi ed solid adso p ion, e c. [62,63]. While he li e a u e indica es
ha he wo-si e model is he mos commonly used, i appea s ha he
obse a ion o non-equilib ium so p ion phenomena du ing 1D ans-
po o PFAS in sand columns is mos ly obse ed o PFOS, while he
b eak h ough cu es o PFOA and PFHxS, o example, a e o en
compa ible wi h equilib ium (non-linea ) so p ion model [60]. On he
o he hand, o he bes o ou knowledge, no wo k has ye applied any o
he abo e models o ep oduce deso p ion expe imen s using a luid
o he han he one used du ing con amina ion, whe eas his si ua ion
mimics a widely used amily o emedia ion echnology, as discussed
abo e.
The objec i e o his s udy is o e alua e he e ec i eness o he
polyme -alcohol mix u e in emo ing ou PFAS including PFOS, PFOA,
PFHxS, and PFBS om con amina ed soil. The i s phase in ol ed
assessing he heological beha io o he xan han-e hanol mix u e a
a ious concen a ions o polyme in he bulk. Subsequen ly, a se ies o
ba ch so p ion and deso p ion expe imen s we e conduc ed o unde -
s and he so p ion beha io o hese compounds as well as he e iciency
o e hanol wi h and wi hou xan han gum on he eco e y o PFAS. In
addi ion o hese expe imen s, a se ies o 1D po ous column expe imen s
we e conduc ed o assess he e icacy o he in oduced polyme in
e hanol solu ions o PFAS eco e y. Addi ionally, he simula ion pa o
his wo k is o compa e he expe imen al da a wi h he con ec ion-
dispe sion-so p ion model, using an equilib ium, non-linea , app oach
o so p ion, applied o adso p ion and deso p ion wi h he backg ound
solu ion ee o PFAS and o he luids (polyme , e hanol). Conside ing
he pauci y o in es iga ions ega ding he e iciency o non-New onian
luids as mix u e pa ne s o he eco e y o PFAS-con amina ed soil,
ou s udy p oposes an analysis o he po en ial bene i s o combining a
solubilizing agen and a non-New onian agen .
2. Ma e ials and me hods
2.1. Ma e ials
Fou PFAS ep esen a i es including, PFOS (CAS# 1763–23-1, Sigma
Ald ich, 99.8% pu i y), PFBS (CAS# 375–73-5, Sigma Ald ich, 99.8%
pu i y), PFHxS (CAS# 3871–99-6, Sigma Ald ich, 99.9% pu i y) and
PFOA (CAS# 335–67-1, Sigma Ald ich, 99% pu i y) we e used in
so p ion and deso p ion expe imen s. Ul apu e wa e was used om he
Milli-Q pu i ica ion sys em. Di e en sol en s o ch oma og aphy
including wa e , ammonium ace a e, and glacial ace ic acid (Reagen -
Plus g ade ≥99%) we e supplied by Sigma-Ald ich. Calcium chlo ide
(CaCl
2
) o enhancing he ionic s eng h o he PFAS solu ion was p o-
ided by Ac os O ganics. E hanol (99%), and high-pe o mance liquid
ch oma og aphy (HPLC) g ade me hanol we e ob ained om Fische
Scien i ic. Bio-polyme xan han gum was p o ided by Sigma-Ald ich.
2.2. Me hods
2.2.1. Soil p epa a ion
The soil o po ous media used in his s udy was man-made soil,
which con ains 92% qua z sand, 5% mine al clay, and 3% o ganic
ma e . The soil pH was measu ed in CaCl
2
supe na an s using a VWR pH
me e (pH 1100 H). The supe na an was collec ed om a suspension o
soil (soil/solu ion =1/5) in 0.01 mol.L
-1
o CaCl
2
solu ion acco ding o
ISO p o ocol (ISO 10390:2021) (Table 1). The soil was mixed manually
by hand, using he qua e ing me hod, o app oxima ely 4 h o all he
expe imen s p esen ed in his s udy. The sand was ini ially sie ed o
achie e a pa icle size o 0.8–1.25 mm and insed o elimina e any
deb is. The clay consis ed o a ious mine als including 12.9% smec i e,
10.4% illi e, 7.2% goe hi e, and p edominan ly 45.4% kaolini e.
O ganic ma e sou ced om compos was used o se e al ad an ages
such as high o ganic con en , accessibili y, and cos -e ec i eness The
To al O ganic Ca bon (TOC) in he soil was measu ed using he TOC
Shimadzu de ice. The TOC in he man-made soil is 1.14%, gi en a bulk
densi y o 1.6 g.cm
-3
. The clay and o ganic ma e we e c ushed and
sie ed o a pa icle size smalle han 1.25 mm be o e mixing wi h he
sand. This man-made soil ensu es a homogeneous dis ibu ion o o ganic
ma e and clay in he blend. In o de o main ain homogenei y, he soil
was i s p epa ed by ho oughly mixing sand and clay. A e ha ,
o ganic ma e was p og essi ely added and mixed un il he soil was
comple ely co e ed. Wa e was added g adually while mixing in o de o
achie e a cons an ex u e and mois u e con en . This econs i u ed soil
is ep esen a i e o classic F ench allu ial soils [64,65].
2.2.2. Rheological beha io o polyme -e hanol solu ions
Xan han gum was selec ed based on a ious ac o s, such as biode-
g adabili y, non-New onian beha io , ecological compa ibili y, and
ma ke accessibili y. The polyme solu ion was acqui ed by dissol ing a
speci ied quan i y o xan han gum powde in pu i ied wa e unde
gen le agi a ion using a op-moun ed s i e (IKA RW14) a 250–400
pm o 3 h. E hanol (ETOH) was p epa ed by dilu ing alcohol in wa e
o he co esponding a io (1:1). Xan han/e hanol mix u e (XE) was
p epa ed by in oducing ETOH (50% / ) o xan han gum solu ion
while gen ly s i ing o p e en e hanol om e apo a ing.
The heological beha io o all solu ions p epa ed was analyzed
using a con olled heome e Haake Ma s 60 The mo Fishe (equipped
wi h cone-pla e geome y) in o de o unde s and he e ec o e hanol
on he non-New onian beha io o xan han gum. Each concen a ion o
xan han gum solu ion wi h and wi hou e hanol was examined in ip-
lica e. The shea a e was measu ed o e ime wi h he speci ied o ce.
The applied shea s ess anged om 0.01 o 100 s
-1
.
2.2.3. Ba ch so p ion and deso p ion expe imen s
All ba ch expe imen s we e ca ied ou in 50 mL polyp opylene (PP)
cen i uge ubes. A mix u e o PFAS solu ion was used du ing each
expe imen . The concen a ion o each subs ance was equal o 5 mg.L
-1
.
The PFAS concen a ion chosen ep esen s he a e age concen a ion o
PFOS and PFOA in he g oundwa e o di e en si es such as i e-
aining a eas and manu ac u ing plan s [8]. This concen a ion was
achie ed by dilu ing each PFAS s ock solu ion in a olume o Milli-Q
wa e con aining CaCl
2
a 10 mM. The concen a ion o CaCl
2
was
chosen o enhance he so p ion a e o PFAS on o he soil [66]. So p ion
ubes, each con aining 11.25 g o soil o 25 mL o PFAS solu ion (L/S =
2.22) we e p epa ed in iplica e. The ubes we e subsequen ly mixed
ho izon ally in an o bi al shake o op imize he in e ac ion be ween he
soil and he PFAS solu ion a di e en ime in e als (0.5 h, 2 h, 6 h, and
24 h) a a speed o 160 pm while main aining a empe a u e o 22 ◦C.
The suspension was pe iodically cen i uged a 10000 pm o 10 min.
Following ha , an aliquo o he supe na an was collec ed and analyzed
by Liquid ch oma og aphy- andem-mass spec ome y (LC-MS/MS).
Table 1
Physical and chemical p ope ies o he soil used in he expe imen s.
Soil Sand (%) Clay (%) O ganic ma e (%) Soil pH TOC (%) Pe meabili y k (m
2
) Po osi y (%) Po e olume PV (mL)
Sandy soil 92 5 3 6.5 1.14 93.10
−12
39 150
A. Ba ikh e al.
Jou nal o Haza dous Ma e ials 481 (2025) 136496
3
Fo he deso p ion expe imen s, he esidual we soil om so p ion
es s was u ilized. PFAS- ee solu ions consis ing o e hanol (50% / )
wi h and wi hou xan han gum a se e al concen a ions (0.5, 1 and 2 g.
L
-1
) we e in oduced o he we soil using he same L/S a io as in he
so p ion es . Subsequen ly, he suspensions we e mixed, cen i uged,
and analyzed using he same p ocedu e as ha used o so p ion.
2.2.4. Column expe imen s
A sequence o 1D column expe imen s was conduc ed o de e mine
he so p ion o he in es iga ed PFAS on o he soil and he deso p ion
a e o he lushing solu ions. The isual ep esen a ion o he expe i-
men al se up used o he 1D column expe imen is p esen ed in Fig. 1.
We used a bo osilica e glass column wi h dimensions o 4 cm inne
diame e (ID) ×30 cm (leng h). Two me allic g ids (mesh) wi h a po e
size o 150 µm we e ins alled on bo h sides o he column o hold he soil.
Pha med BPT ubes we e used o limi PFAS so p ion. The in luen o he
column was connec ed o an Isma ec Reglo ICC digi al pe is al ic pump
wi h ou channels. An Eme son di e en ial p essu e ansduce was
connec ed o bo h ends o he column o gauge he p essu e a ia ion
du ing he expe imen s. A mass balance was placed unde he injec ed
solu ion o e i y he mass o he in luen .
The columns we e illed e ically wi h soil in 2 cm laye s, and he
bounda y be ween acc e ions was delica ely mixed wi h a spa ula o
educe s a i ica ion. Once he packing was comple ed, a leak es was
conduc ed o e i y he column’s ai igh ness by in oducing 1 ba o gas
p essu e. Following his, he column unde wen a 30-minu e CO
2
lushing p ocess o enhance wa e sa u a ion, as CO
2
gas exhibi s high
solubili y in wa e . Subsequen ly, ou po e olumes (PV) o demine -
alized wa e we e injec ed e ically upwa d in o he column a a a e o
1 mL.min
-1
. The column weigh was measu ed bo h be o e and a e he
wa e sa u a ion p ocess o calcula e he PV and po osi y. A e
achie ing ull wa e sa u a ion, he pe meabili y es was conduc ed
ho izon ally and was de e mined by measu ing he p essu e d op co -
esponding wi h se e al low a es in oduced acco ding o Da cy’s law.
A non eac i e ace expe imen was conduc ed by in oducing 5 PV o
KB (5 g.L
-1
) o quan i y he dispe si i y and low condi ions o he
po ous media. Exhaus samples we e collec ed by a sample collec o in
PP ubes a a olume o 25 mL. To examine he so p ion beha io o all
PFAS s udied, 5 PV o an aqueous PFAS solu ion wi h a concen a ion o
5 mg.L
-1
was injec ed in a e ical upwa d di ec ion a a low a e o
2 mL.min
-1
o ensu e a g a i y-s able displacemen . Once he so p ion
injec ion was inished, a lush injec ion was ca ied ou by in oducing
ho izon ally 5 PV o PFAS- ee solu ion. E luen b eak h ough cu es
o ace and PFAS we e g aphed as he a io o he ela i e concen-
a ion (C
0
) o he ini ial concen a ion (C) as a unc ion o he injec ed
PV.
2.3. Analysis
2.3.1. Sample analysis
Wa e samples (20 mL) we e collec ed in 50 mL PP ubes as a blank
con ol (con aining 20 mL o HPLC wa e ). A e any dilu ion wi h
wa e , he samples we e mixed wi h 50% o me hanol, excep o he
expe imen wi h xan han gum o which a maximum o 30% o me h-
anol can be used o a oid xan han gum p ecipi a ion. 0.44 mL olume o
he p e ious p epa a ion is ans e ed o a PP ial/cap and spiked wi h
acid ace ic (5%) and 50
μ
L o he in e nal s anda d solu ion (2
μ
g.L
-1
in
me hanol) and o exed, esul ing in a su oga e concen a ion o
200 ng.L
-1
and 0.1% acid ace ic in he dilu ed solu ion. Samples we e
analyzed by LC-MS/MS. To a oid c oss-con amina ion, me hanolic
blanks a e injec ed be ween high-concen a ion samples and wa e
samples a e analyzed o check ha he e is no con amina ion.
PFAS analyses we e ca ied ou using a Wa e s TQXS sys em coupled
o a Wa e s UHPLC sys em equipped wi h an Acqui y BEH C18 Column
(1.7 µm pa icle size, 100 ×2.1 mm, Wa e s) hea ed a 35 ◦C and a
delay C18 column (isola o column 50 ×2.1 mm, Wa e s) o a oid PFAS
con amina ion om he ch oma og aphic sys em. The injec ion olume
was 10
μ
L and he mobile phase was a mix u e o 2 mM Ammonium
Ace a e in H
2
O (A) and 2 mM Ammonium Ace a e in MEOH (B) a a
0.3 mL.min
-1
low. The g adien elu ion s a ed wi h 95% A and g ad-
ually changed up o 95% B wi hin 6.5 min. This a io was kep o
0.5 min and hen e e sed in o he ini ial condi ions o 3 min. MS
analysis was pe o med wi h he TQXS mass spec ome e , which
ope a ed in nega i e Elec osp ay Ioniza ion mode (ESI). The sou ce
condi ions we e se as he ollowing: desol a ion empe a u e 500 ◦C,
desol a ion gas low 1100 L.h
-1
, cone gas low 150 L.h
-1
, capilla y
ol age −1000 V. The ch oma og ams we e p ocessed wi h he Ta ge -
Lynx so wa e. PFAS quan i ica ion was based on 9-poin calib a ion
cu es (10 o 5000 ng.L
-1
) ha ing R
2
>0.99 o all compounds. In hese
condi ions, LQ was es ima ed o be 20 ng.L
-1
(wi hou conside a ion o
sample dilu ion) ega dless o he na u e o he samples. Mass spec al
pa ame e s used o PFAS analysis a e p esen ed in Table S1 in supple-
men a y ma e ials.
2.3.2. Da a analysis
2.3.2.1. T anspo low in po ous media and modeling. The one-
dimensional luid low in po ous media is o en desc ibed using Da cy
eloci y, U (m.s
-1
), which can be exp essed as ollows [67]:
U=Q
S=KΔP
μ
L(1)
whe e Q (m
3
.s
-1
) is he low a e, S (m
2
) is he su ace a ea o he po ous
media, K (m
2
) is he pe meabili y, ΔP (Pa) is he p essu e d op, L (m) is
Fig. 1. Schema ic ep esen a ion o he expe imen al se ups employed in his s udy.
A. Ba ikh e al.
Jou nal o Haza dous Ma e ials 481 (2025) 136496
4
he leng h o he po ous media, and
μ
(Pa.s) is he dynamic iscosi y.
Fo New onian luid, he dynamic iscosi y is he a io o he shea
s ess
τ
(Pa) and he shea a e γ (s
-1
):
μ
=
τ
γ(2)
Rega ding he modeling o he 1D column anspo expe imen s, he
con ec ion/dispe sion equa ion is used o ob ain he longi udinal dis-
pe si i y, and he same equa ion is hen used in combina ion wi h he
Langmui so p ion iso he m o ep oduce he PFAS anspo in he
sa u a ed column, ei he o adso p ion o deso p ion. The con ec ion/
dispe sion/so p ion equa ion eads [68]:
ϕ
∂
C
∂
+
ρ∂
Cs
∂
+u
∂
C
∂
x−D∗
∂
2C
∂
x2=0 (3)
whe e C is he PFAS concen a ion (mol.m
-3
),
ρ
is he d y bulk densi y o
he po ous medium (kg.m
-3
),
Cs is he concen a ion adso bed o he solid (mol.kg
-1
), u =U/ϕ is
he linea a e age eloci y (m.s
-1
),
D∗is he hyd odynamic dispe sion coe icien (m
2
.s
-1
). The Langmui
so p ion iso he m implies ha [69]:
Cs=Cs,max KLC
1+KLC(4)
whe e KL is he Langmui cons an (m
3
.mol
-1
) and Cs,max is he so p ion
maximum (mol.kg
-1
).
The con ec ion/dispe sion equa ion is hen sol ed in COMSOL
Mul iphysics®, a ini e elemen me hod-based so wa e. The geome y is
a 1D geome y o leng h 30 cm. The ini ial PFAS concen a ion is ze o,
and he inle bounda y condi ion is a cons an concen a ion alue based
on he known concen a ion in he injec ed solu ion (Di ichle condi-
ion). The ou le bounda y condi ion is a lux-bounda y condi ion
in ol ing each ime s ep (Cauchy condi ion). Fo deso p ion, he same
app oach is used, bu he inle concen a ion is ze o, and he ini ial
concen a ion is he same as a he end o he adso p ion es s. The
alues o KL and Cs,max a e ound by sol ing a leas -squa e minimiza ion
p oblem, o which he ini ial alues a e based on he li e a u e, and he
accep able alue ange du ing op imiza ion is mo e o less 100 imes he
ini ial alue. The hyd odynamic dispe sion coe icien was i ed based
on he non- eac i e ace expe imen .
2.3.2.2. So p ion and deso p ion ba ch pa ame e s. The concen a ion o
he PFAS compound so bed in he soil a e he so p ion ba ch expe i-
men C
s
(mg.g
-1
), is de e mined acco ding o Eq. 5 [70]:
Cs=(Cin −Cw).V
msoil
(5)
whe e C
in
(mg.L
-1
) ep esen s he ini ial PFAS concen a ion in he s ock
solu ion, C
w
(mg.L
-1
) ep esen s he PFAS concen a ion ob ained om
liquid ch oma og aphy analysis, V (mL) is he olume o PFAS solu ion
used in ba ch so p ion, and m
soil
(g) is he weigh o d y soil.
Fu he mo e, he PFAS so p ion pe cen age, S (%), was compu ed
using he subsequen o mula:
S(%) = Cs.msoil
Cin.V100 (6)
The deso p ion pe cen age D (%) was calcula ed by di iding he
amoun o PFAS emo ed by he one p esen in he soil used o he
deso p ion ba ch expe imen , acco ding o he ollowing equa ion:
D(%) = Cw,des .V
Cin,des .msoil
100 (7)
whe e, C
w, des
(mg.L
-1
) is he concen a ion o PFAS a e deso p ion
analysis, and V (mL) and m
soil
(g), a e he olume o emo al solu ion
and he mass o d y soil used in deso p ion es s. C
in, des
(mg.g
-1
) ep-
esen s he ini ial concen a ion o PFAS in he esidual soil om so p-
ion es s. To be e quan i y his concen a ion, he amoun o PFAS in
esidual wa e om he so p ion es was aken in o accoun ollowing
Eq. 8:
Cin,des =Cs+Cw.V es
msoil
(8)
2.3.2.3. 1D column so p ion and deso p ion pa ame e s. The b eak-
h ough cu e explains he loading beha io o PFAS o be so bed and
deso bed om he soil. I is he plo o he ela i e concen a ion (C
0
) o
he ini ial concen a ion (C) as a unc ion o he o al po e olume
injec ed (PV) [71]. The mass o PFAS so bed (m
PFA
s
so bed
; mg) on he soil
is a unc ion o he o al low a e (Q; mL.min
-1
) injec ed and he a ea
unde so p ion b eak h ough cu e (A) as exp essed in he ollowing
equa ion:
mPFAS so bed =QA
1000 (9)
A=∫ = o al
=0
Ce luen d (10)
whe e C
e luen
(mg.L
-1
) is he concen a ion o PFAS p oduced du ing he
so p ion p ocess.
The mass o o al PFAS injec ed is calcula ed ia he equa ion:
mTo al PFAS injec ed =QC0 o al
1000 (11)
whe e C
0
(mg.L
-1
) is he inle concen a ion o PFAS, and
o al
(min) is
he o al ime o PFAS injec ion.
The so p ion yield (%) o PFAS in he soil is exp essed as he
ollowing equa ion:
PFAS so p ion(%) = mPFAS so bed
mTo al PFAS injec ed
100 (12)
The pe cen PFAS eco e y is calcula ed acco ding o he equa ion
below:
PFAS emo ed(%) = mPFAS e luen a e deso p ion
mPFAS so bed
100 (13)
3. Resul s and discussion
3.1. Rheological beha io o xan han-e hanol mix u e
Xan han gum heological beha io a di e en concen a ions wi h
and wi hou e hanol was measu ed a ambien empe a u e. The s eady
shea iscosi y as a unc ion o di e en shea a es o he h ee con-
cen a ions o xan han gum wi h and wi hou e hanol 50% ( / ) is
p esen ed in Fig. 2. Expe imen al iscosi y da a was i ed by he Ca -
eau model (Eq. 14) [72].
μ
−
μ
in
μ
0−
μ
in
=[1+ (λγ)2]n−1
2(14)
whe e, ze o and in ini y shea a es iscosi ies (Pa.s) a e deno ed as
µ
0
and µ
in
, λ (s) is he elaxa ion ime, γ (s
-1
) is he shea a e, and n (-) is
he dimensionless powe index. Ca eau model i ing pa ame e s a e
p esen ed in Table S2 in supplemen a y ma e ials. The i ing exceeds
98% con idence o xan han gum Fig. 2 models due o i s abili y o
accu a ely ep esen heological beha io a e y low shea a es [73,48,
74].
Acco ding o he esul s ep esen ed in Fig. 2a, he s eady shea
iscosi y o xan han solu ions inc eases while inc easing he concen-
a ion. Expe imen al da a indica es ha doubling he concen a ion
esul s in a no iceable dec ease in he New onian egion wi hin he low
A. Ba ikh e al.
Jou nal o Haza dous Ma e ials 481 (2025) 136496
5
shea a es ange (0.01–0.026 1/s). Addi ionally, a obus beha io o
shea hinning was obse ed wi hin he ange o 0.05 o 100 (1/s),
ega dless o he polyme concen a ion being es ed. This signi ican
non-New onian beha io was caused by he al e a ion o he a ange-
men o he polyme chains in agmen ed o de a high shea a es e-
gion [73].
Fig. 2b, illus a es he in luence o e hanol (50% / ) on he heo-
logical beha io o xan han gum o di e en polyme concen a ions.
Th ee se s o measu emen s we e conduc ed o e e y concen a ion o
xan han gum in he p esence o e hanol (50% / ) by ex ac ing samples
om he uppe , middle, and lowe sec ions o he mix u e. E o ba s a e
compu ed by inding he mean (a e age) o he da a poin s and he
s anda d de ia ion. The uppe end o he e o ba is posi ioned a he
mean plus he s anda d de ia ion, while he lowe end is posi ioned a
he mean minus he s anda d de ia ion. Fo all concen a ions o xan-
han, a homogenei y was obse ed in he mix u e wi h e hanol (50% /
), which is consis en wi h he heological measu emen s as well as
obse a ions epo ed by Flahi e e al. [75].
As depic ed in Fig. 2, he consis en shea hinning beha io was
main ained o all concen a ions o xan han gum in he p esence o
e hanol (50% / ). Fu he mo e, he addi ion o e hanol has no led o
subs an ial changes in he heological cha ac e is ics o xan han gum.
Gi en ha he addi ion o e hanol did no a ec he non-New onian
p ope ies o he polyme , i ollows ha all o hese mix u es examined
in heology will subsequen ly be examined in ba ch scale o de e mine
whe he he polyme as well as i s concen a ion, impac he PFAS e-
co e y by e hanol.
3.2. So p ion ba ch expe imen s
The pe cen age o PFOS, PFOA, PFHxS, and PFBS so p ion om
aqueous solu ion on o soil was examined in his s udy. Fig. 3 shows he
so p ion pe cen age o a ious PFAS a di e en con ac ime in e als
(0–0.5 h, 0.5–2 h, 2–6 h, and 6–24 h). The samples we e aken exac ly a
he speci ied ime poin s (0.5 h, 2 h, 6 h, and 24 h). Howe e , o cla i y
in p esen ing he so p ion beha io o e ime, he esul s a e shown as
cumula i e in e als (0–0.5 h, 0.5–2 h, 2–6 h, and 6–24 h). This
app oach allows o a clea e depic ion o he so p ion p ocess o e hese
speci ic pe iods, highligh ing any inc emen al changes in so p ion
wi hin each in e al.
One can see ha each PFAS componen exhibi ed i s highes so p ion
pe cen age wi hin he ini ial hal hou (48.6% ±1.5% o PFOS, 10.8%
±1.6% o PFOA, 11.5% ±2% o PFHxS, and 2.8% ±0.8% o PFBS).
I can be seen ha he so p ion equilib ium o PFHxS and PFBS was 2 h
as e han PFOS and PFOA which equi ed 24 h. Though he ini ial
aqueous concen a ion o PFAS s udied was he same (5 mg.L
-1
), he
equilib ium concen a ion o PFOS was he lowes one in compa ison o
o he PFAS s udied. Fo ins ance, he concen a ion o PFOS so bed o
soil was (4.83 ±0.4 mg.kg
-1
) much highe han PFOA (1.11 ±0.1 mg.
kg
-1
), PFHxS (0.91 ±0.2 mg.kg
-1
) and PFBS (0.37 ±0.1 mg.kg
-1
) sug-
ges ing he s ong a ini y o PFOS o be so bed on o soil han he o he
PFAS. These indings align wi h p e ious s udies. Li e al. [76] es ed he
so p ion o PFOS, PFOA, and PFBS on di e en soils wi h TOC anging
om 0.25 o 3.28%. They epo ed ha he highes concen a ion o
PFAS so bed was 2.25 mg.kg
-1
o PFOS, 1 mg.kg
-1
o PFOA and
0.45 mg.kg
-1
o PFBS. Fu he mo e, Chen e al. [66] s udied he so p-
ion o PFOA and PFOS on o a ious soil composi ions and ound ha
he equilib ium so p ion ime o PFAS was eached wi hin 10–12 h. The
dis ibu ion coe icien (K
d
) alues o PFAS a ied wi h he leng h o he
pe luo ina ed ca bon chain [77]. Speci ically, he K
d
o PFOS, a
2.85 L.kg
-1
was app oxima ely 10 imes g ea e han he K
d
alues o
PFOA and PFHxS (0.32 and 0.27 L.kg
-1
, espec i ely), and o e 70 imes
highe han ha o PFBS (0.05 L.kg
-1
). These esul s align wi h p e ious
esea ch. Hube e al. [78] epo ed K
d
alues o 2.51 and 0.44 L.kg
-1
o PFOS and PFOA, espec i ely, in soils wi h g ain size o 0.5 o 2 mm
and o ganic con en o almos 1.5%. Simila ly, Oli e e al. [79] ound
compa able alues o PFOA, PFOS, and PFHxS in soils wi h o ganic
con en anging om 0.9 o 1.3%. The esul s addi ionally demons a e
ha he so p ion pe cen age o he PFAS examined on o he soil ollowed
he o de o (PFOS >PFOA >PFHxS >PFBS). The o de o so p ion
pe cen age o he PFAS s udied was consis en wi h he solubili y and
he oc anol-wa e coe icien (log K
ow
) o each compound (Table S3).
The e o e, as PFOS is he mos hyd ophobic and leas soluble in wa e ,
he pe cen age o so p ion eached 56%. Howe e , his pe cen age e-
duces by o e ou imes o PFOA (13.8%) and PFHxS (12%) and by
mo e han en imes o PFBS (3.3%). The signi ican so p ion o PFOS
compa ed o PFOA is due o he p esence o addi ional ca bon in he
hyd ophobic chain. E en hough he PFHxS pe luo ina ed chain is
sho e han PFOA, he log K
ow
alues a e e y compa able, (4.34 o
4.59) leading o a sligh a ia ion in so p ion pe cen age. PFBS showed
he lowes so p ion pe cen age because o i s sho e pe luo ina ed
chain, which explains i s lesse hyd ophobic na u e on he one hand and
i s g ea e wa e solubili y on he o he hand. Gi en he TOC con en
(1.14%), he main mechanism o PFAS so p ion on o soil was he
Fig. 2. Bulk iscosi y o xan han gum solu ion a di e en concen a ions (0.5,
1, and 2 g.L
-1
) wi hou e hanol (a) and wi h e hanol (b) as a unc ion o shea
a e. No es: CM =Ca eau Model; XG =Xan han Gum. Each da a poin and
e o ba a e means and s anda d de ia ions o iplica es, espec i ely.
Fig. 3. Va ia ion o so p ion pe cen age e sus ime in e al o di e en PFAS
on he es ed soil. The L/S a io was 2.22 and he ini ial concen a ion o each
PFAS was 5 mg.L
-1
. Each da a poin and e o ba s a e means and s anda d
de ia ions o iplica es, espec i ely.
A. Ba ikh e al.
Jou nal o Haza dous Ma e ials 481 (2025) 136496
6
in e ac ion be ween he hyd ophobic ail and he soil o ganic ma e , as
has been demons a ed in se e al s udies [80,66,81,70,82]. In e ms o
head g oups, sul ona es exhibi ed no ably g ea e so p ion a ini y
compa ed o hei ca boxyla e analogs wi h equi alen -CF
2
- chain
leng h which is also consis en wi h p e ious s udies [76,83].
Se e al o he ac o s can in luence he so p ion o PFAS such as he
pH, he clay mine al (kaolini e), and he ionic s eng hs o ino ganic
sal s such as CaCl
2
. The e ec o ca ions will be discussed in de ail in he
ollowing sec ion. The measu ed pH o he soil was 6.5, indica ing
sligh ly acidic condi ions. In his pH ange, less nega i ely cha ged soil
enhances he a ac ion be ween PFAS and soil pa icles leading o an
inc ease in PFAS so p ion [77,83]. As no ed by Vie ke e al. [84], he
pKa alues o he 4 PFAS es ed in his s udy a e ela i ely low ( ypi-
cally <3.5), which indica es ha hese compounds p edominan ly
exis ed in hei dep o ona ed s a e [85]. Acco ding o Logana han and
Wilson [86], long-chain pe luo o sul onic acids (PFSA) and pe luo o
ca boxylic acids (PFCA) ha e an a ini y o be s ongly so bed on he
hyd oxyla ed kaolini e su ace, as a esul o he di ec coo dina ion
occu ing be ween he hyd oxyl g oups on he su ace and he pe -
luo oalkyl acids (PFAA).
3.3. E ec o ca ions on PFAS so p ion/deso p ion beha io
Gi en i s complex chemical s uc u e, PFAS may in e ac wi h soils
h ough a a ie y o so p ion mechanisms in he p esence o ca ions such
as Ca
2+
. Elec os a ic in e ac ions wi h mine al and o ganic adso ben
su aces, along wi h hyd ophobic e ec s wi h o ganic ca bon (OC) in
soil a e p ima ily esponsible o hese immobiliza ion mechanisms [59,
76]. Se e al mechanisms con ibu e o he enhancemen o PFAS so p-
ion on soil in he p esence o CaCl
2
as p esen ed by Cai e al. [85] such
as (1) sal ing-ou e ec , (2) ca ion b idging, (3) educ ion o epulsi e
o ces among PFAS molecules as well as be ween PFAS and nega i ely
cha ged su aces and (4) enhancing he hyd ophobic in e ac ion o PFAS
ail wi h o ganic ma e [83].
The sal ing-ou e ec (SEO) [87] and he Ca-b idging e ec [88] may
con ibu e o bo h he educ ion in PFAS deso p ion and he enhance-
men o PFAS so p ion in he p esence o CaCl
2
solu ion. O ganic ma e
in he soil may become glassie due o he ac i i y o Ca
2+
ions in he
solu ion, which may se e as c oss-linking agen s [89]. Thus, while
concu en ly dec easing he deso p ion o PFAS, his p ocess inc eases
i e e sibili y. Se e al s udies demons a ed ha he p esence o ca ions
such as Ca
2+
aises he so p ion a e o PFAS on o soil by he ca ion
b idge mechanism [85,77,88,90]. The so p ion beha io o di e en
o ganic pollu an s can be a ec ed by he p esence o sal in wa e due o
he modi ica ion o he elec ical s a e o he so ben su ace and he
educ ion o he ac i i y o wa e [89]. Sal ions, on he o he hand, may
elec os a ically in e ac wi h wa e molecules, leading o a dec ease in
he ac i i y o wa e and consequen ly o lowe solubili y o o ganic
pollu an s ia he SEO mechanism [91,92]. I has been epo ed ha
PFOS solubili y dec eases om 570 mg.L
-1
in pu e wa e o 25 mg.L
-1
in
il e ed seawa e [93] and o 307 mg.L
-1
in 0.005 mol.L
-1
CaCl
2
solu ion
[88].
Elec os a ic o ces and hyd ophobic in e ac ions u he in luence
PFAS beha io a he soil in e ace [94]. E en in he absence o poly-
alen ca ions, hyd ophobic o ces signi ican ly con ibu e o PFAS
so p ion, pa icula ly o longe -chain PFAS and in soils iche in OC
[95]. Howe e , he p esence o ca ions like Ca
2+
enhances so p ion by
educing elec os a ic epulsion among PFAS molecules and be ween
PFAS and soil su aces, allowing o be e o ien a ion and packing o
PFAS molecules [59,96]. This e ec is pa icula ly p onounced o
long-chain PFAS, which exhibi s onge hyd ophobic in e ac ions and
g ea e so p ion in he p esence o Ca
2+
. In con as , sho -chain PFAS
expe ience a smalle inc ease in so p ion wi h ising ionic s eng h
because he supp ession o epulsi e o ces by Ca
2+
is insu icien o
signi ican ly enhance hei hyd ophobici y and, he e o e, hei so p-
ion. Fo ins ance, Cai e al. [85] ound ha sho -chain PFSA and PFCA
exhibi ed e y low so p ion pe cen ages e en in he p esence o high
ionic s eng h. Fu he mo e, Chen e al. [66] epo ed ha he addi ion
o 10 mM CaCl
2
o a PFAS solu ion educes he nega i e cha ge o he
soil, he eby enhancing he so p ion o PFOS and PFOA.
3.4. Deso p ion ba ch expe imen s
To examine he e ec i eness o a ious eco e y solu ions, a ba ch-
scale expe imen was conduc ed using wa e wi h and wi hou CaCl
2
,
and e hanol (50% / ) wi h and wi hou XG solu ions a a ying con-
cen a ions. Fig. 4 depic s he eco e y pe cen age o PFOA, PFOS,
PFHxS, and PFBS a di e en ime in e als. Fo each eco e y solu ion,
he deso p ion kine ics a e as du ing he i s 30 min, hen emain e y
slow un il equilib ium a e 24 h o agi a ion. PFAS deso p ion om soil
was a esul o a compe i ion be ween he anionic head and he hyd o-
phobic ail. The p esence o o ganic ma e has a majo in luence on he
mobili y o PFAS om soil o he aqueous phase and subsequen ly de-
c eases PFAS deso p ion [97]. Following a 24-hou o agi a ion in wa e ,
he pe cen age o PFAS deso bed was 44.5 ±2%, 79 ±6%, 82 ±7%,
and 100 ±11% o PFOS, PFOA, PFHxS and PFBS, espec i ely. Bo h
PFOA and PFOS ha e 8 ca bons, bu he eigh h ca bon in PFOA’s
unc ional g oup sho ens he chain, making i less hyd ophobic and
mo e mobile. These ea u es esul in highe PFOA mobiliza ion han
PFOS. Al hough PFOA is wo imes mo e soluble han PFHxS, hei
simila log K
ow
and K
d
alues as discussed in p e ious sec ions, lead o
compa able deso p ion pe cen ages. The lowes so p ion o PFBS and i s
highes solubili y explained he deso p ion pe cen age ob ained.
As illus a ed in Fig. 4, mixing wa e wi h e hanol a he same a io
(1:1) led o a majo enhancemen in PFAS eco e y especially o PFOS,
as i s deso p ion pe cen age inc eased wo imes o each 95.5 ±2.5%.
The e ec o e hanol in enhancing o he PFAS deso p ion was mino , as
PFOA and PFHxS emo als inc eased by 15% o each 97.5 ±4.5%, and
97.9 ±1.5%. This shows ha he solubili y o PFAS in e hanol (50% /
) is highe han ha o pu e wa e . These esul s we e compa able o
he li e a u e. Deng e al. [43], used e hanol (50% / ) o he egen-
e a ion o ac i a ed ca bon con amina ed by PFOS and disco e ed ha
a e 24 h, e hanol was capable o emo ing o e 98% o PFOS. Simila
esul s we e also epo ed by Wang e al. [98], as (50% / ) e hanol was
able o egene a e o e 85% o PFOS om GAC and anion-exchange
esins.
Adding h ee di e en concen a ions o xan han gum in o (50% /
) e hanol esul ed in an addi ional 3% inc ease in eco e y, achie ing
99 ±2% e iciency o PFOS, PFOA, and PFHxS. The sligh dec ease in
he eco e y pe cen age o PFBS 4 o 8% is a ibu ed o minimal
so p ion on he soil. These indings sugges ha he concen a ion o
xan han gum has negligible impac on he e ec i eness o 50% e hanol
in PFAS deso p ion, as he eco e y pe cen age emains consis en
ac oss all samples.
In addi ion, we es ed he e ec o CaCl
2
on he eco e y o PFAS and
ound ha inc easing he ionic s eng h o he aqueous solu ion signi -
ican ly a ec s he deso p ion o he sho es PFAS in his s udy (C4). This
esul ed in a educ ion in PFBS eco e y o 35%, 15% o PFOA and
PFHxS, and 4% o PFOS. The obse ed educ ion in PFAS deso p ion
pe cen ages wi h changes in ionic s eng h can be a ibu ed o he
dis inc mechanisms in luencing PFAS so p ion, as discussed in Sec ion
3.3. The pH o he soil emained ela i ely unchanged a e he injec ion
o a ious lushing solu ions, sugges ing ha he obse ed esul s we e
no in luenced by luc ua ions in pH.
The mix u e in es iga ed o PFAS deso p ion in he 1D column
expe imen is he mix u e o xan han and e hanol (XE), whe e, xan han
(XG) is p esen ed a i s lowes concen a ion o 0.05% w/w. This choice
was based on p e ious e idence indica ing ha e hanol did no a ec he
shea hinning beha io o he xan han gum solu ion. Addi ionally, i
has been ound ha he addi ion o di e en concen a ions o XG o
e hanol solu ions enhanced he eco e y pe cen age o he PFAS.
A. Ba ikh e al.
Jou nal o Haza dous Ma e ials 481 (2025) 136496
7
3.5. 1D column so p ion and deso p ion expe imen s
3.5.1. So p ion expe imen s
The so p ion and deso p ion expe imen s o he mix u e o PFAS a a
concen a ion o 5 mg.L
-1
we e conduc ed a a 1D decime ic scale. To
highligh he e ec o adding e hanol (50% / ) o wa e and subse-
quen ly he polyme on he PFAS eco e y, each single PFAS b eak-
h ough cu e (BTC) is p esen ed in Fig. 5 alone as a unc ion o po e
olume injec ed (PV). The ansi ion om PFAS injec ion o PFAS- ee
solu ion lushing is ep esen ed by he black do ed line o he ou
g aphs. The ails o he BTCs o indi idual PFAS o e lapped well o
e e y column, which demons a ed he accu a e epea abili y o he
expe imen s (s anda d de ia ion lowe han 4%). The pe cen age o
PFAS so p ion is p esen ed in Fig. S1 in supplemen a y ma e ials.
Following he expe imen al ou comes, PFBS was he mos apidly elu ed
compound a 0.6 PV. I s as b eak h ough con i med ha his com-
pound was he las so bed. PFHxS and PFOA had a simul aneous
b eak h ough a 0.75 PV. The e a da ion o achie e he comple e
b eak h ough a 3.3 PV o PFOA compa ed o 2.8 PV o PFHxS in-
dica es highe so p ion in he po ous media. PFOS was he mos so bed
compound, in e ms o BTC ail, ime, and s abiliza ion as i s elu ion was
a 2.5 PV, and showed no comple e b eak h ough a e 5.2 PV o in-
jec ion (C/C
0
=0.4). These indings co ela ed wi h he physio-chemical
p ope ies o each PFAS and we e consis en wi h ba ch so p ion es s.
PFBS’s high wa e solubili y and low hyd ophobici y explained i s lowe
so p ion in soil (26 ±3%). The simul aneous b eak h ough o PFOA and
PFHxS was due o he highe wa e solubili y o PFOA, which acili a ed
i s mobiliza ion. Al hough i emains mo e hyd ophobic han PFHxS (C8
o C6), hei so p ion pe cen ages we e compa able a equilib ium (40
±2% o 36 ±4%) as demons a ed in ba ch so p ion (Sec ion 3.2).
PFOS’s long ca bon chain and lowe wa e solubili y enable i o be
s ongly e ained by he po ous medium, esul ing in a slowe b eak-
h ough and a s ong so p ion pe cen age (89 ±3%). The high so p ion
is a ibu ed o he a ia ion in PFAS chain leng hs, which esul s in
di e ing le els o hyd ophobici y [83]. O he ac o s ha may in luence
he so p ion beha io o each PFAS include he unc ional g oup o he
head, wi h he sul ona e head g oup leading o s onge so p ion
compa ed o he ca boxylic g oup [99], and he p esence o Ca
2
⁺ in he
solu ion, as p e iously discussed. The b eak h ough cu e indica es how
PFBS beha es in en i onmen al ma ices, as i s sho e chain leng h (C4)
gi es i a pe cola ing capaci y ha makes i mo e mobile in g oundwa e
compa ed o longe -chain PFAS.
3.5.2. Deso p ion expe imen s
Va ious lushing solu ions, comp ising e hanol wi h and wi hou
xan han gum, pu e wa e , and wa e wi h CaCl
2
, unde wen examina-
ion o assess hei e ec i eness in emo ing PFAS a e so p ion ex-
pe imen s. As shown in Fig. 5, PFAS delayed o app oxima ely 1PV has
a esponse o he deso p ion solu ions used. A simila end o b eak-
h ough beha io o PFAS was no iced o all solu ions excep sal y
wa e .
The a e o dec ease in PFAS concen a ion du ing he injec ion o
wa e wi h CaCl
2
was in luenced by he hyd ophobici y o each com-
pound. Fo ins ance, PFBS exhibi ed a mo e apid dec ease in concen-
a ions. The ela i e concen a ion o PFOS equi ed he en i e injec ion
pe iod o decline o 20% o i s ini ial so p ion le el. The ime equi ed
o PFOA o each C/C
0
nea ly ze o was highe han PFHxS o mo e han
1PV. Zhang e al. [100] demons a ed ha he p esence o di alen
ca ions such as Ca
2+
signi ican ly enhances he so p ion and e a da ion
o PFOA in soil compa ed o mono alen ca ions like Na
+
. This sugges s
ha he p esence o CaCl
2
in wa e educes he solubili y o PFAS mol-
ecules h ough he sal ing-ou e ec , he eby enhancing hei so p ion
on o soil pa icles due o he ca ion b idging e ec and educ ion in
epulsi e o ces. As discussed in Sec ion 3.3, his p ocess in luences he
anspo o PFAS molecules in he po ous medium leading o mo e
e ec i e e en ion and educed mobili y.
Howe e , an inc ease in concen a ions (peak) o long-chain PFAS
a e hei b eak h ough was no iced in wa e and e hanol wi h and
wi hou XG. The in ensi y and he a ea o he peak ob ained a e
lushing wi h wa e became lowe and igh e while he ca bon chain
Fig. 4. Reco e y pe cen age o (a) PFOS, (b) PFOA, (c) PFHxS, and (d) PFBS a di e en ime in e als and eco e y solu ions. No es: ETOH =E hanol; XG
=Xan han Gum; XE =xan han-e hanol mix u e. Each da a poin and e o ba s a e means and s anda d de ia ions o iplica es, espec i ely.
A. Ba ikh e al.
Jou nal o Haza dous Ma e ials 481 (2025) 136496
8
and hyd ophobici y o PFAS dec eased (Table S4 in Supplemen a y
ma e ials). This issue is add essed in sec ion 3.5.3. Fu he mo e, he
e luen concen a ion o PFOS did no each ze o a e comple e wa e
injec ion, which was no he case o o he PFAS e en i some o hem
delayed mo e han o he s o each his alue. The elu ion ime o PFAS
was as e in e hanol (50% / ) wi h and wi hou XG han in wa e . The
e ec o ime elu ion was mo e no iceable o longe -chain PFAS (C ≥6).
PFOS (C =8) elu ed o 0.3PV as e in e hanol solu ions han in wa e .
PFOA (C=8) and PFHxS (C=6) showed a synch onous b eak h ough in
e hanol solu ions which was as e han in wa e o 0.2PV and 0.25 PV.
This as e b eak h ough sugges ed ha adding e hanol (50% / ) o
wa e inc eases he solubili y o PFAS, and enhances solubili y o ces
e sus hyd ophobic o ces. Lauwe s e al. [101] showed ha PFAS’s
hyd ophobic ail can be sol a ed by o ganic sol en s such as e hanol,
making he hyd ophobic in e ac ion weake . When compa ing he peaks
o long-chain compounds ob ained a e lushing wi h e hanol ( ed
colo ) and e hanol-polyme mix u e (blue colo ), he concen a ions o
PFOS and PFHxS in e hanol–polyme eluen we e 20% o hose in
e hanol. In he case o PFOA, he a io was almos 40%. These esul s
indica e ha anspo o he ca boxylic unc ional g oup was wice
mo e enhanced han sul ona e g oups. This di e ence is due o he
weake elec os a ic in e ac ion be ween ca boxyla e PFAS and he
so ben , leading o a lowe so p ion a ini y o PFCA compa ed o PFSA
[102].
One o he main issues in g oundwa e emedia ion is densi y-d i en
low. O e idden low occu s when a less dense luid displaces a dense
luid, while unde idden low happens when a dense luid displaces a
less dense luid. Taylo e al. [103] in a se ies o wo-dimensional ex-
pe imen s, obse ed ha e en a mino densi y di e ence (0.008 g/mL)
be ween an injec ing e hanol-su ac an mix u e and wa e nea a
pe chlo oe hylene (PCE)-con amina ed zone can esul in
densi y-o e idden low. G ubb and Si a , [104], du ing e hanol injec-
ion in wo-dimensional uni o m sand packs, obse ed e hanol g a i y
o e ide wi h an inc easing inclina ion angle o he e hanol on as
in asion p og essed. Alamoo i e al. [105] demons a ed ha o a oid
densi y-d i en issues du ing he displacemen o dense non-aqueous
phase liquid (DNAPL) in an uncon ined aqui e , i is necessa y o
nulli y g a i y o ces by balancing he densi y o he polyme and
DNAPL. Al hough densi ying he e hanol-wa e solu ion o ma ch he
wa e densi y could cancel ou g a i y o ces, he addi ion o xan han
can inc ease iscous o ces, he eby o e coming g a i y-o e idden low
[105] To a oid densi y-o e idden low du ing he emedia ion o
PFAS-sa u a ed soil, xan han was added o an e hanol-wa e mix u e.
To unde s and he densi y-d i en low, g a i y numbe analysis can
be used [105]. The g a i y numbe is de ined as he a io o buoyancy
o ces o iscous o ces, indica ing he balance be ween hem and
de e mining he low di ec ion. I can be exp essed as [106].
NG=Δ
ρ
gk
μ
(15)
whe e Δ
ρ
is he densi y di e ence (kg.m−3), g is he g a i a ional ac-
cele a ion (m.s−2), k is he in insic pe meabili y (m2), is he eloci y
magni ude o he in ading phase (m.s
-1
),
μ
is he iscosi y o he
in ading phase (Pa.s). Alamoo i e al. [105] demons a ed ha o
coun e ac g a i y o ces du ing he emedia ion o sa u a ed soil, i is
necessa y o main ain he g a i y numbe close o ze o. In he con ex o
e hanol mix u e injec ion o PFAS mobiliza ion, g a i y numbe anal-
ysis shows ha wi hou polyme , he g a i y numbe is app oxima ely
−3.62, indica ing an o e iding low. Howe e , when xan han is added
o he mix u e, his alue inc eases o a ound −0.009, which is nea
ze o, ep esen ing an ideal condi ion o a oiding densi y-d i en low.
The PFAS eco e y pe cen ages we e calcula ed acco ding o Eq. 13.
As depic ed in Fig. 6, he eco e y o PFAS inc eased p opo ionally wi h
he addi ion o e hanol and polyme o a pu e wa e solu ion. The
p esence o 50% / e hanol in wa e solu ion inc eased he eco e y
pe cen age by almos 20% o each 94% o PFOA, 85% o PFHxS, and
84% o PFOS excep o PFBS, as discussed ea lie ega ding i s
inc eased solubili y. These esul s con i m he epo ed high eco e y o
PFOS and PFOA using e hanol o egene a e ac i a ed ca bon [43,46].
The p esence o xan han gum in e hanol (50% / ) enhanced he
Fig. 5. Column b eak h ough cu es o (a) PFOS, (b) PFOA, (c) PFHxS, and (d)
PFBS in soil. The ansi ion om PFAS injec ion o PFAS- ee solu ion lushing is
ep esen ed by he e ical black do ed line. Each da a poin and e o ba s a e
means and s anda d de ia ions o iplica es, espec i ely.
Fig. 6. To al PFAS eco e y pe cen ages a e using di e en solu ions in he
1D column.
A. Ba ikh e al.
Jou nal o Haza dous Ma e ials 481 (2025) 136496
9
[114] Weng, Z., Yu, J., Deng, Y., Cai, Y., Wang, L., 2023. Mechanical beha io and
s eng hening mechanism o ed clay solidi ied by xan han gum biopolyme .
Jou nal o Cen al Sou h Uni e si y. 1948‑1963 30.
[115] S ab, M., Kubal, M., Mülle o a, M., Raschman, R., 2009. Soil lushing by
su ac an solu ion: Pilo -scale demons a ion o comple e echnology. J Haza d
Ma e 163 (1), 410–417. h ps://doi.o g/10.1016/j.jhazma .2008.06.116.
[116] Yang, Y., Boo s, K., Zhang, D., 2012. A Sus ainable E hanol Dis illa ion Sys em.
Sus ainabili y 4, 92–105. h ps://doi.o g/10.3390/su4010092.
[117] Sel a aj, M., Bana , F., 2019. E hanol-Wa e Sepa a ion Using Memb ane
Technology. In: Bas idas-Oyanedel, J.-R., Schmid , J.E. (Eds.), Bio e ine y:
In eg a ed Sus ainable P ocesses o Biomass Con e sion o Bioma e ials,
Bio uels, and Fe ilize s. Sp inge In e na ional Publishing, pp. 211–232. h ps://
doi.o g/10.1007/978-3-030-10961-5_9.
[118] de B uyn, W.J., Cla k, C.D., Sens ad, M., Toms, N., Ha ison, A.W., 2020.
Biological deg ada ion o e hanol in Sou he n Cali o nia coas al seawa e . Ma
Chem 218, 103703. h ps://doi.o g/10.1016/j.ma chem.2019.103703.
[119] T ang, B., Li, Y., Xue, X.-S., A eia, M., Houk, K.N., Dich el, W.R., 2022. Low-
empe a u e mine aliza ion o pe luo oca boxylic acids. Science 377 (6608),
839–845. h ps://doi.o g/10.1126/science.abm8868.
[120] Abu Elella, M.H., Goda, E.S., Gab-Allah, M.A., Hong, S.E., Pandi , B., Lee, S.,
Gamal, H., Rehman, A. u , Yoon, K.R., 2021. Xan han gum-de i ed ma e ials o
applica ions in en i onmen and eco- iendly ma e ials: A e iew. J En i on
Chem Eng 9 (1), 104702. h ps://doi.o g/10.1016/j.jece.2020.104702.
[121] Chang, I., Im, J., P asidhi, A.K., Cho, G.-C., 2015. E ec s o Xan han gum
biopolyme on soil s eng hening. Cons Build Ma e 74, 65–72. h ps://doi.o g/
10.1016/j.conbuildma .2014.10.026.
[122] Mai e, J., Joube , A., Kai as, D., In e nizzi, T., Ma duel, J., Colombano, S.,
Cazaux, D., Ma ion, C., Klein, P.-Y., Dumes e, A., Fa in-Rouge, N., 2018.
Assessmen o lushing me hods o he emo al o hea y chlo ina ed compounds
DNAPL in an allu ial aqui e . Sci To al En i on 612, 1149–1158. h ps://doi.o g/
10.1016/j.sci o en .2017.08.309.
A. Ba ikh e al.
Jou nal o Haza dous Ma e ials 481 (2025) 136496
16
