Co esponding au ho : Jean Claude BIBILA MAFOUMBA
Copy igh © 2021 Au ho (s) e ain he copy igh o his a icle. This a icle is published unde he e ms o he C ea i e Commons A ibu ion Liscense 4.0.
Physicochemical and mine alogical cha ac e iza ion o B azza ille land ill soils:
Assessmen o me cu y (Hg), nickel (Ni) and zinc (Zn) ion con amina ion
Jean Claude BIBILA MAFOUMBA 1, 2, *, Ch is Ba doul ENGAMBE 1, 2, Raunel LOUBAKI 2, A in h Ca mel
KOUNAMPO-OKOUO 1, 3, Me line Lady KOUHININA BANZOUZI 1, 2 and Ma in TCHOUMOU 2, 3
1 Facul y o Applied Sciences, Denis Sassous N'guesso Uni e si y, Kin élé-Congo.
2 Labo a o y o Mine al and Applied Chemis y, Ma ien Ngouabi Uni e si y, B azza ille-Congo.
3 Plan and Li e Chemis y Uni , Facul y o Science and Technology, Ma ien Ngouabi Uni e si y, B azza ille-Congo
Wo ld Jou nal o Ad anced Resea ch and Re iews, 2025, 27(02), 1294-1305
Publica ion his o y: Recei ed on 28 June 2025; e ised on 12 Augus ; accep ed on 15 Augus 2025
A icle DOI: h ps://doi.o g/10.30574/wja .2025.27.2.2873
Abs ac
The aim o his s udy was o cha ac e ize in dep h he soils om six u ban land ill si es in B azza ille (Dia a, Glaciè e,
Kinsoundi, Moukondo, Tsiémé and Mikalou) by assessing hei physicochemical p ope ies, mine alogy and me al ion
con amina ion (Hg, Ni, Zn). Using samples aken acco ding o a igo ous me hodology, we analysed wa e con en , pH,
o ganic ma e , mine alogy ia X- ay di ac ion (XRD), and me al ion concen a ion using Induc i ely Coupled Plasma
- Op ical Emission Spec oscopy (ICP-OES). The esul s highligh signi ican a iabili y in pa ame e s be ween si es,
wi h concen a ions o Hg²⁺, Ni²⁺ and Zn²⁺ sys ema ically exceeding egula o y h esholds, unde lining he po en ial
en i onmen al and heal h impac . S a is ical analyses e eal s ong co ela ions be ween ce ain physicochemical
pa ame e s and he p esence o hea y me als, indica ing a po en ial ela ionship be ween soil composi ion and me al
con amina ion. Fu he mo e, he dis ibu ion o pa ame e s and hea y me als is p edominan ly asymme ical, excep
o o ganic ma e in he Tsiémé land ill, whe e a symme ical dis ibu ion is obse ed. These esul s con ibu e o a
be e unde s anding o he dynamics o u ban soil con amina ion, and unde line he u gen need o sus ainable and
app op ia e managemen o hese land ill si es.
Keywo ds: Cha ac e iza ion; Physicochemical p ope ies; Mine alogy (XRD); Soil con amina ion; Hea y me als;
U ban land ills
1. In oduc ion
U ban land ill si es a e a majo componen o was e managemen in many de eloping ci ies, pa icula ly B azza ille.
Thei accumula ion leads o en i onmen al and heal h isks, mainly associa ed wi h he leaching o oxic subs ances,
pa icula ly hea y me als and o he oxic elemen s, which a e esponsible o ans e ing pollu an s o g oundwa e
and in o he ood chain [1]. Soil con amina ion by hea y me als is due o an inc ease in he o al concen a ions o hese
elemen s in he soil ollowing majo an h opogenic inpu s [2].
The dumping o solid was e in he g ound, wi hou any p io ea men o p o ec ion o he subsoil a land ill si es, can
be a isk ac o o en i onmen al con amina ion by hea y me als [3,4,5,6]. In soil pollu ion by hea y me als, soil-me al
ca ion in e ac ions play a key ole in egula ing he beha iou o hese hea y me als, pa icula ly hei dis ibu ion in
he solid phase. Released pollu an s can be anspo ed by in il a ion wa e o he unde lying na u al soil and
g oundwa e . The accumula ion o hea y me als in soils is a conce n in ag icul u al p oduc ion because o hei ad e se
e ec s on c op g ow h, ood quali y and en i onmen al heal h [7].
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Among hese con aminan s, me cu y (Hg), nickel (Ni) and zinc (Zn) a e o pa icula conce n because o hei oxici y,
bioaccumula ion and pe sis ence in he en i onmen .
Me cu y, o en associa ed wi h elec onic o medical was e, poses a high isk due o i s con e sion in o me hylme cu y,
a powe ul neu o oxican . Nickel and zinc, pa ly om indus ial ac i i ies and ba e ies, can con amina e soil and
g oundwa e , a ec ing biodi e si y and human heal h [8].
The deg ee o me allic con amina ion in soils is o en assessed on he basis o he o al con en o ace me allic elemen s
de e mined in he su ace ho izon [9]. Many esea che s ha e ca ied ou esea ch in o soil con amina ion by hea y
me als om land ill si es [10,11,12]. These s udies ha e shown ha land ill si es a e among he sou ces o me al
con amina ion in soil.
The objec i e o his s udy is o cha ac e ize he soils o B azza ille's six land ill si es in e ms o hei physicochemical
and mine alogical p ope ies, and o quan i y hei le els o Hg2+, Ni2+ and Zn2+ con amina ion, in o de o p o ide da a
o in o med en i onmen al managemen .
2. Ma e ials and me hods
2.1. Loca ion and desc ip ion o he s udy a ea
Loca ed be ween la i udes 4°6' and 4°23' Sou h and longi udes 15°5' and 15°25' Eas . B azza ille is he capi al and mos
populous ci y o he Republic o Congo. I is loca ed in he sou h o he Republic o Congo, on he banks o he Ri e
Congo, on he no h bank o he Pool Malebo opposi e Kinshasa. I has a e y ex ensi e pe i-u ban a ea in bo h i s
no he n and sou h-wes e n pa s. B azza ille has a popula ion o a ound 1,838,348, co e s an a ea o o e 309 km2
and has 9 a ondissemen s. Figu e 1 shows a map o he ci y o B azza ille wi h he selec ed land ill si es.
Figu e 1 Map o B azza ille ( ed do s ep esen land ill si es)
Wo ld Jou nal o Ad anced Resea ch and Re iews, 2025, 27(02), 1294-1305
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Table 1 Geog aphical coo dina es o he land ills s udied
Con ac de ails
Kinsoundi
Glaciè e
Dia a
Moukondo
Tsiémé
Mikalou
La i ude (°)
04.28635
04.28619
04.27211
04.22756
04.22994
04.21942
Longi ude (°)
015.21398
015.26225
015.24971
015.26872
015.28378
015.26983
2.2. Sample collec ion and p ocessing
Soil samples we e collec ed om a dep h o 0-25 cm, using a s ainless-s eel auge , in acco dance wi h ISO s anda d
18400-102 [13]. Th ee sampling poin s pe si e we e selec ed acco ding o a sys ema ic plan o ep esen spa ial
a iabili y. The samples we e s o ed in clean plas ic bags and anspo ed o he labo a o y. In o de o ob ain a
composi e sample o each land ill, 2 kg o each sub-sample was mixed oge he , ai -d ied o en days, g ound using an
aga e mo a , sie ed o 2 mm and s o ed unde s able condi ions.
2.3. Physicochemical analysis
• Measu emen o wa e con en :
Wa e con en was de e mined by weigh los a e hea ing a 105°C o cons an mass (ISO 11465) [14].
• Measu emen o pH:
The pH was measu ed in he supe na an o a 1:2.5 (soil/wa e ) soil suspension using a HANNA- ype pH me e in
acco dance wi h he s anda d (AFNOR, 1953) [15].
• Measu emen o o ganic ma e
The Walkley and Black me hod was used o de e mine he o ganic ma e con en o soil samples. This me hod is based
on he oxida ion o o ganic ca bon by an excess o po assium dich oma e (K2C 2O7) in an acid medium, ollowed by an
assay o his excess using Moh 's sal [16].
2.4. Mine alogical analysis
Mine alogical analyses using X- ay di ac ion on samples o hese soils we e ca ied ou a he scien i ic and inno a ion
cen e o he Felix Houphouë -Boigny Uni e si y (Abidjan, Republic o he I o y Coas ). Powde X- ay di ac ion (XRD)
pa e ns we e eco ded a oom empe a u e on B uke 's Siemens D5005 di ac ome e o e he 2θ angula ange
om 5° o 90° wi h a scan speed o 2° pe minu e (inc emen : 0.05). The adia ion used was CuKα (λ=1.5406 Å). The
collec ion ol age and cu en a e 40 KV and 35 mA espec i ely.
2.5. De e mina ion o me al ions
The concen a ions o Hg, Ni and Zn we e de e mined by ICP-OES a e mine aliza ion o 0.5 g o he composi e soil
sample wi h 9 ml o hyd ochlo ic acid (HCl) and 3 ml o ni ic acid (HNO3) (aqua egia). This s ep was ca ied ou a a
empe a u e o 95°C o a du a ion o 75 minu es using a hea ing block. The mine alisa e ob ained was educed o 50
ml in acco dance wi h he s anda d NF ISO 11466 [7].
2.5.1. Specia ion o hea y me als
The sequen ial ex ac ion scheme was used o s udy he specia ion o hea y me als in soil samples collec ed in he
ollowing s ages:
• S age 1: exchangeable ac ion: 1 g o soil sample was dissol ed in 16 mL CaCl2 (1 M) and s i ed o 2 h a oom
empe a u e.
• S age 2: oxidizable ac ion (o ganic ac ion and sulphides): he pelle om s age 1 is dissol ed in 16 mL o he
mix u e H2O2 8.8 M + HNO3 0.02 M ( / ) (5+3) and s i ed o 5 h a oom empe a u e and o 1 h a 98°C. The
ex ac ion was ca ied ou in 10 ml o 3.5 M CH3 COONH4 and placed unde agi a ion o 1 h a oom empe a u e.
• S age 3: acid-soluble ac ion (ca bona es): he pelle om s age 2 is dissol ed in 35 ml o 1 M CH3COOH + 0.6 M
CH3COONH4 ( / ) (1+1) and s i ed o 5 h a oom empe a u e.
Wo ld Jou nal o Ad anced Resea ch and Re iews, 2025, 27(02), 1294-1305
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• S age 4: educible ac ion (Fe and Mn oxide): he pelle om s age 3 is dissol ed in 35 mL NH2OH, 0.1 M HCl +
25% ( / ) CH3COOH (1+1) and s i ed o 4 h a oom empe a u e and 1 h a 98°C. Ex ac ion is ca ied ou in
10 mL 3.5 M CH3COONH4 and s i ed o 1 h a oom empe a u e.
• S age 5: esidual ac ion: he pelle om s age 4 is calcined o 2 h a 550°C in a mu le u nace. The esidue is
solubilised in 20 mL o concen a ed HCl (12 M) and HF 40% ( / ).
Sequen ial ex ac ions we e pe o med in polye hylene cen i uge ubes. Be ween wo s ages, he suspensions we e
cen i uged o 30 min a 5,300g. Hea y me als we e measu ed in he supe na an o each phase [18].
3. Resul s and discussion
3.1. Physicochemical cha ac e is ics
3.1.1. Mois u e con en (MC)
The esul s (Table 2) show ha mois u e con en a ies om 2.7% (Glaciè e) o 38% (Mikalou), indica ing di e ences
in ex u e and wa e sa u a ion pe sampling campaign.
The highes wa e con en alues we e consis en ly eco ded du ing he hi d sampling campaign, while he lowes
alues we e eco ded du ing he i s campaign o he Kinsoundi, Dia a, Moukondo, and Tsiémé dumps, and du ing he
second campaign o he Glaciè e and Mikalou dumps. The inc ease in wa e con en du ing he hi d campaign can be
explained by he ac ha i was ca ied ou du ing he ainy season. Soils a e we e in he ainy season han in he d y
season.
The e olu ion o he land ill is guided by mic obiological ac i i y. This ac i i y depends on he land ill's wa e con en .
Was e can emain in ac o a e y long ime due o he low mois u e con en wi hin he was e mass [19]. Gene ally,
deg ada ion and gas p oduc ion a es inc ease as he wa e con en o he was e inc eases [20].
3.1.2. pH alues
The pH a ies be ween 6.7 (Mikalou) and 7.2 (Dia a), cha ac e is ic o mode a ely acidic o neu al soils (Table 2).
The a ia ion in pH eco ded in he land ill soils is shown in Figu e 3. The pH eco ded in hese soils is a ound neu al,
which could indica e ha hese soils a e no ich in ca bona e. These esul s a e in ag eemen wi h hose o he XRD,
whose di ac og am shows e y li le ca bona e a a ound 2θ=30°.
The pH alues ob ained in hese land ill soils a e simila o hose ound in he soil o he uncon olled land ill o Tangie
in Mo occo [21], bu hey do no ag ee wi h hose ound in 2015 by El Baghdadi e al [22], in soil solu ions om he
land ill o he ci y o Béni-Mellal in Mo occo, in ac , hey had eco ded basic pH alues. The a e age pH alues ob ained
o ou s udy a he a ious si es a e accep able [23].
3.1.3. Ra e o o ganic ma e (OM)
O ganic ma e anges om 0.13% (Moukondo, Kinsoundi and Dia a) o 9.9% (Kinsoundi) (Table 2). The a e age
o ganic ma e con en eco ded in he land ills is highe han he guide alue (1% o 2%) accep ed o mine alised
soils. These a e age o ganic ma e alues a e e en highe han hose eco ded in he soil o he Bè-A e o land ill in
Lomé, Togo [1]. The p esence o o ganic ma e in land ill soils can be jus i ied by he ac ha e men able ma e
accoun s o a la ge p opo ion o he physical composi ion o household was e, and he p esence o limes one in a soil
inc eases he o al o ganic ma e con en . The p esence o o ganic ma e can also be linked o he s ong
mine alisa ion o dead lea es o ca dboa d was e caused by he ac ion o speci ic enzymes [24].
Table 2 Summa y alues o measu emen s o physicochemical pa ame e s in land ill soil
Pa ame e s
TE (%) o Hu (%)
pH
M.O (%)
Compaigns
C1
C2
C3
C1
C2
C3
C1
C2
C3
Kinsoundi
12
14
18
7.14
7.01
7.17
9.9
0.13
0.15
Glacie e
9
2.7
17
7.2
7.02
7.21
0.55
1.72
1.95
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Dia a
11.8
14
18
7.1
7.2
7.58
1.55
0.13
2.47
Moukondo
5.6
14
18
6.9
6.9
7.32
0.13
5.47
4.62
Tsie me
15
16
23
6.9
6.9
6.95
3.69
7.24
5.43
Mikalou
15
14
38
6.9
6.7
8.02
2.27
8.15
0.16
Minimum
12
2.7
17
6.85
6.7
6.95
0.13
0.13
0.15
Maximum
15
16
38
7.14
7.2
8.02
9.9
8.15
5.43
A e ages
1.4±0.63
12.45±3.25
20±
3.94
7.01±
0.14
6.96±
0.11
7.37±
0.34
2.92±
3.56
3.21±
2.56
1.2±2.02
WHO
s anda ds
6.5 – 8.5
3.2. Mine alogical analysis o land ill soils
The esul s o X- ay di ac ion (XRD) analyses o he soil samples s udied, aken om he a ge ed public land ills, a e
shown in Figu e 2 below. Applying B agg's ela ion, he peaks loca ed a 2ϴ (°) = 21; 26.5; 39; 42.5; 45.5; 50; 55; 60; 68
and 80 co esponding espec i ely o he ollowing in e e icula dis ances (dhkl in Å) 3.86; 3.065; 2.27; 2.105; 1.938;
1.816; 1.66; 1.52; 1.405; 1.256 and 1.082, a e he cha ac e is ic peaks o qua e s. The ac ha he in ensi ies o hese
peaks a e he highes would e lec he abundance o qua z in hese soils. The peaks loca ed a 2ϴ = 29.5° in he
di ac og ams o he Tsiémé (PS01T XY) and Dia a (PS01D (1) XY) land ill soils, co esponding o dhkl = 2.759 Å, could
indica e he p esence o calci e (CaCO3). As he in ensi ies o hese peaks a e low, his could indica e ha calci e is no
abundan in hese land ill soils. This alue o dhkl = 2.759 Å would also p obably co espond o he (111) plane o
sphale i e (ZnS) [25,26].
Gi en ha qua z is a species cha ac e is ic o sand, he land ill soils s udied a e consequen ly sandy soils. We can
deduce ha hese soils ha e a low wa e e en ion capaci y, and may acili a e he mig a ion o pollu an s h ough he
e ical mo emen o ainwa e owa ds he wa e able.
Figu e 2 X- ay di ac ion o soil om selec ed land ills
3.3. Concen a ions o Hg2+, Ni2+ and Zn2+
Concen a ions o me cu y, nickel and zinc ions (Table 3) show signi ican a iabili y.
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3.3.1. - Me cu y ion
The esul s ob ained o de e mining me cu y le els in land ill soil a e p esen ed in able 3. These esul s indica e ha
he highes me cu y le els we e eco ded du ing he second and hi d sampling campaigns. The me cu y ion
concen a ions eco ded in he soils o he Glaciè e, Dia a, Tsiémé and Mikalou land ills a e well in excess o he s anda d
ecommended by he WHO (2mg/kg) [27]. High concen a ions o me cu y ion in soils, compa ed wi h o he elemen s,
ha e also been epo ed by many au ho s [1,28]. This indica es signi ican con amina ion by his me al in he soils o
hese land ill si es. The high me cu y ion le els could be explained by he ac ha o a long ime he land ill si es
ecei ed was e con aining me cu y.
3.3.2. - Ion Nickel
Compa ed wi h he WHO s anda d, which se s a limi alue o nickel a 35 mg/kg [27], i can be deduced ha he soil
a he Tsiémé, Dia a and Moukondo land ills is con amina ed and pollu ed by nickel. The high accumula ion o nickel in
ce ain land ills can be explained by he composi ion and na u e o household was e. The main sou ces o nickel in
household was e a e me als, ba e ies, dyes used in ex iles and glass [29].
Nickel le els in he Kinsoundi, Glaciè e and Mikalou land ills a e low compa ed wi h hose in he li e a u e [20,30].
These low le els a e hough o be due no only o he eco e y o ce ain nickel-con aining ma e ials o possible
eco e y ( ecycling, euse, e c.), bu also o he ac ha nickel is an elemen ha is held e y poo ly by he soil, and
o en mig a es o he dep hs [30].
3.3.3. - Zinc ion (Zn2+)
The a e age le els o zinc ion in land ill soils ob ained in ou s udy a e well abo e he WHO s anda d (50 mg/kg) [27].
This is in ag eemen wi h he s a emen s o Au élie e al, [31], who es ima ed ha he concen a ion o zinc ion is 5 o
127 imes highe in land ill soils han in na u al soils. The high concen a ions o zinc ion in land ill soils may be linked
o i s use, gi en i s impo ance wo ldwide. Zinc is he mos abundan elemen in soils a e i on. The p esence o zinc in
land ill soils is no homogeneous, which may be due o he he e ogeneous na u e o he was e o o non-uni o m
deg ada ion o he was e [21]. Zinc in land ill soil may o igina e om ki chen u ensil was e. High concen a ions o zinc
ion in soils, compa ed wi h o he elemen s, ha e also been epo ed by many au ho s [20,21,32,23]. Howe e , hey a e
lowe han hose ob ained in he soil om he Akouédo land ill [7].
Table 3 Summa y o hea y me al concen a ions in land ill soil (in ed: concen a ions abo e WHO s anda ds; in bold:
minimum and maximum concen a ions)
Pa ame e
s
Hg2+ (mg/kg)
Ni2+ (mg/kg)
Zn2+ (mg/kg)
Compaigns
C1
C2
C3
C1
C2
C3
C1
C2
C3
Kinsoundi
0.2
0.25
1.9
18
21
34
690
5100
440
Glacie e
2.4
2.7
3.8
57
12
15
850
540
580
Dia a
0.44
1.2
1.8
7500
4300
27
12000
2800
1700
Moukondo
0.66
1.5
0.2
5400
57
11
710
1200
850
Tsie me
0.38
1.9
2.3
70
12000
15
910
3600
1700
Mikalou
1.9
1.7
2..3
35
9
10
1000
450
380
Minimum
0.2
0.25
0.19
18
9
10
670
450
380
Maximum
2.4
2.7
3.8
7500
12000
34
12000
5100
1700
A e ages
1±0.
2
1.5±0.
5
1.5±1.
1
2180±3373
.6
2733±611.
2
16.33
± 8.81
2693.3±4560
.8
2281.67
±
1551.7
762.9±568.
9
WHO
s anda ds
[27]
1
35
50
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The esul s o he physicochemical analyses highligh mode a ely acidic o neu al soils, wi h a iable o ganic ma e ,
which may in luence me al e en ion capaci y. The qua z- ich mine alogy indica es he signi ican p esence o sand,
which is esponsible o he possible in il a ion o me al ions a dep h.
Concen a ions o Hg2+, Ni2+ and Zn2+ ions a y conside ably be ween si es, wi h Tsiémé showing excep ionally high
le els, linked o he na u e o he was e (indus ial, elec onic). The p esence o Hg2+ ions in quan i ies close o o abo e
egula o y h esholds indica es a po en ial isk o he en i onmen and human heal h, pa icula ly h ough
bioaccumula ion.
Fac o s in luencing con amina ion include was e composi ion, wa e dynamics (pe meabili y, sa u a ion) and soil
adso p ion capaci y. Leaching o me als in o g oundwa e is likely, equi ing inc eased moni o ing.
3.4. S a is ical es on he dis ibu ion o physicochemical pa ame e s and hea y me als in land ill soils
3.4.1. - Physicochemical pa ame e s
The esul s ob ained om es s on he dis ibu ion o physicochemical pa ame e s in land ill soils a e p esen ed in
igu es 3 o 5. These esul s show ha hese pa ame e s a e asymme ically dis ibu ed, excep o o ganic ma e ,
which is symme ically dis ibu ed in he Tsiémé land ill.
Figu e 3 Dis ibu ion o mois u e con en in land ill soils
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1301
Figu e 4 pH dis ibu ion in land ill soil
Figu e 5 Dis ibu ion o o ganic ma e in land ill soils
3.4.2. Concen a ion o Hg2+, Zn2+ and Ni2+ ions
Figu es 6 o 8 show ha he dispe sion o hea y me als (Hg, Zn and Ni) in land ill soils is asymme ical. This indica es
ha hese elemen s a e no s able in hese soils. This may be due o p ocesses o mig a ion, di usion and di e en ia ed
con amina ion depending on p oximi y o sou ces. In ac , i is possible ha a la ge p opo ion o he elemen s mobilised
in he was e a e dissol ed h ough he complex chemical eac ions ha ake place a he soil-was e in e ace and hen
anspo ed by in il a ion h ough he soil owa ds he g oundwa e . Howe e , gi en ha he analyses we e ca ied
ou on composi e samples, we can also suspec a dilu ion phenomenon by samples con aining a majo i y o e y low o
mode a e le els and a mino i y o e y high le els o hese elemen s, o en associa ed wi h he p oximi y o speci ic
pollu ion sou ces [34].
Wo ld Jou nal o Ad anced Resea ch and Re iews, 2025, 27(02), 1294-1305
1302
Figu e 6 Dis ibu ion o me cu y in land ill soil
Figu e 7 Zinc dis ibu ion in land ill soils
