Chemosphe e 334 (2023) 138973
A ailable online 19 May 2023
0045-6535/© 2023 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/).
Me al and semime al loadings in sedimen s and wa e om mang o e
ecosys ems: A p elimina y assessmen o an h opogenic en ichmen in S˜
ao
Tom´
e island (cen al A ica)
F. A onso
a
,
*
, C. Palma
b
,
**
, A.C. B i o
a
,
c
, P. Chainho
a
,
d
, R. de Lima
e
,
,
g
,
h
, J.A. Heumülle
a
,
F. Ribei o
a
, P.M. F´
elix
a
a
MARE – Ma ine and En i onmen al Sciences Cen e/ ARNET - Aqua ic Resea ch Ne wo k, Faculdade de Ciˆ
encias, Uni e sidade de Lisboa, Campo G ande, 1749-016
Lisboa, Po ugal
b
Ins i u o Hid og ´
a ico, Rua das T inas 49, 1249-093 Lisboa, Po ugal
c
Depa amen o de Biologia Vege al, Faculdade de Ciˆ
encias da Uni e sidade de Lisboa, Campo G ande 016, 1749-016 Lisboa, Po ugal
d
CINEA and ESTS, IPS – Ene gy and En i onmen Resea ch Cen e , Ins i u o Poli ´
ecnico de Se úbal, Es e anilha, 2910-761 Se úbal, Po ugal
e
Depa amen o de Biologia Animal, Faculdade de Ciˆ
encias da Uni e sidade de Lisboa, Campo G ande 016, 1749-016 Lisboa, Po ugal
cE3c - Cen e o Ecology, E olu ion and En i onmen al Changes, Faculdade de Ciˆ
encias da Uni e sidade de Lisboa, Campo G ande 016, 1749-016 Lisboa, Po ugal
g
CHANGE - Global Change and Sus ainabili y Ins i u e, Faculdade de Ciˆ
encias da Uni e sidade de Lisboa, Campo G ande 016, 1749-016 Lisboa, Po ugal
h
CBGG - Cen o de Biodi e sidade do Gol o da Guin´
e, S˜
ao Tom´
e, S˜
ao Tom´
e Island, Sao Tome and P incipe
HIGHLIGHTS GRAPHICAL ABSTRACT
•High concen a ions o Cu and Ni in S˜
ao
Tom´
e mang o es ha e a li hogenic
o igin.
•Con amina ion by As and C sugges a
s ong con ibu ion om human
ac i i ies.
•Smalles sys ems had highe me al con-
en in wa e , bu no sedimen
con amina ion.
•Highe wa e con amina ion ep esen s
he con inuous inpu om was e and
chemicals.
•Non-indus ialized landscapes may also
show se e e con amina ion by human
ac i i ies.
ARTICLE INFO
Handling Edi o : Giulia GUERRIERO
Keywo ds:
Geochemical index
Heal h isk
Me al con amina ion
Pollu ion sou ce
ABSTRACT
Mang o es ac as bu e a eas o ma ine sys ems, p o iding a ba ie o con amina ion om con inen al sou ces
by e aining me al pollu an s. This s udy e alua es me al and semime al con amina ion in he wa e column and
sedimen s o ou mang o es loca ed on he olcanic island o S˜
ao Tom´
e. Se e al me als had a widesp ead
dis ibu ion, wi h occasional high concen a ions, linked o po en ial sou ces o con amina ion. Howe e , he wo
smalle mang o es, loca ed in he no he n pa o he island, ended o ha e high me al concen a ions. A senic
and ch omium concen a ions we e no ably conce ning, pa icula ly i we conside his is an isola ed and non-
* Co esponding au ho .MARE – Ma ine and En i onmen al Sciences Cen e, Faculdade de Ciˆ
encias da Uni e sidade de Lisboa, Campo G ande, 1749-016 Lisboa,
Po ugal.
** Co esponding au ho .
E-mail add esses: [email p o ec ed] (F. A onso), [email p o ec ed] (C. Palma).
Con en s lis s a ailable a ScienceDi ec
Chemosphe e
jou nal homepage: www.else ie .com/loca e/chemosphe e
h ps://doi.o g/10.1016/j.chemosphe e.2023.138973
Recei ed 1 Ma ch 2023; Recei ed in e ised o m 11 May 2023; Accep ed 16 May 2023
Chemosphe e 334 (2023) 138973
2
T ansi ional aqua ic sys ems
Volcanic en ichmen
indus ialized island. This wo k highligh s he need o u he assessmen s and a be e unde s anding o p o-
cesses and implica ions o me al con amina ion in mang o es. This assumes a pa icula ele ance in a eas ha
ha e speci ic geochemical composi ions (i.e., olcanic o igin) and in de eloping coun ies, whe e people o en
ely di ec ly and hea ily on esou ces ob ained om hese ecosys ems.
1. In oduc ion
Mang o es a e ansi ional aqua ic sys ems ha connec e es ial,
i e ine and ma ine sys ems. They a e mos ly ound in de eloping
coun ies loca ed in opical a eas, and p o ide a conside able numbe
o se ices, no only locally (A onso e al., 2021) bu also on wide scales
(Bayen, 2012). One o he aluable se ices hey p o ide is p o ec ion
om me al pollu ion and o he con aminan s due o hei bu e ing
capaci y. As ecei e s o con inen al un-o , hey can in luence he
occu ence and a ailabili y o me als, due o hei abili y o ap hese
elemen s, hus, hal ing he con amina ion o adjacen ma ine ecosys-
ems (Ha bison, 1986; Scha elke e al., 2005). Mang o e sedimen is
ich in sulphide and o ganic ma e (Sil a e al., 1990; Tam and Wong,
2000), which a ou s he e en ion o me als ha o m complexes wi h
sulphides (Cla k e al., 1998). Despi e he abili y o plan oo s o
egula e me al up ake, hese complexes end o acili a e me al mobili-
za ion and bioa ailabili y o oo up ake, a ou ing accumula ion in he
plan s (Cla k e al., 1998; MacFa lane and Bu che , 2002). While sed-
imen s end o ap me als, he wa e column anspo s hem, bu
emobiliza ion can con ey me als om he sedimen back o he wa e
column in a dynamic cycle (Caccia e al., 2003; MacFa lane e al., 2007;
Zhang e al., 2017). This means ha emobiliza ion can ans o m he
sedimen in o a seconda y sou ce o me al con amina ion o he wa e
column (Bodin e al., 2013). Ne e heless, he e is a gap in knowledge o
opical eco oxicology, namely ega ding he esponse o mang o es o
he in usion o me als (Dua e e al., 2019).
Me al occu ence in ecosys ems can ha e na u al o an h opogenic
sou ces, and his dis inc ion is impo an when assessing en i onmen al
isk (Dias and Edwa ds, 2003). Apa om soil and ock wea he ing,
olcanism is also an impo an na u al sou ce o me als (Gnandi e al.,
2011). Me al pollu ion is conside ed o be one o he mos damaging
ypes o an h opogenic con amina ion, due o hei oxici y, pe sis ence,
ubiqui y, non-biodeg adabili y, and bioaccumula ion (Duman e al.,
2007; MacFa lane e al., 2007). In mang o es, an h opogenic me al
con amina ion has been linked o u baniza ion, ag icul u e un-o , in-
dus ial e luen s, leaching om domes ic ga bage dumps, boa emis-
sions, and an i- ouling chemicals om boa pain (Pe e s e al., 1997).
Coun e in ui i ely, we land con amina ion is no necessa ily mo e se-
e e in de eloped coun ies. The Nige Del a, Nige ia, showcases his
p oposi ion, as i is conside ed he mos se e ely damaged ecosys em in
he wo ld (Kada a, 2012).
Some me als a e essen ial o human heal h, while o he s can be oxic
e en a low concen a ions. When in oduced in ecosys ems on which
people a e s ongly dependen , hese elemen s can ha e se ious e ec s
on he physiological p ocesses o he human body, leading o se e e
heal h consequences (Bosch e al., 2016; Rehman e al., 2018). Apa
om inges ion, me als can also en e he human body by inhala ion o
de mal con ac (F´
elix, 2012). In child en up o six yea s old, one speci ic
ga eway o me al in ake is he hand- o-mou h beha iou ha leads
hem o inges 39–271 mg day
−1
o soil (Ljung e al., 2007; Wang e al.,
2021). Conside ing he po en ial damage ha me als can ha e on human
heal h and ecosys ems, i is essen ial o imp o e en i onmen al isk
assessmen .
The e a e se e al ools o assess me al con amina ion, and o
dis inguish li hogenic and an h opogenic sou ces. Se e al empi ical
me hodologies a e used o assess he s a us o me al pollu ion, and o
es ima e he impac o human ac i i ies on ecosys em heal h (Alzah ani
e al., 2018; Chabukdha a and Nema, 2012). O hese, he geochemical
indices, such as he con amina ion ac o and he en ichmen ac o ,
compa e ield measu emen s o s anda d alues o de e mine a
con amina ion deg ee (B ady e al., 2015; Na h e al., 2014). The
en ichmen ac o compa es me al concen a ions o hose o a e e ence
si ua ion, allowing he quan i ica ion o human-induced changes in he
ecosys em (OSPAR Commision, 2009).
The dominan ac o o de e mining he me al con en in soils is he
pa en ock, and olcanic soils end o show high concen a ions o me al
elemen s (B nický e al., 2020), namely ch omium, me cu y, and cad-
mium (Ahn and Chon, 2010; McMu y e al., 1995). This s udy aims o
de e mine me al and semime al concen a ions and po en ial an h o-
pogenic en ichmen in he sedimen and in he wa e column o man-
g o es loca ed on he olcanic island o S˜
ao Tom´
e, Gul o Guinea. Fou
mang o es wi h con as ing ea u es a e used o compa e an h opogenic
con amina ion. This in o ma ion is i al o s a iden i ying haza dous
e ec s o po en ial high concen a ions o me als on people and eco-
sys ems, and o de ine s a egies o maximize he capaci y o mang o es
o sink me allic elemen s.
2. Ma e ials and me hods
2.1. S udy a ea
The s udy was de eloped on he olcanic island o S˜
ao Tom´
e (S˜
ao
Tom´
e and P íncipe, Gul o Guinea, cen al A ica), which is p edomi-
nan ly composed o ecen basal ic la as (Caldei a and Munh´
a, 2002).
Fou mang o es (Fig. 1), displaying con as ing en i onmen al con ex s
and le els o an h opogenic p essu e, we e selec ed: Malanza, Ango-
la es, P aia das Conchas, and Diogo Nunes (Table 1). Malanza (Fig. 1)
and P aia das Conchas (Fig. 1) a e bo h in dis inc excla es o he Obˆ
o
Na u al Pa k, and bo h a e open sys ems ha ha e cons ic ions in hei
connec ions o he sea (F´
elix e al., 2017). Diogo Nunes (Fig. 1), loca ed
e y close o he ai po , is no in a p o ec ed a ea, i has he la ges
hyd og aphic basin o all s udied mang o es and i is an in e idal
mang o e ha is domina ed by sal wa e in usions du ing he high ide,
and eshwa e on low ide.
Angola es (Fig. 1) is also no in a p o ec ed a ea. I con eys wo
sepa a e con iguous hyd og aphic basins and, hus, has wo ibu a ies
d aining in o he mang o e, c ea ing wo a ms. The sou he n a m is
pe manen ly open, while he no he n one is a lagoon ha is pe iodically
closed by a sand ba ie due o he accumula ion o sedimen s by idal
in luence. This ba ie b eaks pe iodically, mos ly du ing pe iods o
s ong ains, due o i e ine in luence. Wa e accumula ion builds
p essu e and, e en ually, b eaks he sand ba ie , which can emain
open o a a iable pe iod o ime, depending on he balance be ween
eshwa e and coas al dynamics, as in enclosed lagoons (F´
elix e al.,
2013). The no he n a m o his sys em is closes o he S˜
ao Jo˜
ao dos
Angola es ci y, easily accessible o locals o ishing, ba hing, and li e
dumping (A onso e al., 2022).
A S˜
ao Tom´
e, i e s a e o en commonly used as laund y a eas,
whe e soaps and de e gen s a e used e e y day (A onso e al., 2022).
Mos p oduc s om his ac i i y en e he mang o es ia un-o , bu a
P aia das Conchas and Diogo Nunes laund y akes place di ec ly in he
mang o es, whene e hese a e domina ed by eshwa e . Bo h hese
sys ems a e also highly used o ash dump.
The I´
ogoi´
ogo bay is a ma ine a ea adjacen o he Malanza mang o e,
which is in ensi ely used by he nea by communi ies, no ably o suppo
hei ishing ac i i ies, and has a s ong pollu ing po en ial, namely
conside ing ha was e p oduc s om hese ac i i ies a e commonly
dumped a he po a ea. Two main docks we e iden i ied in his bay: he
F. A onso e al.
Chemosphe e 334 (2023) 138973
3
ishing boa ha bou a Po o Aleg e , whe e boa and gea epai occu ,
bu also washing, pain ing and ga bage dumping; and he Pon a Baleia
docking a ea, whe e mos passenge s and goods a e anspo ed o and
om he Ilh´
eu das Rolas eso , 2.5 km sou h o he main island o S˜
ao
Tom´
e (Fig. 1).
2.2. Sample collec ion and p epa a ion
Wa e and sedimen sampling occu ed in Augus 2017, ep esen ing
he sys ems’ en i onmen al a iabili y and especially he es ua ine
longi udinal g adien . Sampling e o depended mos ly on mang o e
size and a iabili y, wi h sampling s a ions selec ed a P aia das Con-
chas, Diogo Nunes Angola es, Malanza, and a I´
ogoi´
ogo bay (Fig. 1).
All eagen s used we e ul a-pu e (u.p.), and u.p. wa e (MilliQ, 18.2
MΩ.cm pu i ied by a Q-POD® Elemen Me ck Millipo e) was used in he
p epa a ion o all solu ions. All sampling con aine s we e p e iously
washed using 10% ni ic acid and hen insed wi h ul a-pu e MilliQ
wa e .
A o al o 32 wa e samples we e collec ed a all sampling s a ions: 3
samples om P aia das Conchas, 3 samples om Diogo Nunes, 6 samples
om Angola es, 7 samples om Malanza and 13 samples om I´
ogoi´
ogo
bay. The samples we e collec ed di ec ly o 1 L polye hylene con aine s,
and hen acidi ied wi h concen a ed HNO
3
o a pH <2, and e ige a ed
a 4 ◦C un il analysis. Be o e collec ion, con aine s we e insed h ee
imes wi h wa e om he sampling loca ion, immedia ely be o e
collec ion. Samples we e il e ed h ough p e-cleaned Wha man WCA
0.45
μ
m il e s.
A o al o 19 su ace sedimen samples we e collec ed: 3 samples
om P aia das Conchas, 4 samples om Diogo Nunes, 5 samples om
Angola es and 7 samples om Malanza. The op 3 cm o he sedimen
we e collec ed di ec ly in o 2 di e en polye hylene con aine s, by
p essing he con aine , upside-down, agains he sedimen , ca e ully
scooping he ma e ial and co e ing he con aine s wi hou manipula-
ion. All samples we e ozen be ween collec ion and analysis. To al
o ganic ma e (TOM) in he sedimen was ob ained by loss on igni ion
(EN15169, 2007). One o he con aine s was used o de e mine he
g anulome y by he sepa a ion o d ied samples wi h calib a ed sie es
and classi ied in o sil (<0.063
μ
m), ine sand (0.063
μ
m ≤x <0.250
μ
m), medium sand (0.250
μ
m ≤x <0.500
μ
m) and coa se sand (0.500
μ
m ≤x <2 mm), acco ding o (Blo and Pye, 2001).
2.3. Me al analysis
To analyse me al concen a ion in he wa e (Cd, Cu, Fe, Mn, Ni, Pb
and Zn), samples we e subjec ed o a p e-concen a ion by solid-phase
ex ac ion (SPE) using selec i e ca idges ha e ain he me als while
gene al ca ions o he saline samples a e elimina ed. To op imize he
ex ac ion, samples we e p e iously adjus ed o a pH o 6.5, using
Fig. 1. S˜
ao Tom´
e Island (main map on he le ), showing he loca ion o he mang o es a ge ed o his s udy (P aia das Conchas, Diogo Nunes, Angola es, and
Malanza), de ailed on he igh -hand inse s. The inse on he op le shows he loca ion o S˜
ao Tom´
e in A ica.
F. A onso e al.
Chemosphe e 334 (2023) 138973
4
ammonia ace a e (0.5 M), ammonia (20–22%) and ni ic acid (2 M). The
ca idges we e placed in he acuum ex ac ion sys em (Mani old),
condi ioned wi h HNO
3
(2 M), u.p H
2
O and ammonia ace a e (0.5 M).
Samples we e hen placed in he ca idges, which we e washed wi h
H
2
O u.p.. The elu ion o me als wi h HNO
3
(2 M) was hen pe o med.
This p ocedu e ollows ha o he DigiSep Blue Label ca idges om
SCP Science ( e : CATALOG NUMBER MK-MKG003-SPEB-2.0-E).
Quan i ica ion was done by A omic Abso p ion Spec oscopy (AAS) in
a Solaa –The mo Elemen al equipmen . Cd, Pb and Ni we e analysed by
g aphi e chambe , and Cu, Fe and Zn by lame. The calib a ion cu e
was ob ained om ex e nal s anda ds, and he wo king solu ions o
me als we e p epa ed using 1000 mg L
−1
(Me ck) s anda d solu ions.
The de ec ion limi was 0.01 mg L
−1
o Ni, Cd and Pb, 0.1 mg L
−1
o Cu,
Mn and Zn, and 0.3 mg L
−1
o Fe. The quali y con ol p ocedu e
included analysis o duplica e samples (one o e e y ba ch o en
samples), blanks be ween samples, eco e y es s and pa icipa ion in
he in e calib a ion exe cise QUASIMEME (Quali y Assu ance o In o -
ma ion in Ma ine En i onmen al Moni o ing) o ex e nal quali y con-
ol. The esul s ob ained du ing he pe iod o his analysis showed a z-
sco e <1, he a e age eco e ies o he s anda d solu ions we e be ween
80 and 110% o all he me als, which con i med he accu acy o he
me hod. The p ecision o he me hod was con i med by he duplica e
samples.
To assess me al concen a ion in he sedimen (same elemen s ana-
lysed in he wa e plus Al and C ), he <2 mm ac ion (using a cali-
b a ed sie e) was eeze-d ied, homogenised, and educed o a ine
powde using a mo a and pes le (acco ding o OSPAR Commission,
2015). Sedimen aliquo s o 0.45–0.55 g we e placed in Te lon essels (2
ml HF (40%) and 6 ml o aqua egia – HNO
3
(65%) and HCl (30%) (1:3),
and hen acid-diges ed in a Miles one® ETHOS PLUS mic owa e o en .
A e diges ion, each solu ion was neu alised wi h bo ic acid and
dilu ed o 50 ml wi h ul apu e wa e . Me al concen a ions we e ana-
lysed ia lame a omic abso p ion spec ome y in a The mo Scien i ic
iCE™ 3500 (EPA 3051A s anda d, 2007; OSPAR Commission, 2015),
excep o As, which was analysed in a hyd ide gene a o , wi h sodium
bo ohyd ide added o con e As (III) o he ola ile hyd ide ha was
hen pu ged om he solu ion by a s eam o a gon gas in a The mo
Elemen al-VP90 Con inuous Flow apou Accesso y (ISO 17378-2:2014
E). The calib a ion cu e was ob ained by ex e nal s anda ds, and he
wo king solu ions o me als we e p epa ed using 1000 mg L
−1
(Me ck)
s anda d solu ions. The de ec ion limi s we e 1.6 mg kg
−1
o Cu, Fe, Mn
and C , 0.6 mg kg
−1
o Zn, 16 mg kg
−1
o Al, 3 mg kg
−1
o Pb, 2,5 mg
kg
−1
o Ni, 0,16 mg kg
−1
o Cd and As, and 2.7 mg kg
−1
o Hg. All
eagen s we e o Me ck Sup apu e quali y and he u.p wa e used . The
analy ical p ocedu e included one eagen blank in each ba ch o 20
samples, analysis o duplica e samples (one o e e y ba ch o en
samples), eco e y o s anda d solu ions, ce i ied e e ence ma e ials
(CRMs), and pa icipa ion in he QUASIMEME o ex e nal quali y
con ol. CRMs (LGC 6187 and MESS-4) we e analysed ollowing he
same p ocedu e. Ce i ied and measu ed alues ma ched, wi h eco e y
be ween 80% and 120% o all CRMs and me als. Pa icipa ion in 50
QUASIMEME exe cises ( u he demons a ing da a quali y, wi h mo e
han 90% accep able esul s (z-sco e <2)). This analysis con i med he
p ecision and accu acy o he me hods o all he me als. All me al
concen a ions we e calcula ed on a d y weigh basis, and wa e con en
was measu ed by d ying known amoun s o sedimen a 105 ◦C.
2.4. Da a analysis
A e age sedimen me al concen a ions ob ained in S˜
ao Tom´
e
mang o es was compa ed o hose om o he mang o es and olcanic
islands, compiled om he li e a u e.
The po en ial o an h opogenic inpu o me als in o he en i onmen
was assessed h ough se e al widely used me hods, only a ailable o
sedimen concen a ions: The En ichmen Fac o (EF), he Geo-
accumula ion Index (Igeo), and he Con amina ion Fac o (CF). The EF
Table 1
Fea u es o he ou mang o es s udied in S˜
ao Tom´
e Island (adap ed om A onso e al., 2021; Caldei a e al., 2003). Dash indica es ha his alue was no a ailable.
Mang o e Malanza Angola es Diogo Nunes P aia das Conchas
Mang o e a ea (km
2
) 2.83 0.68 0.12 0.0012
A ea o he hyd og aphic basin (km
2
) 7.41 7.82 23.35 13.31
Geologic composi ion o he hyd og aphic basin(s) Basal - achyphonoli e la as; allu ial deposi s; py oclas ic and la a cones Basal - achyphonoli e la as Basal ic la as; py oclas ic and la a cones Basal ic la as; allu ial deposi s
Size o he closes human se lemen (habi an s) 1345 2037 392 180
Land use dominance in he su oundings Mang o e (53.6%) Ag o o es y (59.4%) Ag icul u e (47.5%) –
F. A onso e al.
Chemosphe e 334 (2023) 138973
5
di e en ia es an h opogenic and na u al sou ces o sedimen en ich-
men o each elemen (Sze e e al., 1999). I was calcula ed using a
o mula ha uses Al as he no malize o me al concen a ions:
EF =(C/CAl)sample
(C/CAl) e e ence
whe e (C/C
Al
) is he a io o concen a ion o he elemen o conce n (C)
o ha o Al (C
Al
), in bo h he sedimen sample (sample) and in an un-
pollu ed e e ence sample ( e e ence). In he p esen s udy, he e e ence
sample alues we e aken om he bibliog aphic e e ence o shallow
wa e sedimen ha was closes o he condi ions ound in he s udy a ea
(Salomons and Fo s ne , 1984). Fi e con amina ion ca ego ies a e
acknowledged on he basis o he en ichmen ac o : 2 <EF <5 - de i-
ciency o mode a e en ichmen ; 5 <EF <10 - mode a ely se e e
en ichmen , 10 <EF <25 - se e e en ichmen ; 25 <EF <50 - e y
se e e en ichmen ; and EF >50 - ex emely high en ichmen (Bi ch and
Olmos, 2008).
The Igeo quan i ies he deg ee o me al pollu ion (Mülle , 1979), and
has been used in s udies o ace me al s udies in sedimen s and soils (e.
g., Amin e al., 2009a). I was calcula ed as:
Igeo =log2(Cn
1.5Bn)
whe e C
n
is he concen a ion o a me al in he sedimen , and B
n
is he
geochemical backg ound alue o ha same me al in shallow wa e
sedimen (Mülle , 1979). The Igeo is hen classi ied in o se en classes:
0 (p ac ically uncon amina ed) - Igeo<0; 1 (uncon amina ed o
mode a ely con amina ed) - 0 <Igeo<1; 2 (mode a ely con amina ed) -
1 <Igeo<2; 3 (mode a ely o hea ily con amina ed) - 2 <Igeo<3; 4
Fig. 2. Me al concen a ions (
μ
g/L) in he wa e o S˜
ao Tom´
e s udied mang o e sys ems. Si es wi h unusually high concen a ion a e agged.
F. A onso e al.

Chemosphe e 334 (2023) 138973
6
(hea ily con amina ed) - 3 <Igeo<4; 5 (hea ily o ex emely con ami-
na ed) - 4 <Igeo<5; 6 (ex emely con amina ed) - 5 <Igeo.
The CF exp esses he le el o me al con amina ion o sedimen , being
calcula ed as:
CF =Cn
Bn
whe e C
n
is he concen a ion o a gi en me al in he sample, and B
n
is
he geochemical backg ound alue o ha same me al in shallow wa e
sedimen (Mülle , 1979). CF alues we e in e p e ed as: low con ami-
na ion o CF <1; mode a e con amina ion o 1 <CF <3; conside able
con amina ion o 3 <CF <6; and e y high con amina ion o CF >6
(Hakanson, 1980).
3. Resul s
3.1. Me al concen a ion in he wa e
Me al concen a ions in he wa e column we e highly a iable be-
ween si es and elemen s, wi h se e al si es highligh ed by high con-
cen a ions o some elemen s (Table S1 – Fig. 2). The highes
concen a ions in he wa e we e he ollowing: ups eam in Malanza o
cadmium (M6 – 0.73
μ
g/L); downs eam in Diogo Nunes (D1 – 3.46
μ
g/
L) and in P aia das Conchas (PC1 – 2.99
μ
g/L), and nea he ishing
ha bou in I´
ogoi´
ogo Bay o coppe (B0 – 3.47
μ
g/L); ups eam in
Malanza o i on (M7 – 4345.68
μ
g/L) downs eam in Diogo Nunes (DN1
– 134.44
μ
g/L) and P aia das Conchas (PC1 – 139.08
μ
g/L), and up-
s eam in Malanza o manganese (M6 – 142.03
μ
g/L, M7 – 121.60
μ
g/
L); downs eam in Diogo Nunes (D1 – 46.79
μ
g/L) and in a small shallow
pound in Malanza o nickel (M1 – 13.57
μ
g/L). The highes lead con-
cen a ions we e ound in one o he a ms o Diogo Nunes, and nea he
passenge docking a ea and no h sec ion o Malanza bay (DN3 – 2.45
μ
g/L, B0 2.64
μ
g/L, B5 3.58
μ
g/L, Tables S1 – Fig. 2). Zinc concen a-
ions we e highe in wa e samples om Angola es no h a m, ups eam
a ea (A4 – 19.33
μ
g/L, Table S1 – Fig. 2), in he small shallow pond o
Malanza (M1 – 15.51
μ
g/L, Table S1 – Fig. 2), and nea he ishing
ha bou in Malanza bay (B0 – 13.83
μ
g/L, Table S1 – Fig. 2).
The compa ison o backg ound alues o me al con en (nickel,
cadmium, lead, coppe , and zinc) showed ha S˜
ao Tom´
e mang o e
wa e had highe concen a ions o coppe (Table S1). P aia das Conchas
and Diogo Nunes p esen ed concen a ions o nickel, cadmium and zinc
ha we e pa icula ly highe han he e e ence alues (Table S1).
3.2. Me al loadings in su ace sedimen s
3.2.1. Sedimen cha ac e iza ion: g anulome y and o ganic ma e con en
G anulome y o su ace sedimen was highly a iable be ween and
some imes wi hin mang o es, e en hough i was mos ly composed by
sands and sil s (Fig. 3). All samples om Diogo Nunes we e classi ied as
sand wi h small amoun s o o ganic ma e . The downs eam a eas o
Angola es om bo h a ms we e p edominan ly sandy (99% a A1, and
98.8% a A2), while he no he n a m had muddy sand in he middle
(A3, A4 – 54% and 67% sand espec i ely) and sandy g a el ups eam
(A5 – 20% sand). In Malanza, he sedimen was e y homogenous in
ups eam a ea, being mos ly muddy sand (61% sand a M5, 56% a M6,
and 65% a M7) wi h high amoun s o o ganic ma e (42%, 61% and
63% espec i ely), while downs eam loca ions (99% sand a M2, 85%
and M3, and 85% a M4) we e mos ly sandy wi h a small p opo ion o
o ganic ma e (7%, 11% and 13%, espec i ely). P aia das Conchas had
muddy sand ups eam (80% sand a P3), sandy g a el in he middle
(51% g a el and 48% sand a P2), and sand downs eam (98% sand a
P1).
Fig. 3. G anulome y e na y diag am. Each colou ep esen s a sampling loca ion, and he size o he ci cles indica es o ganic ma e con en (i.e., la ge ci cles
indica e highe amoun s o o ganic ma e ). (Fo in e p e a ion o he e e ences o colou in his igu e legend, he eade is e e ed o he Web e sion o
his a icle.)
F. A onso e al.
Chemosphe e 334 (2023) 138973
7
3.2.2. Compa ing sedimen me al concen a ion in S˜
ao Tom´
e mang o es
wi h simila sys ems
We s a ed by compa ing a e age elemen al concen a ions ob ained
in S˜
ao Tom´
e mang o es wi h hose om o he mang o e and olcanic
islands, compiled om he li e a u e. Since alues wi h aluminium
no maliza ion a e mos ly applied in sedimen s wi h ma ine o igin
(He u and Sandle , 2006), he compa ison was based only on absolu e
concen a ions. S˜
ao Tom´
e mang o e sedimen s ended o p esen highe
mean me al concen a ions when compa ed o o he mang o es and
olcanic islands, excep o lead in o he mang o e sys ems and coppe
and nickel in o he olcanic islands (Table 2).
3.2.3. En ichmen and con amina ion
En ichmen (EF) and con amina ion (Igeo and CF) based on me al
concen a ions in he su ace sedimen (Table S2), we e highly a iable
be ween si es and elemen s, also showing ele an di e ences be ween
indices (Table 3). Cadmium concen a ions in he sedimen we e e y
close o he quan i ica ion le el, he e o e he indices we e no calcu-
la ed. S˜
ao Tom´
e mang o es had consis en ly low en ichmen and
con amina ion by coppe , li hium and lead, while i on, me cu y and zinc
had only occasional high alues o en ichmen , ups eam in Malanza
(M6). Manganese en ichemen was ound a all sampling poin s o Diogo
Nunes, ups eam a Malanza (again, M6) and downs eam a P aia das
Conchas (P1), while nickel en ichemen was ound ups eam a Diogo
Nunes (D3 and D4) and ac oss mos sampling poin s o Malanza (excep
M6 and M7) and showed occasional con amina ion a he small
con iguous pond in Malanza (M1) and ups eam a P aia das Conchas
(P3). Only a senic and ch omium p esen ed a widesp ead en ichmen
and con amina ion, and e y se e e en ichmen and hea y con amina-
ion a a ew loca ions. A senic en ichmen and con amina ion we e
pa icula ly no iceable a Diogo Nunes and Malanza.
4. Discussion
The assessmen o he me al loadings in ou mang o es in S˜
ao Tom´
e
Island depic ed, gene ally, he same pa e ns as in hose ound in Wes
A ican egions, which a e gene ally iche in cadmium, ch omium,
nickel, and zinc, especially in coas al a eas (Gnandi e al., 2011). P aia
das Conchas and Diogo Nunes e en being he smalles s udy a eas we e
cha ac e is ically he sys ems ha p esen ed highe me al con en . On
he o he hand, Angola es p esen ed he lowes en ichmen and
con amina ion le els.
Table 2
Mean sedimen me al concen a ions (absolu e alues, mg kg
−1
) o S˜
ao Tom´
e mang o es (cu en s udy), and in o he mang o e sys ems and olcanic islands
( aken om he li e a u e). Values highligh ed in g ey show mean concen a ions ha we e lowe han hose ound in S˜
ao Tom´
e mang o es. Dashes indica e ha
hose alues we e no a ailable.
[1] (K ui wagen e al., 2008); [2] (Gnandi e al., 2011); [3] (Cuong e al., 2005); [4] (Essien e al., 2009); [5] (Amin e al., 2009b); [6] (Vane e al., 2009); [7]
(Ma chand e al., 2006); [8] (P eda and Cox, 2002); [9] (Coelho e al., 2016); [10] (Dœlsch e al., 2006); [11] (Ahn and Chon, 2010); [12] (B nický e al., 2020);
[13] (Cab al Pin o e al., 2015); [14] (Ama al e al., 2006); [15] (Mo a e al., 2012); [16] (Mendoza-G im´
on e al., 2014); [17] (Su he land and Tack, 2000); [18]
(Kazakou e al., 2010).
F. A onso e al.
Chemosphe e 334 (2023) 138973
8
4.1. Me al loadings in wa e and sedimen
In P aia das Conchas and Diogo Nunes despi e being sys ems wi h
high me al con en , he e was no con amina ion o mos o he assessed
me als and a e, simul aneously, ep esen ed by a eas wi h small
amoun s o sedimen o ganic ma e . Due o he s ong a ini y be ween
o ganic ma e and me als, he e is less abili y o he sedimen o ap
and s o e he me als a ailable in he sys em. Al hough hese sys ems had
a high me al con en in wa e and sedimen samples, he indices did no
show con amina ion o mos o he me als assessed. Con a ily, Malanza
was he sys em wi h he highes p opo ions o sil and o ganic ma e in
he sedimen , which inc eases he numbe o co alen bonds wi h
me als, a ou ing hei accumula ion in he sedimen . Hence, hese si es
could ha e an impac on he elemen e en ion in he sedimen , e en
hough his phenomenon alone canno explain he con amina ion and
en ichmen in he sys em.
Table 3
Indices es ima ed o each me al in samples om all s udy a eas (EF- En ichmen Fac o ; Igeo – Geoacumula ion index; CF – Con am-
ina ion Fac o ).
F. A onso e al.
Chemosphe e 334 (2023) 138973
9
4.2. Na u al and an h opogenic sou ces o me al en ichmen and
con amina ion
To be e unde s and he na u al endency o me al concen a ion,
he collec ed da a was compa ed wi h he esul s om sedimen samples
om o he mang o es in he opical egion and wi h olcanic islands.
Compa ison be ween sedimen s om he s udy a ea wi h o he
mang o e sys ems has shown San omean mang o es o ha e highe
me al con en s. Howe e , land sys ems om o he olcanic islands
p esen ed highe coppe , lead and nickel concen a ions, al hough he
backg ound alues (OSPAR Commision, 2009) o coppe and nickel a e
lowe han he alues de ec ed in S˜
ao Tom´
e. This sugges s ha he
highe con en in coppe and nickel migh ha e a li hogenic o igin.
Ne e heless, he backg ound alues conside ed a e es ic i ely ep e-
sen a i e o he No h-Eas A lan ic Region which means ha conclu-
sions based on hese alues mus be aken wi h cau ion due o di e en
geological o ma ions.
A common obse a ion in all sys ems was he high en ichmen and
con amina ion wi h a senic and ch omium. In non- olcanic islands, he
con amina ion wi h a senic has been p o en o be de i ed om ag i-
cul u e uno and he use o disin ec ion and pes elimina ion de e gen s
in aquacul u e p ac ices, while he ch omium con amina ion was
conside ed o be mainly a esul o ag icul u e uno (Li e al., 2022). In
olcanic islands, he a senic con amina ion in mang o e sys ems esul-
ed om na u al p ocesses, such as he leaching o olcanic ocks, bu
also om an h opogenic o igin, linked o ha bou s and was ewa e
discha ge. The same ype o con amina ion wi h a senic was ound in
mang o es om he mainland possibly caused by an h opogenic ac i -
i ies, o ins ance, pe ochemical was es and desalina ion plan s
(Al-Kah any e al., 2018). Howe e , ch omium con amina ion is mos
commonly he esul o eshwa e inpu and e osion o olcanic ocks
(Ca y, 1982).
In P aia das Conchas and Diogo Nunes, he sou ces o en ichmen in
i on and zinc a e mos p obably local and sho - e m, due o he
an h opogenic ac i i ies ha a e common in he sys em (i.e., laund y
washing and ash deposi ion). Diogo Nunes, howe e , showed a
con amina ion wi h ch omium and manganese, which can esul om a
long- e m elease o hese me als, possibly om ag icul u e un-o , he
main land use in he a ea.
Angola es p esen ed he lowes concen a ion o mos o he me als
and ewe signs o sedimen con amina ion ou o all s udied mang o es.
Con a y o wha was expec ed, conside ing he p oximi y o he land ill
om he sou h a m, i was he no he n a m ha p esen ed highe me al
con amina ion. This may be explained by ei he he p oximi y o he ci y
o S˜
ao Jo˜
ao dos Angola es, o by a highe me al con ibu ion o ha
pa icula hyd og aphic basin.
In Malanza, besides he possible sou ces o pollu ion om he i e
ibu a ies, his sys em may also ha e on o he possible ex e nal sou ce
o con amina ion, he I´
ogoi´
ogo bay, due o in ense ishing and o he
an h opogenic ac i i ies and he egula boa a ic. Fo ins ance, nea
he ha bou , he concen a ion o coppe , lead, and zinc was clea ly
highe , and hese a e me als usually p esen in boa emissions and
an i ouling chemicals used in boa pain s (Bad e al., 2009; Nase , 2013;
Usman e al., 2013; Zhang e al., 2012). This may also jus i y he
di e en me als p esen in he wa e column o he Malanza mang o e
om he ups eam and downs eam a eas, as a esul o seawa e
in usion om he nea by bay, as he ha bou is close o he mang o e.
Sedimen s can be used o assess he en i onmen al condi ion o a
speci ic ecosys em, based on en ichmen and con amina ion indexes ha
e alua e he sample and me al load. Howe e , he use o se e al indices
can esul in i egula ou pu s and inconsis encies be ween hem. Fo
ins ance, he Igeo scale can ange om nega i e o posi i e alues, while
all he o he indices ha e di e en scales ha only ange in posi i e
alues, being ambiguous how hey complemen each o he and which
classes a e equi alen (Bi ch, 2023). Thus, e en hough classi ica ion
schemes o sedimen s can be an ad an age o any s udy ela ed o he
e alua ion o sedimen quali y and me al pollu ion, he ou pu s mus be
conside ed wi h cau ion.
4.3. Heal h implica ions
In de eloping coun ies, u baniza ion had a apid ad ance in he las
yea s, howe e , he lack o managemen plans associa ed wi h he
excessi e use o e ilize s and disposal o domes ic was e in inapp o-
p ia e a eas ha e caused de imen al e ec s on he quali y o wa e ,
sedimen , and aqua ic auna (Ali e al., 2016; Isa e al., 2014; Ledin e al.,
1989). Addi ionally, he coun ies’ legisla ion abou ecosys em
con amina ion is weak and he lack o mone a y suppo comp omises
he ac ual law en o cemen (Kumie and Kloos, 2006). As a consequence
o some o hose limi a ions, i was c ea ed he One Heal h app oach
(www.oneheal hcommision.o g) ocused on p o ec ing people’s heal h,
animals, and he en i onmen . This app oach add esses he oo causes
and sea ches o sus ainable solu ions applicable o ood and wa e
sa e y, as well as pollu ion managemen . In his scope, and conside ing
he speci ic case o S˜
ao Tom´
e mang o es, some o he possible esponses
o p e en mo e heal h damages by me al con amina ion would be he
implemen a ion o policies o ecosys em moni o ing (i.e., moni o ing
me al concen a ion in shell ish and ish om local ma ke s), as well as
he implemen a ion o an i- o low-pollu ion policies. The de elopmen
and in es men in educa ion p og ams a e also impo an ools o aise
awa eness on he bes p ac ices o sys em p o ec ion, pollu ion sou ces
and impac s on he ecosys ems and human heal h (Beyene e al., 2009).
Fu he mo e, engaging wi h he communi ies can help educe heal h
isk inc easing p ac ices, as well as o de ec ea ly symp oms o me al
con amina ion.
5. Conclusions
To he bes o ou knowledge, his was he i s assessmen o he
me al concen a ion in he mang o es om S˜
ao Tom´
e. I showed ha
hese sys ems p esen highe me al concen a ions han mos mang o es
and olcanic islands, p obably due o he combina ion o a olcanic
o igin, which ends o inc ease he na u al me al concen a ions han
si es wi h o he li hogenic o igins, and sedimen composi ion ha a-
ou s he e en ion o hose me als. Howe e , occasional high concen-
a ions and high con amina ion alues sugges ha , a leas in some
cases, he high concen a ion o some me als ha e an an h opogenic
o igin. A senic and ch omium showed se e e en ichmen and con am-
ina ion a di e en si es, which aises heal h conce ns. These esul s
ein o ce he need o gain a be e unde s anding o ac ual sou ces o
me al con amina ion in S˜
ao Tom´
e, which can hen enable he p epa a-
ion and applica ion o mi iga ion measu es. Fu u e s udies and moni-
o ing o me al concen a ions, en ichmen and con amina ion in S˜
ao
Tom´
e should go beyond mang o e a eas, ex ending o o he aqua ic and
e es ial ecosys ems, and including he s udy o bioaccumula ion.
O e all, his s udy shows how me al pollu ion migh be ele an e en in
a emo e and non-indus ialized island, highligh ing he need o a
be e unde s anding o how me als a e dis ibu ed in he en i onmen ,
and pa icula ly in de eloping coun ies, whe e people a e o en mo e
di ec ly elian on na u al esou ces and mo e likely o unknowingly be
exposed o high me al concen a ions and i s dele e ious heal h
consequences.
C edi au ho s a emen
Filipa A onso: In es iga ion, W i ing – o iginal d a , Visualiza ion;
Ca la Palma: Valida ion, Fo mal analysis, Resou ces, W i ing – e iew &
edi ing, Visualiza ion; Ana C. B i o: W i ing – e iew & edi ing; Paula
Chainho: In es iga ion, W i ing – e iew & edi ing; Rica do de Lima:
In es iga ion, W i ing – e iew & edi ing, Visualiza ion; Joshua A.
Heumülle : In es iga ion, W i ing – e iew & edi ing; Filipe Ribei o:
In es iga ion, W i ing – e iew & edi ing; Ped o M. F´
elix:
F. A onso e al.