Article
pubs.acs.org/est
Atmospheric Polychlorinated Naphthalenes in Ghana
Jonathan N. Hogarh,†,‡ Nobuyasu Seike,§ Yuso Kobara,§ and Shigeki Masunaga*,†
†
Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku,
Yokohama, Kanagawa 240-8501, Japan
‡
Department of Theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
§
National Institute for Agro-Environmental Sciences, Tsukuba, Ibaraki 305-8604, Japan
S Supporting Information
*
ABSTRACT: A nationwide monitoring of atmospheric POPs
(persistent organic pollutants) was conducted in Ghana between
May and July 2010, applying polyurethane foam (PUF) disk passive air
samplers (PAS). Reported here are preliminary findings on PCNs, an
industrial organic contaminant currently under review for possible
listing under the global chemical treaty. The present results constitute
the first set of nationwide data on air PCNs from a West African
country. Contrary to expectation, air PCNs levels were quite high in
Ghana, at an average of 49 ± 5.4 pg/m3. The coastal (southern) zone
of Ghana appeared the most impacted, with crude open burning of
waste, industrial emissions, and the harbor environment identified
among possible emission factors. Tri- and tetra-CNs (the lowly
chlorinated homologues) predominated in the atmosphere, altogether
constituting approximately 90% of total PCN homologues composition. Increased volatilization under tropical conditions was
presumed a key factor that contributed to this high atmospheric input of lowly chlorinated homologues. We further observed a
significant level of fractionation of PCN homologues across the breadth of the country. The percentage composition of the lowly
chlorinated homologues increased northwards, probably because of their transportation in the direction of prevailing winds.
From congener profile analysis, PCN-45/36 is proposed as a possible source marker for emissions preempted by uncontrolled
waste burning activities. Dioxin-like toxicity of air PCNs in Ghana was estimated to range 0.49−5.6 fg TEQ/m3. This study
brought to the fore the emerging problems of nonagricultural organohalogens that covertly might be confronting the
environment in African nations like Ghana.
■
INTRODUCTION
Persistent organic pollutants are a group of organohalogens
considered undesirable in the environment because of their
high level of persistence, toxicity, and bioaccumulativeness.
Emissions of POPs have been reported at various sites in the
world, from the tropics to polar regions.1−4 They are
distributed partly by long-range atmospheric transport
(LRAT), hypothesized to occur in a grasshopper-like fashion.5,6
Notable sources of POPs in the environment can be
categorized into three − agricultural, industrial, and unintentional formation. For most African countries, much of the
information available on POPs concerns residues from
agrochemicals such as DDT, endosulfan, hexachlorocyclohexane (HCH), hexachlorobenzene (HCB), dieldrin, etc.;7−11
perhaps a reflection of the agricultural-base economy operated
in many African countries. On the contrary, information is
scanty on POPs generated from industrial sources or by
unintentional formation in Africa. The few studies conducted
so far nevertheless suggest that these categories of POPs are of
contemporary relevance in African countries.12−16 In the West
African region, emissions of polychlorinated biphenyls (PCBs)
for instance were recently reported to be relatively high, a
© 2012 American Chemical Society
situation blamed on factors such as illegal dumping of PCB
containing wastes, uncontrolled burning of wastes, and the
breakup of old ships.12 Analysis of human breast milk from
Ghana for certain organic contaminants has further revealed
impacts from industrial organohalogens such as PCBs and
polybromonated diphenylethers (PBDEs), which otherwise
have no known production or usage history in Ghana.16
Polychlorinated naphthalenes (PCNs) remain one of the
least scrutinized organohalogens on the continent of Africa.
PCNs constitute a complex mixture of 75 congeners, some of
which are planar in structure with similar biochemical toxicity
behavior as polychlorinated dibenzo-p-dioxins/dibenzofurans
(PCDDs/PCDFs) and coplanar PCBs. 17−21 PCNs are
currently under review for possible listing under the global
chemical treaty. They were initially manufactured as high
volume chemicals under various trade names such as Halowax
(in Japan), Nibren wax, Perna wax, and Basileum (all in
Received:
Revised:
Accepted:
Published:
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October 8, 2011
January 15, 2012
January 30, 2012
January 30, 2012
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Figure 1. Sampling sites and spatial distribution of air PCNs in Ghana.
dumping grounds in the world.32−34 Various toxics contained
in obsolete electronics and gadgets and industrial wastes
continue to be illicitly shipped to developing countries from
rich nations. Parallel with this, might be a shifting of POPs
burden from industrialized nations to poor ones.35 The
quantum of e-waste that reaches the shores of Africa is difficult
to quantify. Conservative figures from Nigeria however suggest
that a volume of e-waste equivalent to about 100,000
computers or CPUs or 44,000 Cathode Ray Tube TVs enter
Africa through Nigeria alone each month.32 The estimate for
Ghana, we assume, is not any less. The environmental risk
associated with e-waste in Ghana is compounded by the crude
means of retrieving various valuable metals from these obsolete
gadgets. Metal wires retrieved from e-wastes are usually burnt
to remove their polyvinyl chloride (PVC) protective covering.33,34 These activities are accompanied by lots of emissions
into the atmosphere, some of which may be toxic. Presumably,
old POPs contained in some of these e-wastes could be released
or unintentional ones could be formed.
In this report, we focused on atmospheric contamination
from PCNs in Ghana, considering the contemporary and future
relevance of this group of pollutants as POPs. The spatial
distribution of air PCNs was highlighted for the first time across
the country. Pertinent source factors of ambient PCNs were
subsequently characterized and the extent of dioxin-like toxicity
by PCNs estimated.
Germany), Seekay wax (in Great Britain), Clonacire (in
France), Cerifal materials (in Italy), and N-oil and N-wax (in
the USA)22 and applied in industry as insulators, lubricants,
dielectrics, flame-retardants, plasticizers, etc.23 However, since
the 1970s to 1980s, most countries voluntarily avoided
production and new application of PCNs formulations, in
response to the environmental health dangers that later became
associated with these compounds. PCNs nevertheless continue
to be detected in the environment. Industrial combustion and
waste incineration are key source factors identified in the
contemporary emissions of these compounds.24−28 A variety of
pathways have been suggested for combustion byproduct
PCNs. These include chlorination of already present
naphthalenes, de novo synthesis from polycyclic aromatic
hydrocarbons (PAHs), and chlorophenol condensation.25 The
mechanisms involved are thought to be closely linked to
PCDDs/PCDFs formation.29,30
In 2001, elevated levels of air PCNs were picked up from
locations off the coasts of West and South Africa.31 This is the
most significant detection of air PCNs closest to the African
continent. Although precise sources were not fully resolved,
these pollutants might have emanated from countries bordering
the west and south coasts of Africa in taking into consideration
the movement directions of air mass which reached the
respective offshore sampling locations. Presumably, there are
hotspots of PCNs emissions in certain African countries that
should be investigated. These may arise as combustion
byproduct or from toxic wastes exported to the continent.
Both issues constitute grave environmental challenges in
Ghana. For instance, substantial amount of the municipal
solid waste (MSW) generated in Ghana is burnt uncontrollably
in the open at waste dumpsites, as incineration and proper
landfill facilities are lacking. Putrescible fractions, plastics,
metals, papers, etc. in the waste stream are all burnt together.
Potentially, this could generate unintentional POPs. On the
issue of e-waste, Ghana and indeed many African countries
have the unenviable status of ranking among the major
■
MATERIALS AND METHODS
Study Area, Sampling Process, and Pretreatment. The
study was conducted in Ghana deploying polyurethane foam
(PUF) disk passive air samplers (PAS) at 13 sites across the
country (Figure 1). The PUF disk PAS has been described
elsewhere.36,37 They were deployed continuously for 8 weeks,
starting in May 2010. The exact start date though varied slightly
from site to site, as it took different traveling days to reach the
various sites spread across the country, some very remotely
located. The first sampler was deployed 5th May, 2010 and final
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ambient PCNs in Ghana. Rather, a south−north gradient was
observed, with concentrations in the southern belt almost twice
as those in the middle and northern belts (Figure 1). Averagely,
ambient PCN levels were similar between the middle and
northern belts.
Homologue Composition and Fractionation. Clearly,
tri-CNs and tetra-CNs (the lowly chlorinated homologues)
predominated in Ghana’s atmosphere (Figure 2). These two
deployment on 20th May, 2010 (Table S1). Deployment points
extended between latitude 4.8−10.8°N and longitude 0−2.5°E.
At each sampling point, PUF-disk PAS were mounted at roof
level in a way that ensured unobstructed flow of air through the
sampler (Figure S1 in Supporting Information 2). The PUF
disks applied in this study were supplied by Klaus Ziemer
GmbH, Germany, and have the following dimensions: diameter
− 14 cm; thickness − 1.35 cm; surface area − 365 cm2; mass −
4.40 g; volume − 207 cm3; and density − 0.0213 g/cm (Figure
S1). PUF disks were precleaned by washing in water and
Soxhlet extracted with acetone for 12 h. They were then dried
under vacuum, sealed in airtight zipper bags, wrapped securely
in aluminum foil, and stored in the dark at room temperature at
the National Institute for Agro-Environmental Sciences
(NIAES), Tsukuba, Japan, until shipment to Ghana for
sampling. At the end of deployment in Ghana, PUF disks
were harvested in airtight package for the security from
photoexposure and returned to NIAES in the same package for
chemical analysis.
Chemical Analysis and Quality Control. Harvested
PUFs were Soxhlet extracted with acetone for approximately
12 h, and the extracts were concentrated, treated in cleanup,
and then analyzed for 63 PCN congeners using high resolution
gas chromatography/high resolution mass spectrometry
(HRGC/HRMS). The HRGC (HP6890) and HRMS (Auto
Spec Ultima-Micromass) were operated using settings similar as
those applied by Guruge et al.38 Description of the extraction
and cleanup processes and the recovery and internal standards
used have been summarized in Supporting Information 2.
Average percentage recoveries of PCNs were as follows:
tetra-CN 74%, penta-CN 94%, hexa-CN 102%, hepta-CN
107%, and octa-CN 81%. Peaks were mostly integrated when
signals were at least three times greater than the background
noise. Other peaks with lower S/N ratios, given the specificity
of retention time and fair height above noise level, were not
discarded but considered as indicating the presence of a
particular congener in trace amount. Method detection limits
(MDLs) were derived from laboratory blank PUFs and
quantified as the mean congener concentration plus three
times standard deviation. For 24 different congeners/coeluents
measured in blanks, the MDLs ranged between 0.001 and 0.03
pg/sample, with a mean value of 0.01 and standard deviation
0.008 pg/sample.
Figure 2. Homologue profiles of ambient PCNs in Ghana compared
to those of East Asian countries.
homologues constituted approximately 90% of total PCN
homologues composition in the atmosphere in Ghana in
comparison to about 80% in East Asian countries.40 The
relatively greater composition of lighter homologues in the
atmosphere in Ghana probably is a manifestation of strong
volatilization effect under high tropical temperatures. There was
a progressive increase in ambient composition of tri-CNs and
decrease in tetra-CNs as one traversed from south to north of
the country (Figure 2). As deduced from Figure 1, the bulk of
the PCN emissions occurred in the southern belt. We
presumed a northward atmospheric transport of aerial PCNs
from the southern parts of Ghana. This study was conducted
between May and July, when the West African monsoon, the
major wind system that affects this region, blows southwesterly
(i.e., from southwest to northeast).41 Indeed, back trajectory
analysis (applying METEX − Meteorological Data Explorer)
showed movement of air masses from the coastal south to the
northern parts of Ghana (Supporting Information 3). This
seemed to have triggered air PCN homologue fractionation
across the breadth of the country. Much of tri-CNs, being
lighter and more susceptible to atmospheric transport, appeared
blown and accumulated further north than the tetra-CNs
(Figure 2). Generally, less of the heavier homologues were
transported up north.
In Sunyani, Wa, and Tumu, the PCNs were blown from the
southern parts of neighboring Cote d’Ivoire (Supporting
Information 3). Yet, the homologue compositions at these
sites were consistent with the identified trend of homologue
fractionation (Figure 2). On this score, it is assumed that the
southern parts of Ghana and Cote d’Ivoire share similar
characteristics of PCN emission factors. It is worth noting that
the southern parts of Cote d’Ivoire had a major encounter with
illegally dumped hazardous waste in 2006.42
PCN homologue profiles at the Teshie and Tema sites were
strikingly dominated by tetra-CNs, constituting about 80% and
60% of their respective homologue compositions (Figure 2).
Samples from Teshie were collected from the point close to a
■
RESULTS AND DISCUSSION
Spatial Distribution of Atmospheric PCNs in Ghana.
Table S2 shows air PCN congener concentrations at various
locations in Ghana. ∑63PCNs ranged between 27 and 95 pg/
m3 with a national average of 49 ± 5.4 pg/m3 (Figure 1),
applying a sampling rate of 3.5 m3/day.36,39 These concentrations were unexpectedly high but were included within the
range of value (0.3−86 pg/m3) of air PCNs, which was
reported by Jaward et al. along the north−south Atlantic
transect near West Africa in 2001.31 They not only reported the
highest concentrations of air PCNs in Europe but also indicated
the existence of hotspots off the coasts of West and South
Africa. In the present study, we found air PCNs to be highest
along the coastal stretch of Ghana, which somehow might
implicate that these coastal areas are the emission sources of
these pollutants (Figure 1). The highest concentration (95 pg/
m3) was detected at Teshie near Accra (the national capital)
and the lowest (27 pg/m3) at Kumasi (the second largest city).
We did not find much evidence of rural-urban gradient of
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Figure 3. (a) Congener profiles of aerial PCNs at sites located within the southern belt of Ghana. (b) Congener profiles of aerial PCNs at sites
located within the middle belt of Ghana. (c) Congener profiles of aerial PCNs at sites located within the northern belt of Ghana.
respectively; together contributing approximately 78% of total
tri-CNs composition. Averagely, the tetra-CNs were dominated
by PCN-37/33/34 (15%) and -45/36 (30%); penta-CNs by
PCN-52/60 (18%) and -59 (19%); and hexa-CNs by PCN-66/
67 (42%). Many of these congeners that dominated in the
atmosphere in Ghana (PCN-14, -21, -26/25, -37/33/34, -45/
36, -52/60, and -66/67) are reportedly enrich in combustion
sources,23,25 making combustion a key factor of PCN emissions
in Ghana.
The PCN congener profiles appeared different between the
Takoradi, Teshie, and Tema sites but fairly consistent in the
remaining sites within the southern zone (Figure 3). Profiles
were, however, generally consistent in the middle zone and
variable in the northern zone. The profile for Teshie was
overwhelmingly dominated by PCN-45/36, constituting nearly
60% of total congener composition (Figure 3a). The Teshie site
is proximate to a solid waste dumpsite, so it is presumed that
congener profile at this site reflected directly the impact from
such a source, and PCN-45/36 might qualify as a marker for
this source. Indeed, the PCN congener profile at the Teshie site
is consistent with the pattern reported in MSW by Noma et al.,
as one dominated by PCN-45/36.29 Thus, the general
prominence of this particular congener in various profiles
provides the possibility that many sites might have been
impacted by MSW related sources. Open waste dumpsites are
widespread in Ghana and often characterized by a complex
mixture of waste materials that include e-wastes, plastics
(including PVCs), car tires, and metals,33,34 all of which provide
solid waste dumpsite where uncontrolled waste burning
activities were observed. Tema on the other hand is the
industrial city of Ghana and at the heart of Ghana’s industrial
development plan. Industrial activities at Tema include oil
refinery, metal smelting, steel production, manufacturing of
plastic products, cement, paints, etc.; in all of which energy are
expended intensively, with combustion byproducts. Tema also
hosts a shipping harbor. Our sampling site in the Tema district
was close to the Tema Oil Refinery. With such point sources of
combustion identified, it was assumed that the high tetra-CNs
at these two sites was a direct impact from combustion. We are
unsure if local practices of burning such waste items as plastics,
PVC coatings of copper wires, and car tires has in any way
influenced the air PCN homologue pattern in Ghana. Noma et
al., however, have shown through laboratory-scale incineration
experiment that incinerating certain synthetic rubber products
emitted PCNs with tetra-CNs constituting nearly 60% of the
homologue composition.29 There is also evidence suggesting
that petrochemical activities, for instance, might generate PCNs
with relatively high levels of tetra-CNs (judging from the
amounts measured in surrounding soils); the researchers
however did not report on tri-CNs.28
Congener Profiles for Source Characterization. Out of
63 PCN congeners screened, 58 were routinely detected and
quantified (Table S2). The congener patterns from the various
sampling points are presented in Figure 3. PCN-21/24/14,
-26/25, and -23 generally dominated the tri-CNs, accounting
for 31%, 23%, and 24% of average tri-CNs composition,
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Figure 4. Factor loadings plot (left) and corresponding factor score plot (right) for PCN congeners. Numbers on factor loadings plot are IUPAC
PCN congener numbers. Prominent combustion markers were obtained from Falandysz, 1998; Meijer et al., 2001; Takasuga et al., 2004; Noma et
al., 2006; Lee et al., 2007.1,18,27,29,44 The congeners abundant in fly ash were obtained from Noma et al., 2006; Lee et al., 2007.1,29 The congeners
enrich in halowax and equivalents were obtained from Falandysz, 1998; Falandysz et al., 2006.18,45
Majority of the sites located in the mid to northern regions
e.g. Kumasi, Sunyani, Ejura, Tamale, and Wa related to PC3,
which is associated with Group 3 cluster of congeners. This
cluster is dominated by highly chlorinated congeners (PCN-63,
-69, -71/72, -73, -74, and -75). As heavier congeners with
relatively poor traveling capacity in air, our immediate
impression was that the cluster expressed a certain element of
marginal local influence at several sites, most of which are quite
distant from the important sources identified in the southern
regions. It is suggested that the sites in the mid to northern
regions were not important emission points of the lowly
chlorinated congeners that accumulated in these regions but
might have received these congeners following LRAT from the
southern zone.
Potential Toxicity. The toxicological significance of the
levels of PCNs measured in air was assessed considering their
dioxin-like equivalency (Figure 5). As PCNs toxicity is
ingredients for possible de novo synthesis of organohalogens
such as PCNs.25 PCN-66/67, which constituted approximately
42% of average hexa-CNs composition, provides further
evidence of combustion source, considering that this congener
is generated mainly as a combustion byproduct.23
As atmospheric POPs generally show congener specific
variations between seasons, we assume that the present data
which reflect PCN congener patterns in the rainy season might
differ from data obtained in the dry season.27,43
Principal Component Analysis (PCA). Applying STATISTICA 7 software, three major principal components (PC1−
PC3) were extracted as underlying PCN emissions in Ghana.
These accounted for 49%, 22%, and 11%, respectively, of total
variance. The factor loadings plot in Figure 4 indicates the three
significant congener clusters. Group 1 cluster of congeners
correlated with PC1, Group 2 with PC2, and Group 3 with
PC3. In Group 1, we find notable combustion markers of PCNs
such as PCN-52/60, -50, -51, -54, and -66/67.1,18,27,29,44 In
addition, PCN-45/36 and -39 occurring in this group are
reportedly among the most abundant tetra-CNs in fly ashes
from MSW.1,29 From the factor scores plot in Figure 4, the
Tema and Teshie sites relate to the Group 1 set of congeners.
This implies that the sources of PCN emissions at Tema and
Teshie were most likely related to combustion predominantly.
As expressed earlier, Tema is an industrial city, as such
combustion byproduct were anticipated; while at Teshie, we
assumed the aforementioned factor of waste burning.
Some of the most enrich congeners included in Halowax
(technical PCN formulations) as characterized by Falandysz et
al. (e.g., PCN-23, -37/33/34, -48/35, -46, and -61) clustered
into Group 2.45 But these congeners are also fairly prominent
among trace PCN contaminants present in technical PCB
formulations.46 It is, therefore, difficult to indicate precisely
which formulations might have emitted them. Per the factor
score plot, however, Group 2 could be associated with the
Takoradi site, where PAS were placed close to the Takoradi
shipping harbor. Thus, this cluster possibly suggests an impact
from the harbor environment. As an old harbor, possible factors
of PCN emissions might include old applied paints as well as
broken down/abandoned ships. Thus far, the implication of the
PCA is that such point sources contributed the most to air
PCNs at Takoradi closest to the coastal line.
Figure 5. Dioxin-like toxicity associated with PCN (PCN TEQ) in the
atmosphere of Ghana.
mediated via a similar mechanism as the dioxins, toxic
equivalent factors (TEFs) have been determined for some of
the PCN congeners, weighing their toxicity against the most
toxic dioxin 2,3,7,8-TCDD, which is assigned the TEF of
1.17,19,21,47,48 In this study, 17 PCN congeners with known
TEFs were used to assess overall PCN toxic equivalency
(TEQ) (Table S3). These congeners are within the tetra- to
octa-CN homologue groups, as the tri-CN homologues have no
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Environmental Risk (SLER) at the Yokohama National
University funded by Japan Science and Technology Agency
and the Global Center of Excellence (GCOE) Program “Global
Eco-Risk Management from Asian Viewpoints” of the Ministry
of Education, Culture, Sports, Science and Technology of
Japan.
or low dioxin-like activities and TEFs. The highest value was
applied among multiple TEFs for a particular congener. In
addition, if TEF is available for only one of coeluting congeners
(usually the congener with greater content), this factor was
assumed applicable for both congeners. For the 17 PCN
congeners (coeluting congeners considered as a unit), TEQ
17
was estimated as ∑n=1
Cn × TEFn, where Cn and TEFn are
concentration and TEF of the nth congener, respectively. We
estimated PCN TEQ concentrations to range between 0.49 and
5.6 fg TEQ/m3, with a national average of 2.1 fg TEQ/m3.
∑TEQ was highest in the southern parts of Ghana and least in
the northern regions (Figure 5). Averagely, the southern, mid,
and northern belts of the country registered TEQ of 3.1, 1.0,
and 0.80 fg TEQ/m3, respectively. The worst case scenario of
dioxin-like toxicity by PCNs via inhalation in Ghana could be
estimated at Legon as follows: TEQLegon × approximate air
volume inhaled per day = 5.6 fg TEQ/m3 × 15 m3/day = 84 fg
TEQ/day. The tolerable daily intake (TDI) of dioxin toxicity as
stipulated by the WHO is 1−4 pg TEQ/kg body weight/day.48
For any adult of body weight 60 kg, maximum WHO-TDI of
dioxin toxicity is estimated as 4 pg TEQ/kg/day × 60 kg = 240
pg TEQ/day. Thus, it is estimated that a daily exposure to the
highest dioxin-like toxicity by air PCNs in Ghana might account
for about 0.04% of the maximum WHO-TDI of dioxin toxicity.
In summary, the present study has revealed an emerging
burden of air PCNs in Ghana and reiterates the need for
thorough monitoring of industrial and unintentional POPs in
Ghana and other West African countries. The fraction of
dioxin-like toxicity by air PCNs was low, but other routes of
exposure such as by food and water and other dioxin-like
compounds in these media should be monitored to help
evaluate the total dioxin-related burden in Ghana.
■
■
ASSOCIATED CONTENT
S Supporting Information
*
Additional experimental details, data, and back trajectory
information. This material is available free of charge via the
Internet at http://pubs.acs.org.
■
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AUTHOR INFORMATION
Corresponding Author
*Phone: +81 45 339 4352. Fax: +81 45 339 4373. E-mail:
[email protected].
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
We are very thankful to the following colleagues for the
immense help they provided during sampling in Ghana: Mr.
Eric A. Amoako (Department of Urban Roads, Accra), Mr.
John Terlarbi (Department of Theoretical and Applied Biology,
Kwame Nkrumah University of Science and Technology,
Kumasi), Mrs. Nora N. Terlarbi (Ghana Food and Drugs
Board, Kumasi), Prof. Derick Carboo (Department of
Chemistry, University of Ghana, Legon, Accra), Dr. Noah
Adametey (formerly of Ghana Atomic Energy Commission,
Kwabenya, Accra), Dr. Kwabena Ofosu-Budu (University of
Ghana Agricultural Research Centre, Kade), and Mr. Gordon
Foli (Department of Geological Engineering, Kwame Nkrumah
University of Science and Technology, Kumasi).
This study was supported by the International Environmental Leadership Program in Sustainable Living with
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Environmental Science & Technology
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