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JOURNAL OF PLANT AND ANIMAL ECOLOGY
ISSN NO: 2637-6075
Research
Distribution Spread and Environmental Risk Status of Pb, Cd And Cr in Soils of an Open-Air Waste
Dumpsite along Tombia/Amassoma Road in Yenagoa Metropolis
Aigberua Omozemoje Ayobami1,*, Okumoko Pearce Dokumo2
1Department of Environment, Research and Development, Anal Concept Limited, Elelenwo, Rivers State, Nigeria
2Department of Earth Sciences, Federal University of Petroleum Resources, Effurun, Delta State, Nigeria
Abstract
In spite of the popularity of open-air waste dumping in Nigeria, it remains a relatively less effective
waste management option across the globe because of its associated environmental impacts which includes the
release of green house gases (GHGs), persistent organic pollutants (POPs), and metal micro-pollutants amongst
others. This study aims to assess the potential environmental risks associated to metals released and vertically
delineated across the soil profile within surroundings of dumpsite. Heavy metals in soil samples were
acid-digested using the aqua-regia mixture of hydrochloric and nitric acid, followed by instrumentation analysis
using the GBC 908 PBMT model atomic absorption spectrophotometer. Contaminated sites showed metal
concentrations ranging from 1.493 to 109.460 mg/kg, 0.133 to 4.237 mg/kg, and 5.200 to 25.367 mg/kg for
lead, cadmium and chromium respectively, with location 1 land area showing the most contamination. Only soil
chromium was observed within regulatory stipulations in all cases. There was significant variation (p < 0.05)
between the different sample locations, thereby indicating variations in composition of dumped wastes. Lead
and cadmium showed the strongest positive correlation (r = 0.855, p < 0.01) and the application of some heavy
metal pollution indicators revealed relatively higher metal loads and degree of contamination, as well as
depicting potential ecological risk for soils of location 1. The significant heavy metal contamination of soils in the
Tombia-Amassoma waste dumpsite requires that the local environmental sanitation and regulatory authorities
take necessary remedial action to forestall the escalation of public health concerns that may emanate from this
open-air dump.
DOI: 10.14302/issn.2637-6075.jpae-20-3322
Corresponding author: Aigberua Omozemoje Ayobami, Department of Environment, Research and
Development, Anal Concept Limited, Elelenwo, Rivers State, Nigeria, E-mail: ozedee101@gmail.com
Keywords: Tombia-Amassoma waste dumpsite, green house gases (GHGs), persistent organic pollutants
(POPs), heavy metal micro-pollutants, regulatory stipulation.
Received: Apr 15, 2020 Accepted: Apr 17, 2020 Published: Apr 20, 2020
Editor: Sylvester C. IZAH, PhD, Department of Biological Science, Niger Delta University, Nigeria
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Introduction
Solid waste trash in urban environments is the
nature-derived products of man’s daily undertakings,
especially in populated, bustling cities of developing
nations. Whilst urbanization leads to a rapid rise in
human population growth, it equally mounts pressure on
production to meet demands. Consequently, the
increasing multiplication of wastes, coupled with
inappropriate waste discharge options continues to pose
a major health challenge for the government and people
to tackle [1]. Waste dumping, though a popular waste
management practice, is among the less effective and
desired options of managing trash. In spite of this, vast
tonnes of waste are still being junked in open-air solid
waste dumpsites globally [1-2]. The limited capacity to
reprocess wastes, especially in economically developing
nations is reason for having a higher fraction of
municipal debris going to open waste dumps [3]. Often
times, these wastes are not segregated into their
decomposable and non-decomposable fractions [4]. In
fact, tendencies are that numerous metropolitan cities of
emergent countries will continue to be hounded with the
varying adverse ecological changes posed by this waste
management practice [5]. Quite frankly, the Nigerian
perspective for dealing with wastes does not reflect any
positive deviation from this trend as six of the largest
dumpsites in Africa are situated in the metropolitan cities
of Lagos (Oluosun, Solous 2 and Epe), Ibadan (Awotan-
Apete and Lapite) and Port Harcourt (Eneka) open
dumpsites [1, 6].
Municipal waste dumping has become an urban
menace due to limited infrastructure to cater for the
rapid development of sprawling towns and cities. Many
cities are unable to provide basic social utilities spanning
from housing, portable underground water and effective
handling of solid squanders, thereby resulting to the
mounting heaps of trash in sanitary landfills and
open-air dumps, serving as hotbed for disease-carrying
rodents and insects. Garbage dumping grounds are
dotted within, and at outlying areas of Nigerian towns,
which as a result of poor waste handling methods have
continued to compromise the health conditions of those
residing within close proximity of scrap sites. A
decimation of self-reported illnesses has been reported
with extended distances of human residence from dump
grounds [7], while land-fills in the vicinity of riverine
communities may often result in overwhelming
eutrophication processes [8].
Every day, several million tons of municipal
scrap wastes are been disposed worldwide, with
methane (a greenhouse gas (GHG)) making up about
half the fractional constituent of land-fill gas (LFG) and
responsible for over 10% global emissions of methane.
The rising levels of atmospheric methane, one of the
GHGs responsible for global warming is sufficient reason
for governments, especially of third-world countries, to
enlighten and initiate modern waste reprocessing
operations, reduce GHGs and similar atmospheric
emissions by trapping as land-fill gas energy, one that
will not only serve as an ameliorative policy to reduce
the impact of ozone depletion but also aid in restoring
the environment and decimating associated public health
hazards, alongside improving energy independence and
exploiting other socio-economic benefits [1, 9-10].
The high mobility and bioavailability of
contaminant heavy metals in dump yards increases their
risk of infiltrating surrounding ground water systems and
stretches their toxic impact through the food chain. Most
especially, lead and cadmium are among the metals on
“red alert” based on their environmental unfriendliness,
bio-accumulation tendencies and cumulative toxicant
effects to body tissues and organs. Even trace
contamination of soil by heavy metals can have far-
reaching effects on the health of man and his
environment, whilst constituting prolonged menace to
water and ecosystems, or absorbing through plant roots
and other biodiversity growing in abandoned waste
dumpsites [4, 11-16]. The menace from leaching
municipal waste dumps is proliferated depending on the
waste content, bulk volume of trash, lifetime of waste
dung, prevailing thermal conditions, water content,
oxygenation levels, soil formation type and comparative
separation from human and aquatic
habitation [13, 17-18].
The key operational shortfalls that were
observed at dumpsites in the Niger Delta were poor
sanitary practices, poor manning and monitoring of daily
activities, an evident lack of tools and equipment
required for executing routine cleaning operations, the
absence of anti-contamination apparatus for detoxifying
leached dump effluents, unavailability of gas recollection
systems, non-existent fire-fighting instrument, dearth of
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environmental buffer areas and the absence of
barricades around waste dump yards, followed by the
lack of safety training for waste handlers and the
likelihood of their exposure to disease conditions [19].
About 2.1% of responses from some interviewed
Yenagoa residents revealed good recognition of waste
handling procedures (95.4%), utilization of waste
receptacles (86.7%), relatively effective waste collection
by environmental sanitation authorities (70.4%),
practice of open-air incineration (6.3%), dumping into
rivers and storm water drains, or by roadsides (5.0%),
stacking at backyards (2.1%) [20].
Apart from the atmospheric concomitants that
are released from open dumpsites, the surrounding soils
and leachate from trash dumpsites pose potential
pollution problems by way of reducing soil fertility and
compromising surface and underground water quality as
a result of the vertical delineation of micro-pollutants
such as trace/heavy metals, persistent organic
pollutants and anions through the soil strata. From the
foregoing, this study aims to assess the extent of
environmental risks posed by some soil available trace
metals within vicinity of the Tombia/Amassoma
dumpsite by applying some heavy metal pollution
indices.
Materials and Method
Description of Study Area
Like the rest of Niger Delta environment,
climate is classified into the dry and rainy seasons with
temperatures reaching about 35oC all through the
year [21]. The dumpsite at Tombia-Amassoma road is
located in Yenagoa Local Government Area of Bayelsa
State. It is strategically sited over 1 km away from the
closest human habitation, within the geographical
coordinates of latitude N4o58’57.654” and longitude
E6o19’27.498”. Also, the control site is located about 3
km away from trash site, within close proximity of
Tombia junction.
Sample Collection
A triangular soil sampling section was
established around the Tombia-Amassoma garbage
dumpsite. Eleven (11) grab samples of soil was
collected at three (3) depths of 0.3, 0.5 and 1.0 m
respectively for each of three (3) locations at each edge
of the triangular sampling quadrant, as well as duplicate
top soil zones (0.3 metre) of control location.
Specifically, nine (9) waste dump soils and another two
(2) from control were collected for metal analysis. The
triangular sample distribution was chosen in a manner
that reflected zones of heavy and mild municipal waste
contamination of soil. This was done with the intent of
assessing the impact and associated environmental risk
of heavy metals released from the waste dung on soil
quality. Sample area and control site information are
highlighted in Table 1 below.
Sampling was executed during the dry season
period of March 2020. The samples were collected at
different geo-spatial locations and the co-ordinates
established via a Garmin Etrex GPS instrument. The
control point was sited way off the waste dump area at
a distance of about 3 km away. Soil samples were
collected using depth-calibrated soil auger and
transferred into Ziploc bags before being transported to
the laboratory.
Materials & Methods
Acid Digestion Protocol for Heavy Metals in Soil
Room temperature air-dried soil samples were
homogenized by grinding and segregated into the
required soil diameter of ≤ 2 mm by sieving through 2
mm mesh sieve. Exactly 5 g of each soil was
sub-sampled into 100 ml glass beaker, followed by the
addition of 1 ml concentrated nitric acid (HNO3) (s.g
1.42), 10 ml of concentrated hydrochloric acid (HCl) (s.g
1.19) and about 20 ml distilled water. Another empty
glass beaker containing the same ratio of acid/water
mixtures was digested and labeled as “reagent blank”.
Samples were digested on a Corning PC-351 model hot
plate at medium to low heat until about 5 ml
concentrated extract was remaining. The content of the
beaker was left to cool for around 30 minutes.
Afterwards, solutions were filtered and quantitatively
conveyed into 50 ml standard flasks. Finally, filtered
solutions were marked up with distilled water [21-22].
Test metals were determined using the GBC 908PBMT
model Flame Atomic Absorption Spectrophotometer
(FAAS). Each sample was individually presented for
aspiration into the FAAS and their vaporized fractions
were nebulized in the air-acetylene flame using different
fuel/oxidant ratios (Table 2). Instrument calibration
standards for metals, and the respective sample
concentrations were recorded in mg/l units. The heavy
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Table 1. Field sample information for waste dumpsite and control point
Sampling
Location Latitude Longi-
tude
Site descrip-
tion
0.3m
depth
0.5m
depth
1.0m
depth
Number of
samples
Location
1
N4o58’57.
654”
E6o19’27.4
98”
Heavily polluted
area Sampled Sampled Sampled 3
Location
2
N4o58’54.
102”
E6o19’25.0
86”
Medium (mildly)
polluted area Sampled Sampled Sampled 3
Location
3
N4o58’56.
19”
E6o19’21.4
62”
Medium (mildly)
polluted area Sampled Sampled Sampled 3
Control
½
N4o57’42.
264”
E6o21’7.88
4”
No visible trace
of pollution Sampled Not sam-
pled
Not sam-
pled 2
Metals
-
Slit
width
(nm)
Wavelength
(nm)
Lamp
current
(mA)
Flame composition
Acetylene Air
(L/min) (L/min)
Check standard
concentration,
(mg/L)
Detection
limit
(mg/L)
Pb 1.00 217.0 5.0 2.0 10.0 0.5 0.02
Cr 0.2 357.9 6.0 3.2 10.0 0.5 0.006
Cd 0.5 228.8 3.0 2.0 10.0 0.5 0.001
Table 2. Operational settings and condition of FAAS
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metal stock solutions of 1,000 mg/l were sub-stocked
into working concentrations of 0.5, 1.0, 2.0, 5.0, 10.0
and 100.0 mg/l for lead, cadmium and chromium. Each
of the metals was detected at wavelengths of 217.0,
228.8 and 357.9 nm for lead, cadmium and chromium
respectively. To gain assurance of quality, distilled water
was aspirated by the FAAS as blank solution [21].
Analysis of Statistics
In order to determine the relation and variance
among the different heavy metals of Tombia-Amassoma
waste dumpsite soil, descriptive statistical analysis by
statistical package for social science (SPSS) version 20
was applied. Data was recorded as mean ± standard
error. The range of values obtained for the sampling
points were equally presented. One way analysis of
variance (ANOVA) was used to reveal significant
variation at P = 0.05. Where significant variation was
depicted, Waller-Duncan statistics was applied for mean
value comparison of test metals. Heavy metal
relationships were correlated by the Spearman’s rho
correlation matrix.
Establishment of Baseline/control Values for the
Assessment of Environmental Risk Factors
Heavy metal data from the control/
uncontaminated soil was compared against results from
the waste dump contaminated soil, information obtained
was used to assess environmental risk factors. This has
previously been applied in different environmental
contamination scenarios (oil contaminated soil and
sediment) [22-24].
Environmental Risks
Contamination Factor and Degree of Contamination
Contamination factor and degree of
contamination was calculated on the basis of method
developed by [25].
Contamination factor =
…. (1)
The values obtained were classified as; C
f
< 1
(low contamination), 1 ≤ C
f
< 3 (moderate
contamination), 3 ≤ C
f
<6 (considerable contamination)
and C
f
≥ 6 (very high contamination).
Degree of contamination =
…… (2)
The degree of contamination was classify as; C
d
< 8 (low risk), 8 ≤ C
d
<16 (moderate risk), 16 ≤ C
d
<
32 (considerable risk) and C
d
> 32 (very high risk).
Pollution Load Index
Pollution load index calculations were applied on
the basis of methods previously given [26-29]. The
pollution load indicator was categorized as; PLI < 1 (no
pollution); 1 < PLI < 2 (moderate pollution); 2 < PLI <
3 (heavy pollution); 3 < PLI (extremely heavy pollution).
Pollution Load Index =
.…… (3)
Geo-accumulation Index
The geo-accumulation indicator was calculated
as per method developed by [30] and categorized using
the formula given by [27], thus, I-geo ≤ 0
(uncontaminated), 0 < I-geo ≤ 1 (tending from
uncontaminated to moderate contamination), 1 < I-geo
≤ 2 (moderate contamination), 2 < I-geo ≤ 3 (tending
from moderate to heavy contamination), 3 < I-geo ≤ 4
(heavy contamination), 4 < I-geo ≤ 5 (tending from
heavy to extreme contamination) and I-geo ≥ 5
(extreme contamination).
Geo-accumulation index = Log2
...…… (4)
Where HM(s) is metal concentration in affected
soil and HM(c) is metal concentration in control/
unaffected plot.
Quantification of Contamination
Quantification of contamination was deduced by
the application of method previously given by [27].
Basically, positive values depict contamination.
Quantification of contamination, QoC (%) =
……… (5)
Where, C
n
and B
n
represent the metal levels in
the contaminated site and baseline (control station)
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respectively.
Potential Ecological Risk (PER)
Potential ecological risk indicator and risk
indicator was calculated based on the methods
developed by Hakanson [25].
Potential ecological risk = toxic factor x contamination
factor.
Mathematically expressed as
......... (6)
The toxic factor for the various metals studied
include Pb = 5, Cd = 30 and Cr = 2 [25]. The ecological
risks were classified as Er < 40 (low PER), 40 ≤ Er < 80
(moderate PER), 80 ≤ Er < 160 (considerable PER), 160
≤ Er < 320 (high PER) and Er ≥ 320 (very high PER).
Risk index, RI =
……… (7)
The values were classified as; R’ < 150 (low RI),
150 ≤ R’ < 300 (moderate RI), 300 ≤ R’ < 600
(considerable RI) and R’ ≥ 600 (very high RI).
Results and Discussion
Table 3 presents the heavy metals in soils
around the dumpsite along Tombia-Amassoma road in
Yenagoa metropolis, while the Spearman’s rho
correlation matrix of heavy metals in dumpsite soil is
highlighted in Table 4. Lead concentrations ranged from
5.597 to 109.460 mg/kg, 1.763 to 75.427 mg/kg and
1.493 to 67.470 mg/kg for top soils (0.3 m), mid-depth
soils (0.5 m) and bottom soils (1.0 m) of dumpsite
contaminated soils respectively. Cadmium levels
reportedly between 0.550 and 3.143 mg/kg, 0.247 and
4.237 mg/kg and 0.133 and 2.807 mg/kg for top soils
(0.3 m), mid-depth soils (0.5 m) and bottom soils
(1.0m) of the dumpsite contaminated soils respectively.
Finally, chromium concentrations ranged from 8.377 to
22.183 mg/kg, 6.443 to 25.367 mg/kg and 5.200 to
14.877 mg/kg for top soils (0.3 m), mid-depth soils (0.5
m) and bottom soils (1.0m) of the dumpsite
contaminated soils respectively (Table 3).
On the other hand, only top soils (0.3 m) were
collected for the control locations with values ranging
from lead (1.660 to 2.957 mg/kg), cadmium (0.210 to
0.223 mg/kg) and chromium (9.453 to 10.107 mg/kg)
respectively. Apart from the top soil of dumpsite location
1 (0.3 m), lead in soil was predominantly within the
Department of Petroleum Resources (DPR) target value
of 85 mg/kg. Also, soil chromium was within DPR target
value of 100 mg/kg for all dumpsite-contaminated
locations. However, all three (3) soil depths of sample
location 1 and top soil (0.3 m) of location 2 showed
cadmium values exceeding the DPR target
concentration. In spite of the conformance of metal
concentrations recorded in the dumpsite to DPR
intervention levels, it is pertinent to identify
concentrations exceeding target values as being
environmentally significant and possessing hazardous
potential. On the other hand, soils of both control
locations revealed relatively lower heavy metal
concentrations, with all values being within stipulated
DPR target and intervention levels. All other sampling
locations and depths were within the specified
regulatory target and intervention levels of 0.8 and 12
mg/kg for cadmium in soil (Table 3) [31].
Most notably is the fact that all sampled depths
of location 1 and the top soil of location 2 consistently
showed significant difference (p < 0.05) for all the
metals been analyzed. The locations with no significant
difference (p > 0.05) includes: midpoint (0.5 m) and
bottom soils (1.0 m) of locations 2 and 3 for lead and
cadmium, and bottom soils (1.0 m) of locations 2 and 3
for chromium (Table 3). In addition, the strongest and
weakest positive correlations were between lead and
cadmium (r = 0.855, p < 0.01), and lead and chromium
(r = 0.787, p < 0.01) respectively, with cadmium also
showing positive correlation with chromium (r = 0.829,
p < 0.01) (Table 4).
Heavy metal levels in the study area is higher
than values previously reported in soils around the
embankment of effluent wastewater retention pits in the
Niger Delta [32], the oil flow station at Imiringi
community in Bayelsa State [21], Rumuolukwu
community oil spill site [22], residual fractions of
dumpsite soils in a mangrove forest at Eagle Island [33],
crude oil contaminated soils of Bdere community in
Ogoni land [34-35]. However, chromium values in this
study was lower than earlier reported by [36] for soils
from an abattoir dumping site. Statistically, the soil
metals showed positive correlation with each other,
suggesting that they may be from similar
source [21, 37-38]. The correlation trend of heavy
metals in sediment, as reported in this study,
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Locations Pb Cd Cr
TA Loc SS1T 109.460±5.049f 3.143±0.178e 22.183±1.747g
TA Loc SS1M 75.427±2.935e 4.237±0.458f 25.367±1.420h
TA Loc SS1B 67.470±3.318d 2.807±0.316d 14.877±1.078f
TA Loc SS2T 15.217±0.908c 0.910±0.141c 12.550±0.620e
TA Loc SS2M 2.097±0.220ab 0.437±0.085ab 6.443±0.716ab
TA Loc SS2B 1.493±0.159a 0.133±0.025a 5.200±0.360a
TA Loc SS3T 5.597±0.571b 0.550±0.070b 8.377±1.058cd
TA Loc SS3M 1.763±0.279ab 0.247±0.050ab 7.397±0.950bc
TA Loc SS3B 3.463±0.339ab 0.197±0.040a 5.310±0.338a
TA Control SS1T 1.660±0.244a 0.210±0.040ab 9.453±0.794d
TA Control SS2T 2.957±0.285ab 0.223±0.025ab 10.107±0.725d
Table 3. Heavy metals distribution in contaminated and uncontaminated soils
Data are expressed as mean ± standard error; different letters along the column indicate significant variations
(p < 0.05) according to Duncan statistics
Table 4. Spearman's rho correlation matrix for test metals
**. Correlation is significant at the 0.01 level (2-tailed).
Metals Pb Cd Cr
Pb 1.000
Cd .855** 1.000
Cr .787** .829** 1.000
Table 5. Contamination factors, degree of contamination and pollution load index of test metals in soils of
Tombia-Amassoma waste dumpsite
Locations Contamination factor Degree of contamination Pollution Load
index
Pb Cd Cr
TA Loc SS1T 47.4 14.5 2.3 64.2 11.6
TA Loc SS1M 32.7 19.5 2.6 54.8 11.8
TA Loc SS1B 29.2 12.9 1.5 43.7 8.3
TA Loc SS2T 6.6 4.2 1.3 12.1 3.3
TA Loc SS2M 0.9 2.0 0.7 3.6 1.1
TA Loc SS2B 0.7 0.6 0.5 1.8 0.6
TA Loc SS3T 2.4 2.5 0.9 5.8 1.7
TA Loc SS3M 0.8 1.1 0.8 2.7 0.9
TA Loc SS3B 1.5 0.9 0.5 3.0 0.9
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corroborates the report of [21] where lead, nickel and
iron depicted positive correlations. Similar to the findings
of [39] where statistical analysis revealed statistical
variations in metal levels of dumpsite soils, this study
revealed similar trend among metal concentrations and
locations.
Obviously, there is a connection between soil
quality and heavy metal levels [39-43]. Most metal
contaminants often depict elevated levels of distribution
spread during the dry season [14, 22, 36]. Hence, the
concentration of heavy metals in soils within vicinity of
open-air dumpsite is observed to be higher than those
collected from natural uncontaminated environments
[14, 33]. Furthermore, studies have shown that the
levels of these contaminant metals in soils around
municipal waste dumpsites are not dependent on the life
time of the dump area but on the origin/cause, make up
and terrain of the waste dump [44].
Mutually Dependent and Independent Heavy Metal
Associations in Soils of Open Waste-Dump
Cluster analysis was applied in the identification
of variables (sample location/depths and metals
distribution spread) of close affiliation within the study
area. Heavy metals of common dependence showed
homogeneity in element while those of correlative
independence depicted diverging attributes. For the test
metals, there was similarity between soil cadmium (Cd)
and chromium (Cr) across the study locations. Hence,
lead (Pb) was reflected as the mutually independent
heavy metal variable (Figure 1). On the other hand,
dumpsite-contaminated sections at the top (0.3 m),
midpoint (0.5 m) and bottom soils (1.0 m) of location 1
showed mutual dependence. However, soil strata from
location 1 were mutually independent of soils from
control, locations 2 and 3. Hence, all other metals of the
control and sample locations 2 and 3 were closely
interlinked (Figure 2). Contrary to the reported metal
association between cadmium (Cd) and chromium (Cr)
as highlighted in this study, [35] had reported strong
relationship between chromium (Cr) and iron (Fe) for
soils contaminated with crude oil. Also, there was strong
association between lead (Pb) and cadmium (Cd) in soils
of a waste dumpsite in a mangrove forest within Eagle
Island, Rivers State [33].
There was very high contamination factor across
the top, mid and bottom soil depths of location 1 and
the top soil of location 2 (C
f
≥ 6). Apart from the top
(0.3 m) and bottom (1.0 m) depths of location 3 which
depicted moderate contamination (1 ≤ C
f
< 3), all other
points revealed relatively low contamination (C
f
< 1)
(Table 5). Based on the result of this study, C
f
values
were lower than earlier reported for oil contaminated
soils of Rumuolukwu [22]. However, the values
exceeded those reported for sediments of the Nun
River [24] and sediments of Kolo creek [21]. Even
though lead and cadmium contamination factors in this
study exceeded those reported in sediments of
communities of Taylor creek, they were lower than the
chromium contamination factors reported by [45].
In addition, only soil profile within location 1
showed high degree of contamination risk (C
d
> 32),
followed by the top soil of location 2 which revealed
moderate degree of contamination risk (8 ≤ C
d
< 16), all
other soil profiles across the different soil locations were
at low risk of contamination (C
d
< 8) (Table 5). The
degree of contamination risk in this study exceeded
levels reported in sediments of Kolo creek under median
and geometric mean considerations [21]. Also, it
surpassed C
d
values reported for cassava effluent
contaminated soils [46] and sediments from
communities around Taylor creek [45].
Furthermore, pollution load index deductions
showed extremely heavy pollution (3 < PLI) for all
sample depths of location 1 and the top soil of location
2. On the other hand, soils collected at midpoint and top
soil zones of locations 2 and 3 respectively showed
moderate pollution (1 < PLI < 2) while the remaining
sampling zones and profiles depicted no pollution (PLI <
1) (Table 5). Pollution levels were extremely heavy,
especially in location 1 as compared to ranges between
none to moderate pollution for sediments of the River
Nun [24], none to heavy pollution for sediments of
Taylor creek [45] and Kolo creek [21].
Stipulated Limits for Contamination Factor (Cf):
C
f
< 1 (low contamination); 1 ≤ C
f
< 3
(moderate contamination); 3 ≤ C
f
< 6 (considerable
contamination); C
f
≥ 6 (very high contamination).
Stipulated Limits for Degree of Contamination (Cd):
C
d
< 8 (low risk); 8 ≤ C
d
< 16 (moderate risk);
16 ≤ C
d
< 32 (considerable risk); C
d
> 32 (very high
risk).
Stipulated Limits for Pollution Load Index (PLI):
PLI < 1 (no pollution); 1 < PLI < 2 (moderate
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pollution); 2 < PLI < 3 (heavy pollution); 3 < PLI
(extremely heavy pollution).
Generally, the geo-accumulation index of lead
showed tendencies between the range of
uncontaminated to moderate contamination (0 < I-geo
≤ 1) and extreme contamination (I-geo > 5). Samples
from location 1 showed extreme contamination up to the
depth of 1.0 m. Only the top soil (0.3 m) of location 2
reflected moderate contamination levels (1 < I-geo < 2)
while other contaminated soil locations revealed
tendencies from uncontaminated to moderate
contamination (0 < I-geo < 1) (Table 6). Also, cadmium
I-geo depicted ranges between uncontaminated to
moderate contamination (0 < I-geo ≤ 1) and heavy
contamination (3 < I-geo ≤ 4). The land area of most
contamination was location 1, especially mid-depth (0.5
m) soil which showed heavy contamination whilst the
top (0.3 m) and bottom (1.0 m) soils of location 1
showed tendency from moderate to heavy
contamination (2 < I-geo ≤ 3). On the other hand,
samples across soil profiles of locations 2 and 3 revealed
tendencies of uncontaminated to moderate
contamination (0 < I-geo ≤ 1) (Table 6). In terms of
chromium, all sample locations and the different soil
depths portends I-geo tending from uncontaminated to
moderate contamination (0 < I-geo ≤ 1) (Table 6).
Based on the baseline/control plot consideration, results
of this work showed higher levels of geo-accumulation
index (
I-geo
) relative to the report of [27] for
underground water, Izah
et al
. [47] for soils
contaminated with cassava mill leachates, [24] for oil-
contaminated sediments of the River Nun, [45] for
sediments of Taylor creek, [38] on surface water
sediment along Nun river in Bayelsa state, and [21] for
surface water and sediment within vicinity of flow
stations at Kolo creek. In addition, the high
I-geo
values
was in contrast to predominantly low values reported by
[21], the difference in trend may have emanated from
the application of background consideration and/or the
lithological value of 1.5 in the geo-accumulation index
calculation [48].
The quantification of contamination of lead
indicated contamination for all samples of location 1, top
and mid-depth soils of location 2 and the top and
bottom soils of location 3. However, the highest
quantification of contamination was depicted in location
1. For cadmium, there was evidence of contamination in
all samples apart from bottom (1.0 m) soils of locations
2 and 3. Finally, chromium revealed contamination
across the three (3) soil depths of location 1 and the top
profile of location 2. All other soil depths and sampling
locations remained relatively uncontaminated (Table 6).
Overall, samples revealed considerable extent of vertical
pollution across the soil profiles, especially in soils of
location 1. Similar to [21], sample locations of this study
depicted positive values for quantification of
contamination, giving credence to the anthropogenic
sources of heavy metals from soils of the trash site
environment.
Stipulated Limits for Geo-accumulation Index
I-geo ≤ 0 (uncontaminated), 0 < I-geo ≤ 1
(tending from uncontaminated to moderate
contamination), 1 < I-geo ≤ 2 (moderate
contamination), 2 < I-geo ≤ 3 (tending from moderate
to heavy contamination), 3 < I-geo ≤ 4 (heavy
contamination), 4 < I-geo ≤ 5 (tending from heavy to
extreme contamination) and I-geo ≥ 5 (extreme
contamination).
Quantification of Contamination
Positive Values Indicate Contamination.
In terms of the potential ecological risk of
available lead in soils of the waste dumpsite, only top
and mid-depth soils of location 1 showed high risk (160
≤ E
r
< 320), followed by the bottom soil of location 1
which reflected considerable risk (80 ≤ E
r
< 160).
Alternately, all other sample locations portend low risk
(E
r
< 40). Similarly, PER of cadmium revealed very high
risk (E
r
≥ 320) for all sample depths of location 1,
considerable risk (40 ≤ E
r
< 80) in the top soil of
location 2, moderate risk for mid-depth and top soils of
location 2 and 3 respectively, while all other locations
depicted low risk (E
r
< 40). For chromium, all sampling
locations and soil profiles revealed low risk (E
r
< 40). E
r
data obtained in this study far exceeded the ranges for
lead (1.55 to 12.40) and cadmium (16.80 to 75.90)
reported for sediments of Kolo creek in Bayelsa
state [21]. Overall, cadmium reflected greater ecological
risk than lead for both studies. Conversely, [22] had
reported higher ecological risk factor ranges of (5.0 to
283.0) and (2.8 to 12.4) for lead and chromium
respectively. Table 7
Risk index showed very high risk (R’ ≥ 600) for
top and midpoint soils of location 1, considerable (300 ≤
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Table 6. Geo-accumulation index and quantification of contamination of test metals in soils of
Tombia-Amassoma waste dumpsite
Locations
Geo-accumulation index Quantification of contamination
Pb Cd Cr Pb Cd Cr
TA Loc SS1T 9.5 2.9 0.5 97.9 93.1 55.9
TA Loc SS1M 6.6 3.9 0.5 96.9 94.9 61.4
TA Loc SS1B 5.9 2.6 0.3 96.6 92.3 34.3
TA Loc SS2T 1.3 0.8 0.3 84.8 76.2 22.1
TA Loc SS2M 0.2 0.4 0.1 -10.1 50.3 -51.8
TA Loc SS2B 0.1 0.1 0.1 -54.7 -63.2 -88.1
TA Loc SS3T 0.5 0.5 0.2 58.7 60.5 -16.7
TA Loc SS3M 0.2 0.2 0.2 -31.0 12.1 -32.2
TA Loc SS3B 0.3 0.2 0.1 33.3 -10.2 -84.2
Locations
Potential ecological risk
Risk index
Pb Cd Cr
TA Loc SS1T 237.1 434.4 4.5 676.0
TA Loc SS1M 163.4 585.9 5.2 754.5
TA Loc SS1B 146.1 388.2 3.0 537.3
TA Loc SS2T 33.0 125.7 2.6 161.3
TA Loc SS2M 4.6 60.3 1.3 66.2
TA Loc SS2B 3.3 18.3 1.1 22.7
TA Loc SS3T 12.1 75.9 1.7 89.7
TA Loc SS3M 3.8 34.2 1.5 39.5
TA Loc SS3B 7.5 27.3 1.1 35.9
Table 7. Potential ecological risk and risk index of test metals in soils of Tombia-Amassoma waste dumpsite
LocationsRisk index
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R’ < 600) and moderate (150 ≤ R’ < 300) risks for top
and bottom soils of locations 1 and 2 respectively. All
other sample locations were of low risk on the index
scale. Similarly, RI data from this work surpassed the
reported range of 24.30 to 93.15 in Kolo creek
sediments [21].
Stipulated Limits for Potential Ecological Risk (PER):
E
r
< 40 (low risk), 40 ≤ E
r
< 80 (moderate
risk), 80 ≤ E
r
< 160 (considerable risk), 160 ≤ E
r
< 320
(high risk) and E
r
≥ 320 (very high risk).
Stipulated Limits for Risk Index (RI)
R’ < 150 (low risk), 150 ≤ R’ < 300 (moderate
risk), 300 ≤ R’ < 600 (considerable risk) and R’ ≥ 600
(very high risk)
Conclusions
The soil quality status of the Tombia-Amassoma
waste dumpsite is observed to be severely impacted by
the leached waste run-offs resulting in reasonable
vertical seepage of heavy metal micro-pollutants within
the soil profile, even up to the depth of 1 m. Compared
to the non-impacted control locations, the waste dump
site showed relatively higher distribution of test metals,
especially at location 1, where two non-essential metals
(lead and cadmium) recorded toxic concentrations
exceeding stipulated regulatory limits. There was
statistical significance across the varying sample
locations which depicted varying contamination point
sources. This may have emanated from the divergent
origins of dumped waste. Lead and cadmium were
strongly associated contaminants, both reflecting
elevated environmental metal loading, potential
ecological risk and significant contamination levels. In
view of the prevailing metal contamination within the
impacted soil environment, it is pertinent that proactive
steps are taken by relevant local environmental
authorities and stakeholders to ensure that proper
sanitary conditions are kept, an environmental
remediation plan is instituted and more effective waste
management options are adopted in order to cope with
emerging waste generation challenges which will likely
persist as a result of increasing urbanization and
industrialization of Yenagoa metropolis.
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