Vol. 14(3), pp. 42-50, July-September 2020
DOI: 10.5897/AJPAC2019.0814
Article Number: 56D137F64141
ISSN: 1996 - 0840
Copyright ©2020
Author(s) retain the copyright of this article
http://www.academicjournals.org/AJPAC
African Journal of Pure and Applied
Chemistry
Health risk assessment on humans by contamination of
heavy metals in some edible crops and fish at Galena
mining area of Nahuta, Alkaleri Local Government Area,
Bauchi State, Nigeria
Usman Y. M.1*, Nasiru Yahaya P.1 and Modibbo U. U.2
1
Department of Chemistry, Gombe State University P. M. B. 127 Gombe, Gombe State. Nigeria.
Department of Chemistry, Modibbo Adama University of Technology Yola, P.M.B. 2076 Yola, Adamawa State, Nigeria.
2
Received 21 August, 2019; Accepted 24 January, 2020
This work investigated the human health risk effects of heavy metal contamination at Galena mining
area. 10 elements were identified in both irrigated and wet season edible crops and fish were collected
from five sampling locations at Galena mining area. Wet season crops held higher concentrations of
heavy metals than irrigated crops. Study showed carcinogenic heavy metals Pb (1.42 E +08), Cd (1.36 E
+14), Cr (1.31E – 07), As (3.92 E -06), Co (9.42E + 12), Cd (1.36 E +14) while non-carcinogenic heavy
metals exposure showed assessment of health risk which indicated three major exposure pathways for
people: ingestion, dermal contact and inhalation for non-carcinogenic while carcinogenic metals were
exposure through ingestion and inhalation only. HI and HQ levels are < 1 indicating health risks of
heavy metals in crops and fish, while carcinogenic Pb showed higher HI through ingestion by children
and adults exposure. In this study, the routes of heavy metals exposure especially Pb as the major
constituent element of galena was greater than 1.0 indicating higher health risks hence adequate
diagnosis should be upheld in the area.
Key words: Galena, heavy metal, carcinogenic, non-carcinogenic, health risk
INTRODUCTION
Sediments and associated minerals conceived many
heavy metals due to chemical weathering from rock
surfaces; they are released into the environment at
various rates and their concentrations from natural
materials which are considered as pollutants, such as
arsenic released from the weathering of arsenical pyrite
(Gordon et al., 1999). Cadmium is a heavy metal with
high toxicity and it is a non-essential element in foods
and natural waters that accumulates principally in the
kidneys and liver. Higher values of Cadmium have been
previously reported for leafy vegetables cultivated along
road sides (0.27 mg/kg) by Oluwole et al. (2013). Pb is
also a highly toxic and carcinogenic metal causes chronic
health risks, including headache, irritability, abdominal
pain, nerve damages, kidney damage, blood pressure,
lung cancer, stomach cancer and gliomas. The children
are most susceptible to Pb toxicity, their exposure to high
levels of Pb cause severe health complexities such as
behavioral disturbances, memory deterioration and
reduced ability to understand, while long-term Pb
exposure may lead to anemia (Koki et al., 2015).
Chromium is known to help maintain normal blood
glucose levels by enhancing the effects of insulin (Chove
et al., 2006). The most widespread human effect is
chromium allergy caused by exposure to body, especially
Cr6+ compounds are assumed to cause cancer risk.
*Corresponding author. E-mail: usmanym45@gmail.com.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution
License 4.0 International License
Usman et al.
Arsenic, for instance, is regarded a human carcinogen
from extremely low levels of exposure. Acute exposure to
arsenic compounds may cause nausea, vomiting,
abdominal pain, muscle cramps and diarrhoea while
chronic exposure is associated with peripheral nerve
damage causing diabetes (Caspah et al., 2016). Cobalt is
also the required metals needed for normal body
functions as a metal component of vitamin B12. However,
high intake of Co via consumption of contaminated food
and water can cause abnormal thyroid artery,
polycythemia, over-production of red blood cells (RBCs)
and right coronary artery problems as reported by (Koki
et al., 2015).
Humans are exposed to heavy metals at the vicinity of
Galena mining area through inhalation of air pollutants,
consumption of contaminated drinking water, exposure to
contaminated soils or industrial waste, or consumption of
contaminated food. The sources of food affected are
commonly grown daily consumed vegetables, grains,
fruits, fish and shellfish can become contaminated by
accumulating metals from surrounding soil and water as
reported by Abhishek and Surendra (2016). This
research was aimed to assess the level carcinogenic
heavy metals in commonly consumed vegetable and
grains species in the vicinity of galena mining area, and
also to assess the potential health risk levels with their
daily exposure rate and impacts on humans.
43
Mudfish (Clarotex anguillaris), Catfish (Clarotex laticeps), Trunk fish
(mormyrus rume) and Nile tilapia (Heterotis niloticus).
Water sampling
Water samples was collected using water sampler by submerging
the sampler bottle when close into the water location and opened
up to collect water and then capped while submerged to avoid
mixing with contaminants as adopted by APHA (1992). Water
samples was also collected in plastic sample bottles, thereafter
each sample of water was mixed with 1.5 ml of 70% HNO3 in a litre
that gave a pH < 2 for preservation due to analysis of elements
present.
Study area
Galena mining Area at Nahuta is located at latitude 10° 48’ 42” E
and longitude 9° 34’ 45” N along Futuk Road near Yalo in Alkaleri
Local Government Area of Bauchi State. The village was located on
bearing of 180° South of Yalo, whereby the direction of Nahuta is
about 20 km drive from Yalo. The village can also be accessible
from Billiri Road heading to Kashere in Gombe State or preferrably
from Alkaleri Road leading to Yalo in Bauchi State. In terms of size,
the village occupied a total land area of about 10 km2 (Futuk, 1975).
Geologically, Nahuta has a Bima-formation rock types with few
mining settlements having sparse population of about 2000 per
square km. The mining operation started as far back in 1990, and
the initial mining state was carried out by local miners, which was
later sponsored by Chinese based company. The mineral
exploration methods are underground mining. The Galena mining at
this area is currently used for export purpose.
MATERIALS AND METHODS
Sediments sampling
Sediment sampler was used to collect bottom sediment samples at
center of Mine Lake by the effort of a good swimmer at different
locations of about 100 m apart. The equipment for these sampling
varies with deep of water and texture of the sediment. Five samples
was collected and kept in polythene bag for the analysis as adopted
by Titus et al. (2012).
Plants sampling
The plants collected are; Maize (Zea mays), Rice (Oryza glaberimo),
Beans (Phaseohus vulgaris), Tomato (Lycopericon esculentum),
and Okro (Hibiscus esculentum ). Five samples at interval of 5 m
apart of the above-mentioned plants were collected at two locations
of Nahuta Upstream and Nahuta Downstream along the mining site
during dry and raining seasons. The sampling method adopted was
to ensure relation to proper identifications of species and
constituents present in the samples. Samples collected was kept in
polythene bags to avoid evaporation of important constituents and
later dried and preserved for analysis at the laboratory as adopted
by Titus et al. (2012).
Sampling and sample preparation
Plants samples analysis
Collected plants and vegetable samples from different locations
were washed with water to remove impurities. Succulent’s samples
such as okro and tomatoes were cut and sliced for easy drying
while hard grains like rice and maize were chaffed to remove
pericarp and the endocarp was then grinded into powder form using
mortar and pestle. The samples was dried at constant weight at
90°C in an oven and quartered to obtain a 100 g of representative
fraction for analysis as described by Titus et al. (2012).
Fish samples analysis
Fish species that have been used for this analysis are; Tilapia (O.
niloticus), Mudfish (C. anguillaris), Catfish (C. laticeps) and Trunk
fish (M. rume). Fish species were treated differently by removing
the parts and dried in an oven at 105°C at constant weight.
Thereafter, samples were pulverized in a clean mortar dried, was
then sieved to less than 125 um, quartered to obtain 100 g of
representative fraction and stored in plastic bottles for analysis as
adopted by Titus et al. (2012).
Fish sampling
Digestion methods for preparation of MP-AES
Five commonly occurring species of fresh catch of fish was
purchased at the mine lake bank at Nahuta from the fishermen as
stated by Titus et al. (2012). Fish samples were preserved in
coolers in contact with ice blocks and taken to the laboratory for
analysis. The species used are; Tilapia (Oreochromis niloticus),
Method involving sample preparation procedure in relation to the
acid digestion of sediments, sludge, and soils was used. A short
description of this digestion procedure was given below. Initially, 10
cm3 of 1:1 HNO3 was added to 1.00 g of soil sample in a 25 × 150
44
Afr. J. Pure Appl. Chem.
Table 1. Comparatives mean concentrations of irrigated and wet seasons samples contaminated by heavy metals (mg/kg).
Metals
Cd
Cu
Ni
As
Co
Zn
Fe
Pb
Mn
Cr
IB
0.34
0.071
0.037
1.54
0.13
0.34
6.58
0.10
0.15
0.17
WSB
0.012
0.058
0.061
0.62
0.009
0.36
13.16
0.10
0.25
0.021
Fish
0.019
0.91
0.01
0.55
0.008
1.48
14.7
162.2
0.87
0.024
IM
0.013
0.031
0.012
0.296
-0.029
0.33
2.89
0.18
0.23
0.015
WSM
0.015
0.044
0.016
0.299
0.033
0.39
3.10
0.15
0.071
0.015
IO
0.009
0.123
0.035
0.68
0.04
0.44
1.03
0.23
0.59
0.018
WSO
0.023
0.065
0.010
0.46
-0.013
0.45
1.85
1.41
0.018
0.013
IR
0.008
0.054
0.024
0.10
0.010
0.18
5.0
0.066
1.00
0.016
WSR
0.030
0.085
-0.004
1.23
0.055
0.29
5.70
0.57
0.074
0.015
IT
0.096
0.022
0.041
0.92
0.048
1.78
5.70
0.64
0.088
0.016
WST
0.032
0.085
0.085
1.23
0.055
0.299
5.70
0.056
0.0744
0.015
IB: Irrigated Beans, WSB: Wet Season Beans, IM: Irrigated Maize, WSM: Wet Season Maize, IO: Irrigated Okro, WSO: Wet Season Okro, IR:
Irrigated Rice, WSO: Wet Season Rice, IT: Irrigated Tomatoes, WST: Wet Season Tomatoes.
mm glass digestion tube. The samples were then heated to 95 ±
10°C for about 15 min. When cool, 5 cm3 of HNO3 was added and
heat was applied for another 30 min. The digests were again
allowed to cool, before 2 cm3 of Milli-Q water and 3 cm3 of 30%
H2O2 was added and heated to 95 ± 5°C. After the digests were
cooled again, another 1 cm3 of 30% H2O2 was added. Heating
continued until the sample volumes reduced to approximately 5
cm3. The digests were then allowed to cool again before being
diluted to 50 cm3 with Milli-Q water. Prior to analysis, the soil digests
were further diluted ten-fold. The 2% moisture content given in the
certificate of analysis of the sample was incorporated into the
calculation on specific intensities that would analyze metals
contents present (Stefan et al., 2014).
RESULTS AND DISCUSSION
Heavy metals exposure analyzed were determined
through three pathways of ingestion, inhalation and
dermal intake of heavy metals from the soil through
various routes that grasped the crops, and exhibits health
risk effects on humans. The results of the enrichment
factors ranged from insignificant to moderate
contamination of heavy metal elements at sample
locations. The hazard quotient (HQ) evaluation
investigations of non-carcinogenic effects, showed
ingestion to be the route of exposure to soil dust that
results in a higher risk for heavy metals, followed by
dermal contact as stated by Afrifa et al. (2015). Hazard
Index of non-carcinogenic Heavy metals showed greater
than one, indicating likely adverse health risk effects.
Carcinogenic heavy metals showed highest Hazard Index
through inhalation of Pb (1.79 E + 07) as well as highest
Hazard Index through ingestion.
Concentrations of irrigated and wet seasons sample
contaminated by heavy metals
Table 1 showed mean concentrations of heavy metals in
fish exposed Pb = 162.228 ± 352.33 mg/kg as the highest
followed by Fe with 14.7 ± 8.237 mg/kg, and ± 0.588
mg/kg, while Ni = 0.0098 ± 0.0061 formed the least
among them.
Wet season beans at Galena mine area showed
highest concentrations of Fe = 6.58 ± 10.601 mg/kg in
irrigated beans but shows Fe = 13.16 ± 14.345 mg/kg in
wet season beans due to constant absorption of Fe
cations by the roots of beans during wet season. Both
irrigated and wet season beans showed the same
concentration of Pb = 0.010 ± 0.050 mg/kg. Mn = 0.1 45 ±
0.374 mg/kg and 0.25 ± 0.374 mg/kg for irrigated and wet
season beans. Irrigated beans showed Cr = 0.172 ±
0.0018 mg/kg while wet season beans showed Cr = 0.21
± 0.0084 mg/kg.
Irrigated maize showed highest concentrations of Fe =
2.89 ± 5.167 mg/kg in irrigated maize and Fe = 3.102 ±
4.836 mg/kg in wet season maize, while the least
concentration Co = -0.0290 ± 0.0775 in irrigated maize
and Co = 0.0332 ± 0.0089 mg/kg in wet season maize.
Irrigated okro showed Fe = 1.0263 ± 0.1841 mg/kg in
irrigated okro and Fe = 1.850 ± 0.011 mg/kg in wet
season okro. Pb = 0.239 ± 0.320 mg/kg in irrigated and
Pb = 1.413 ± 2.234 mg/kg in wet season okro, while Cr =
0.0224 ± 0.0043 mg/kg in irrigated okro and Cr = 0.0132
± 0.0013 mg/kg in wet season is the lowest. Adedokun et
al. (2016) reported that heavy metals content in
vegetables across the markets ranged as follow; Cd (0.05
– 0.20 mg/kg); Pb (0.34 – 5.44 mg/kg), Zn (4.21 – 20.80
mg/kg), Cr (0.25 – 1.51 mg/kg), Ni (0.13 –2.91 mg/kg)
and Cu (2.34 – 14.08 mg/kg).
Wet season and irrigated rice showed concentrations of
Fe in irrigated rice is higher than wet season rice with
values of 5.006 ± 7.179 mg/kg compared to 2.825 ±
0.371 mg/kg followed by concentrations of Fe in irrigated
rice that is higher than wet season rice with values of
5.006 ± 7.179 mg/kg compared to 2.825 ± 0.371 mg/kg.
Chromium showed Cr = 0.0198 ± 0.0055 mg/kg in
irrigated rice compared to Cr = 0.0144 ± 0.0023 mg/kg of
wet season rice as the lowest.
Tomatoes of wet season showed mean Fe = 2.545 ±
2.621 mg/kg in irrigated tomatoes compared to Fe = 5.70
Usman et al.
± 6.264 mg/kg in wet season tomatoes; thus, Fe
concentrations in wet season tomatoes are higher than
irrigated samples followed by Zn = 1.633 ± 3.123 mg/kg
in irrigated tomatoes and Zn = 0.295 ± 0.377 mg/kg of
wet season tomatoes. Cr = 0.0164 ± 0.00288 in irrigated
tomatoes compared to 0.0150 ± 0.0031 mg/kg in wet
season tomatoes showed the lowest concentrations. In
comparison, Adedokun et al. (2016) reported that heavy
metals content in vegetables across the markets ranged
as follow; Cd (0.05 – 0.20 mg/kg); Pb (0.34 – 5.44
mg/kg), Zn (4.21 – 20.80 mg/kg), Cr (0.25 – 1.51 mg/kg),
Ni (0.13 –2.91 mg/kg) and Cu (2.34 – 14.08 mg/kg).
Concentrations of heavy metals analyzed showed that
Fe = 2.5 mg/kg and 5.7 mg/kg in tomatoes and 1.2 mg/kg
in beans, while As = 1.54 ± 0.186. Other heavy metals of
Zn, Pb, Mn Fe and As in fish and rice contain higher
proportion above Mn = 0.1- 0.4 mg/kg, Fe = 0.06- 0.05
mg/kg, As = 0.01- 0.31 mg/kg, Cd = 0.03 mg/kg, Cu = 2.0
mg/kg, Pb = 0.01 mg/kg as reported by Khan et al., 2008)
along with NAFDAC as recommended levels, while Co,
Mn and Cr concentrations in edible crops of maize, okro
and tomatoes at Nahuta remain harmless in all the edible
crops with range values of 0.01 to 0.05 mg/kg. Results
also exposed that fish surviving within the Nahuta Galena
mine lake should be avoided completely due to high
concentrations of harmful heavy metals that have health
risk. Wet season crops held higher concentrations of
heavy metals than irrigated crops due to effects of
percolations and erosion process, hence contamination
affect the edible crops at the vicinity of Galena mine area
which are generally harmful when exposure daily as food.
Health risk assessment exposure
Health risks assessment of carcinogenic and noncarcinogenic risk through heavy metals present in some
edible crops and fish samples at Nahuta Galena mine
area has been determined to be above 1.0 from the
mean concentrations of heavy metals using exposure
pathways of inhalation, ingestion and dermal to
determine health risk human as evidence for taking
decision (USEPA, 1989; Hu et al., 2016, 2017). Other
studies by Abhishek and Surendra (2016) reported that
calculated Average Daily Exposure (ADE) of heavy
metals of As (0.74 mg/kg), Hg (1064.61 mg/kg) Cr (86.18
mg/kg) and Pb (23.22 mg/kg) for the different samples of
different locations were compared to reference value of
USEPA (1989). Generally, the hazard Index (HI) obtained
for the heavy metals (V, Cr, Mn, Cu, Zn and Pb) below
1.0, indicate non-cancer adverse health effects to be
most unlikely. Cancer risk index evaluated for Pb was
below 1.0 which shows little or insignificant cancer
adverse effect (Afrifa et al., 2015). Meanwhile, Adedokun
et al. (2016) reported that THQ values range showed that
Cd was0.048 – 0.192, Pb was 0.150 – 0.587, Zn was
0.021 –0.190, Cr was 0.0001 – 0.001, Ni was 0.050 –
0.120 and Cu was 0.148 – 0.239.
45
Based on the THQ equation and the RfDs of heavy
metals published by the United States Environmental
Protection Agency (USEPA), the safety limits of heavy
metals in seafood were Cr (2.9 mg/kg), Cu (3.9 mg/kg),
Zn (292 mg/kg), Cd (1.0 mg/kg), Hg (0.1 mg/kg), As (2.9
mg/kg) and Ni (19 mg/kg) as reported by (Koki et al.,
2015). Methods adopted was through USEPA (1989) and
are mentioned below.
Ingestion of heavy metals through soil
ADing (mg/kg-1 day-1) =
1989)
(USEPA,
Inhalation of heavy metals via soil particulates
ADinh (mg/kg-1 day-1) =
(USEPA, 1989)
Dermal contact with soil
ADder (mg/kg-1 day-1) =
1989)
(USEPA,
Where AD (mg/kg-1 day-1) is the absorbed dose of
exposure to through ingestion (ADing), inhalation (ADinh),
and dermal contact (ADder)
CS = Chemical concentration in soil (mg/kg)
IRing = Ingestion rate (mg soil/day): 100 mg/day (Liu et al.,
2013; USEPA, 2011)
FI = Fraction ingestion from contaminated source: 1 at
reasonable maximum exposure (USEPA, 2011).
EF: Exposure frequency: 350 days for non-carcinogenic
effect (Liu et al., 2013; USEPA, 2011).
SA= Exposure skin area: 5700 cm3 (USEPA, 2011; Liu et
al., 2013).
AF: Soil to skin adherence factor (mg/cm3): 0.07 mg/cm3
(USEPA, 2011; Liu et al., 2013).
ABS: Absorption factor (mg/cm3) 0.03 (As) 1 (USEPA,
2011; Liu et al., 2013).
BW: Body weight in (kg): 70 kg for adult average
(USEPA, 1989).
PEF: P article Emission factor: 1.36 × 109 m3.kg-1 (Liu et
al., 2013).
AT: Average: 365 × ED for non-carcinogenic effect and
365 × 70 for carcinogenic effect.
CF: Conversion factor (10-6) (USEPA, 2011; Liu et al.,
2013).
Non-carcinogenic risk assessment
The
hazard
quotient (HQ) represents the potential
46
Afr. J. Pure Appl. Chem.
6.00E+01
Hazard Index
5.00E+01
4.00E+01
3.00E+01
2.00E+01
1.00E+01
0.00E+00
Cd
Cu
Ni
Co
Fe
Cr
Heavy metals
Figure 1. Hazard Index of Non-carcinogenic Heavy metals in samples at Galena mining area.
Hazard Index
1.00E+18
8.00E+17
6.00E+17
4.00E+17
2.00E+17
0.00E+00
As
Mn
Heavy metals
Figure 2. Hazard index of non-carcinogenic heavy metals in samples at Galena mining area.
non-carcinogenic risk for an individual heavy metal. The
HQ is the ratio of mean daily exposure dose (AD) to the
reference dose (RfD) in mg/kg/day (USEPA, 2011; Hu et
al., 2017).
HQ =
Reference dose for (RfDing.) ingestion, (RfDinh.) inhalation
and (RfDderm.) dermal constant values of heavy metals for
this research have been estimated as;
The RfDing (mg/kg/day) of heavy metals values are; Cd =
1.00 x 10-3, Cr = 3.00 x 10-3 , Co = 3.00 x 10-4, Cu = 4.00 x
10-2 Pb = 3.5 x 10-3, Zn = 3.00 x 10-1 (Zheng et al., 2015),
Mn = 1.40 x 10-1, As = 3.00 x 10-4 (Bortey-Sam et al.,
2015), Ni = 2.00 x 10-2 (Caspah et al., 2016), and Fe =
7.00 x 10-1 (Patrick et al., 2014).
The RfDinh (mg/kg/day), constant values are; Cd = 1.00 x
10-3, Cr = 2.86 x 10-5, Co = 5.71 x 10-6, Cu = 4.02 x 10-2,
Pb = 3.52 x 10-3, Zn = 3.00 x 10-1 (Zheng et al., 2015), Mn
= 1.84 x 10-5, As = 3.00 x 10-4, Ni = 0 (Caspah et al.,
2016), and Fe = 8.25 (Patrick et al., 2014).
The RfDderm(mg/kg/day),constant values are; Cd = 1.00 x
10-5, Cr = 6.00 x 10-5, Co = 3.00 x 10-2, Cu = 1.20 x 10-2,
Pb = 5.25 x 10-4, Zn = 6.00 x 10-2 (Zheng et al., 2015), Mn
= 1.84 x 10-3, As = 1.23 x 10-4, Ni = 5.6 x 10-3 (Caspah et
al., 2016) and Fe = 7.00 x 10-1 (Patrick et al., 2014).
Hazard index and daily exposure dose of heavy
metals within the Galena mining area
Hazard Index was expressed in Figure 1 where Cr
showed the highest hazard Index of 5.08E+01 while Cd
showed the lowest hazard index of 0.00E+00. Figure 2
showed As metal with Hazard Index of 8.29E+17 and Mn
with least values of Hazard Index crop plants and aquatic
animals was analyzed at the vicinity of Galena mining
area using the formula above.
Figure 3 showed daily dose exposure of Pb with 7.67E
00, Fe (5.17E + 00), Zn (1.98E + 00), Ni (2.02E + 00) and
Mn showed 1.29E + 07, indicating that Pb showed higher
Usman et al.
47
9.00E+00
ADtot(mg.kg/daily)
8.00E+00
7.00E+00
6.00E+00
5.00E+00
4.00E+00
3.00E+00
2.00E+00
1.00E+00
0.00E+00
Ni
Zn
HeavyFemetals
Pb
Mn
Figure 3. Total daily exposure dose of heavy metals in all samples at Galena mining area.
ADtot(mg.kg/daily)
2.50E-02
2.00E-02
1.50E-02
1.00E-02
5.00E-03
0.00E+00
Cd
Cu
Cr
Heavy metals
ADtot(mg.kg/daily)
Figure 4. Total daily exposure dose of heavy metals in all samples at Galena mining area.
1.20E+15
1.00E+15
8.00E+14
6.00E+14
4.00E+14
2.00E+14
0.00E+00
As
Co
Heavy metals
Figure 5. Total daily exposure dose of heavy metals in all samples at Galena mining area.
daily dose while Pb was below 1.0 as reported by Afrifa
et al (2015). Figure 4 showed the daily exposure dose
whereby Cu showed 2.01E -07 followed by Cr with 3.11E
-03, while Cd showed the least daily exposure dose of
2.79E -07. However, Figure 5 showed the highest daily
exposure dose revealed by Co with 1.04E +15 whereas
Arsenic metals showed 1.02E +14.
The daily exposure dose of heavy metals of analyzed in
samples shown on Table 2 within the vicinity of Galena
mining area were expressed in decreasing order of Co >
As > Pb > Fe > Ni > Zn > Mn > Cu > Cd > Cr. Hazard
Index are determined through three different pathways of
48
Afr. J. Pure Appl. Chem.
Table 2. Mean daily intake (ADI) values for heavy metals in mg/kg/day.
Pathway
ADing tot
RfDing
HQ
Cd
0.00E+00
1.00E-03
0.00E+00
Cu
Ni
As
2.01E-02 4.80E-02 7.61E-06
4.00E-02 2.00E-02 3.00E-04
5.03E-01 2.40E+00 2.54E-02
Co
6.17E-04
3.00E-04
2.06E+00
Zn
2.48E-02
3.00E-01
8.27E-02
Fe
Pb
Mn
7.09E+00 7.59E+00 1.08E-03
7.00E-01 3.50E-03 1.40E-01
1.01E+01 2.17E+03 7.71E-03
ADinhtot
RfDinh
HQ
1.56E-10
1.00E-03
1.56E-07
3.00E-08 1.97E+00 1.54E-09
4.02E-02
3.00E-04
7.46E-07
5.13E-06
1.04E+15
5.71E--6
1.82E-20
8.19E-02
3.00E-01
2.73E-01
1.25E-08
8.25
1.52E-09
ADdertot
RfDder
HQ
2.79E-07
1.00E-05
2.79E-02
2.76E-06
1.20E-02
2.30E-04
4.40E-03
1.60E-02
2.75E-01
1.87E+00 -1.92E+00 8.05E-02 1.29E+07 3.05E-03
6.00E-05
7.00E-1 5.25E-04 1.84E-03 6.00E-05
3.12E+04 -2.74E00 1.53E+02 7.01E+09 5.08E+01
6.53E-08 1.02E+14
5.60E-03 1.23E-04
1.17E-05 8.29E+17
Cr
6.48E-05
3.00E-03
2.16E-02
6.19E-08 1.53E-02 6.51E-11
3.52E-03 1.43E-05 2.86E-05
1.76E-05 1.07E+03 2.28E-06
Table 3. Hazard Index (HI) for non-carcinogenic heavy metals of samples from Galena mining area.
Pathway
HQ ing
HQ inh
HQ derm
HI
Cd
0.00E+00
1.56E-07
2.79E-02
2.79E-02
Cu
5.03E-01
7.46E-07
2.30E-04
5.03E-01
Ni
2.40E+00
1.17E-05
2.40E+00
As
Co
Zn
2.54E-02 2.06E+00 8.27E-02
5.13E-06 1.82E-20 2.73E-01
8.29E+17 2.75E-01 3.12E+04
8.29E+17 2.34E+00 3.12E+04
Fe
1.01E+01
1.52E-09
-2.74E+00
7.36E+00
Pb
2.17E+03
1.76E-05
1.53E+02
2.32E+03
Mn
7.71E-03
1.07E+03
7.01E+09
7.01E+09
Cr
2.16E-02
2.28E-06
5.08E+01
5.08E+01
Table 4. Ingestion cancer risk for carcinogenic metals from Galena mining area.
Parameter
Total AD ing.
Mean AD ing.
SF
C Risk
Co
7.20E+12
6.00E+11
0.00E+00
As
1.51E-06
1.25E-07
1.50E+00
1.88E-07
Cr
1.84E-08
1.53E-09
5.00E-01
7.65E-10
Pb
2.54E+10
2.11E+09
8.50E-03
1.79E+07
Cd
1.62E+14
1.35E+13
0.00E+00
Table 5. Inhalation cancer risk for carcinogenic metals from Galena mining area.
Parameter
Total AD inh.
Mean AD inh.
SF
C Risk
Co
1.15E+13
9.61E+11
9.80E+00
9.42E+12
As
3.14E-06
2.61E-07
1.50E+01
3.92E-06
ingestion as shown in Table 3. Inhalation and dermal are
both in agreement with research reported by Zheng et al.
(2015).
Carcinogenic risk assessment
Carcinogenic risk assessment of samples within the
Galena mining area
Carcinogenic effects of risk assessment are determined
Cr
3.83E-08
3.19E-09
4.10E+01
1.31E-07
Pb
4.07E+10
3.39E+09
4.20E-02
1.42E+08
Cd
2.60E+14
2.16E+13
6.30E+00
1.36E+14
through ingestion and inhalation while dermal pathways
are neglected only for carcinogenic heavy metals such as
Cd, Co, Cr, As and Pb as reported by Caspah et al.
(2016). Average daily intake (ADI) values in mg/kg/day
for adults and children in soil from the mining area for
carcinogenic risk calculations are as reported by Afrifa et
al. (2015).
Tables 4 and 5 showed carcinogenic cancer risk
assessment determined by multiplying daily exposure
dose by their corresponding slope factor of individual
Cancer Risk Index
Usman et al.
49
1.50E+14
1.00E+14
Ing
5.00E+13
Inh
0.00E+00
Co
As
Cr
Pb
Cd
Heavy metals
Figure 6. Mean carcinogenic risk index of samples at the vicinity of Galena mining area.
carcinogenic heavy metals to arrive at cancer risk values.
Slope factor for ingestion in mg/kgday-1 of As = 1.50E +
00, Pb = 8.50E -03, Cr = 5.0E – 01, Co = 0, while slope
factor for inhalation of carcinogenic heavy metals are As
= 1.50 E + 01, Pb = 4.20 E – 02, Cd= 6.30 E + 00, Cr =
4.10 E + 01, and Co = 9.80 E + 00 (Caspah et al., 2016;
Zheng et al., 2015).
Figure 6 showed mean carcinogenic cancer risk of
heavy metals analyzed within the Galena mining area,
whereby Cd inhalation showed 1.36E +14 while ingestion
in Cr was 0.00E + 00. Highest prolonged inhalation risk
index of all the carcinogenic metals go to Cd in the
analyzed heavy metals within the Galena mining area.
The major constituent metal of Galena was Pb which has
carcinogenic inhalation risk of 1.42E +08 but ingestion
risk of only 1.79E + 07, Co has inhalation risk index
values of 9.42E + 12 but showed zero ingestion risk
index. Cr showed inhalation risk index of 1.31E – 07
compared to 7.65E -10 ingestion risk index. Arsenic
heavy metal (As) showed inhalation risk index of 3.92 E 06 while ingestion risk index of As showed only 1.88E 07.
Mean inhalation of carcinogenic heavy metal cancer
risk index was 2.91 E + 13 while mean ingestion of
carcinogenic heavy metal cancer risk index was 3.58E +
06 respectively. Cancer risk index of carcinogenic heavy
metals analyzed within the Galena mining area follows
the order Cd > Co > Pb > As > Cr, through inhalation risk
index, while ingestion cancer risk index order was Pb >
Cd > Co > As > Cr as related to Afrifa et al. (2015).
Carcinogens are assumed to have no effective
threshold. This assumption implies that there is risk of
cancer developing with exposures at low doses and,
therefore, there is no safe threshold for exposure to
carcinogenic chemicals. Carcinogens are expressed by
their Cancer Potency Factor (Koki et al., 2015).
Conclusions
The heavy metal contaminations at Galena mining area
of Nahuta were investigated in this study. Hazard index of
non-carcinogenic heavy metals showed greater than one,
indicating likely adverse health risk effects. Carcinogenic
heavy metals showed in Figure 6 revealed highest
Hazard Index through inhalation of Pb (1.42 E +08), Cd
(1.36 E +14), Cr (1.31E – 07), As (3.92 E -06), Co (9.42E
+ 12), and Cd (1.36 E +14) while Pb (1.79 E + 07)
showed highest hazard index through ingestion. Children
are more vulnerable to health risks at Galena mining area
due to their constant incorporation to soil, air and water
pollutants.
CONFLICT OF INTERESTS
The authors have not declared any conflict of interests.
ACKNOWLEDGEMENT
The authors thank ABU Zaria Multi User Laboratory for
the assistance rendered during instrumental analysis of
MP AES (Micro Plasma Atomic Emission Spectroscopy)
of elements present in some edible crops and fish
throughout the research period.
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