Download Evaluation of Some Heavy Metals in Food Crops of Lead Polluted

International Journal of Food Nutrition and Safety, 2015, 6(2): 67-73
International Journal of Food Nutrition and Safety
ISSN: 2165-896X
Florida, USA
Journal homepage: www.ModernScientificPress.com/Journals/IJFNS.aspx
Article
Evaluation of Some Heavy Metals in Food Crops of Lead
Polluted Sites of Zamfara State, Nigeria
Yahaya, M.Y.1*, Umar, R.A.1, Wasagu, R.S.U.1 and Gwandu, H.A.2
1
Department of Biochemistry, Faculty of Science, Usmanu Danfodiyo University, Sokoto, Sokoto State,
Nigeria.
2
Department of Crop Science, Faculty of Agriculture, Usmanu Danfodiyo University, Sokoto, Sokoto
State, Nigeria
* Author to whom correspondence should be addressed; e-mail: [email protected]
Article history: Received 15 May 2015, Received in revised form 26 June 2015, Accepted 10 July
2015, Published 15 July 2015.
Abstract: Lead pollution has become an important public health issue nationwide
especially in the Northern part of Nigeria, where some of the populace in the rural areas
indulge in mining and smelting. The Level of heavy metals (Pb, Cd, Hg, Ni, Co) in three
cereals collected from Dareta, Bagega and Abare villages of Anka L.G.A, Zamfara State
were determined using atomic absorption spectrometer (AAS). Maize from Bagega
(0.003±0.019 mg/g) has the highest Pb content and is significantly (P<0.05) higher than
that from Dareta (0.050± 0.003 mg/g) and control (0.003±0.000 mg/g). Cadmium level is
highest in maize grains from Dareta (0.005 ± 0.001 mg/g), compared to maize from the
other two villages sampled. Nickel is highest in sorghum from Dareta (0.073±0.018 mg/g)
and is significantly (P<0.05) higher than that from Abare (0.001±0.000 mg/g) and Bagega
(0.072 ± 0.015 mg/g). Cobalt is highest in rice from Bagega (0.012± 0.003 mg/g) while
mercury is highest in maize from the control site (0.124±0.007 mg/g), and is significantly
(P<0.05) higher than that from Dareta (not detected). The concentration of all these metals
was found to be above the WHO safe limits. This could be attributed to mining activities,
organic and inorganic fertilizers application and acidification of the soil. Continued intake
of these cereals may result in accumulation of the metals in the tissues of the villagers
which may have a biochemical and toxicological implication.
Keywords: Heavy metals, cereals, levels, Zamfara, lead poisoning.
Copyright © 2015 by Modern Scientific Press Company, Florida, USA
Int. J. Food Nutr. Saf. 2015, 6(2): 67-73
68
1. Introduction
In the recent years, the rate at which humans are exposed to heavy metals poisoning has
become an increasing concern due to the health risks they tend to pose. Exposure can be agricultural,
commercial or industrial. Cereals can absorb these metals from the soil or dust containing them
(SEPA, 1993). The 2009 lead poisoning disaster in some parts of Zamfara State, Nigeria was the
largest in magnitude in the history of man. It involved more than one hundred and ninety nine (199)
villages with a death toll of four hundred (400) (Anonymous, 2010). Rice, maize and sorghum were
used to determine the levels of some heavy metals from Zamfara State. These three cereals were
chosen as they belong in the thirty (30) most consumed crops in the world (Reddy, 2012) and also in
our area of study. The elements of interest in this research are lead, cadmium, nickel, cobalt and
mercury. Lead taken internally in any of its forms is highly toxic; the effects usually felt after it has
accumulated in the body over a period of time (Guidotti and Ragain, 2007). Effects of lead exposure in
humans include, abdominal pain, peripheral neuropathy and behavioral changes such as increased
aggression with symptoms like anemia, colic, palsy, body weakness, constipation, and often paralysis
of the ankles and wrists (Guidotti and Ragain, 2007).
Buildup of cadmium levels in water, air, and soil has been occurring particularly in industrial
areas. Acute exposure to cadmium fumes may cause flu like symptoms including chills, fever, and
muscle ache sometimes referred to as "the cadmium blues." Symptoms may show after a week in the
absence of respiratory damage (Shannon et al., 1998). More severe exposures can cause tracheobronchitis, pneumonitis, and pulmonary edema. Symptoms of inflammation may start hours after the
exposure and include cough, dryness and irritation of the nose and throat, headache, dizziness, body
weakness, fever, chills, and chest pain (Shannon et al., 1998).
Exposure to cobalt can be through food since high levels are found in fish, nuts, green leafy
vegetables and fresh cereals and most of the cobalt ingested is inorganic in nature (Barceloux, 1999).
However, cobalt (as sulphate) is included in some multi-constituent licensed medicines, at a maximum
daily dose of 0.25 mg. Occupational exposure to cobalt occurs usually through inhalation (“Cobalt”).
Nickel is present in a number of enzymes in both plants and microorganisms and in humans it
influences iron absorption and metabolism (Lenntech, 2011). Humans may be exposed to its pollution
through breathing, drinking water, eating food (especially large quantities of vegetables) (Lenntech,
2011) or smoking cigarettes (“Nickel”). Mercury, a free-flowing liquid at room temperature
(Henderson, 2000) known as ‘liquid silver’ occurs in deposits mostly as cinnabar. This metal is highly
toxic by ingestion or inhalation of the dust. Mercury poisoning can occur from exposure to any of its
form through inhalation of mercury vapor or ingestion, which is mostly by eating seafood
(“Mercury”).
Copyright © 2015 by Modern Scientific Press Company, Florida, USA
Int. J. Food Nutr. Saf. 2015, 6(2): 67-73
69
2. Materials and Methods
2.1. Collection and Preparation of Samples
Twenty seven composite samples were collected from three local (Bagega, Dareta and Abare)
villages in Zamfara State while the control was taken from Kaduna State. The representative samples
were further pulverized into small pieces using mortar and pestle. The semi-fine powdered form was
then stored in plastic bags before they were subjected to dry ashing and dissolution in preparation for
further analysis.
2.2. Chemicals
All chemicals and solvents were collected form the Department of Biochemistry, Usmanu
Danfodiyo University, Sokoto.
2.3. Dry Ashing
2.0g from each representative sample was placed inside a marked crucible and then placed into
a furnace (Lenton, UK) with a fixed temperature of 6000C. It was left to be fully burned, that is turned
into ash matter which took 3hrs.
2.4. Elemental Analysis
The heavy metals lead, cadmium, nickel, cobalt and mercury were detected using the fast
sequential atomic absorption spectrophotometer (Varian-AA240-FS model, US) using four (4) lamps
with optimized determination time that sorts the elements in the standard and digested samples by
wavelength and flame type.
2.4. Statistical Analysis
The data were expressed in mean±standard error (SE) and analyzed using Graph Pad Instat
Software, Sandiego USA) application. One-way ANOVA and Turkey’s multiple comparisons were
carried out to test for any significant differences between the means.
3. Results and Discussion
Upon completion of the analysis, the final results were computed and presented in table 1
below.
Levels of heavy metals in maize, rice and sorghum obtained from lead polluted areas in Anka
LGA, where estimated using Atomic absorption spectrometer (AAS). Pb concentration in maize
samples were higher (table 1 above) than the Food and Agriculture Organization/ World Health
Copyright © 2015 by Modern Scientific Press Company, Florida, USA
Int. J. Food Nutr. Saf. 2015, 6(2): 67-73
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Organization (FAO/WHO) 1986 codex (0.0003mg/g) and also far above previous values reported by
Choi (2011) who reported the maximum level of lead to be 6ppm (0.006mg/g). Going by Choi’s work
(2011), all other grains apart from those collected from Bagega and Dareta have lead levels that were
within allowable limits. These levels were observed to be significantly (P<0.05) higher than the control
and this can be explained by the absence of mining activities in the control area.
Table 1: Heavy Metal Content of Cereals from Bagega, Dareta, Abare villages and Control in mg/g.
Pb
BAGEGA
(mg/g)
0.081±0.019a
DARETA (mg/g) ABARE (mg/g) CONTROL
(mg/g)
0.050±0.003a
0.003/±0.000b 0.003±0.000b
Cd
0.001±0.001a
0.005±0.001b
BDL a-
BDL a
Ni
0.055±0.006a
0.060±0.010a
BDL b
BDL b
Co
0.008±0.008
0.006±0.003
0.001±0.000
0.001±0.000
Hg
0.043±0.043
BDL a
0.000±0.013
0.124±0.007b
Pb
0.036±0.011
0.042±0.031
0.005±0.000
0.003±0.000
Cd
0.002±0.000a
0.003±0.007a
BDL b
BDL b
Ni
0.056±0.007a
0.063±0.006a
0.001±0.000b
0.001±0.000b
Co
0.012±0.003
0.002±0.002
0.001±0.000
0.006±0.006
Hg
0.031±0.031
BDL
BDL
0.060±0.005
Pb
0.028±0.008
0.017±0.017
0.004±0.000
0.002±0.000
Cd
0.003±0.001
0.004±0.002a
BDL b
BDL b
Ni
0.072±0.015a
0.073±0.018a
0.001±0.000b
BDL b
Co
0.009±0.005
0.002±0.002
0.001±0.000
BDL
Hg
BDL a
BDL a
BDL a
0.080±0.001b
SAMPLE
MAIZE
RICE
SORGHUM
BDL=Below detection limit; Values are mean±SE; P<0.05)
Values with different superscript across the row differ significantly
Low blood level of lead may be problematic over a long period as it exerts its toxicity mainly
through the inhibition of heme synthesis whereby it competes with Fe 2+ at the site of porphyrin
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Int. J. Food Nutr. Saf. 2015, 6(2): 67-73
71
biosynthesis (hemoglobin)(Goldberg, 1968). This effect results in porphyria, a medical condition
caused by the body’s failure to metabolize porphyrin.
Cadmium in cereals according to the Food and Agriculture Organization/ World Health
Organization (FAO/WHO) codex is 0.0002mg/g. Going by this, the detected values in this work
present unsafe concentrations. Apart from the crops from Abare and the rice and sorghum grains from
the control site, all other grains contained cadmium far above the safe limit, this discovery can be due
to the remediation exercise that was carried out not long before this research. But previous work by
Afshar et al., (1995) on Amol rice (a variety in Iran) reported lower values of cadmium compared to
this work. The values reported of (0.00009mg/g) were lower than the WHO values (0.0002mg/g).
Cadmium is relatively poorly absorbed into the body, but once absorbed, is slowly excreted like other
metals, and accumulates in the kidney causing renal damage (“Cadmium”).
The mechanism by which cadmium exerts its toxicity involves increasing oxidative stress due
to it being a catalyst in the formation of reactive oxygen species, further increasing lipid peroxidation
(oxidative degradation of lipids) (ATSDR, 2013).
Bagega and Dareta heavy metal (nickel) content was higher than the reported levels in yam
powder of lead and cadmium (Mei et al., 2013). However, the nickel content of Abare grains were
similar to the earlier report (Mei et al., 2013). Other values for nickel were reported between the
ranges of 0.00052-0.00814mg/g in maize sample (Mei et al., 2013). The above range was lower than
the ones in this work in the grains collected from Bagega and Dareta respectively. Remarkably, the
nickel content in all the grains are higher than the standard limit of 0.0004mg/g set by the Organization
for Safety and Health Administration (OSHA, 2008).
Foodstuffs naturally contain small amounts of nickel and its intake increases when people
consume large quantities of vegetables from polluted soils since plants are known to accumulate nickel
(Lenntech, 2011).
Nickel exposure is associated with oxidative damage to DNA bases, inhibition of DNA repair
enzymes (DNA polymerases ε, polymerase δ and DNA ligase which puts the final touch) and
increase in reactive oxygen species by reduction and oxidation of metal ions (Fe2+/Fe3+). The mercury
levels found in our samples are higher than those reported by the National Food Safety Standard on
Contaminants in Food (2010), which presented a value of 0.00002mg/g Hg in grains. Mercury toxicity
is mediated by inhibition of human thioredoxin system (Carvalho et al., 2008).
Mercury can naturally be found deposited in soil, plants, rocks and tend to be much higher in
seafood. Therefore, the levels could have been absorbed by the plants from the water or transferred
through the air or dust (“Mercury”).
The levels of cobalt recorded in this work are higher than the standard limit set by OSHA
(0.000042mg/g). Cobalt has been reported to be essential to both humans and animals (“Cobalt”). It is
Copyright © 2015 by Modern Scientific Press Company, Florida, USA
Int. J. Food Nutr. Saf. 2015, 6(2): 67-73
72
a key constituent of cobalamin, also known as vitamin B12, which is the primary biological reservoir
of cobalt as an "ultra trace" element (“Cobalt”). Cobalt is an essential element in life required in
minute amounts (“Cobalt”). After nickel and chromium, cobalt is a major cause of contact dermatitis
(“Cobalt”).
Fortunately, the body system has glutathione as its primary detoxification mechanism and as
such is responsible for the removal of these toxic metals from the body.
4. Conclusion
The study established the presence of some heavy metals in the cereals from the area of study.
Although the cereals may have absorbed the metals either from the mining sites through dust or were
exposed to through soil and water as a result of acidification, which increases the heavy metal level in
the soil. Another factor could have been through the application of in-organic fertilizers during
farming. If the residents continue taking these cereals, their blood will eventually contain high levels of
these metals.
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