| Newport International Journal

Evaluation of the heavy metal levels from selected food cultivars, from coal mining communities of Enugu State, Nigeria

¹Uhama Kingsley Chukwuka*, ²Aneke Chinwe Jacinta, ¹Akpata Ebere Immaculata and ³Nwaigbo Olive Chika

¹Department of Biochemistry, Faculty of Applied Natural Sciences, Enugu State University of Science and Technology, (ESUT), Nigeria.

²Department of Applied Microbiology and Brewery Faculty of Applied Natural Sciences, Enugu State University of Science and Technology.

³Enugu State University of Science, Nigeria.

Email: kingsley.uhama@esut.edu.ng

ABSTRACT

Food cultivars from Akwuke, Ngwo and Udi were analyzed for their heavy metal content using the atomic absorption spectrometry (AAS). The mean concentrations of Manganese in leafy vegetable ranges from 1170±6.20µg/g and in chromium from 110±0.0 µg/g, in lead from 320±210, in cadmium from 30±10 µg/g and nickel from 10±0 µg/g all in Akwuke. The transfer factors results for the three communities shows that the pumpkin leafy have the highest transfer factor for manganese, 2.6 in Akwukeand chromium yam 2.465 in Udi, while Nickel has the least transfer factor in all the food cultivars in the three communities with 0 result. This study has revealed high concentration of manganese, lead, chromium cadmium and nickel in food cultivars in the three studied area Akwuke, Ngwo and Udi, all in Enugu State. Though the concentrations of these heavy metals were not high in any of the soil samples, but high concentration of these heavy metals, compared to WHO/FAO in food cultivars were observed, especially in Udi and Ngwo community.

Keywords: Heavy metal, levels, food cultivars, Enugu State and Nigeria.

INTRODUCTION

Diseases associated with the heavy metal toxicity include, pulmonary, abdominal pain, chronic bronchitis, kidney disease, pulmonary edema (accumulation of fluid in the lungs), cancer of the lungs and nasal sinus ulcers, convulsion, liver damage and even death [1].Heavy metals get into the environments: water, soil and food cultivars through activities like intense agriculture, power generation, industrial discharges seepages and municipal landfills, septic tank effluents etc. Many authors have reported high levels of heavy metals ions in the soil and groundwater in different areas of Nigeria [2]. Several studies have shown that heavy metals such as lead, cadmium, nickel, manganese and chromium amongst others are responsible for certain diseases [1]. In general heavy metals are systemic toxins with specific neutrotoxic, nephrotoxic, fetotoxic and tetratogenic effect [1]. Heavy metals can directly influence behaviour by impairing mental and neurological function, influencing neurotransmitter production and utilization and altering numerous metabolic processes. Systems in which toxic metal elements can induce impairment and dysfunction include the blood and cardiovascular, eliminative pathways (colon, liver, kidney, skin), endocrine (hormonal), energy production pathways, enzymatic, gastrointestinal, immune, nervous (central and peripheral), reproductive and urinary that have lethal effects on man and animals [1]. Heavy metal pollution poses a great potential threat to the environment and human health. Coal as source of fuel and one of natural endowment has constituted a repository of heavy metal to the environment. Heavy metal contaminate the soil, water and thus enter the food chain in these manner, humans are indirectly exposed to heavy metals through food chain.

Aim of the Study

This research work is aimed at evaluating the heavy metal levels from selected food cultivars of Enugu State, Nigeria.

Objective of the Study

To determine the heavy metal levels from selected food cultivars of Enugu State, Nigeria.

MATERIALS AND METHOD

Sample collection

Soil samples; these were collected from there different locations (Akwuke, Ngwo and Udi ) in three different local Government area in Enugu state and the soil sample were collected from a depth of 15-30cm using a metal auger and transferred into prewashed polyethylene nylon bag to avoid contamination.

Water sample; well water sample were collected from three different locations (Akwuke, Ngwo and Udi), according to the method recommended by [3] and [4]. According to the method, two litres plastic container was rinsed with detergent and rinsed with the sample to be collected at least three times before samples are finally collected and stored in 1ml HCl to avoid microbial growth.

Food cultivars; leafy vegetables and tubers were collected from three different location (Akwuke, Udi and Ngwo) in three different Local Government Area in Enugu State, with the consent of the owners of the farm, and the tubers were also collected from their storage bans with the consent of the farmers .

Sample preparation

Preparation of soil samples: After collection, samples were brought to the laboratory and initial treatment was given for the preservation and further analysed according to the following methods. The soil samples collected from the selected areas were initially treated by adopting the method recommended by [5]. According to this method, samples were air dried in sun light for a day. Then the samples were finally dried in oven at 105^oC till a constant weight was acquired. Then about half of each sample was passed through 0.5mm nylon mesh sieve. Then soil samples were repacked with the complete labeling and preserved for further analysis. Preparation of plant samples: the sample preparation technique for plants involves steps like, washing, drying, grinding, and storage. The plant samples were prepared according to the method recommended by [6] and [7]. The plant sample were washed with water and air dried firstly and then in an oven at 70-80^0C until a constant dry weight was attained. The dried samples were ground in wooden mortar to make a fine powder. The finely ground samples were passed through 0.5mm nylon mesh sieve and packed in the air tight polythene bags to prevent the absorption of water from the humid environments

DIGESTION OF SAMPLES

Digestion of soil samples

Soil samples were dried at 105^oC and sieved with 100 mesh (152um Bs screen 410). 1g of the dried soil sample was weighed into a labeled 100ml conical flask and 20ml of mixture of concentrated HCL and concentrated HNO₃ (1:1) were added and well shaken. The solution was kept overnight after which it was filtered through with whatman N0.1 filter paper formerly leached by pouring cupious quantity of dilute HNO₃ on the filter paper while in the funnel. The clear solution obtained was made up to 100ml using a standard flask and transferred into a plastic bottle [8]. The sample solutions were analyzed at various wavelengths for each metal using Varian AA240 Atomic Absorption Spectrophotometer according to the method of APHA [9].

Digestion of food cultivars

Exactly 1g of the ground sample was weighed into a breaker. 10cm³ of 1:1 dilution of the concentrated HNO₃ and water was mixed and then covered with a watch glass. The solution was placed on a hot plate to reflux for 10 to 15 minutes without boiling. The beaker was allowed to cool and then 2cm³ of distilled water and 3cm³ of 30% H₂O₂ were added, cover with watch glass and placed over a hot plate. After the effervescence had subsided, the solution was removed and cooled .HCl (5cm³) and 10cm³ of distilled water were added and then heated for another 15minutes without boiling. The solution was when transferred to 100cm³ beaker and made up to mark using deionized water and taken for AAS determination of lead, chromium, Nickel, cadmium and manganese.

Principles of AAS: Atomic Absorption Spectrophotometer working principle is based on the sample being aspirated into the flame and atomized when the AAS light beam is directed through the flame into the monochrometor, and onto the detector that measures the amount of light absorbed by the atomized element in the flame. Since metal have their own characteristic absorption wave length, a source lamp composed of that element is used in making the method relatively free from spectral or radiationalinterferences.The amount of energy of the characteristic wavelength absorbed is proportional to the concentration of the element in the sample.

Phosphate Determination

Phosphate was measured using Standard Method 4500-P B.5 and 4500-PE [10].

Procedure: Exactly 100ml of the homogenized and filtered sample was pipetted into a conical flask. The same volume of distilled water (serving as control) was also pipetted into another conical flask. 1ml of 18M H₂S0₄ and 0.89g of ammonium persulphate were added to both conical flasks and gently boiled for 1½ hrs, keeping the volume of 25-50cm³ with distilled water. It was then cooled; one drop of phenolpthelein indicator was added and after neutralized to a faint pink color with the 2M NaOH solution. The pink color was discharged by drop wise addition of 2M HC1, and the solution made up to 100ml with distilled water. For the colorimetric analysis, 20ml of the sample was pipetted into test tubes, 10ml of the combined reagent added, shaken and left to stand for 10mins before reading the absorbance at 690nm on a spectrophotometer, using 20ml of distilled water plus 1ml of the reagent as reference.

Methods for Calibration

Standard phosphate solution: 219.5 mg of dried AR potassium hydrogen phosphate was dissolved in distilled water and made up to 1000ml, where 1ml = 50.0µg. of phosphate. 10ml of the stock solution was made up to 1000ml to give 1ml – 0.05 mg. Standards of strength ranging from 0 (blank) to 0.05mg/L at intervals of 0.05mg is prepared by diluting the stock with distilled water.

Conc. of sample = Abs of sample x conc of std

Abs of Std

Chloride Determination

Chloride analyzed according to APHA standard method (APHA; 1998).

Procedure:

A 100ml of the clear sample was introduced using pipette into an Erlenmeyer flask and the pH adjusted to 7-10 with either H₂S0₄ or NaOH solution. Then 100ml of K₂Cr0₄ indicator solution was added with standard solution of AgN0₃ in a permanent reddish brown colouration. The AgNo₃ titrant was standardized and a reagent blank established. A blank of 0.2-0.3ml is usual for the method Calculation

Chloride cone = Titre value (x) x 10 =10xmg/l

Sulphate Determination

Sulphate analysed according to APHA standard method (APHA; 1998).

Procedure: A 250cm³ of the water sample was evaporated to dryness on a dish. The residue was moisten with a few drop of concentrated. HC1 and 30cm³ distilled water was added. This was boiled and men filtered.The dish was rinsed and the filter paper washed with several portions, of distilled water and both filterate and washings added together. This was heated to boiling and then 10cm³ of 10% BaCb solution was added, drop by drop with constant stirring. The mixture was digested for about 30minutes, filtered and the filter paper washed with warm distilled water. It was then ignited, cooled and weighed in an already weighed crucible.

Calculation: Mg/dm³S0₄^2- = mg BaS0₄ x 411.5cm³ of water sample

Nitrate Determination

Nitrate is determined using PD303 UV spectrophotometer (APHA, 1998)

Procedure

A known volume (50ml) of the sample was pipette into a poecelain dish and evaporated to dryness on a hot water bath. 2ml of phenol disulphonic acid was added to dissolve the residue by constant stirring with a glass rod. Concentrated solution of sodium hydroxide and distilled water was added with stirring to make it alkaline. This was filtered into a Nesslers tube and made up to 50ml with distilled water, the absorbance was read at 410nm using a spectrophotometric after the development of color. The standard graph was plotted by taking concentration along X – axis and the spectrophotometeric readings (absorbance) along Y-axis. The value of nitrate was found by comparing absorbance of sample with the standard curve and expressed in mg/1.

Conc, of sample = Abs of sample x Conc, of std

Abs of Std

RESULTS

HEAVY METAL CONCENTRATION IN CASSAVA FROM COAL MINING COMMUNITIES

Result of heavy metal levels in cassava from coal mining communities in Enugu State showed that Mn, Cr and Pb levels in cassava from Ngwo were significantly higher (p<0.05) when compared to Udi and Akwuke, while Cd level inUdi was significantly highest (p<0.05), followed by Ngwo and Akwuke. Ni level were below detectable level in cassava from all the communities (Table 1).

Table 1: Heavy metal levels in cassava from coal mining communities

TraceMetals( µg/g)	Udi	Ngwo	Akwuke	WHO/FAO( µg/g)
Mn	110.00 0.02^C	250 0.01^a	180.00 0.01^b	5.00
Cr	0 0.01^c	40.00 0.01a	20.00 0.01^b	1.30
Pb	350.00 0.01^b	420.00 0.01^a	300.00 0.01^c	2.00
Cd	90 0.10^a	20.00 0.01b	20.00 0.01^b	0.02
Ni	0.00 0.01^a	0.00 0.01^a	0 0.01^a	10.00

Values are mean ± standard deviation of triplicatedetermination

Values in the same row bearing the same superscript letters are not statistically significant at P<0.05

HEAVY METAL CONCENTRATION IN YAM FROM COAL MINING COMMUNITIES

The result of heavy metal levels in yam from coal mining communities in Enugu State showed that Cr, Pb and Cd levels in yam from Udi were significantly higher (p<0.05) when compared to Ngwo and Akwuke , while Mn level in Akwuke was significantly highes (p<0.05), followed by Ngwo and Udi. Ni level were below detectable level in yam from all the communities (Table 2).

Table 2: Heavy Metal Level of Yam from Coal mining Communities

TraceMetals(µg/g)	Udi	Ngwo	Akwuke	WHO/FAO( µg/g)
Mn	30.00 0.01^C	140.00 0.01^b	170.00 0.01^a	5.00
Cr	320.00 0.01^a	170.00 0.01^b	70.00 0.01^c	1.30
Pb	340.00 0.01^a	200.00 0.01^c	290.00 0.01^b	2.00
Cd	60 0.10^a	10.00 0.01^b	10.00 0.01^b	0.02
Ni	0.00 0.01^a	0.00 0.01^a	0 0.01^a	10.00