The level of heavy metal lead cadium zinc magnesium and copper were determined in cassava from different locations of oil exploration areas in Delta- State, Nigeria. The locations were Afiesere, Ekiugbo, Orogun and Ofoma all in Ughelli North L.G.A. These heavy metal were determined using atomic absorption spectrophotometer model AA 701. The results heavy metals obtained are Zn (III. 67mg/l in Afiesere cassava) Cd (4.65mg/l in Ekiugbo cassava ) and Pb (<0.002mg/l in all the cassava from different location) have higher values compared with WHO standard. The most essential element copper was less in Afiesere cassava (1.2mg/l). These findings give cause for concern, particularly as heavy metals are bio-accumulative in the system and portend a serious health risk to man such as inflammation of the lung, vomiting fever and so on. 



The petroleum industry is organized into four broad sectors: exploration and production of crude oil and natural gas; transport, refining, as well as marketing and distribution. This study addresses only exploration and production operations. Activities of oil prospecting and other industries resulting in pollution through gas flares, constant oil spills and industrial effluence which affect both aquatic and terrestrial ecosystems, with destruction of forest and farmland is alarming (Dambo, 2000).

Delta- state which is one of the nine (9) states in the Niger Delta region of Nigeria, is greatly endowed with abundant natural resources giving rise to increased industrial activities in the region . refining and petrochemical companies account for about 70-75 percent of industrial activities in the region (Odjurwederhie,et al, 2006)

Environmental degradation of the oil rich Niger-Delta region has caused a wanton destruction and continuous harm to their health, social and economic consequences for its people, for over three decades. Petroleum refineries produce a wide variety of air and water pollutants and hazardous solid wastes. The specific means of pollutants varies and processes involved. Frequently emitted pollutants include all the distillation products of refining and rapid industrialization , intensive agriculture and other anthropogenic activities have led to land degradation, environmental pollution and decline in crop productivity and sustainability. These have been of great concern to human and animal health (Worgu, 2000).

One of the prominent source contributing to increased load of soil contamination is the disposal of municipal and industrial wastes. These wastes are either dumped on roadsides or used as land fills, while sewage is used for irrigation . These wastes although useful as a source of nutrient are also source of carcinogens and toxic metals. Other industrial activities that take place include those from these industrial activities, pollute the air, water and soil, endangering the environment as they ultimately find their way into food chain, albeit in small doses. These accumulate and across trophic levels to pose serious health hazards to man (Pickering et al, 2000).

In the study of the socio-economic impact of oil pollution (Worgu, 2000) stated that crude oil exploration has had adverse environmental effect on soil, forests and water bodies in host communities in the Niger –delta . All stages of oil exploitation impact negatively on the environment and the greatest single intractable environmental problem caused by crude oil exploration in the Niger Delta region is oil spillage. According to Annual reports, Department of petroleum resource (DPR) 1997, over 6000 spills had been recorded in the 40 years of oil exploration in Nigeria with an average of 150 spills per annum. In the period 1976 – 1996, 647 incidents occurred resulting in the spillage of 2,369,407.04 barrels of crude oil. With only 549,060.38 barrel recovered, 1,820,410.50 barrels of oil were lost to the ecosystem as shown in table 1.

YearNumber of spillsQuality spilled (barrels)Quality recovered (barrel)Net loss to the environment (barrel)

Table 1; Oil spill in Nigeria (1976 – 1996)

(Annual report of department of petroleum resource (DPR) 1997) 

These chemicals can pollute the soil and groundwater system in the areas where such operations are being carried out if they are not properly controlled according to guidelines and standards set by regulating agencies like the Department of Petroleum Resource (DPR) now Federal Ministry of Environment.

Formation water and effluents discharges are high essential in  total dissolved solids and some chemical injected into the wells to inhibit corrosion of equipment or enhance the separation of oil from water. Such water could have detrimental effects on plants and animals (Amatya et al, 2002). The side effect of petroleum activities can be severe. The problems range from soil degradation to pollution of surface water and groundwater. These problems often lead to lower land values and loss of certain land use capacities. 

Exposure to very low level of elements such as lead, cadmium and mercury have been shown to have cumulative effect since there is no homeostatic mechanism which can operate to regulate the levels of these toxic substance. The major pollutants from industrial discharge have been shown to be lead, mercury, nickel arsenic, zinc and copper. Lead intoxication has been reported to be associated with neurological problems, renal tabular dysfunction and anemia. Although zinc and copper are essential trace elements which may also serve as plant nutrient they may be used as components of paint pigments. Consequently, their undue presence in the environment through industrial discharge can also be hazardous to man.

Heavy metal absorption is governed by soil, characteristics such as pH and inorganic matter content. Thus, high levels of heavy metals in the soil do not always indicate similar high concentration in plants. The extent of accumulation will depend on the plant and heavy metal species under consideration.

In Nigeria, a study of metal concentration near Warri refinery found three to seven times elevated levels of various heavy metals in the soil. (Ndiokwere et al 2000). Although the petroleum industry is by far the largest industrial sub sector in the Niger Delta , at least six of the eight most polluting industrial sub sectors in Nigeria (steel works, metal fabrication, food processing, textiles, refineries and paint manufacturing) operate in the Niger Delta.

The increasing industrialization, particularly due to oil exploration and exploitation in the Niger Delta region, Nigeria has create consciousness of the pollution of the environment and possible dangers emanating from such activities. Whilst literature is replete with data on heavy metal. Concentration in crops, aquatic life and the mangrove Swamp, data exist in the Niger Delta region on heavy metal concentration in food crops.

Most states in the Niger Delta indulge in indigenous farming and fishing as their major occupation, According to federal office statistics 1995, in Delta state, about 50 percent of the active labour force is engaged in one form of agricultural activity or another with cassava, yam, maize, cocyam, plantain and vegetables as the predominant food crops in the area.

Cassava (Manihot esculenta) is one of the major food crop cultivated in Delta state. Cassava the plant originated to central or south America, possibly Brazil and was domesticated and widely distributed well before the time of Columbus. The cassava plant is a slightly woody, perennial shrub reaching 10 ft (3m) in height . The leaves as deeply palmately lobed. The flowers are inconspicuous and prominent capsules are three seeded and explosive at maturity. The roots are enlarged by deposition of starch and constitute the principal source of food from the plant normal yield are about (4.5kg) per plant. The leaves are also eaten. (after cooking) and are note worthy for their high protein content. The plant is propagated from mature stems, which are planted without special treatment.

 Cassava is a source of flour called garri in western Africa and of toasted starch granules normally called tapioca. It can be processed into maconi and a rice like food. In the form of dried chip, cassava root is an important animal feed inspite of popularity, its protein content is extremely low and its consumption as a staple food is associated with protein deficiency disease kwashiorkor. In addition, part of the plant contain glycosides of hydrocyanic acid substance which on decomposition yield poison hydro cyanic acid (CHCN) prussic acid . chronic disease including goiter are common in regions were cassava is a staple food (Franklin, 1997) . The increasing industrialization, particularly due to oil exploration and exploitation in Delta state, Nigeria has created consciousness of the pollution of the environment and possible dangers emanating from such activities. Hence this study was therefore designed to investigate the level os heavy metal in cassava harvested around some oil prospecting and other industrial area of Delta state in Nigeria. {mospagebreak}



Cassava is commonly known as manioc, scientific name Manihot esculenta belong to the family Euphorbiaceae is originated in Brazil and Paraguay (Stephen, 1995). Cassava root, not a tuberous root. The root cannot serve for vegetative propagation. Root size and shape depend on variety and environment conditions. Variability in size and shape depend on variety and environment conditions. Variability in size within a variety is greater than that found in other root crops. Cassava roots are generally from 15-100cm long and 3-15cm wide. They are cylindrical, conical or oval, with a coffee, pink or cream coloured peel which is covered by a thin brown bark. The parenchyma is generally white, cream or yellow. The root is composed of three distinctive bark (periderm) peel and parenchyma. The parenchyma is the edible potion of fresh root and comprise approximately 85% of the total weights, the parenchyma consist of xylem vesels redially distributed in a matrix of starch-containing cells. A central fibrous vascular bundle becomes progressively large as the root mature. Other fibrous bundles may develop throughout the root . the peel layer comprises scelerenchyma, cortical parenchyma and phloem and constitutes 12% of the root weight, with periderm layer comprising another 20%. The cassava plant is a highly efficient production of carbohydrate mainly in the form of starch. It is the fourth most important source of calories in human diet in tropical region of the world. (Wheatley, 1995). 

The crop status of cassava is a perennial woody shrub grown as an annual. Cassava is a major source of low cost carbohydrate for population in the humid tropics (Onwueme, 1995).

The Nutritional Value And Uses Of Cassava 

Cassava is grown for its enlarge starch filled roots, which contains nearly the maximum theoretical concentration of starch on a dry weight basis among food crops. Fresh root contain about 30% starch and very little protein. Roots are prepared much like potato. They can be peeled and boiled, baked or fried. It is not recommended to eat cassava uncooked, because of potentially toxic concentrations of cyanogenic glycosides that are reduced to innocuous levels through cooking. In Africa, roots are processed in several different ways. They may be first fermented in water . Then they are either sun-dried for storage or grated and made into a dough that is cooked. Alcoholic beverages can be made from the roots.

Young tender leaves can used as a potherb, containing high levels of protein (8 – 10%) prepared in a similar manner as spinach , care should be taken to eliminate toxic compound during the cooking. One clone with variegated leaves is planted as an Ornamental (Cock, 2000).

Toxicities: Cassava is famous for the presence of free and bound cyanogenic glucosides, linamarin and totaustralin. They are converted to HCN to the presence of linamarase, a naturally occurring enzyme in cassava. Linamarase acts on the glucoside when the cells are ruptured. All plant part contain cyanogenic glucosides with the leaves having the highest concentration. In the past, cassava was categorized as either sweet or bitter , signifying the absence or presence of toxic levels of cyanogenic glucosides. Sweet cultivar can produce as little as 20mg of HCN per kg of fresh roots while bitter ones may produce more than 50 times as much. The bitterness is identified through taste and smell. This is not a total valid system, since sweetness is not absolutely correlated with HCN producing ability. In case of human malnutrition, where the diet lacks protein and iodine, under processed roots of high HCN cultivars may result in serious health problems. According to Coursey, 2000, among others have reported chronic and aculacyancide toxicity in humans and animal in cassava diets .

Ecology of Cassava

Cassava is a tropical root crops, requiring at least 8 months of warm weather to produce a crop. It is traditionally grown in a savanna climate but can be grown in extreme of rainfall. In moist areas, it does not tolerate flooding , in droughty areas , it losses it leaves to conserve moisture, producing new leaves when rains resume . it takes 18 or more months to produce a crop under adverse condition such as cool or dry weather . cassava does not tolerate freezing conditions. It tolerate a wide vrange of soil pH 4.0 to 8.0 and is most productive in full sun.

Production Practices  

Cassava is planted using 7-30cm portions of the mature stem as propagules. The selection of healthy disease free and pest free propagules is essential. The stem, cuttings are sometimes referred to as "stakes" . in areas where freezing temperatures are possible the cuttings are planted as soon as dangers of frost has past. The cuttings are planted by hand in moist, prepared soil, burying the lower half when soil are too shallow to plant the cutting in an upright or slanted position, the cutting are laid flat and covered with 2-3cm soil. Mechanical planters have been developed in Brazil to reduce labour inputs. Observing the polarity of the cutting is essential in successful establishment of the cutting. The top of the cutting must be placed up. Typical plant spacing is lm by lm.

Most cassava is harvested by hand, lifting the lower part of stem and pulling the root out of the ground then removing them from the base of the plant by hand. The upper parts of the stems with the leaves are removed before harvest. Levers and roots can be used to assist harvesting. A mechanical harvester has been developed in Brazil. It grabs onto the stem and lift the roots from the ground. Care must be taken during the harvesting process to minimize damage to the roots, as this greatly reduces shelf life. During the harvesting process, the cuttings for the next crop are selected. These must be kept in a protected location to prevent desiccation.

The shelf life of cassava is only a few days unless the roots receive special treatment. Removing the leaves two weeks before harvest lengthen the shelf life two weeks . Dipping the roots in paraffin or a wax or storing them in plastic bags reduces the incidence of vascular streaking and extend the shelf life to three or four weeks. Root can be peeled and frozen. Traditional methods include packing the roots in moist mulch to extend shelf life. 

Oil Pollution, Sickness and Death

Heavy metals focuses on toxic metal like lead, iron, copper, nickels, zinc, cadmium, manganese, and mercury which is caused by oil spill in the Niger Delta region. These heavy metals are well known pollutant that have caused severe damage in most part of the Niger Delta. (Asia, et al 2007).

Lead Poisoning

Unlike most of the west petroleum retained for automobiles is still laden with lead. The team of Nigeria scientist Akeredu et al, in their study of lead poisoning in children in Nigeria, provides remarkabsle evidence of the far reaching effect. Albeit indirect of the oil industry on the health of Nigeria children . in their randomized sample of children between the age of 1-6, they found the average blood level to be 106 micrograms per liter and 2% of the children had a blood level greater than 300 micrograms per liter. The five year old Nigerian children in their study were found to have to most elevated serum lead levels for comparison the acceptable upper limit of normal from the united states is severable, but ranges from 10-15 microgram ldl. (Davidson,2005)

Other authors of similar studies came to parallel and ascribe this finding to long stem exposure to environmental pollution during playtimes outside . they report the total amount of atmospheric bead emission to be about 300 metric tons a year . The main culprits for this problem were found to be the use of lead gasoline in car and combustion from the oil industry.

There is suggestive information about the role of lead in hypertension . However, link to kidney diseases and neurological damage, blindness, brain damages, seizure disorders have been firmly established convenience sample surveys of individual living in this part of Nigeria suggest that these disorder could be a problem amongst delta inhabitants , through careful studies are needed to confirm this.


Arsenic is widely distributed through the earth's crust, in the environment, arsenic is combined with oxygen, chloride and sulphur to form inorganic compound. Arsenic in plants and animals combine with carbon and hydrogen to form organic arsenic compounds . In organic arsenic is the toxic form of arsenic for human s . Arsenic has been found in the well dugs for drinking water in the river Niger Delta and longterm exposure has been linked to a variety of illness. Including hypertension , diabetes, cardiovascular disease and infertility, cancer of the skin, lungs, urinary bladder and kidney.


Toxina such as phenol cyanide and sulfide suspended solids are also found in large concentration in the Niger Delta . Cyanide is a particular problem, because cassava – a primary food source contain cyanide at its early stages of the growth. People have evolved in association with this staple crop and have this survived in the presence of substantial high serum level of cyanide. But shell's oil pollution, particularly through leaks and spills, has led to the concentration to this toxin in animals fish and plant ingested by human.


Copper is a metal that occurs naturally in the environment, and also plants and animals. As a trace metal, low levels of copper are essential for maintaining good health. High level can cause harmful effect such as irritation of the nose, mouth and eyes, nausea, vomiting, diarrhea and stomach cramps .


Mercury occurs naturally in the environment and it can also be released into the air through industrial pollution. Bacteria present in water can change mercury into methylmecury . Methylmecury bind tightly to the protein in fish tissues. As smaller fish are eaten by bigger fish ,the methylmercury accumulates. Predatory fish species (such as shark) tend to have higher levels than non predatory fish or species lower down the food chain. High amount of mercury can damage the central nervous system which can cause memory loss, slurred speech, hearing loss, lack of coordination, loss of sensation in finger and toes, reproductive problem coma and possibly death.


Small amount of nickel are needed by the human body to produce red blood cells, however in excessive amounts can become mildly toxic. Short-term overexposure to nickel is not known to cause any health problem , but long term exposure can cause decreased body weight, heart and liver damage and skin irritation.

Below is the table of WHO standard concentration of metal in Mg

Table 3: WHO standard concentration of metals in Mg (Friberg, 1997)









Concentration in Mg









The concentration of heavy metals has been of great concern to many researchers in the Niger Delta region according to Hart et al 2005, the concentration of trace metals, lead, iron, copper and zinc were estimated in crops (Cassava , cocoyam, Okra, pumpkin and water leaf) harvested in some oil prospecting location in River state, Nigeria . the study revealed higher concentration of heavy metal of lead, with corresponding high level of iron, copper and zinc in various food crops harvested at areas of high industrial activities in River state in Nigeria compared to the non- industrialized area.

The effect of petroleum exploration and production operation on the heavy metals content of soil and water sample obtained from four sampling point, around on oil well head, flare site, waste pit and effulent discharge point in an exploration area in the Niger Delta were analyzed were analyzed for their heavy metal content. The result of the study, revealed the exploration and production activities introduced lot of heavy metals into the soil and groundwater were such activities are carried out.

With the literature above, oil exploration and production of crude oil in the Niger delta has had adverse environmental effect on soil, plant and underground water which has in turn posed heavy metals on the ecosystem. {mospagebreak}



Samples Cassava from different locations

Materials / Reagent : Conc. Hydrochloric acid

Conc. Trioxonitrate(v) acid

Hydrofluoric acid

Apparatus: Knife (Domestic knife)

Metter balance

Teflon crucible

100 ml measuring cylinder 


250 ml volumetric flask

Mortar and pestle

Atomic absorption spectrophotometer model

Schimadzu AA6701 METHOD

Study location

The study location were Afiesere, Ekiugbo, Orogun and Ofoma all in Ughelli North local government area of Delta-state Nigeria. These location were chosen because they are oil prospecting exploration areas in the Niger Delta region of Nigeria. 

The samples (cassava) used in this project were harvested at the peak of the harvest period(August). The peak of the harvest period were chosen when farm crops were generally in their bloom, bearing the fact that heavy metal concentration in plant varies with the age of the plant as well as the season . By arrangement with the prospective farm owner ,the crops were harvest by hand -uprooting . The samples collected were wrapped in a polyethene bag and transport to the laboratory for drying and analyzing.

Preparation of Samples

The sample (cassava) were washed in water to remove soil and dirt cleaned carefully, the samples were allowed to about 5 minutes to dry-up water, then peeled and sliced thinly before drying. All samples were dried in an air oven at 60oC for about 72 hours then cooled to ambient temperature, milled by means of mortar. The milled samples were stored in airtight plastic container until required for analysis .

Digestion of samples using aqua- righa method

0.2g of the ground oven- dried samples were weighed and put in teflon crucible. Conc HCL solution of 45ml and 15ml of HNO3 solution was added up to four-fifth (4/5) of the crucible and 2ml of Hf acid was also added. The crucible was taken to the oven and the contents digested slowly at 200oC for 45 min. The digest was then cooled. Using 250ml of volumetric flask, little distilled was added, digested samples was poured into it and distilled water was added to make-up to the mark. The digested samples were analyzed for heavy metals using the atomic absorption spectrophotometer model schimadzu A-A 6701 in an air acetylene flame starting with blank followed by the samples to determine the metal ions of Cu, Zn, Pb, Mg, and Cd in cassava. The absorbance of the test solution were compared against the standard of each metal ion and concentration of the heavy metals in the sample were calculated by interpolation , using standard curves plotted by the computer using each metal as standard. The absorbance obtained were used in calculating the concentration of the metals in the samples. Thus, slop is the absorbance against concentration

Result : M.F. X absorbance X D.F.

Where : M.F. = Multiplication factor ( Inverse of slope) 

 D.F=dilution factor



The atomic absorption spectrophotometer result of the heavy metals analyzed in

Table 2: level of heavy metals found in the cassava

Parameters in (mg/l)Afiesere cassavaEkiugbo cassavaOrogun








From the result of the analysis, the level of lead was found to be <0.002mg/l in all the samples which is lower than that of W H O standard of 0.1mg. This low concentration makes it fit for human consumption but further accumulation of this metal can lead to vomiting, Kidney damage and neurological effect in children.

The level of cadium ranges from 4.28 mg/l in Orogun to 4.88kg/l in Afiesere while Ofoma and Ekiugbo are 4.52 mg/l and 4.63 mg/l respectively. This result extremely high in concentration when compared to the WHO standard of 3 mg for cadium. The higher concentration of cadium in these areas are due to the activities of oil exploitation done around these locations. Much intake of cadium causes initiation to the stomach assistive in vomiting and diarrhoea.

For zinc, Afiesere has 111.67mg/l, Ekiugbo 16.27 mg/l Orogun 23.86 mg/l and Ofoma 14.33mg/l. these are relatively high when considered with WHO standard of 15mg for zinc except for Ofoma which is a little bit lower than the standard. The significantly higher concentration of Zinc in Afiesere strongly indicates the presence of heavy metal pollution from oil exploration activities done in Afiesere flow station where the sample was collected for this analysis while others are due to cases of oil spill oil exploration in the Niger - Delta region of Nigeria.

For magnesium, Afiesere having 0.065mg/l found to be higher in magnesium concentration compare with the other locations. This is as a result of the activities of oil exploration in the Afiesere flow station were the sample was collected for this analysis.

The level of copper ranges from 1.21mg/l in Afiesere , 1.93mg/l in Ekiugbo, 2.86mg/l in Orogun and 2.06 mg/l in Ofoma. These ranges falls within the WHO standard of 1.5 â€“ 3.0 mg. The above ranges of copper can be essential for maintaining god health but accumulation can cause harmful effect such as irritation of the nose, mouth and eyes, vomiting, diarrheoa and stomach cramps. 


This study has revealed high concentration of heavy metal zinc, with correspondingly high level of cadium magnesium and copper but less concentration of heavy metal lead in various cassava from different locations harvested at locations of oil exploration activities in Delta state of Nigeria compared to the WHO standard, these findings are indicative of industrial pollution although the essential elements are beneficial to man and plant but when found in excessive amount well above the levels normally found in food can prove detrimental to health. 


Although well regulated in some countries, industry has been the source of many contaminants and chemicals in food. Major industrial activities has the potential for generating air emissions, waste water effluence and solid wastes, all of which enter the food chain and cause danger to man, animal and plant. In view of these findings , there is need to monitor more closely the environment under review and put in place appreciate checks and balance to preserve the health of communities within the vicinity of the oil exploration areas, particularly as the effect of heavy metals are bioaccumulative and pose great dangers to the health of humans, animals and plants. 


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