Microbiology Project Topics

Assessment of Some Toxic Metals in Variety of Cassava Cultivated in Damagum L.G.A of Yobe State

Assessment of Some Toxic Metals in Variety of Cassava Cultivated in Damagum L.G.A of Yobe State

Assessment of Some Toxic Metals in Variety of Cassava Cultivated in Damagum L.G.A of Yobe State

Chapter One

Objectives of the study

The main objective of the study is to carry out an assessment of some toxic metals in variety of cassava Cultivated in Damagum L.G.A of Yobe State. The following are the specific objectives of the study:

  1. To examine the concentrations of Heavy metals in cassava plants.
  2. To determine the Plant Transfer factor (Tf) of mean of metals in cassava plants
  3. To determine the correlation of heavy metals in soil at different distance and cassava plants



 Cassava Plant (Manihot esculenta crantz)

Cassava Plant (Manihot esculenta crantz) belong to the family of Euphorbiaceae (Spurge family), native of Brazil and Paraguay that is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, is a major source of carbohydrates.

The cassava root is long and tapered with a firm homogenous flesh encased in a detectable rind about 1mm thick, rough and brown on the outside. Commercial varieties can be 5 to 10 cm in diameter at the top and 50 to 80 cm long. A woody cordon runs along the root’s axis. The flesh tuber can be chalk-white or yellowish.

Cassava roots are very rich in starch and contain significant amount of calcium (50 mg/100g), phosphorus (40 mg/100g) and vitamin C (25 mg/100g), however they are poor in protein and other nutrients. In contrast, cassava leaves are a good source of protein, it is supplemented with the amino acid methionine despite containing cyanide.

Cassava root size and shape depends on varietal and environmental factors. Cassava is a tropical root crop 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 most areas, it does not tolerate flooding, in droughty areas, it losses its leaves to conserve moisture, producing new leaves when rain 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 tolerates a wide range of soil pH 4.0 to 8.0 and is most productive in full sun.

    History of the Cassava Plant

The oldest direct evidence of cassava cultivation came from a 1,400 years old Maya site in El Salvador, although the specie Manihot esculenta originated further in South Brazil and Paraguay. Wild population of Manihot esculenta sub specie, Flebellifolia, is shown to be the progenitor of domesticated cassava found in west central Brazil where it was likely first domesticated not more than 10,000 years A.D.  By 6,600 B.C, manioc pollen appears in the gulf of Mexico lowlands at the San Andres archaeological site. With its high food potential, it had become a staple food of the native population of North and South America, South Mesoamerica and the Caribbean by the time of the Spanish conquest and its cultivation was continued by the Colonial Portuguese. Forms of the modern domesticated specie can be found growing in the South of Brazil and there are several wild Manihot species, all varieties of Manihot esculenta are cultigens.

  Production / Economic Impact of Cassava  

Cassava is one of the most staple food crops of more than 500 million people and is a typical crop in developing countries. Cassava is considered an important source of energy in diets. Cassava is known to produce 250,000 calories/hectare/day compared to 200,000 for maize, 176,600 for rice, 114,000 for sorghum and 110,000 for wheat. Cassava is the third largest source of human food in the world, with Africa as its largest centre of production. Cassava plays a major role in efforts to alleviate the African food crisis because of its efficient production of food energy, year-round availability, tolerance to extreme stress conditions and suitability to present farming and food systems in Africa.

World production of cassava root was estimated to be 184 million tonnes in 2012. The majority of production is in Africa where 99.1 million tonnes were grown, 51.5 million tonnes were grown in Asia and 33.2 million tonnes in Latin America and the Carribean. Nigeria is the world’s largest producer of cassava. However, based on the statistics from the Food and Agricultural Organization (FAO) of the United Nations, Thailand is the largest   world exporter of cassava in 2005. The second largest exporting country is Vietnam with 13.6%, and then increased to 55.8% and Costa Rica 2.1%. World-wide cassava production increased by 15.5% between 1988 and 1990. Cassava plays a role in developing countries farming especially in sub-saharan Africa because it thrives well on poor soil and low rainfall and is a perennial crop that can be harvested as required. Its wide harvesting window allows it to act as a famine reserve crop and is invaluable in managing labour schedules. Cassava is regarded as subsistence or cash crop of low-income families or resource poor farmers.

A 1992 study revealed that about 42% of harvested cassava roots in West and East Africa are processed into dried chips and flour. In Ghana, cassava and yam occupy important positions in the agricultural economy and contribute about 46% of agricultural gross domestic product (GDP). Cassava accounts for a daily calorie intake of 3% in Ghana and it is grown by every farming family. The importance of cassava to many Africans is epitomized in the Ewe (a language spoken in Ghana, Togo and Benin) name for the plant, meaning “there is life”.




Study Area

Fune is a Local Government Area in Yobe State, Nigeria. Its headquarters are in the town of Damagum in the southwest of the area on the A3 highway at11°40′39″N 11°20′04″E. It has an area of 4,948 km2 and a population of 300,760 at the 2006 census. The postal code of the area is 622. In 1987, the 8,000-year-old Dufuna canoe was discovered in Fune, near the village of Dufuna and the Komadugu Gana River. Damagum has a tropical wet climate with average temperature is 26.4°C; sits in the rain forest, and produces many agricultural products, such as yams, cassava, corn, rubber and palm products.

 Sample Collection

Samples of soil, cassava leaves and roots were randomly collected from three farmlands situated in Damagum labeled as Farm 1, Farm 2 and Farm 3. The variety of cassava collected was the The variety of cassava used in carrying out this study was the TMS 300555. Control samples were collected from another cassava farmland in a rural settlement in Damagum. Samples were collected at 0 – 10 cm depth at distance intervals of 10, 15, and 20 meters from the roadway with sterilized auger in a polythene bag. Three soil samples were taken from three points from each distance and mixed together to form composite samples.




Concentrations of Heavy metals in cassava plants in farmlands




This study was carried out on the Assessment of some toxic metals in variety of cassava Cultivated in Damagum L.G.A of Yobe State. The overall results showed evidence of some heavy metal pollution on the soils and bio-accumulation in cassava plants, from farmlands in Damagum LGA. The heavy metal levels tended to be lower in control samples. Cr and Hg recorded high transfer factors along different sites sampled. While Hg showed a positive correlation, Pb showed a negative correlation. This implies that increase in the concentration of Hg in soil causes a highly significant increase in Hg in the root of Cassava plant while an increase in concentration of Pb in soil causes significant decrease in the in the root concentration.


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