Manhot esculenta, or cassava, is one of the crops that withstands drought the best. Even in areas with poor soil, where many other crops struggle to thrive, it may be cultivated effectively. Depending on whether cyanogenic glucosides are present or absent, cassava varieties are often divided into bitter and sweet cultivars (Gideon-Ogero, 2008). About 800 million people worldwide primarily use cassava as a staple meal (IFAD/FAO, 2005a). Global production of cassava root was estimated to be 277 million tons in 2016, with Nigeria being the largest producer at about 21 percent of this total (FAOSTAT, 2017). The crop is one of the most widely grown food crops in southern Nigeria, where almost every family grows it. For the poor who do not have access to a wide range of cuisines, it serves as their main staple diet and a major source of nutrients.
Concern has lately been raised about the crop's potential for heavy metal contamination. In addition to weathering and dissolving, a number of human activities, including ore mining, agriculture, and industry, can contribute to heavy metal contamination in soil. According to Ogunmodede et al. (2015) and Oyedele et al. (2008), soil is necessary for human nutrition, the sinking and recycling of liquid and solid wastes, and the production of high-quality food. Unregulated mining activities and illicit mining in developing countries have exposed the environment to serious hazards due to the generation of vast volumes of waste, most of which is highly hazardous and badly impacts both human health and the ecosystem (Tomov and Kouzmova, 2005). In mining communities such as Ishiagu, Nigeria, mining activity by both commercial and local miners is one of the primary causes of lead and cadmium contamination. High concentrations of Pb (13671), Cu (4 to 36.5), Ni (2 to 40), Cd (0.5 to 10 mg/kg), Zn (7.5 to 1460.5), and Co (0.5 to 146.5) mg/kg were found in agricultural soils near the Ishiagu mining site, according to Eze and Chukwu. (2011). Heavy metal contamination of the soil, water, and atmosphere is a developing environmental issue that has an impact on human health and food quality due to an increase in anthropogenic activity. Concerns and inquiries abound over the condition of the soil and the caliber of food crops, fruits, and vegetables that are farmed in regions where extensive mining and exploration are taking place.
Cassava has the ability to transmit and bioaccumulate heavy metals. Udiba et al. (2019) discovered lead (Pb) in peeled cassava tubers in agricultural soil near a mining site in Nasarawa, Northern Nigeria, with a mean level of 2.59 mg/kg. Osuocha et al. (2014) examined the bioaccumulation of heavy metals in certain tuber crops from farmlands near quarry mining sites in Ishiagu, Ebonyi State. They discovered that the greatest values of Pb, Cd, Cr, and Ni were 1.54, 0.55, 0.49, and 1.75 mg/kg, respectively, in cassava tubers. Studies (Okereke et al., 2020; Abah et al., 2013; IGCP (2012); Nkwocha et al., 2011) have reported that cassava tubers also absorb a considerable number of heavy metals. These investigations all point to the possibility that cassava was poisoned by heavy metals.
Unquestionably, the elevated exposure to heavy metals has detrimental effects on human health (Khlifi et al., 2010; Jaishankar et al., 2014). According to Duruibe et al. (2007) and Jaishankar et al. (2014), toxic metals are the main culprits behind conditions like renal failure, gastrointestinal cancer, decreased IQ in children, nervous system damage, pulmonary edema and lung lesions, tachycardia, vomiting, diarrhea, and abdominal pain, liver effects, and neurological effects like aches, gastrointestinal effects like chills, nausea, irritability, and tremors. For the majority of people, the primary exposure pathway is through food consumption. Therefore, it makes sense to speculate that consumers may be at risk for health problems from cassava, a staple crop that contains heavy metals.
Situated between latitudes N5° 55´ and N6° 00´ and longitudes E7° 30´ and E7° 35´, Ishiagu is a town in the Ivo Local Government Area of Ebonyi State, Nigeria. The research region has an undulating, lowland terrain. A lead and zinc open-pit mine was established in 1965 and shut down seventeen years later (Aroh et al., 2010). Ishiagu was a major market for lead glances sold by small-scale vendors who served as both local requirements' suppliers and exporters' agents. Some of the ores have already been mined by several mining companies. People and groups became abruptly involved when certain mining enterprises began operating in Ishiagu, since many had been exposed to one or more mining procedures throughout organized mining times. The residents in the area gained a sizable source of income as many pits and mining sites opened. Handpicked lead glance and zinc often consist of coarse-grained minerals, leaving more widely distributed masses of galena, sphalerite, and other mixed minerals in tailings and wastes. Heavy metal contamination in Ishiagu's agricultural soils and some food crops has been documented by other studies (Okereke et al., 2020; Osuocha et al., 2014 Eze and Chukwu, 2011).
To the best of our knowledge, no research has been published on the concentration of heavy metals in cassava harvested from farms near closed Pb-Zn mines or on the exposure assessment conducted at Ishiagu in Ebonyi State, Nigeria. A health risk assessment that takes into account many age groups and the cooperative efforts of the government, regulatory agencies, and volunteer work will be necessary for effective environmental cleanup (Sinnett et al., 2022). Health risk information can help regulatory agencies and the government identify and mitigate potential environmental risks. Additionally, by understanding more about the risk and helping with the execution of environmental remediation programs, the public that is exposed to dangers may collaborate with decision-makers to successfully reduce environmental pollution (Gunjyal et al., 2023).
For the purpose of determining the danger to human health, information on the concentration of heavy metals in the edible tissues of food crops and their dietary intake is crucial (Addo et al., 2013, Zhuang et al., 2009). The purpose of this study was to determine the amounts of heavy metals in the soil, as well as how much the tubers are absorbed and accumulated by them. Furthermore, we also determine if eating tubers from farms near closed lead-zinc mines in Ishiagu, Ebonyi State, may pose a health concern.