Cassava (Manihot esculenta Crantz) is a critical staple crop and a major source of calories in Sub-Saharan Africa, Latin America, and parts of Asia, yet its cultivation increasingly intersects with heavy metal–contaminated soils that can transfer cadmium, lead, mercury, arsenic, and other metals into edible tubers. This literature review synthesizes contamination sources, soil-to-plant transfer mechanisms, and resulting health risks, emphasizing that children experience disproportionate risk due to higher intake per body weight and developmental sensitivity. The review then evaluates practical remediation strategies spanning soil amendments (notably biochar and organic amendments), phytostabilization and varietal selection, and biological approaches including plant growth–promoting rhizobacteria, endophytes, and mycorrhizal associations. Across contexts, the evidence supports integrated packages that combine amendments, biological inputs, monitoring, and policy support, because single interventions are often incomplete or context-limited. The central translational conclusion is that cassava safety can be materially improved through locally tailored, field-validated remediation programs that simultaneously reduce metal bioavailability and protect livelihoods in resource-limited regions.
Cassava; Manihot esculenta; heavy metal contamination; soil-to-crop transfer; biochar; organic amendments; phytoremediation; microbial remediation; health risk assessment.
Cassava (Manihot esculenta Crantz) stands as the fourth most important source of calories for the global human population, serving as a vital staple crop particularly in Sub-Saharan Africa, Latin America, and parts of Asia. However, cassava cultivation faces an emerging and critical challenge: the accumulation of heavy metals from contaminated soils into edible tubers, which directly threatens the health of millions of consumers who depend on this crop as a dietary staple.
Cassava (Manihot esculenta Crantz) stands as the fourth most important source of calories for the global human population [1], serving as a vital staple crop particularly in Sub-Saharan Africa, Latin America, and parts of Asia. The crop’s adaptability to marginal and nutrient-poor soils, combined with its drought tolerance and high productivity potential, has made it indispensable for food security in resource-poor communities [2]. However, cassava cultivation faces an emerging and critical challenge: the accumulation of heavy metals from contaminated soils into edible tubers, which directly threatens the health of millions of consumers who depend on this crop as a dietary staple.
Heavy metal contamination in agricultural soils has become a global environmental concern with far-reaching implications for food safety and human health [3]. The persistence and bioaccumulative nature of metals such as cadmium (Cd), lead (Pb), mercury (Hg), and arsenic (As) means they accumulate in soil environments and are subsequently taken up by food crops, creating a direct pathway to human toxicity through dietary exposure [4]. While cassava’s resilience to poor growing conditions represents a significant advantage for food security, this same characteristic creates a vulnerability—the crop can thrive in contaminated environments, yet accumulate dangerous levels of heavy metals that render its tubers unsafe for consumption.
The global cassava production system faces unprecedented pressure from both natural and anthropogenic sources of heavy metal contamination. Industrial effluents, mining operations, inappropriate waste disposal practices, atmospheric deposition, and the excessive application of agrochemicals including fertilizers and pesticides all contribute to elevated heavy metal levels in agricultural soils [5]. In developing nations where cassava serves critical food security functions, the regulation and monitoring of soil quality remains inadequate, exacerbating the problem. The situation is particularly acute in countries undergoing rapid industrialization or in regions with active mining operations, where cassava-growing communities face cumulative contamination pressures that threaten both environmental and human health.
Cassava’s role in global food security cannot be overstated. With production exceeding 215 million tons annually globally, and Nigeria accounting for approximately 20.3% of global production [6], cassava provides reliable caloric intake for vulnerable populations. The crop is particularly important in Sub-Saharan Africa, where it serves as a strategic crop for meeting the dietary needs of resource-limited households. Beyond direct consumption, cassava supports multiple value chains including flour production for bread-making, animal feed preparation, and starch extraction, creating income opportunities for smallholder farmers [7]. In developing countries facing the dual burden of food insecurity and malnutrition, cassava has emerged as an orphan crop—understudied relative to major cereals but critically important for local food systems and livelihoods [8].
Cassava’s propensity to accumulate heavy metals stems from multiple physiological and environmental factors. The crop exhibits specific transport mechanisms for metal uptake, with evidence suggesting differential accumulation patterns across plant tissues. Studies comparing cassava tuber compartments have revealed that heavy metal concentrations vary significantly between the pith, bark, epidermis, and flesh of tubers [9], with some tissues showing substantially higher accumulation than others. Root tuber crops like cassava naturally concentrate minerals and trace elements as part of their storage function, and this same mechanism can result in unintended accumulation of toxic metals when soil bioavailability is elevated [10].
The bioaccumulation characteristics of cassava have been documented in multiple environmental contexts. In crude oil-impacted areas of Niger Delta, Nigeria, cassava demonstrated strong bioaccumulation capacity for copper, with perfect correlation (r = 1.00) between soil and plant concentrations suggesting cassava’s potential as a bioindicator crop [11]. Similarly, research from Ghana demonstrated that 30% of cassava samples exceeded permissible lead concentrations set by international standards, with bioconcentration factors for nickel indicating higher absorption capacity into cassava from soil compared to other heavy metals [12]. This evidence suggests that cassava’s metal uptake is not random but follows plant-specific physiological pathways that can be targeted for remediation interventions.
Geographic distribution of cassava contamination reveals particular vulnerability in regions subject to mining impacts, industrial development, and improper waste disposal. In Ecuador’s gold mining areas, cassava and other food crops showed trace element concentrations exceeding maximum permissible levels, with hazard quotients and cancer risk values indicating significant health risks, particularly for children [13]. In Nigeria, cassava grown around cement factories accumulated heavy metals at levels far exceeding WHO/FAO standards [14], while cassava from crude oil-impacted communities in the Niger Delta showed Hazard Index values exceeding the USEPA safety threshold [4]. These geographic patterns underscore the urgent need for context-specific remediation strategies tailored to local contamination profiles and farming practices.
Numerous studies have documented heavy metal levels in cassava grown across various contamination contexts. In Machakos County, Kenya, single-cropped cassava farms showed cadmium levels ranging from 0.09-0.59 mg/kg in soil, with cassava tuber pith accumulating mean values of 4.7 mg/kg for cadmium [9]. Intercropped systems showed even higher accumulation, with cadmium values reaching 7.8 mg/kg in tuber pith, indicating that agricultural management practices influence metal bioavailability and plant uptake. Research from multiple mining-affected sites in Ghana demonstrated that cassava tubers accumulated copper and mercury above FAO/WHO permissible limits, with strong positive correlations between soil and plant copper concentrations establishing cassava as a reliable bioindicator for this metal [11].
The distribution of heavy metals within cassava tubers is not uniform. Tissue-specific analysis reveals that the pith and bark accumulate substantially higher metal concentrations than the flesh [9], an important finding for food safety implications given that different populations consume cassava in varied forms. In some regions, tubers are peeled before consumption, potentially reducing exposure if outer tissues contain higher concentrations; however, whole-tuber consumption or incomplete peeling exposes consumers to the highest metal burdens. In crude oil-impacted communities where cassava grows, zinc was the dominant metal, with concentrations reaching 7.91×10⁻¹ mg/kg/day in estimated daily intake for children [4], far exceeding safe exposure levels and indicating the magnitude of dietary risk from cassava consumption in these areas.
Heavy metal contamination of cassava-growing soils originates from diverse sources, with scientific understanding advancing through source apportionment studies. The dominant sources include mining activities (both artisanal and industrial), industrial emissions, atmospheric deposition, agricultural intensification through fertilizer and pesticide application, and improper waste disposal [15]. In North China Plain agricultural soils, policy factors controlling fertilizer and pesticide use emerged as the dominant influence on heavy metal accumulation, with the policy factor explaining more variation than atmospheric deposition or agrochemical application alone [16]. This finding suggests that agricultural management practices and policy environments significantly shape contamination outcomes, opening potential leverage points for intervention.
In mining-affected cassava-growing regions, mining operations represent the primary contamination source. In Ghana’s illegal mining areas, the combination of artisanal small-scale gold mining (ASGM) operations and subsequent terrestrial transport of mercury created widespread contamination. Cassava roots accumulated mercury at concentrations ranging from 0.097 to 5.09 mg/kg dry weight, while leaves reached 0.350 to 8.84 mg/kg, with children exhibiting significantly higher health risks than adults due to their body weight-adjusted exposure [17]. The source differentiation observed through multivariate analysis in diverse agricultural regions consistently identifies anthropogenic sources as dominant contributors, with petroleum activities contributing lead and cadmium, while agrochemical use drives copper accumulation [4].
Understanding how heavy metals move from soil into cassava tissues represents a critical knowledge area for developing remediation strategies. The soil-plant transfer depends on multiple interacting factors including soil pH, organic matter content, metal speciation, and plant-available metal concentration in the rhizosphere. Soil pH emerges as a particularly critical parameter, with acidic soils promoting greater metal mobility and plant uptake [18]. Low soil pH directly increases the concentration of metals in soil solution, enhancing bioavailability to plant roots, while neutral to slightly basic pH reduces solubility of many metals, limiting uptake. In some cassava-growing regions, low soil organic matter exacerbates contamination risk by reducing the soil’s capacity to bind and immobilize metals.
The bioaccumulation capacity of cassava for specific metals appears partly dependent on soil chemical properties. In studies of cassava from illicitly mined areas in Ghana, mercury showed weak or negative correlations between soil and plant concentrations, suggesting limited bioavailability influenced by soil pH and organic matter [11]. In contrast, copper exhibited a perfect positive correlation (r = 1.00) between soil and plant concentrations, indicating direct proportional relationships. These differential transfer patterns suggest that remediation strategies targeting specific metals may require tailored approaches addressing the particular soil chemistry governing bioavailability of those metals.
Root morphology and the rhizosphere ecology of cassava influence metal uptake dynamics. Arbuscular mycorrhizal fungi (AMF) associated with cassava roots can both increase and decrease metal availability depending on the metal type and soil conditions. In cadmium-contaminated farmland soils, AMF increased cassava root surface area and volume while modulating low-molecular-weight organic acid (LMWOA) secretion, influencing the speciation and bioavailability of soil metals [19]. These microbial interactions create opportunities for biological remediation approaches that leverage plant-microbe associations to reduce metal translocation to edible tissues.
The health significance of cassava contamination emerges clearly when dietary exposure is quantified through risk assessment methodologies. Children consistently face higher health risks than adults due to their lower body weight relative to intake, as well as developmental sensitivity to heavy metal toxicity. In crude oil-impacted areas of Nigeria, zinc Hazard Index (HI) values peaked at 5.5 for cocoyam but cassava also showed concerning values, with total lifetime cancer risk for arsenic reaching 1.5×10⁻⁴, exceeding the USEPA acceptable limit of 1×10⁻⁴ [4]. Estimated daily intake (EDI) calculations for children revealed maximum values for zinc of 7.91×10⁻¹ mg/kg/day, substantially above safe exposure levels.
The carcinogenic and non-carcinogenic risk profiles vary by metal and population. In Ghanaian mining communities, the target hazard quotient (THQ) for lead in cassava exceeded 1 in children from multiple communities (Techiman, Wangarakrom, Samahu, and Tebe), indicating unacceptable health risk [12]. A systematic review of Nigerian food crops revealed that among heavy metals and organochlorine pesticides, cadmium was present at the lowest average concentrations while iron had the highest, but the HQ-based non-carcinogenic risk (NCR) estimates for lead, cadmium, copper, and manganese exceeded 1 in both adults and children [20]. These risk values translate to substantial disease burden in populations depending on cassava as a staple food source.
Heavy metal toxicity mechanisms in human health include disruption of cellular homeostasis, generation of oxidative stress, interference with nutrient metabolism, and in the case of carcinogens like cadmium and arsenic, direct mutagenic effects. Lead exposure impairs cognitive development in children and increases hypertension risk in adults. Cadmium accumulates in kidney and bone tissues, causing renal dysfunction and osteoporosis with long-term exposure. These health impacts create urgent imperatives for cassava contamination reduction, particularly in communities where alternatives to cassava as a dietary staple are limited.
Biochar, a carbon-rich material produced through pyrolysis of agricultural and forestry waste, has emerged as one of the most promising soil amendments for reducing heavy metal bioavailability in contaminated soils. The mechanisms underlying biochar’s effectiveness include high surface area and porosity providing adsorption sites for metal ions, abundant surface functional groups (carboxyl, hydroxyl, amino) that chelate metals, and elevated soil pH increasing metal precipitation and reducing solubility [21]. Biochar application rates typically range from 5-20 tons per hectare, with soil incorporation depth and timing of application influencing effectiveness.
The effectiveness of biochar for cassava-specific contamination remediation has been directly evaluated. In mining-degraded cassava-growing landscapes in Ghana, biochar amendment reduced arsenic accumulation in cassava by 168.9% compared to control soils, while lead accumulation decreased by 149.8% [22]. This dramatic reduction occurred even in severely contaminated mining-degraded soils, demonstrating biochar’s potential for remediation of highly contaminated cassava production systems. When combined with poultry manure, biochar enhanced both remediation effectiveness and cassava stover biomass production, suggesting additive or synergistic effects of combined amendments.
The interactions between biochar and soil conditions influence remediation outcomes. Biochar application enhances soil pH, which reduces the solubility of many cationic metals including cadmium, lead, and zinc. Additionally, biochar increases soil water-holding capacity and organic carbon content, promoting beneficial microbial communities that can further immobilize metals. However, long-term stability of biochar’s remediation effects requires monitoring, as the material’s own leaching behavior could potentially mobilize adsorbed metals over extended time periods [23]. The sustainability assessment of biochar-based remediation must consider the energy inputs in biochar production, the availability of suitable feedstocks, and the economics of application at farm scale.
Organic amendments, including compost, manure, and agricultural residues, represent accessible remediation tools particularly suitable for smallholder cassava farmers in resource-limited settings. These materials reduce metal bioavailability through multiple mechanisms: increased organic matter binds metals through chelation and sorption; elevated pH from organic matter decomposition reduces metal solubility; and stimulation of beneficial soil microorganisms creates additional binding sites for metals in the rhizosphere [24]. The effectiveness varies with amendment source, degree of decomposition, and soil conditions.
Application of cow dung and urban waste compost to cadmium-contaminated soil reduced cadmium transfer to amaranth by 90%, while lead transfer was reduced by 70%, demonstrating substantial protective effects for food crops [25]. Bone meal and chicken manure amendments applied to cassava grown on cadmium-contaminated soil reduced cadmium bioavailability, achieving low accumulation values of 3.2 mg/kg in cassava tissues despite substantial soil concentrations of 3.1 mg/kg [26]. These results indicate that even moderate organic amendments can substantially reduce metal translocation to edible cassava tubers.
The protective mechanisms of organic amendments operate partly through their influence on soil pH and metal speciation. Decomposition of organic matter generates organic acids that can form soluble complexes with metals, either increasing or decreasing bioavailability depending on concentration and metal type. Low molecular weight organic acids (LMWOAs) at appropriate concentrations enhance metal immobilization, while excessive concentrations may mobilize metals [27]. This concentration-dependent effect suggests that optimization of amendment application rates is critical for effective remediation, and excessive amendment application could paradoxically worsen contamination outcomes.
The integration of biochar with complementary organic amendments has demonstrated synergistic effects exceeding those of single-amendment approaches. In cassava cultivation on mining-degraded land, the combination of biochar and poultry manure produced superior cassava stover biomass (22.9 ton/ha) and greater metal accumulation reduction compared to either amendment alone [22]. The synergistic mechanisms likely involve complementary effects: biochar provides physical adsorption capacity and pH elevation, while organic matter supplies readily available nutrients and promotes beneficial soil biology.
Combined biochar and nanoscale iron (nZVI) amendments with phytoremediation (earthworms and sunflowers) demonstrated enhanced remediation of lead and cadmium pollution through improved soil microbial diversity and more complex microbial community structure [28]. The microbial community shifts associated with combined amendments can accelerate metal transformation into less mobile species and enhance the capacity of the soil system to immobilize metals. These integrated approaches suggest that maximizing remediation efficiency requires optimization of amendment combinations tailored to specific contamination profiles and soil conditions.
Nanotechnology offers novel remediation possibilities through the development of engineered nanoparticles with enhanced sorption capacities for heavy metals. Zinc oxide nanoparticles (ZnO NPs) combined with sugarcane bagasse reduced cadmium accumulation in wheat shoots by 43.3% and seeds by 46.3%, while the combined treatment achieved 74.1% and 62.9% reductions respectively [29]. These nanomaterial-based amendments demonstrate dramatically enhanced remediation efficiency compared to conventional amendments, though questions about environmental fate and potential hazards of nanoparticles themselves require further investigation.
Metal-organic frameworks (MOFs) and nanohybrid biochar materials represent cutting-edge amendment technologies with potential for cassava contamination remediation. Nano-modified biochar hybrids enhance heavy metal adsorption capacity through improved physicochemical properties and increased availability of active sorption sites [30]. However, the environmental persistence and potential toxicity of nanoparticles necessitate comprehensive life cycle assessment and long-term monitoring before widespread adoption in cassava production systems. The reversibility of nanomaterial-based immobilization mechanisms also requires clarification, as metals adsorbed on nanoparticles might mobilize if environmental conditions change.
Phytostabilization, where plants restrict metal uptake and accumulation while immobilizing metals in soil, offers a practical approach compatible with continued cassava cultivation in mildly to moderately contaminated areas. Rather than extracting metals from soil, phytostabilization confines metals to root zones or accumulates them in root tissues rather than edible shoots [31]. This approach is particularly suitable for cassava since the edible portion is the underground tuber, making root-concentrated accumulation patterns preferable to shoot accumulation.
The combination of cassava cultivation with soil amendments achieving phytostabilization creates a sustainable production system for contaminated areas. Cassava varieties responsive to soil amendments show enhanced growth on contaminated soils when protected by organic amendments. In one study, the bone meal and chicken manure combination reduced cassava cadmium uptake to 127.8 mg per plant from soils containing 3.1 mg/kg cadmium, while untreated controls would have absorbed substantially more [26]. However, this same study noted that cassava exhibited toxicity symptoms after harvest, suggesting that true phytostabilization of cassava may face physiological constraints, and cassava may be more suitable for gentle phytoextraction (partial removal) than complete stabilization.
The selection or breeding of low-metal-accumulating cassava varieties could enhance the effectiveness of phytostabilization strategies. Genetic variation in metal uptake capacity exists among cassava germplasm, as evidenced by differential responses to identical contamination and amendment conditions [32]. Investment in screening cassava breeding lines for reduced cadmium and lead accumulation could identify varieties maintaining productivity while accumulating less metal from contaminated soils. These “low-accumulator” varieties could then be promoted in contaminated regions, providing food security benefits while reducing health risks.
Genetic engineering and conventional breeding can enhance cassava’s ability to thrive on contaminated soils while maintaining acceptable metal levels in edible tissues. The MeGLYI-13 gene cloned from cassava demonstrated enhanced tolerance to zinc and copper stresses in yeast and Arabidopsis models [33], suggesting that genetic modification could enhance cassava’s inherent stress tolerance. However, the pleiotrophic effects of metallothionein and glutathione S-transferase genes—which enhance metal tolerance while potentially affecting nutrient uptake and translocation—require careful assessment before field deployment.
Classical breeding approaches offer a more immediately deployable strategy for developing cassava varieties with reduced metal accumulation. Selecting parental lines with naturally lower metal uptake and concentrating these traits through successive generations could rapidly generate improved varieties without the regulatory challenges of genetic modification. Recent advances in mutation breeding and genomics have demonstrated that induced mutations can rapidly generate variation in metal tolerance and accumulation patterns [34]. For cassava-producing communities in contaminated regions, the development of locally adapted low-metal varieties through participatory breeding approaches could provide sustainable, farmer-managed solutions to contamination challenges.
The regulatory environment for genetically modified cassava varies substantially across regions, with adoption more readily accepted in some contexts than others. In Africa, where cassava serves critical food security functions, substantial investment in understanding genetic and genomic bases of metal tolerance could facilitate more rapid breeding progress for both improved productivity and reduced metal accumulation. The integration of genomic selection with conventional breeding could accelerate variety development timelines, bringing improved varieties to farmers more rapidly than traditional approaches [35].
Exogenous application of chelating agents can enhance metal uptake by plants, facilitating phytoextraction where metals are actively removed from soil into harvestable plant tissues. Malic acid and tartaric acid applied at optimal concentrations significantly enhanced cadmium and lead uptake by sunflower plants, with the highest accumulations achieved through careful optimization of acid concentration [36]. However, the applicability of this approach to cassava remains uncertain, as excessive chelation can mobilize metals throughout the soil profile, potentially causing deeper contamination or enhanced leaching to groundwater.
The concentration-dependent effects of chelating agents create narrow optimization windows for effective phytoextraction. Low concentrations of tartaric acid (2 mmol/kg soil) enhanced immobilization of cadmium, lead, and zinc in contaminated soils, while higher concentrations reversed this effect, mobilizing metals and increasing bioavailability [27]. Similarly, oxalic acid at all tested concentrations enhanced metal mobility, suggesting that different organic acids have fundamentally different soil chemistry effects. For cassava-based phytoextraction systems, the optimal approach would identify the specific chelating conditions promoting maximum metal uptake by cassava without mobilizing metals into undesirable soil horizons.
In practice, chelate-assisted phytoextraction requires careful management including continuous monitoring of soil metal concentrations to detect any unwanted mobilization. The metal-loaded cassava tissues must then be properly disposed through specialized waste management channels, as removing metals from soil only transfers contamination to plant tissues that subsequently become waste [37]. This disposal challenge creates practical limitations for implementation of phytoextraction approaches in cassava-producing regions with limited waste management infrastructure.
Intercropping cassava with complementary crop species can enhance both remediation outcomes and productivity through synergistic interactions. Research from Kenya demonstrated that intercropping systems showed higher heavy metal concentrations in both soil and cassava compared to monoculture systems [9], suggesting that competition between crops or changes in soil chemical conditions affect metal availability. However, careful selection of intercrop species—particularly those with rhizosphere-modifying characteristics or metal-accumulating capabilities—could convert this challenge into an opportunity.
Designing intercropping systems where cassava grows alongside metal-hyperaccumulating or -accumulating species could enhance overall metal removal from soils. For instance, growing cassava intercropped with amaranth (which readily accumulates certain metals) or other leafy vegetables could allow harvesting of high-metal plant material from intercrop while cassava tubers remain relatively protected. The polyculture approach offers additional benefits including reduced pest and disease pressure, improved soil structure from diverse root systems, and greater overall productivity per unit area [38]. These multiple benefits align with climate-smart agriculture principles that address both food security and environmental sustainability.
The biodiversity benefits of polyculture cassava systems enhance soil biological functions that support metal immobilization. More diverse crop mixtures support greater soil microbial diversity and functional complexity, enhancing the soil’s capacity to immobilize metals and suppress plant-pathogenic organisms [28]. The reduction of simple monoculture systems in favor of more complex polycultures addresses multiple production constraints simultaneously—contamination, soil degradation, declining productivity, and pest pressure—making these systems particularly attractive for resource-limited cassava farmers.
Beneficial microorganisms residing in cassava root systems can substantially reduce heavy metal stress and accumulation through multiple mechanisms including metal chelation, precipitation, and enzymatic transformation. Exopolysaccharide-producing Bacillus species (Z23 and Z39) screened from heavy metal-contaminated farmland achieved 88.6-93.2% removal efficiency for cadmium and lead through precipitation of metal-phosphate complexes in soil solution [39]. These bacteria simultaneously enhanced plant growth and reduced metal accumulation in lettuce tissues by 40.1-61.7%, while increasing soil microaggregate content and exopolysaccharide concentrations in the rhizosphere.
The endophytic microorganisms residing within cassava tissues can employ chelation, complexation, precipitation, and enzymatic transformation to mitigate heavy metal toxicity at the cellular level [40]. Endophytes enhance plant growth in metal-contaminated soils while contributing to reduced heavy metal accumulation through both direct metal immobilization and indirect enhancement of plant stress tolerance mechanisms. The intimate association between endophytes and plant tissues, compared to free-living rhizosphere bacteria, potentially allows more efficient delivery of metal-detoxifying metabolites directly to plant cells experiencing metal stress.
Mycorrhizal fungi associated with cassava roots demonstrate similar potential for reducing metal stress and accumulation. Arbuscular mycorrhizal fungi (AMF) increased cassava root morphological traits and enhanced secretion of low-molecular-weight organic acids (LMWOA) in the rhizosphere [19]. However, the relationship between AMF-enhanced root growth and metal accumulation is complex, as improved root systems could theoretically increase metal uptake if bioavailability is not simultaneously reduced. The net outcome depends on whether AMF effects on LMWOA secretion favor metal immobilization or mobilization—a concentration- and metal-dependent phenomenon requiring careful evaluation for each fungal-plant-contamination combination.
Inoculation of cassava with specifically selected metal-resistant bacterial strains can enhance plant tolerance to heavy metal stress through multiple physiological mechanisms. Beneficial bacteria produce phytohormones including auxins and cytokinins that enhance root development and improve water and nutrient uptake, increasing plant vigor in stressed conditions [41]. Additionally, bacterial production of enzymatic and non-enzymatic antioxidants combats the oxidative stress generated by heavy metal accumulation in plant tissues.
The selection of appropriate bacterial strains for cassava inoculation requires screening for both metal tolerance and plant growth promotion capacity. Strains demonstrating high heavy metal tolerance in laboratory conditions may be ineffective in field soils if they cannot colonize cassava roots or compete with indigenous soil microbiota. Conversely, excellent plant growth promoters in pristine soils may not survive in heavily contaminated environments [42]. The optimization process requires evaluation of specific strain-cassava variety-contamination condition combinations, recognizing that universal solutions may not exist and local adaptation is necessary.
The practical application of bacterial inoculation in cassava production requires development of formulations maintaining bacterial viability during storage and transport, appropriate inoculation methods reaching target root systems, and cost-effective production at scales relevant to smallholder farmers [43]. Seed coating with inoculant bacteria offers one approach achieving efficient delivery of beneficial strains to developing cassava seedlings. As cassava is typically propagated vegetatively from cuttings rather than seeds, alternative inoculation methods including direct cutting or soil inoculation with stabilized formulations may be more appropriate for cassava-specific applications.
Microbially induced calcium carbonate precipitation (MICP) represents an innovative bioremediation technique leveraging metabolic activity of ureolytic microorganisms to precipitate calcium carbonate (CaCO3), sequestering heavy metals as stable metal-carbonate complexes [44]. This approach differs fundamentally from passive stabilization, actively transforming soluble metal ions into precipitated mineral phases. The technology has demonstrated efficacy for lead (Pb), cadmium (Cd), and arsenic (As) immobilization in laboratory and field settings.
The mechanisms of MICP involve bacterial urease catalyzing hydrolysis of urea, generating ammonia and carbon dioxide that combine with calcium to form precipitates. The pH elevation from this process simultaneously reduces metal solubility while creating favorable conditions for metal carbonate formation [44]. The advantages of MICP include minimal disturbance to soil structure, potential for selective mobilization during implementation, and relatively straightforward monitoring of process through pH and conductivity measurements. However, long-term stability of carbonate precipitates under varying soil water conditions requires further investigation.
Application of MICP to cassava contamination remediation would require adaptation of existing protocols to agricultural soil conditions. The approach depends on maintaining adequate moisture and nutrient conditions for bacterial activity, factors that vary substantially across cassava-growing regions. In addition, the scalability of MICP from laboratory reactors to field soils requires development of practical protocols for bacterial inoculation, urea provision, and continuous monitoring. The cost-effectiveness at farm scale remains uncertain, particularly in regions with limited infrastructure for technical implementation.
Enzyme-induced calcium carbonate precipitation (EICP) offers greater control over remediation conditions compared to MICP by directly applying urease enzymes rather than relying on living microorganisms [44]. This approach enables precise regulation of reaction rates, pH, temperature, and timing independent of microbial growth dynamics. The immobilization of heavy metals through EICP has shown comparable or superior effectiveness to MICP in laboratory conditions, with potential advantages in environments unfavorable to microbial survival.
The practical advantages of EICP include elimination of microbial growth constraints and potential introduction of undesired organisms, enabling application in sterilized or near-sterile conditions if required. The enzyme can be sourced from pure culture or synthesized through biotechnological approaches, providing standardized preparations. However, enzyme cost, stability during storage and transport, and activity maintenance in field soil conditions present practical challenges. The effectiveness of EICP in the heterogeneous, dynamic soil environment differs substantially from controlled laboratory systems, requiring field validation before recommendation for cassava contamination remediation.
Hybrid approaches combining EICP with other remediation strategies might optimize outcomes. For example, EICP application could be followed by soil amendment with organic matter promoting long-term biological processes that maintain immobilization. The integration of enzyme-catalyzed precipitation with plant-based remediation strategies through intercropping could create multi-component systems addressing contamination through complementary mechanisms. However, such integrated approaches require careful optimization to avoid conflicting effects, such as conditions favoring metal mobility in some system components while aiming for immobilization in others.
The principle of Integrated Soil Fertility Management (ISFM) adapted for contaminated cassava-growing systems combines multiple strategies—inorganic and organic amendments, soil- and plant-based interventions, agronomic practices, and biological approaches—into comprehensive soil management packages addressing both heavy metal contamination and nutrient deficiency [38]. This systems approach recognizes that cassava production on contaminated soils requires addressing multiple constraints simultaneously: excessive heavy metal levels, declining soil organic matter, nutrient imbalances, and suboptimal soil biological activity.
The empirical basis for ISFM in contaminated cassava systems comes from studies demonstrating that single interventions often provide incomplete remediation, while combinations of approaches achieve superior outcomes. The combination of biochar, organic amendments, selected crop varieties, and microbial inoculations created synergistic effects exceeding the sum of individual component benefits [22]. The context-specific optimization of amendment combinations—considering local soil properties, contamination profiles, available resources, and farmer capacity—creates ISFM packages tailored to distinct agroecological zones and contamination scenarios.
Policy support for ISFM implementation in cassava production systems requires investment in farmer training, extension service capacity building, and potentially subsidized access to amendment materials for resource-limited farmers [45]. The success of ISFM adoption depends on demonstrable improvements in cassava yield and income, alongside health risk reduction. Communication of the non-visible health benefits (reduction of heavy metal intake) alongside visible economic returns (improved yield) may require integration with public health messaging and community engagement.
Effective cassava contamination remediation requires supportive policy environments regulating heavy metal sources, monitoring soil and crop contamination, and establishing safe consumption thresholds. Nigeria’s existing legislative framework for heavy metal pollution, while robust on paper, faces implementation challenges including insufficient funding, limited regulatory capacity, and weak enforcement [45]. Similar regulatory gaps exist across cassava-producing regions, creating conditions where contamination persists unchecked and remediation receives inadequate priority in agricultural extension services.
The establishment of mandatory soil testing programs before cassava cultivation, combined with certification of safe cassava production areas, could reduce consumer exposure to contaminated tubers. However, such programs require laboratory capacity, reliable analytical methods, and standardized interpretation protocols—infrastructure that remains inadequate in most cassava-producing regions. The development of regional soil testing networks and capacity strengthening initiatives represents an important prerequisite for evidence-based remediation decision-making.
Public-private partnerships could accelerate monitoring and remediation capacity development. Food safety testing protocols could be integrated into cassava flour mills and processing facilities, providing feedback to farmers on product safety and economic incentives for implementing remediation practices [45]. The integration of cassava contamination monitoring with broader agricultural surveillance systems, rather than treating it as an isolated issue, would improve cost-effectiveness and facilitate coordination across sectors.
While reducing heavy metal contamination remains essential, simultaneously enhancing the nutritional quality of cassava through biofortification addresses the reality that cassava-based diets often fail to meet micronutrient requirements [1]. Biofortified provitamin A-rich cassava varieties have benefited 2.6 million people in sub-Saharan Africa and Brazil [46], demonstrating the potential of genetic improvement in cassava quality. The integration of enhanced micronutrient content (zinc, iron, vitamin A) alongside reduced heavy metal accumulation creates varieties addressing multiple nutritional constraints simultaneously.
The enrichment of cassava flour with cassava leaves, which contain substantial protein, fiber, and micronutrient content, provides a practical biofortification approach compatible with existing processing infrastructure [47]. Cassava leaf flour incorporates into bread production, improving nutritional profiles while creating additional value for farmers growing cassava foliage. However, cassava leaves may accumulate heavy metals at different rates than tubers, requiring separate monitoring and management to ensure that leaf incorporation does not inadvertently increase consumer metal exposure.
The potential for agricultural biofortification through targeted soil amendment and foliar nutrient application offers opportunities to simultaneously reduce metal bioavailability while enhancing micronutrient density. Zinc oxide nanoparticles applied folially enhanced plant zinc concentration while reducing cadmium accumulation [29], suggesting that some amendment strategies provide dual benefits. The optimization of such approaches specifically for cassava would require evaluation of foliar application timing, rates, and product forms achieving maximum efficacy.
Emerging digital technologies including remote sensing, geographic information systems (GIS), and low-cost soil testing devices enable real-time monitoring of cassava contamination at spatial scales relevant for management decision-making. Mobile phone-based reporting systems could connect smallholder cassava farmers with testing services and remediation recommendations, creating feedback loops currently absent in most contexts. The integration of contamination data with crop production information would enable geographically explicit recommendations for remediation strategy selection based on contamination severity and local conditions.
Climate change impacts on cassava contamination dynamics remain poorly understood. Climate-driven changes in soil water status, temperature, and vegetation patterns will alter metal mobility, plant-available concentrations, and cassava metal accumulation rates [48]. The adaptation of cassava production systems to climate change requires concurrent attention to contamination risk management, ensuring that strategies enhancing climate resilience do not inadvertently increase heavy metal accumulation. For example, enhanced water retention through soil amendment could mobilize certain metals, requiring careful assessment of multi-contaminant interactions.
The transformative potential of cassava production systems that simultaneously address food security, environmental contamination, climate resilience, and livelihood sustainability represents an aspirational target for agricultural research and development. This transformation requires integration of agronomic innovation with rural development, food system strengthening, and public health engagement [43]. The multi-sectoral approach recognizing cassava contamination as embedded within broader development challenges offers more realistic pathways for impact than narrow technical solutions neglecting the socioeconomic context of cassava farming communities.
The evidence presented throughout this review demonstrates that heavy metal contamination of cassava represents a serious but addressable challenge to food security and human health in developing regions. The range of remediation strategies documented—from simple soil amendments to advanced biotechnologies—provides multiple options for contamination management. However, no single approach universally works across all contexts. Instead, successful remediation requires integration of context-specific strategies accounting for local contamination profiles, soil properties, farmer capacity, available resources, and broader development priorities.
For cassava-producing regions with mild to moderate contamination, organic amendment-based strategies combined with selection of low-accumulating varieties offer practical, cost-effective approaches compatible with smallholder farming systems. The application of compost, animal manure, and biochar at rates appropriate for local soil conditions can substantially reduce metal bioavailability while improving overall soil quality and productivity. These amendments provide multiple co-benefits including nutrient cycling, water retention, and carbon sequestration, justifying investment even where contamination risk is uncertain.
In severely contaminated areas, particularly those impacted by mining or industrial operations, more intensive interventions including biochar application at rates of 10-20 tons/hectare, combined with microbial inoculation and targeted soil management, may be necessary to achieve sufficient metal immobilization. The phytostabilization strategy maintaining cassava cultivation on contaminated soils through amendment-assisted growth represents a livelihood-preserving approach for communities unable to relocate production. However, the requirement for ongoing monitoring and adaptive management must be clearly communicated to farmers to ensure sustained effectiveness.
The critical importance of monitoring programs and community engagement cannot be overstated. Remediation strategies succeed only when farmers understand contamination risks, perceive concrete benefits from management practices, and have access to reliable feedback on effectiveness [45]. The integration of cassava contamination remediation with broader food safety and agricultural development initiatives increases the likelihood of adoption and sustained implementation. Public investment in monitoring infrastructure, farmer training, and research on locally adapted remediation strategies represents the foundation for meaningful progress.
Cassava contamination with heavy metals represents a critical threat to food security and human health in developing regions where cassava serves essential dietary and livelihood functions. The evidence reviewed demonstrates that cassava exhibits significant capacity for bioaccumulation of cadmium, lead, mercury, and other metals, with documented health risks particularly affecting children in contaminated regions. However, the same evidence also demonstrates that multiple intervention strategies—soil amendments, microbial remediation, phytostabilization, and integrated management approaches—can substantially reduce metal bioavailability and plant accumulation when appropriately applied.
The pathway forward for cassava contamination remediation requires moving beyond technical innovation toward integration of multiple strategies within supportive policy environments and farmer-centered development approaches. The most promising strategies combine local resource utilization (biochar from agricultural waste, manure-based amendments) with scientific evidence regarding optimal application and monitoring. The parallel development of low-accumulating cassava varieties, compatible with local farming systems and farmer preferences, creates opportunities for sustained improvement in cassava food safety.
The integration of cassava contamination remediation with broader agricultural development priorities—including climate adaptation, nutritional enhancement, and livelihood improvement—increases both the feasibility and potential impact of interventions. Single-focus remediation projects are unlikely to generate sustained farmer adoption or investment. Instead, comprehensive approaches addressing multiple constraints simultaneously align with farmer priorities and create economic incentives for management practice change.
Future research priorities should include: (1) field-scale validation of integrated remediation approaches in diverse agroecological and contamination contexts; (2) development and evaluation of locally-adapted cassava varieties with reduced metal accumulation; (3) investigation of policy instruments and market incentives promoting safe cassava production; (4) integration of contamination monitoring with early warning systems for food safety threats; and (5) capacity strengthening in cassava-producing regions enabling sustained implementation of evidence-based remediation strategies.
The remediation of heavy metal contamination in cassava production is fundamentally solvable through application of available knowledge, technologies, and management practices. The challenge lies not in technical limitations but in bridging the gap between scientific evidence and farmer implementation, within ic constraints of limited resources, inadequate infrastructure, and competing development priorities in resource-limited regions.
The transformation of cassava from a potential health risk into a reliable safe food source requires commitment from multiple stakeholders: agricultural researchers developing and validating context-appropriate solutions; policymakers establishing supportive regulatory frameworks and resource allocation; development practitioners facilitating farmer adoption and knowledge exchange; and cassava farmers themselves taking ownership of contamination management as integral to production. When these actors work synergistically within integrated programs addressing multiple development goals simultaneously, cassava can continue fulfilling its critical role in food security while protecting the health of the millions who depend on this essential crop [2], [46].
The evidence presented in this review provides a scientific foundation for such transformation. The remediation strategies documented—from simple amendments to advanced biotechnologies—have been demonstrated to reduce heavy metal accumulation in food crops under diverse conditions. The challenge ahead is not discovering new solutions but rather implementing available solutions at scale, with attention to local context, farmer participation, and sustained monitoring. Investment in this implementation agenda represents not merely an agricultural intervention but a health equity initiative, addressing preventable illness and premature mortality among vulnerable populations who depend on cassava for survival.
[1] P. A. D. Tatis and C. E. L. Carrascal, “YUCA: PAN y CARNE, UNA ALTERNATIVA POTENCIAL PARA HACER FRENTE AL HAMBRE OCULTA,” 2021.
[2] N. Sakadzo, A. Kugedera, N. Ranganai, and L. Kokerai, “Cassava: Practices and technologies to improve food security in sub-saharan africa,” Cogent Food & Agriculture, 2025.
[3] H. I. Mohamed et al., “Heavy metals toxicity in plants: Understanding mechanisms and developing coping strategies for remediation: A review,” Bioresources and Bioprocessing, 2025.
[4] A. VK et al., “Human health risk assessment of metals and metalloid in food crops harvested from crude oil impacted community in niger delta, nigeria.” 2025.
[5] Y. Wan, J. Liu, Z. Zhong, Q. Wang, and H. Li, “Heavy metals in agricultural soils: Sources, influencing factors, and remediation strategies,” Toxics, 2024.
[6] S. C. Izah, S. E. Bassey, and E. I. Ohimain, “Impacts of cassava mill effluents in nigeria,” None, 2018.
[7] A. Abass et al., “Can food technology innovation change the status of a food security crop? A review of cassava transformation into bread in africa,” 2018.
[8] T. Z, “African orphan crops under abiotic stresses: Challenges and opportunities.” 2018.
[9] E. M. Kasyoka, G. W. Mbugua, R. Wanjau, G. N. Nambafu, and J. Ndiritu, “Levels of cadmium, copper, and lead in soils and cassava tubers grown in machakos county, kenya,” Applied and Environmental Soil Science, 2024.
[10] W. Nobuntou, P. Parkpian, N. T. K. Oanh, A. Noomhorm, R. D. DeLaune, and A. Jugsujinda, “Lead distribution and its potential risk to the environment: Lesson learned from environmental monitoring of abandon mine,” None, 2010.
[11] W. A. Oduro and E. Eduful, “Soil-to-crop transfer, bioaccumulation, and health risk assessment of heavy metals in cassava grown in illicitly mined areas of noyem and nyafoman, eastern ghana,” International Journal of Latest Technology in Engineering Management & Applied Science, 2025.
[12] N. BorteySam et al., “Accumulation of heavy metals and metalloid in foodstuffs from agricultural soils around tarkwa area in ghana, and associated human health risks,” Multidisciplinary Digital Publishing Institute, 2015.
[13] R.-C. P et al., “Trace elements in farmland soils and crops, and probabilistic health risk assessment in areas influenced by mining activity in ecuador.” 2023.
[14] O. M. Makanjuola et al., “Evaluation of heavy metals in cassava tubers grown around two major cement factories in ogun state, nigeria,” None, 2016.
[15] W. Xu, Y. Jin, and G. Zeng, “Introduction of heavy metals contamination in the water and soil: A review on source, toxicity and remediation methods,” Green Chemistry Letters and Reviews, 2024.
[16] Z. W. Liu, Y. Bai, J. Gao, and J. Y. Li, “Driving factors on accumulation of cadmium, lead, copper, zinc in agricultural soil and products of the north china plain,” Scientific Reports, 2023.
[17] T. Agustiani et al., “Mercury contamination and human health risk by artisanal small-scale gold mining (ASGM) activity in gunung pongkor, west java, indonesia,” Earth, 2025.
[18] W. L. Wong, M. Emre, and G. Talukdar, “Groundwater contamination by heavy metals in malaysia: Sources, transport, and remediation strategies,” Tropical Environment, Biology, and Technology, 2024.
[19] J. Chen et al., “Effects of an arbuscular mycorrhizal fungus on the growth of and cadmium uptake in maize grown on polluted wasteland, farmland and slopeland soils in a lead-zinc mining area,” Toxics, 2022.
[20] A. SO and A. CG, “Systematic literature review of radionuclides, heavy metals, and organochlorine pesticides in nigerian food crops: Assessment of carcinogenic and non-carcinogenic health risk.” 2025.
[21] L. Xu, F. Zhao, J. Peng, M. Ji, and B. L. Li, “A comprehensive review of the application and potential of straw biochar in the remediation of heavy metal-contaminated soil,” Toxics, 2025.
[22] K. Asante, S. Abugre, D. S. Akoto, and N. S. A. Derkyi, “Cassava (manihot esculenta) yield, nutrition, and heavy metal bioaccumulation responses to circular economy-based innovations in a mining-degraded landscape,” International Journal of Plant & Soil Science, 2023.
[23] L. Wang, J. Rinklebe, F. Tack, and D. Hou, “A review of green remediation strategies for heavy metal contaminated soil,” Soil use and management, 2021.
[24] Geeta and Dr. S. Choudhary, “Soil quality degradation due to heavy metal concentration in contaminated soil and its remediation,” Journal of Science Innovations and Nature of Earth, 2025.
[25] Z. R. M. Nadge, S. W. Paul, S. I. T. Cathrine, N. R. W. Alice, and S. Alidou, “Effect of cow dung and urban waste compost in reducing the accumulation of cadmium (cd) and lead (pb) in amaranth grown in contaminated soil,” International Journal of Plant & Soil Science, 2024.
[26] T. P, H. K, and M. W, “Organic amendment additions to cadmium-contaminated soils for phytostabilization of three bioenergy crops.” 2022.
[27] Md. S. Islam, Z. Song, R. Gao, Q. Fu, and H. Hu, “Cadmium, lead, and zinc immobilization in soil by rice husk biochar in the presence of low molecular weight organic acids,” Environmental technology, 2021.
[28] Y. Zhao et al., “Biochemical combination benefits remediation of soil lead and cadmium pollution: Evidence from sunflowers, earthworms, and soil microorganisms,” Soil & sediment contamination, 2025.
[29] E. Hafez et al., “Synergistic effect of sugarcane bagasse and zinc oxide nanoparticles on eco-remediation of cadmium-contaminated saline soils in wheat cultivation,” Plants, 2024.
[30] A. R, K. A, S. R, and P. C, “Nano modifications of biochar to enhance heavy metal adsorption from wastewaters: A review.” 2022.
[31] Y. Zhakypbek et al., “Reducing heavy metal contamination in soil and water using phytoremediation,” Plants, 2024.
[32] P. Taeprayoon, K. Homyog, and W. Meeinkuirt, “Organic amendment additions to cadmium-contaminated soils for phytostabilization of three bioenergy crops,” Nature Portfolio, 2022.
[33] L. R et al., “MeGLYI-13, a glyoxalase i gene in cassava, enhances the tolerance of yeast and <i>arabidopsis</i> to zinc and copper stresses.” 2023.
[34] M. A. Khah, “The potential of mutation breeding for ensuring sustainable food security,” International journal for advanced research in science & technology, 2025.
[35] A. Komiska, A. Wiszniewska, E. Hanus-Fajerska, and E. Muszyska, “Recent strategies of increasing metal tolerance and phytoremediation potential using genetic transformation of plants,” Springer Science+Business Media, 2018.
[36] Z. Niu, P. Guo, Z. Wang, H. Wang, and X. Li, “Study on the potential of malic acid and tartaric acid assisted in improving the phytoextraction of cadmium and lead by sunflower (helianthus annuus l.),” Soil & sediment contamination, 2025.
[37] M. Alsafran, M. Saleem, H. A. jabri, M. Rizwan, and K. Usman, “Principles and applicability of integrated remediation strategies for heavy metal removal/recovery from contaminated environments,” Journal of Plant Growth Regulation, 2022.
[38] Z. Tadele, “Raising crop productivity in africa through intensification,” 2017.
[39] H. Zhang, K. Wang, X. Liu, L. Yao, Z. Chen, and H. Han, “Exopolysaccharide-producing bacteria regulate soil aggregates and bacterial communities to inhibit the uptake of cadmium and lead by lettuce,” Microorganisms, 2024.
[40] A. Bhardwaj, “Endophytes unleashed: Natural allies for heavy metal bioremediation,” Discover Plants, 2025.
[41] H. Zhang and G. Li, “Microbial strategies for enhancing nickel nanoparticle detoxification in plants to mitigate heavy metal stress,” Phyton, 2025.
[42] V. Poria et al., “Plant growth-promoting bacteria (PGPB) integrated phytotechnology: A sustainable approach for remediation of marginal lands,” Frontiers Media, 2022.
[43] M. L et al., “Unlocking the potential of co-applied biochar and plant growth-promoting rhizobacteria (PGPR) for sustainable agriculture under stress conditions.” 2022.
[44] A. Rajasekar, A. Omoregie, and K. F. Kui, “Urease-catalyzed microbial and enzymatic carbonate precipitation for eco-friendly heavy metal remediation.” Letters in Applied Microbiology, 2025.
[45] O. Ogbeide and B. Henry, “Addressing heavy metal pollution in nigeria: Evaluating policies, assessing impacts, and enhancing remediation strategies,” Journal of Applied Sciences and Environmental Management, 2024.
[46] D. SL, G.-O. AL, G. M, and O. R, “Biofortification to avoid malnutrition in humans in a changing climate: Enhancing micronutrient bioavailability in seed, tuber, and storage roots.” 2023.
[47] B. I et al., “Bioguided optimization of the nutrition-health, antioxidant, and immunomodulatory properties of <i>manihot esculenta</i> (cassava) flour enriched with cassava leaves.” 2024.
[48] W. W, M. IA, A. S, and O.-S. AY, “Climate change as a game changer: Rethinking africa”s food security- health outcome nexus through a multi-sectoral lens.” 2025.
This work is licensed under a Creative Commons Attribution 4.0 International License.
Arsenic Levels in Rice-Based Products: Implications for Consumer Health
Cadmium Exposure in Protein Powders: Risk Assessment and Remediation
