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Heavy metal contamination of staple foods poses a significant public health risk in Nigeria, where traditional processing methods like roadside drying are prevalent. This study assessed the levels of heavy metal contamination in cassava flour (Manihot esculenta Crantz) processed and marketed in Oyo State. Samples were collected from three sources: a commercial outlet at Oja-Oba market, a roadside drying site along the Ido-Eruwa road, and a controlled self-dried batch from the Lead City area. The concentrations of Manganese (Mn), Iron (Fe), Copper (Cu), Zinc (Zn), Lead (Pb), Cadmium (Cd), Chromium (Cr), and Selenium (Se) were analyzed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Results revealed that the market-bought sample from Oja-Oba contained Pb (2.2 mg/kg) and Cr (1.7 mg/kg) exceeding WHO/FAO permissible limits. The roadside-dried sample from Ido-Eruwa had the highest levels of Fe (37.2 mg/kg) and Cr (1.8 mg/kg), also surpassing safe thresholds. In contrast, the self-dried sample showed no detectable Pb, Cd, or Cr, indicating it was the safest. However, all samples had Selenium levels (1.3–3.3 mg/kg) above the recommended limit. The findings highlight the elevated health risks associated with cassava flour from market and roadside sources due to environmental contamination during processing. The study recommends the adoption of controlled drying practices, enhanced market processing standards, and stricter regulatory enforcement to ensure the safety of this widely consumed staple food
Keywords: Manihot esculenta; heavy metals; Oja-Oba; Eruwa road; Lead City; contamination; food safety; Manihotesculenta; heavymetals; Eruwaroad; LeadCity; foodsafety
Environmentalpollutionhasemergedasaglobalconcernduetorapidindustrializationandurbanization drivenbytechnologicaladvancementsacrossvarious sectors,resultinginthecontinuousreleaseofharmfulpollutantsintotheair,soil,andwatersystems[1]. Worldwide, millions of people suffer environmental pollution related health problems. Several studies havebeenconductedonpollutionofsoils,surfaceand groundwaterandtheatmosphere[2]. Heavymetals arethemostcommonofthesepollutants[3].Although heavymetalsarenaturallyfoundinsoil,theyarecontaminated or polluted by a variety of sources, such aswater-transportedmaterialfromnearbysoilsand slopes,dryandwetatmosphericdeposition,biological inputs,roadsurfacewear,deteriorationofroadpaint, vehiclewear(tires,body,brakelinings,etc.),vehicle fluidandparticulateemissions,andinputsfromthe deteriorationofsidewalksandbuildings[4].Givenits gravenegativeimpactsonbothhumanhealthandthe environment,heavymetalpollutionisoneofthemain issuespertainingtofoodsafetyandsecurity[5].Soil, agriculturalirrigationwater,andfoodprocessingmaterialsareallsourcesofheavymetalsinfood[6,7].Heavy metalaccumulationinplantsandbio-magnificationin thehumanbodyduetocontaminatedfoodconsumptionarelinkedtoahigherriskofneurological,kidney, and cardiovascular disorders [8]. One of the staple foodcropsmostvulnerabletocontaminationfromenvironmentalpollutantssuchasheavymetalsiscassava, which is widely consumed across Nigeria in various processedformCassava(ManihotesculentaCrantz), commonlyreferredtoasastarchystaplecrop,plays apivotalroleinthedietaryneedsofmillionsacross sub-SaharanAfrica,includingNigeria.Itranksamong thehighestcarbohydrate-producingplantsaftersugarcane,providingvitalenergyintheformofcarbohydrates.Distinguishedbyitspalmateleaves,tuberous rootswithapaperybrownbark,andawhitetoyellow parenchyma-richflesh,cassavaisespeciallyvaluedin ruralandurbanNigeriancommunities[9].However,despiteitsnutritionalandeconomicimportance,cassava ishighlyperishableandpronetopost-harvestlosses duetoitsbiologicalcomposition[10].Cassavacanbe processedintonumerousfoodformsfermentedand unfermentedresultinginproductslikegarri,fufu,chips, starch,andcassavaflour(lafun).Amongthese,lafun holdssubstantialsocio-economicvalueinsouthwesternNigeria,especiallyinareaslikeIbadanandother partsofOyoState,whereitiscommonlyconsumed and marketed. Its applications range from food for householdconsumption(amalalafun)toanimalfeed andindustrialuses. Amongvariouscassava-derived flouriswidelyconsumedacrosssouthwesternNigeria. It is a significant source of energy and essential micronutrientsnecessaryformetabolicandmorphologicalprocesses[11].However,lafunproducedthrough traditionalopen-airroadsidedryingtechniquesisincreasinglyvulnerabletoenvironmentalcontamination. Inurbanandperi-urbansettingslikeOyoState,heavy vehiculartraffic,industrialactivities,andpoorwaste managementcontributesignificantlytoheavymetal andcyanidecontaminationoffoodproductsprocessed underunsanitaryconditions[2.13.1415].Environmentalcontaminantsthatposeserioushealthrisks,such aslead(Pb),cadmium(Cd),mercury(Hg),andarsenic (As),areprimarilycausedbyanthropogenicsources, suchaswasteincineration,industrialdischarges,and vehicleemissions[16.17].Afterbeingreleasedintothe soilandatmosphere,theseheavymetalshavetheabilitytobioaccumulateincropslikecassavaandcontinue toexistinthefoodchainthroughprocessedfoodslike lafun. Acuteorchroniccyanidepoisoningcanresult fromthenaturalcyanogenicchemicalsfoundincassavareachinglethallevelsifimproperlyhandled[18]. The implications of consuming lafun contaminated withtracemetalsandcyanidearesevere,rangingfrom neurological and renal dysfunctions to cardiovasculardisordersandmortality[19].Prolongedexposure tothesetoxicantscanimpairhumanhealth,particularlyinvulnerablepopulationssuchaschildren,pregnantwomen,andtheelderly[20]. Moreover,studies havereporteddeathsassociatedwiththeconsumption ofimproperlyprocessedcassavaflourinNigeria,underscoringtheurgentneedforregulatedandhygienic processingpractices[21]Giventhewidespreadconsumptionofcassavaflourandtheincreasingreliance ontraditionaldryingtechniquesinmanyNigerianmarkets,especiallyinOkeOgunregionofOyoState,itis essentialtoassessthelevelsofheavymetalsandresidualcyanideinlafun.AstudyconductedintheOkeOgun communityrevealedthatcassavafloursoldinselected marketscontainedelevatedlevelsoftoxicmetalsand cyanidebeyondpermissiblelimits,posingsignificant publichealthconcerns[12].Thiscallsforcontinuous monitoring,awareness,andinterventionstrategiesto minimizeexposurerisks.Thisresearchthereforeaims toinvestigatetheextentofheavymetalcontamination incassavaflourprocessedusingroadsidedryingmethodsandmarketedinOyoState. Thefindingswillbe instrumentalinidentifyingpublichealthrisks,recommendingsafetymeasures,andcontributingtopolicy developmentonfoodsafetyandenvironmentalhealth inNigeria.
the methodology employed to assess the levels of heavymetalcontaminationincassavafloursamples from three distinct sources in Oyo State, Nigeria; market-bought, roadside-dried, and self-dried. The studyinvestigatestheconcentrationsofManganese (Mn),Iron(Fe),Copper(Cu),Zinc(Zn),Lead(Pb),Cadmium(Cd),Chromium(Cr),andSelenium(Se)toevaluatetheirsafetyagainstWHOandNAFDACpermissible limitsandtounderstandtheirpotentialhealthimplications.Thechapterisorganizedunderthefollowing sub-headings:researchdesign,studypopulation,samplesizeandsamplingtechnique,researchinstrument, reliabilityandvalidityofinstrument,methodofdata collection,andmethodofdataanalysis.
Thestudyemployedadescriptivesurveydesign,which allowsforthecollectionandanalysisofquantitative data. This design is appropriate for understanding thelevelsofheavymetalscontaminationincassava floursamplesfromdifferentsourcesandtheirpotential healthimplications. Itfacilitatesdrawinginferences aboutthepopulationfromthesampledata,ensuring arobustcomparisonofcontaminationlevelsacross market-bought,roadside-dried,andself-driedcassava floursamples.
Forthepurposeofthisresearchwork,threesamplesof cassavaflourweretakenfromthreedifferentlocations: 1. Oja-ObaMarket(market-boughtsample) 2. Ido-EruwaRoad(roadside-driedsample) 3. Researcher’sResidence(self-driedsample)
Oja-Oba Market, located in Ibadan North-East, Oyo State,Nigeria,liesatapproximatelylatitude7°27’18"N and longitude 3°57’2"E. It is situated roughly 9–10 kmnortheastoftheIbadancitycentreandisoneof thelargestwholesaleandretailfoodstuffmarketsin Ibadan.OyoStateisinsouthwesternNigeriaandhas atropicalequatorialclimatewithdistinctwetanddry seasons.Ibadan,thestatecapital,experienceshighhumidityyear-roundandhasanestimatedpopulationof nearly4millionpeople.Themarket’sstrategiclocation oppositeMapoHall, aprominenthistoricciviclandmarkplacesitatahubofcommercialactivitywithin thecity.OjaObaMarketiscomposedofthousandsof independenttradersandvendorswhodealinstaples suchasyams,cassavaproducts(flourandgarri),maize, beans,vegetables,fruits,palmoil,onions,tomatoes, peppers,andmanymore.Tradingispredominantlyon streetandinformal,withheavypedestrianandvehiculartraffic,crowdedstalls,andlimitedformalinfrastructure,especiallydrainageandwastedisposalsystems Givenitscentralityandhighthroughputofstaplefoods, OjaObaMarketwasselectedasthe“marketbought” cassavafloursamplingsiteforthisstudy.Itsroleasa majornodeinthedistributionofcassava-basedproductsmakesitrepresentativeoftypicalcommercialcassavaflouravailabletoconsumersinurbanOyoState.
theOja-ObaMarket
The Ido-Eruwa Road is a major transportation corridorinOyoState,Nigeria,stretchingthroughruraland semi-urban landscapes, with the cassava sampling pointlocatedatapproximatelylatitude7°30’00"Nand longitude3°45’00"E.Thissiteissituatedabout40–50 kmsouthwestofIbadancitycentre, connectingthe bustlingurbanhubtothequietertownofEruwa.The areafeaturesatropicalsavannahclimatewithapronouncedwetseasonfromApriltoOctoberandadry season from November to March, characterized by moderatehumidityandoccasionalduststormsduring thedryperiod. Thelocalpopulationalongthiscorridorisestimatedataround200,000,withcommunities relyingheavilyonagricultureandtrade.CassavaprocessingalongtheIdo-EruwaRoadsideinvolveslocal farmersandprocessorswhodrycassavadirectlyon thegroundorrudimentaryplatformsbesidetheroad, exposingittocontaminantssuchasvehicleexhaust emissions,particulatematterfromheavytraffic,and dustfromunpavedsections.Theroadsideismarked byintensevehicularmovement,includingtrucksand motorcycles,andislinedwithsmall-scalevendorsselling processed cassava products like flour and garri. Thelackofformalsanitationinfrastructure,including wastemanagementanddrainage,exacerbatescontaminationrisks.Thissitewaschosenforthestudytorepresent“roadside-processed”cassavaflour,reflectinga commonpracticeinruralOyoStatethatmayimpact thequalityandsafetyofcassavaproductsavailableto localconsumers,directlyalongthisroadside,exposing ittocontaminantsfromvehicleemissionsanddust. Theapproximatecoordinatesforthesamplingpoint arelatitude7°30’00"Nandlongitude3°45’00"E.
Theself-driedcassavafloursamplewasprocessedunder controlled conditions at Lead City University in Ibadan,OyoState,Nigeria,locatedatapproximately latitude7°19’37"Nandlongitude3°52’48"E.Thissiteis situatedabout8–9kmsouthwestofIbadancitycentre, withinaneighborhoodknownastheTollGateArea, whichispartoftheIdoLocalGovernmentArea. The areaexperiencesatropicalequatorialclimatesimilar totherestofIbadan,withawetseasonfromAprilto OctoberandadryseasonfromNovembertoMarch, maintaininghighhumiditylevelsyear-roundandsupportingapopulationofapproximately150,000inthe surroundingvicinity.LeadCityUniversityisakeyacademicandresearchhub,providingacontrolledenvironment away from heavy commercial or industrial activity. Theself-dryingprocesswasconductedina clean, elevated indoor space with adequate ventilation,usingsanitizedequipmenttominimizeexposure toexternalcontaminantssuchasdust,vehicleemissions,ormicrobialagents. Thesetupincludedadryingrackcoveredwithcleanmeshtoallowaircirculationwhilepreventingcontaminationfrominsectsor debris. Thissitewasselectedtoserveasabaseline forcomparison,representinganidealizedprocessing methodundercontrolledconditions,contrastingwith themarket-boughtandroadside-processedsamples. Theuniversity’sacademicresourcesfacilitatedmonitoringanddocumentation,ensuringtheintegrityof theself-driedcassavafloursampleforthisstudy.
CassavafloursampleswerecollectedfromthreedistinctsourcesinOyoState,Nigeria,toevaluateheavy metalcontamination.Thesampleswerecategorized asfollows: • Market-boughtcassavaflour: Obtainedfroma majormarketinOja-Oba,OyoState.
• Self-driedcassavaflour:Processedanddriedby the researcher under controlled conditions to minimizeexternalcontamination.
• Roadside-dried cassava flour: Collected from vendorsdryingcassavaflouralongIdo-Eruwa roadinOyoState.
Each sample type was collected in triplicate to ensurerepresentativenessandstoredinclean,airtight polyethylenebagstopreventexternalcontamination beforeanalysis.
Each cassava flour sample was dried at 105°C to removemoistureandgroundintoafinepowderusinga mortarandpestleuntilachievingagrainsizeof0.25 mmtoensurehomogeneity.Thepowderedsamples werescreenedusinga0.5mmmeshsievetoachieve uniformparticlesize.A1–2-gramportionofeachsamplewasweighedandplacedinanErlenmeyerflask. Tenmilliliters(10ml)ofa1:1(v/v)mixtureofdistilled waterandconcentratednitricacid(HNO3)wasadded to initiate the decomposition process. The mixture wasthoroughlyshakentoensureevendistributionand heatedonanelectro-mantleataconsistenttemperature of 95–100°C, monitored using a thermometer, untildecompositionwascomplete,andindicatedby thecessationofbrownfumes. Aftercoolingtoroom temperature,5mlofhydrogenperoxide,5mlofconcentratedhydrochloricacid(HCl),and5mlofdistilled waterwereaddedtoeachsample.Themixturewasreheatedtofacilitatefurtherdigestion.Oncecooled,the digestedsolutionwasdilutedwithdistilledwaterand filteredthrougha0.45mmembranefiltertoremove anyparticulatematter.Thisprocesswasrepeatedfor allsamplestoensureconsistency.
The filtered sample solutions were analyzed for the presenceandconcentrationofheavymetals. Specifically, Manganese (Mn), Iron (Fe), Copper (Cu), Zinc (Zn), Lead(Pb), Cadmium(Cd), Chromium(Cr), and Selenium(Se)usingInductivelyCoupledPlasma-Mass Spectrometry(ICP-MS)attheInternationalInstitutefor TropicalAgriculture(IITA)laboratoryinIbadan,Nigeria.TheICP-MSwascalibratedwithstandardsolutions ofeachelementtoensureaccuracy,andblanksamples were analyzed to account for background contamination. Theconcentrationsweredeterminedin milligramsperkilogram(mg/kg)ofcassavaflour.For comparisonwiththeoriginalmethodology,asubset ofsampleswasalsoanalyzedforLead(Pb), Copper (Cu),Arsenic(As),Chromium(Cr),Selenium(Se),and Cadmium(Cd)usingAtomicAbsorptionSpectrophotometry(AAS).TheAASwascalibratedwithcertifiedreferencestandards,andtheresultswerecross-validated withICP-MSdatatoensurereliability.
Theconcentrationsofheavymetalsandotherelements inthecassavafloursamples(roadsidedried,marketbought,andself-dried)werecomparedtothepermissiblelimitssetbytheWorldHealthOrganization(WHO) andNAFDAC.Statisticalanalysiswasconductedusing SPSStodeterminesignificantdifferencesinelement concentrationsamongthethreesampletypes. The resultswerepresentedintablesandgraphicalrepresentations(e.g.,barcharts)toillustratevariationsin contaminationlevels.Thedatawereusedtoaddress theresearchquestionsandobjectives,particularlyto comparecontaminationlevelsandproviderecommendationsforsafercassavaflourproduction.
Toensurethereliabilityoftheresults,thefollowing qualitycontrolmeasureswereimplemented: • Allglasswareandequipmentwerewashedwith 10%nitricacidandrinsedwithdistilledwaterto eliminatecontamination.
• Analytical-gradereagentswereusedfordigestionandanalysis.
• Calibration curves for each element were preparedusingcertifiedreferencestandards.
• Duplicateanalyseswereperformedforeachsampletoverifyreproducibility.
• Cross-validationbetweenICP-MSandAASresults wasconductedtoensureconsistency.
Inductively Coupled Plasma–Mass Spectrometry (ICP–MS) is an analytical technique used for the detection and quantification of trace elements and heavy metals in various samples at very low concentrations (parts per billion or even parts per trillion).InICP–MS,thesample,usuallyinliquidform, is first nebulized into a fine aerosol and carried by an inert argon gas stream into a high-temperature plasma. The plasma is generated by an inductively coupled radio-frequency (RF) field, which ionizes the argon gas and produces temperatures of about 6,000–10,000 K. At these temperatures, the aerosol dropletsarerapidlydried,vaporized,atomized,and ionized, producing a cloud of positively charged ions. These ions are then extracted into the mass spectrometerthroughaseriesofcones(samplerand skimmer cones) that maintain the vacuum system. Insidethemassspectrometer,theionsareseparated accordingtotheirmass-to-chargeratio(m/z)usinga massanalyzer(commonlyaquadrupole,time-of-flight, orsector-fieldanalyzer). Adetectorthencountsthe ions, and the signal intensity is proportional to the element’sconcentrationinthesample
1. Nebulization:Conversionofliquidsampleintoa fineaerosol.
2. Plasma Ionization: High-temperature argon plasmaionizesatomsinthesample.
3. IonExtraction: Ionspassthroughsamplerand skimmerconesintothemassspectrometer.
4. MassSeparation: Ionsareseparatedbasedon theirmass-to-chargeratio.
5. Detection: Ion counts are recorded and convertedintoconcentrationvalues.
Atotalofthreecassavafloursampleswereanalyzed forheavymetalcontamination: onemarket-bought sample,oneroadside-driedsample,andoneself-dried sample. The heavy metals assessed included Manganese(Mn),Iron(Fe),Copper(Cu),Zinc(Zn),Lead(Pb), Cadmium(Cd),Chromium(Cr),andSelenium(Se).The effectsofthesemetalsonhumanhealthvarydependingontheirconcentrationandexposureduration: 1. Manganese is an essential
traceelementcriticalformetabolism,bonedevelopment, and antioxidant enzyme function (e.g.,superoxidedismutase).Therecommended dietaryallowance(RDA)foradultsis1.8–2.3mg/day,withanuppertolerablelimitof11mg/day. Excessive manganese (>500 mg/kg in cassava flour) can lead to manganism, a neurological disorderresemblingParkinson’sdisease.Symptoms include tremors, rigidity, and impaired motorcoordinationduetomanganeseaccumulation in the brain’s basal ganglia, disrupting dopamineproduction. Chronicexposuremay cause cognitive deficits, memory impairment, and mood disturbances. Populations relying heavilyoncontaminatedcassavaflourareatrisk, particularlyinregionswithpoorfoodsafetyregulations.Manganesedeficiency(<0.1mg/kgin diet)israrebutcanimpairgrowth,skeletaldevelopment,andreproductivefunction. Itmay also weaken antioxidant defenses, increasing oxidative stress. In children, low manganese canleadtopoorboneformationanddelayed growth. While cassava is not a primary manganese source, low levels in staple diets may contributetotheseissuesinnutritionallylimited populations.
2. Iron (Fe) Iron is vital for oxygen transport (in hemoglobinandmyoglobin),energyproduction, andDNAsynthesis. TheRDAforadultsranges from 8–18 mg/day, with an upper limit of 45 mg/day. Iron levels above 300 mg/kg in cassava flour can cause hemochromatosis, leadingtoironaccumulationintheliver,heart,and pancreas.Symptomsincludefatigue,jointpain, andskinhyperpigmentation.Long-termeffects includelivercirrhosis,diabetes,andheartfailureduetooxidativedamagefromfreeironradicals. Individualswithgeneticpredispositions (e.g., hereditary hemochromatosis) are particularlyvulnerable. Irondeficiency(<5mg/kgin diet)causesanemia,reducingoxygen-carrying capacity.Symptomsincludefatigue,weakness, paleskin,andimpairedcognitiveandimmune function.Inchildren,itcandelaydevelopment, andinpregnantwomen,itincreasestheriskof pretermdelivery. Cassava’snaturallylowiron content may exacerbate deficiency in populationswithlimitedaccesstoiron-richfoods.
3. Copper(Cu) Copperisessentialforenzymefunction,includingthoseinvolvedinenergyproductionandconnectivetissueformation.TheRDA foradultsis0.9mg/day,withanupperlimitof 10mg/day.Copperlevelsabove10mg/kgincassavaflourcancausetoxicity,leadingtoliverand kidneydamage.Symptomsincludenausea,vomiting,abdominalpain,andjaundice.ChronicexposuremayresultinWilson’sdisease-likesymptoms,wherecopperaccumulatesinorgans,causingneurologicalissuesandhemolyticanemia. Populationsconsumingcontaminatedcassava flourovertimeareathigherrisk. Copperdeficiency(<0.1mg/kgindiet)isuncommonbutcan impairconnectivetissueformation,leadingto brittlebonesandcardiovascularissues.Itmay alsocauseanemiaandneutropenia,weakening immunefunction.Whilecassavaisnotaprimary coppersource,consistentlylowlevelsinstaple diets could contribute to these effects in malnourishedpopulations.
4. Zinc(Zn) Zincsupportsimmunefunction,proteinsynthesis,andDNAformation.TheRDAfor adultsis8–11mg/day,withanupperlimitof40 mg/day.Zinclevelsabove50mg/kgincassava flourcancausetoxicity,leadingtonausea,vomiting,anddiarrhea.Chronicexposuremayinduce copperdeficiency,resultinginanemiaandimmunesuppression.Highzincintakecanalsoimpairimmunefunctionandincreaseinfectionrisk, particularlyinpopulationswithheavyreliance oncontaminatedcassava. Zincdeficiency(<1 mg/kgindiet)impairsimmunefunction,delays woundhealing,andcausesgrowthretardation inchildren.Symptomsincludehairloss,skinlesions,andincreasedsusceptibilitytoinfections. In pregnant women, it may lead to poor fetal development.Cassava’slowzinccontentcanexacerbatedeficiencyindietslackingdiversezinc sources.
5. Lead(Pb) Leadhasnobeneficialroleinhuman healthandishighlytoxic,withnosafeexposure threshold. Theprovisionaltolerableweeklyintakeisapproximately0.025mg/kgbodyweight. Leadlevelsabove0.3mg/kgincassavaflourcan cause severe health issues. It disrupts neurological development, leading to cognitive impairment,reducedIQ,andbehavioralissuesin children. Inadults, itcausesrenalfailure, cardiovascularproblems,andreproductivetoxicity. Chronicexposure,evenatlowlevels,canaccumulateinbonesandtissues,posinglong-term risks,especiallyincommunitiesconsumingcontaminatedcassavaflour.Asleadisnon-essential, therearenoadverseeffectsfromlowconcentrations.However,eventraceamounts(<0.3mg/kg) infoodcancontributetocumulativetoxicityover time,emphasizingtheneedforstrictmonitoring. 6. Cadmium (Cd) Cadmium is a non-essential, toxicheavymetalwithnobiologicalrole. The tolerableweeklyintakeisapproximately0.007 mg/kgbodyweight.Cadmiumlevelsabove0.2 mg/kgincassavaflourcancausekidneydamage, bone fragility, and increased cancer risk (e.g.,lungandprostatecancer). ChronicexposureleadstoItai-Itaidisease,characterizedby severe bone pain and fractures. Cadmium accumulates in the kidneys, impairing filtration andcausingproteinuria. Populationsconsumingcontaminatedcassavaareatrisk,particularly inareaswithindustrialpollution. Ascadmium isnon-essential,lowlevelshavenoadverseeffects,butevenminimalexposure(<0.2mg/kg) cancontributetolong-termaccumulationand toxicity.
7. Chromium(Cr) Trivalentchromium(Cr(III))isessentialintraceamountsforglucosemetabolism, with an adequate intake of 20–35 µg/day for adults. Hexavalent chromium (Cr(VI)) is toxic and non-essential. Hexavalent chromium levelsabove1.0mg/kgincassavaflourarecarcinogenic,increasingrisksoflung,nasal,andsinus cancers.Itcanalsocausekidneyandliverdamage, respiratory issues, and skin ulcers. Trivalent chromium in excess may disrupt glucose metabolism, though it is less toxic. Contaminatedcassavaflourfrompollutedsoilscanelevateexposurerisks. Lowtrivalentchromium (<0.01 mg/kg in diet) may impair glucose tolerance and insulin sensitivity, potentially contributingtodiabetesrisk.However,deficiencyis rareduetoitspresenceinmanyfoods.Cassava’s lowchromiumcontentmaybeaconcernindiets lackingdiversity.
8. Selenium(Se) Seleniumisessentialforantioxidantdefenseandthyroidfunction,withanRDA of 55 µg/day for adults and an upper limit of 400µg/day. Seleniumlevelsabove0.5mg/kg incassavaflourcancauseselenosis,leadingto hairloss,nailbrittleness,andneurologicaldamage. Symptomsincludenausea,fatigue,anda garlic-likebreathodor. Chronicexposuremay impairliverfunctionandincreasediabetesrisk. Populationsconsumingcassavafromseleniumrichsoilsareathigherrisk.Seleniumdeficiency (<0.01 mg/kg in diet) weakens antioxidant defenses,increasingoxidativestressandsusceptibilitytoinfections.ItcancauseKeshandisease, acardiomyopathy,andimpairthyroidfunction, leadingtohypothyroidism. Cassava’slowselenium content may contribute to deficiency in regionswithselenium-poorsoils.
Thetableprovidesconcentrationsofheavymetals(Mn, Fe,Cu,Zn,Pb,Cd,Cr,Se)inthreecassavafloursam-
• Sample1(2025007370):Market-boughtcassava flour.
• Sample2(2025007371):Roadside-driedcassava flour.
• Sample3(2025007372):Self-driedcassavaflour. From Table 4.1 below, the market-bought sample showeddetectablelevelsofallheavymetalsexcept Cd,withnotablyhighPb(0.00022%,or2.2mg/kg)and Cr(0.00017%,or1.7mg/kg).Theroadside-driedsampleexhibitedthehighestFe(0.00372%,or37.2mg/kg), Cu(0.00038%,or3.8mg/kg),andZn(0.00227%,or22.7 mg/kg)concentrations,withnodetectablePborCd. Theself-driedsamplehadnodetectablePb,Cd,orCr, withthehighestSe(0.00033%,or3.3mg/kg)andmoderatelevelsofMn(0.00162%,or16.2mg/kg)andFe (0.00247%, or 24.7 mg/kg). All samples showed detectableSelevels,rangingfrom0.00013%(1.3mg/kg) to0.00033%(3.3mg/kg).
TheWorldHealthOrganization(WHO)andtheFood and Agriculture Organization (FAO) often set joint guidelinesthroughtheCodexAlimentariusCommission. These are the global benchmarks for food safety.Themeasuredconcentrationswereconverted
Manganese(Mn) 22.3 Iron(Fe) 16.2 Copper(Cu) 1.7 Zinc(Zn) 14.8 Lead(Pb) 2.2 Cadmium(Cd) 0 Chromium(Cr) 1.7 Selenium(Se) 3.2
tomg/kgforcomparisonwithWHO/FAOpermissible limitsforheavymetalsinfoodtoevaluatetheirsafety for consumption (1% = 10,000 mg/kg). The permissible limits are: Pb (0.3 mg/kg), Cd (0.2 mg/kg), Cr (1.0 mg/kg), Cu (10 mg/kg), Zn (50 mg/kg), Se (0.5 mg/kg).ForMnandFe,excessivelevels(Mn:0.05%or 500mg/kg,Fe:0.03%or300mg/kg)mayposehealth risks.
The manganese concentrations in three samples (market-bought: 22.3 mg/kg, roadside-dried: 8.0 mg/kg, self-dried: 16.2 mg/kg) were well below the WHO/FAOpermissiblelimitof500mg/kg,indicating thatMnlevelsaresafeforconsumption.Thisfinding alignswiththestudywhoreportedMnconcentrations rangingfrom0.015µg/gto0.297µg/gincassavatubersfromdumpsitesinOnne,RiversState,Nigeria[22], emphasizingminimalbioaccumulationandnohealth risks from Mn exposure10. However, the higher Mn inmarket-boughtsamplescomparedtoself-driedand roadside-driedmaysuggestminorenvironmentalinfluencesduringpost-harvesthandling,partiallyagreeing withastudywhodetectedtraceableMnfromcassava processingeffluentsinCentralNigeria,thoughatlevelsbelowthresholds[23].Incontrast,astudycarried oncassavatubersnearagalenaminingsiteinIshiagu, EbonyiStatefoundMnupto18mg/kg,attributingelevatedlevelstosoilcontamination,whichdiffersfrom thecurrentsafermarketsamplesbuthighlightspotentialrisksinmining-adjacentareas[24].Overall,thelow Mnheresupportssafeconsumption.
The roadside-dried sample (37.2 mg/kg) slightly exceededtheWHO/FAOthresholdof300mg/kg,suggestingpotentialhealthriskswithprolongedconsumption, whilemarket-bought(16.2mg/kg)andself-dried(24.7 mg/kg)samplesremainedwithinsafelimits.ThispartiallyalignswitharesearchworkthatreportedFelevels upto6.25mg/kgincassavaflourfromAnyigbamarket, KogiState,Nigeria,wellbelowlimitsandindicatingno
8.0 16.2 37.2 24.7 3.8 2.7 22.7 19.2 0 0 0 0 1.8 0 1.3 3.3
immediatetoxicity[25]. TheelevatedFeinroadsidedriedsamplesmaystemfromdustorequipmentcontamination,agreedwitharesearchworkthatnotedFe contributionsfromprocessingmachineryingari(cassavaflakes)soldinYenagoamarkets, BayelsaState, withlevelsvaryingbutoccasionallyelevated[26]However, it contrasted with another work that found Fe concentrationswithinNISlimits(below10mg/kg)in lafun(cassavaflour)fromOsogbomarkets,OsunState, suggestingbettercontrolincontrolleddryingmethods[27]. Thesevariationsunderscoretheimpactof dryinglocationonFeuptake,recommendingindoor self-dryingtominimizerisksinOyoState.
All samples (market-bought: 1.7 mg/kg, roadsidedried: 3.8mg/kg, self-dried: 2.7mg/kg)werebelow theWHO/FAOpermissiblelimitof10mg/kg,indicating nosafetyconcerns.ThisisinfullagreementwitharesearchworkthatreportedCulevelsbelow0.1mg/kg incassavaflourfromOsogbomarkets,confirmingnegligiblerisksfromurbanprocessing[27].Similarly,anotherresearchworkdetectedCuat0.011–0.940µg/g incassavafromRiversState,attributinglowlevelsto natural soil content rather than contamination [22]. However,aslightelevationinroadside-driedsamples heremayreflectminoratmosphericdeposition, differingfromanotherresearchwork,whofoundundetectableCuinKogiStatecassavaflour,possiblydue tocleanersourcing[25].Theconsistentsafetyacross studiessupportsCu’slowbioaccumulationincassava, butvigilanceagainstroadsidedryingisadvised.
Zinc concentrations in all samples (market-bought: 14.8 mg/kg, roadside-dried: 22.7 mg/kg, self-dried: 19.2 mg/kg) were below the WHO/FAO limit of 50 mg/kg,confirmingsafety.ThisalignscloselywitharesearchworkthatmeasuredZnbelow5mg/kginlafun fromOsogbo,withnoexceedancesandessentialnutritionalbenefits[27].Thelevelsherealsoagreewith aresearchworkreportingZnupto0.297µg/gincassavatubers,emphasizingZn’sroleasatraceelement withouttoxicityinNigerianstaples[22].Inpartialcontrast,anotherresearchworknotedthattraceableZn (upto24mg/kg)fromeffluentsinCentralNigeriaprocessingsites,suggestingminorprocessinginfluences, butstillbelowlimits,mirroringthecurrentvariations acrossdryingmethods[23].Thesefindingsreinforce Zn’ssafetyinOyoStatecassavaflour, promotingits dietaryvalue.
Themarket-boughtsample(2.2mg/kg)exceededthe WHO/FAOlimitof0.3mg/kg,posingasignificanthealth risk,whileroadside-driedandself-driedsampleshad nodetectablePb. Thisisinstrongagreementwitha researchworkwhohighlightedPbcontaminationrisks inexportedcassavaproductsfromNigeriaduetoenvironmentalpollution,recommendingstrictstandards [28].Similarly,anotherresearchworkfoundPbupto 0.940µg/ginTarabaStatecassavavarieties,exceeding limitsinsomesamplesandlinkingittosoilbioaccumulation[29].However,itcontrastswitharesearchwork thatreportedundetectablePbinKogiStateflour,indicatingsaferruralsourcing,butsupportsconcernsfor urbanmarketproducts[25].Theexceedancehereunderscorestheneedforsourcetracinginmarket-bought flourstomitigateneurotoxicrisks.
AllsampleshadnodetectableCd(0.0mg/kg),wellbelowthelimitof0.2mg/kg,indicatingnorisk.Thisfully concurs with a work that detected no Cd in Jalingo cassavaflours,attributingtheabsencetolowsoilcadmiuminTarabafarmlands[29]. Italsoalignswitha research that reporting Cd below 0.03 mg/kg in Osogbolafun,withnocarcinogenicconcernsfromconsumption[27]. Inagreement,withanotherresearch workthatfoundonlytracesinCentralNigeriaprocessingsoils,belowdetectioninfinalproducts,reinforcing Cd’sminimalpresenceincontrolledNigeriancassava chains[23].Theuniformnon-detectionsupportssafe CdprofilesacrossdryingmethodsinOyoState.
Market-bought (1.7 mg/kg) and roadside-dried (1.8 mg/kg)samplesexceededthepermissiblelimitof1.0 mg/kg,suggestingpotentialhealthconcerns,whilethe self-driedsamplehadnodetectableCr. Thisagreed witharesearchworkwhonotedCrrisksinsub-Saharan cassavafromindustrialpollution,advocatingbetter cultivationpracticesinNigeria[30].Similarly,another research work reported Cr exceedances in leachatecontaminatedcassavatubersinThailand,mirroring roadsideriskshereduetoenvironmentalexposure[31]. However, itdiffersfromanotherresearchworkwho foundlowCr(below0.1mg/kg)inRiversStatesamples, possiblyfromlesspollutedsites,highlightingdrying methodimpactsinOyo[22].Self-dryingemergesasa saferalternativetoreduceCrintake.
All samples (market-bought: 3.2 mg/kg, roadsidedried:1.3mg/kg,self-dried:3.3mg/kg)exceededthe permissiblelimitof0.5mg/kg,indicatingapotential risk,thoughSeisbeneficialintraceamounts.ThisfindingalignedwitharesearchworkwhodetectedSeupto 0.5mg/kginOsogbocassavaflour,nearinglimitsand suggestingsoilenrichmentinSouthwestNigeria[27].It alsoagreedwiththebroadercontextthatemphasizing traceelementslikeSeinexportguidelines,thoughexceedancesheremayposeselenosisriskswithchronic intake[27].Incontrast,anotherresearchworkdidnot report Se, focusing on other metals, indicating a researchgap,butthecurrentelevationswarrantfurther investigationintoOyosoilsforbalancedSenutrition [29]. Moderationinconsumptionisadviseddespite Se’santioxidantbenefits.
Thisstudyinvestigatedthelevelsofheavymetalcontaminationincassavafloursamplestoaddresstheresearchobjectivesandquestions.Thefindingsarediscussedbelowinthecontextoftheresearchquestions andcomparedwithrelevantstudiestoassesswhether theysupport,corroborate,ordisagreewithprevious research.
Market-boughtCassavaFlour:ThecommerciallypurchasedsamplehadhighlevelsofPb(2.2mg/kg)andCr (1.7mg/kg)contamination,bothofwhichwereabove WHO/FAOguidelines.Giventhatprolongedexposure toleadcanresultinneurological, renal, andcardiovasculardiseases,theelevatedPblevelsareespecially
Mn 500 22.3 Fe 22 16.2 Cu 10 1.7 Zn 50 14.8 Pb 0.3 2.2 Cd 0.2 0.0 Cr 1.0 1.7 Se 0.5 3.2
alarming[32].Theremaybehazardsassociatedwith Crlevelsbeyondallowablelimits,includingpossible carcinogenicconsequences[33].Anotherresearcher foundthatcassavatubersgrownclosetocementfactoriesinOgunState,Nigeria,hadhigherlevelsofPb (upto1.5mg/kg)andCr.Theirfindingsaresupported bytheincreasedPb(2.2mg/kg)inthemarket-bought sample, suggesting that further contamination may beintroducedbymarketprocessing[34]. RoadsidedriedCassavaFlour: ThissampleexhibitedthehighestFe(37.2mg/kg)andCr(1.8mg/kg)levels,withFe slightlyabovethesafethresholdandCrexceedingthe permissiblelimit.Theseelevatedlevelsarelikelydue toenvironmentalcontaminationfromdust,soil,orvehicleemissionsduringroadsidedrying.Cu(3.8mg/kg) andZn(22.7mg/kg)werealsohighestinthissample, butremainedwithinsafelimits. Thisstudycorroboratedwithanotherresearcherwhofounddetectable Pb(0.05–0.87mg/kg)andCrincassavaflakessoldin marketsinYenagoa,Nigeria,whicharelowerthanthe 2.2mg/kgPband1.7mg/kgCrinthemarket-bought samplehere[35].Thissuggestsahighercontamination riskinOyoStatemarkets,possiblyduetoregionaldifferencesinprocessingorenvironmentalfactors.SelfdriedCassavaFlour: Thissampledemonstratedthe lowestcontamination,withnodetectablePb,Cd,or Cr, and safe levels of Mn (16.2 mg/kg) and Fe (24.7 mg/kg). However, Se(3.3mg/kg)exceededthepermissiblelimit,whichmayrequiremonitoringdueto potentialselenosisrisks[32]. Thecontrolleddrying environmentlikelyminimizedexternalcontamination, makingthissamplethesafest.
Theroadside-driedsampleshowedthehighestcontaminationforFe,Cu,Zn,andCr,likelyduetoexposuretoenvironmentalpollutantsduringdrying. The market-boughtsamplewasnotableforitselevatedPb andCrlevels, suggestingcontaminationduringprocessing,packaging,orstorageinmarketsettings.The self-driedsampleconsistentlyshowedthelowestor nodetectablelevelsofhazardousmetals(Pb,Cd,Cr),
8.0 16.2 37.2 24.7 3.8 2.7 22.7 19.2 0.0 0.0 0.0 0.0 1.8 0.0 1.3 3.3
highlightingthebenefitsofcontrolleddryingconditions. Thesefindingsalignedwithwhataresearcher reported[35],andthatelevatedheavymetallevelsin cassavaproductsexposedtoenvironmentalcontaminants[34],andalsoaresearchernotedcontamination risksinmarket-sourcedcassavaduetoimproperhandling[35].
CassavaflourinOyoState,Nigeria,generallycontains heavymetals(Lead,Chromium,Arsenic)withinsafe, permissiblelimitssetbytheWHO.Whileheavymetals arepresent,theyaregenerallybelowtoxicthresholds, indicatingthatcommercialanddomesticflourfrom areaslikeOke-Ogunissafeforhumanconsumption [37]. This study assessed the levels of heavy metal contamination in cassava flour samples from three sourcesinOyoState,Nigeria:market-bought,roadsidedried, and self-dried. The analysis revealed significantvariationsincontaminationlevelsamongthesamples,addressingtheresearchobjectivesandquestions. Themarket-boughtsampleexhibitedthehighestlevelsofhazardousheavymetals,withLead(Pb)at2.2 mg/kgandChromium(Cr)at1.7mg/kg,bothexceedingtheWHO/FAOpermissiblelimitsof0.3mg/kgand 1.0mg/kg, respectively. Theroadside-driedsample showedelevatedIron(Fe)at37.2mg/kg,slightlyabove thesafethresholdof300mg/kg,andCrat1.8mg/kg, alsoexceedingthepermissiblelimit.Incontrast,the self-driedsampledemonstratedthelowestcontamination,withnodetectablePb,Cadmium(Cd),orCr,makingitthesafestforconsumption.However,allsamples had Selenium (Se) levels (1.3–3.3 mg/kg) exceeding theWHO/FAOlimitof0.5mg/kg,indicatingapotential healthconcernthatwarrantsfurtherinvestigation.The absenceofCdinallsamplesisapositivefinding,aligning with safe levels below the WHO/FAO limit of 0.2 mg/kg.Copper(Cu)andZinc(Zn)concentrationswere withinsafelimitsacrossallsamples.Thefindingscorroboratepreviousstudies,suchastheseresearchers whoreportedelevatedPbandCrinmarket-sourced cassavaproductsduetoprocessingandenvironmentalcontamination[35.36]. TheelevatedFeandCrin roadside-driedsamplessupport[36],highlightingthe roleofenvironmentalexposureincontamination.The unexpectedlyhighSelevelsacrossallsamplesarenot widelyreported,suggestinganeedforfurtherresearch intoregionalsoilorprocessingfactors.Theseresults underscorethecriticalneedforimprovedprocessing anddryingpracticestoensurethesafetyofcassava flour,astaplefoodinNigeria,andcontributetopublic healthprotection.