Heavy metals in Yam

Quick read

Yam in the HMI library has 111 reported results for lead, cadmium, total arsenic, total mercury, nickel, chromium, Co, Cu, Fe, Mn and Zn from 10 sources.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}^{2AuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema, Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · 2023Evaluation of pesticide residues and heavy metalsPeer-reviewed articleRead source →}^{3Guerra F, Trevizam AR, Muraoka T, Marcante NC, Canniatti-Brazaca SG · 2012Heavy metals in vegetables and potential risk for human healthScientia Agricola 69(1):54-60Read source →}^{4Brima EI, Haris PI, Frei M · 2025Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketAfrican Journal of Agriculture and Food ScienceRead source →}^{5Iyabo OO, Ogundiran MB, Adebayo OL · 2015Toxic and Essential Metals in Staple Foods Commonly Consumed by Students in Ekiti State, South West, NigeriaInternational Journal of ChemistryRead source →}^{6Orisakwe OE, Nduka JK, Amadi CN, Dike DO, Bede O · 2012Heavy metals health risk assessment for population via consumption of food crops and fruits in Owerri, South Eastern, NigeriaChemistry Central Journal 2012, 6:77Read source →}

Metals measured:
Lead, cadmium, total arsenic, total mercury, nickel and chromium and others, in 111 results from 10 sources.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}^{2AuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema, Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · 2023Evaluation of pesticide residues and heavy metalsPeer-reviewed articleRead source →}^{3Guerra F, Trevizam AR, Muraoka T, Marcante NC, Canniatti-Brazaca SG · 2012Heavy metals in vegetables and potential risk for human healthScientia Agricola 69(1):54-60Read source →}^{4Brima EI, Haris PI, Frei M · 2025Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketAfrican Journal of Agriculture and Food ScienceRead source →}
Main drivers:
Form, basis and where the yam was sampled; reporting limits decide how many results are non-detects.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}^{2AuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema, Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · 2023Evaluation of pesticide residues and heavy metalsPeer-reviewed articleRead source →}^{3Guerra F, Trevizam AR, Muraoka T, Marcante NC, Canniatti-Brazaca SG · 2012Heavy metals in vegetables and potential risk for human healthScientia Agricola 69(1):54-60Read source →}^{4Brima EI, Haris PI, Frei M · 2025Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketAfrican Journal of Agriculture and Food ScienceRead source →}
Practical framing:
Ask for lot results with a quantification limit well below the limit that applies in the destination market.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}^{2AuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema, Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · 2023Evaluation of pesticide residues and heavy metalsPeer-reviewed articleRead source →}^{3Guerra F, Trevizam AR, Muraoka T, Marcante NC, Canniatti-Brazaca SG · 2012Heavy metals in vegetables and potential risk for human healthScientia Agricola 69(1):54-60Read source →}^{4Brima EI, Haris PI, Frei M · 2025Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketAfrican Journal of Agriculture and Food ScienceRead source →}

Yam overview

Yam in the HMI library has 111 reported results for lead, cadmium, total arsenic, total mercury, nickel, chromium, Co, Cu, Fe, Mn and Zn from 10 sources.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}^{2AuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema, Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · 2023Evaluation of pesticide residues and heavy metalsPeer-reviewed articleRead source →}^{3Guerra F, Trevizam AR, Muraoka T, Marcante NC, Canniatti-Brazaca SG · 2012Heavy metals in vegetables and potential risk for human healthScientia Agricola 69(1):54-60Read source →}^{4Brima EI, Haris PI, Frei M · 2025Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketAfrican Journal of Agriculture and Food ScienceRead source →}^{5Iyabo OO, Ogundiran MB, Adebayo OL · 2015Toxic and Essential Metals in Staple Foods Commonly Consumed by Students in Ekiti State, South West, NigeriaInternational Journal of ChemistryRead source →}^{6Orisakwe OE, Nduka JK, Amadi CN, Dike DO, Bede O · 2012Heavy metals health risk assessment for population via consumption of food crops and fruits in Owerri, South Eastern, NigeriaChemistry Central Journal 2012, 6:77Read source →} WHO GEMS/Food submissions reported lead in yam, as sold from 68 results in 4 reporting regions, with subgroup medians from 3.7 to 125 µg/kg.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →} For cadmium, GEMS/Food gave subgroup medians from 1 to 140 µg/kg from 251 results.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}

Guerra et al. 2012 reported lead at 720 µg/kg (mean) and cadmium at 60 µg/kg (mean) in yam, as sold from CEAGESP wholesale market.^{3Guerra F, Trevizam AR, Muraoka T, Marcante NC, Canniatti-Brazaca SG · 2012Heavy metals in vegetables and potential risk for human healthScientia Agricola 69(1):54-60Read source →} Ezema et al. 2023 reported total arsenic at 37 µg/kg (mean) in yam, as sold from Nsukka open market, Enugu State.^{2AuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema, Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · 2023Evaluation of pesticide residues and heavy metalsPeer-reviewed articleRead source →}

For a buyer the practical points are the form bought, the basis a result is reported on, where the yam came from and the laboratory’s reporting limit. Testing finds contamination but does not remove it.

What counts as yam

This page covers yam in 4 forms kept separate in every comparison: yam, as sold (53 results), yam, cooked (38 results), yam, flour or meal (10 results) and yam, peeled or flesh (10 results).^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}^{2AuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema, Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · 2023Evaluation of pesticide residues and heavy metalsPeer-reviewed articleRead source →}^{3Guerra F, Trevizam AR, Muraoka T, Marcante NC, Canniatti-Brazaca SG · 2012Heavy metals in vegetables and potential risk for human healthScientia Agricola 69(1):54-60Read source →}^{4Brima EI, Haris PI, Frei M · 2025Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketAfrican Journal of Agriculture and Food ScienceRead source →}^{5Iyabo OO, Ogundiran MB, Adebayo OL · 2015Toxic and Essential Metals in Staple Foods Commonly Consumed by Students in Ekiti State, South West, NigeriaInternational Journal of ChemistryRead source →}^{6Orisakwe OE, Nduka JK, Amadi CN, Dike DO, Bede O · 2012Heavy metals health risk assessment for population via consumption of food crops and fruits in Owerri, South Eastern, NigeriaChemistry Central Journal 2012, 6:77Read source →}

Results stay on the basis each source reports: as sold or fresh weight, dry weight, or unstated. Dry-weight, as-sold and unstated results are never pooled, and no moisture conversion is applied.

Heavy metal contamination profile of yam

The table holds every extracted yam result: one row for each statistic a source reports for a form, group and metal, 111 rows in all, grouped by metal and form; percentiles, ranges and maxima for the same samples as a mean or median are shown on that row.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}^{2AuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema, Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · 2023Evaluation of pesticide residues and heavy metalsPeer-reviewed articleRead source →}^{3Guerra F, Trevizam AR, Muraoka T, Marcante NC, Canniatti-Brazaca SG · 2012Heavy metals in vegetables and potential risk for human healthScientia Agricola 69(1):54-60Read source →}^{4Brima EI, Haris PI, Frei M · 2025Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketAfrican Journal of Agriculture and Food ScienceRead source →}^{5Iyabo OO, Ogundiran MB, Adebayo OL · 2015Toxic and Essential Metals in Staple Foods Commonly Consumed by Students in Ekiti State, South West, NigeriaInternational Journal of ChemistryRead source →}^{6Orisakwe OE, Nduka JK, Amadi CN, Dike DO, Bede O · 2012Heavy metals health risk assessment for population via consumption of food crops and fruits in Owerri, South Eastern, NigeriaChemistry Central Journal 2012, 6:77Read source →} Monitoring medians are HMI calculations from individual submissions; non-detects remain intervals between zero and the reporting limit and are never read as zero.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}

12 rows can be rated against an HMI reference for the same form and basis, 3 rows have a direct same-study comparison, and the rest stay unrated with the reason recorded. 3 values from 2 sources failed a check against their own source and are shown but not compared.^{4Brima EI, Haris PI, Frei M · 2025Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketAfrican Journal of Agriculture and Food ScienceRead source →}^{5Iyabo OO, Ogundiran MB, Adebayo OL · 2015Toxic and Essential Metals in Staple Foods Commonly Consumed by Students in Ekiti State, South West, NigeriaInternational Journal of ChemistryRead source →}

Comparison methods and scope

Each row is one statistic a source reports for one form of yam, group and metal; percentiles, ranges and maxima reported for the same samples as a mean or median are shown on that row. Different forms and preparation states are kept apart, and dry-weight results never share a reference with as-sold or fresh-weight results. Ratings place a result against an HMI reference built from monitoring results and ordinary-setting medians for the same form and basis. Same-study contrasts compare a contaminated or treated site with its control, targeted with random sampling, a prepared form with the unprocessed one, or one group of a study with the median of its other groups. Held rows failed a check against their own source and are shown but not compared.

About this table

Food formCollection scopeFindingComparisonEvidence

Yam findings from monitoring programmes, total diet studies and every extracted field, market and contaminated-site study, in µg/kg with each source’s form, basis, statistic and censoring retained.
Food form	Collection scope	Finding (µg/kg)

14 findings · 6 studies
Yam, as soldWHO GEMS/Food	AFRO2018As sold / fresh	median.
Yam, as soldWHO GEMS/Food	AFRO2018As sold / fresh	median.
Yam, as soldWHO GEMS/Food	EURO2010–2013As sold / fresh	median.
Yam, as soldWHO GEMS/Food	PAHO2015As sold / fresh	median.
Yam, as soldWHO GEMS/Food	PAHO2016As sold / fresh	median.
Yam, as soldWHO GEMS/Food	PAHO2014–2016As sold / fresh	median.
Yam, as soldWHO GEMS/Food	WPRO2005–2009As sold / fresh	median.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	not detected.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	not detected.
Yam, as soldGuerra et al. 2012	CEAGESP wholesale market2009As sold / fresh	mean.
Yam, as soldWHO GEMS/Food	AFRO2012Dry weight	median.
Yam, as soldBrima et al. 2025	individual sample, text only2023–2024Dry weight	sample value.
Yam, as soldIyabo et al. 2015	tuber group itemCollection date unreportedDry weight	sample value.
Yam, as soldOrisakwe et al. 2012	all samples (Ohaji, Umuagwo, Owerri sites)Collection date unreportedDry weight	not detected.
6 findings · 1 study
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; boiled2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; fried2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; roasted2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; boiled2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; fried2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; roasted2019Basis not stated	mean.
2 findings · 2 studies
Yam, flour or mealIyabo et al. 2015	tuber group itemCollection date unreportedDry weight	sample value.
Yam, flour or mealOfori et al. 2016	laboratory-processed flour from raw material bought atCollection date unreportedDry weight	mean.
2 findings · 1 study
Yam, peeled or fleshAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; unprocessed2019Basis not stated	mean.
Yam, peeled or fleshAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; unprocessed2019Basis not stated	mean.

12 findings · 7 studies
Yam, as soldWHO GEMS/Food	AFRO2018As sold / fresh	median.
Yam, as soldWHO GEMS/Food	AFRO2018As sold / fresh	median.
Yam, as soldWHO GEMS/Food	EURO2010–2013As sold / fresh	median.
Yam, as soldWHO GEMS/Food	WPRO2009–2010As sold / fresh	median.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	not detected.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	not detected.
Yam, as soldGuerra et al. 2012	CEAGESP wholesale market2009As sold / fresh	mean.
Yam, as soldWHO GEMS/Food	AFRO2012Dry weight	median.
Yam, as soldBrima et al. 2025	individual sample, text only2023–2024Dry weight	not detected.
Yam, as soldIyabo et al. 2015	tuber group itemCollection date unreportedDry weight	sample value.
Yam, as soldOrisakwe et al. 2012	all samples (Ohaji, Umuagwo, Owerri sites)Collection date unreportedDry weight	mean.
Yam, as soldJoint FAO/WHO Expert Committee on Food Additives 2022	GEMS/Food contaminants database2011Basis not stated	mean.
6 findings · 1 study
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; boiled2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; fried2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; roasted2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; boiled2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; fried2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; roasted2019Basis not stated	mean.
1 finding · 1 study
Yam, flour or mealIyabo et al. 2015	tuber group itemCollection date unreportedDry weight	not detected.
2 findings · 1 study
Yam, peeled or fleshAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; unprocessed2019Basis not stated	mean.
Yam, peeled or fleshAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; unprocessed2019Basis not stated	mean.

7 findings · 3 studies
Yam, as soldWHO GEMS/Food	AFRO2018As sold / fresh	median.
Yam, as soldWHO GEMS/Food	AFRO2018As sold / fresh	median.
Yam, as soldWHO GEMS/Food	EURO2010–2013As sold / fresh	median.
Yam, as soldWHO GEMS/Food	WPRO2005As sold / fresh	median.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
Yam, as soldBrima et al. 2025	individual sample, text only2023–2024Dry weight	sample value.
14 findings · 2 studies
Yam, cookedClair-Caliot et al. 2021	cooked with water at 0 µg/L As(V)Collection date unreportedAs sold / fresh	mean.
Yam, cookedClair-Caliot et al. 2021	cooked with water at 0 µg/L As(V)Collection date unreportedAs sold / fresh	mean.
Yam, cookedClair-Caliot et al. 2021	cooked with water at 100 µg/L As(V)Collection date unreportedAs sold / fresh	mean.
Yam, cookedClair-Caliot et al. 2021	cooked with water at 100 µg/L As(V)Collection date unreportedAs sold / fresh	mean.
Yam, cookedClair-Caliot et al. 2021	cooked with water at 500 µg/L As(V)Collection date unreportedAs sold / fresh	mean.
Yam, cookedClair-Caliot et al. 2021	cooked with water at 500 µg/L As(V)Collection date unreportedAs sold / fresh	mean.
Yam, cookedClair-Caliot et al. 2021	cooked with water at 1000 µg/L As(V)Collection date unreportedAs sold / fresh	mean.
Yam, cookedClair-Caliot et al. 2021	cooked with water at 1000 µg/L As(V)Collection date unreportedAs sold / fresh	mean.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; boiled2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; fried2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; roasted2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; boiled2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; fried2019Basis not stated	not detected.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; roasted2019Basis not stated	mean.
1 finding · 1 study
Yam, flour or mealOfori et al. 2016	laboratory-processed flour from raw material bought atCollection date unreportedDry weight	mean.
2 findings · 1 study
Yam, peeled or fleshAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; unprocessed2019Basis not stated	mean.
Yam, peeled or fleshAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; unprocessed2019Basis not stated	mean.

6 findings · 3 studies
Yam, as soldWHO GEMS/Food	AFRO2018As sold / fresh	median.
Yam, as soldWHO GEMS/Food	AFRO2018As sold / fresh	median.
Yam, as soldWHO GEMS/Food	EURO2010As sold / fresh	median.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	not detected.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	not detected.
Yam, as soldBrima et al. 2025	individual sample, text only2023–2024Dry weight	not detected.
6 findings · 1 study
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; boiled2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; fried2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; roasted2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; boiled2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; fried2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; roasted2019Basis not stated	mean.
1 finding · 1 study
Yam, flour or mealOfori et al. 2016	laboratory-processed flour from raw material bought atCollection date unreportedDry weight	mean.
2 findings · 1 study
Yam, peeled or fleshAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; unprocessed2019Basis not stated	mean.
Yam, peeled or fleshAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; unprocessed2019Basis not stated	mean.

4 findings · 3 studies
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
Yam, as soldGuerra et al. 2012	CEAGESP wholesale market2009As sold / fresh	mean.
Yam, as soldOrisakwe et al. 2012	all samples (Ohaji, Umuagwo, Owerri sites)Collection date unreportedDry weight	mean.

3 findings · 2 studies
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
Yam, as soldGuerra et al. 2012	CEAGESP wholesale market2009As sold / fresh	mean.

3 findings · 2 studies
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
Yam, as soldGuerra et al. 2012	CEAGESP wholesale market2009As sold / fresh	mean.

1 finding · 1 study
Yam, as soldIyabo et al. 2015	tuber group itemCollection date unreportedDry weight	sample value.
2 findings · 2 studies
Yam, flour or mealIyabo et al. 2015	tuber group itemCollection date unreportedDry weight	sample value.
Yam, flour or mealOfori et al. 2016	laboratory-processed flour from raw material bought atCollection date unreportedDry weight	mean.

1 finding · 1 study
Yam, flour or mealOfori et al. 2016	laboratory-processed flour from raw material bought atCollection date unreportedDry weight	mean.

2 findings · 1 study
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
Yam, as soldEzema et al. 2023	Nsukka open market, Enugu State2022As sold / fresh	mean.
6 findings · 1 study
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; boiled2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; fried2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; roasted2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; boiled2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; fried2019Basis not stated	mean.
Yam, cookedAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; roasted2019Basis not stated	mean.
2 findings · 1 study
Yam, peeled or fleshAdjei-Mensah et al. 2021	Akwatia (diamond mining town), Birim river; unprocessed2019Basis not stated	mean.
Yam, peeled or fleshAdjei-Mensah et al. 2021	Obuasi (gold mining town), Pra and Tano rivers; unprocessed2019Basis not stated	mean.

1 finding · 1 study
Yam, as soldIyabo et al. 2015	tuber group itemCollection date unreportedDry weight	sample value.
2 findings · 2 studies
Yam, flour or mealIyabo et al. 2015	tuber group itemCollection date unreportedDry weight	sample value.
Yam, flour or mealOfori et al. 2016	laboratory-processed flour from raw material bought atCollection date unreportedDry weight	mean.

Shared dataset methods and interpretation

Source summaries retain their original statistic, material, basis and censoring. Each source drawer identifies methods and overlapping samples. No matched reference or pooled distribution is inferred.

HMI yam Pb reference · Yam, as sold

Reference and scope

HMI yam Pb reference · Yam, as sold. Yam, as sold; As sold, as eaten or fresh weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	5.15–6.2 (bounded)	10–20 (bounded)	32.8
Alternative weighting	5.68–9.2 (bounded)	16–21 (bounded)	36.4

13 reference units; 1 sampling family. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
WHO GEMS/Food	13	100%

Methods

HMI pools subgroup medians for yam, as sold on a as sold, as eaten or fresh weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

WHO GEMS/Food is the only compatible sampling family for yam, as sold on this basis in the completed yam ledger, so this single-family reference cannot represent other markets. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

WHO GEMS/Food

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-ed4d8b67588a:1ec76d055d55

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam Pb reference · Yam, as sold, dry weight

Reference and scope

HMI yam Pb reference · Yam, as sold, dry weight. Yam, as sold; Dry weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	≤1	15–15.5 (bounded)	30
Alternative weighting	≤1	15–15.5 (bounded)	30

2 reference units; 2 sampling families. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
WHO GEMS/Food	1	50%
Iyabo et al. 2015	1	50%

Methods

HMI pools subgroup medians for yam, as sold on a dry weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

2 sampling families with different designs; none is a probability sample of world supply. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-cd5af2b96b24:82079d55bfdc

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam Pb reference · Yam, flour or meal, dry weight

Reference and scope

HMI yam Pb reference · Yam, flour or meal, dry weight. Yam, flour or meal; Dry weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	300	300	300
Alternative weighting	300	300	300

1 reference units; 1 sampling family. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
Iyabo et al. 2015	1	100%

Methods

HMI pools subgroup medians for yam, flour or meal on a dry weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

Iyabo et al. 2015 is the only compatible sampling family for yam, flour or meal on this basis in the completed yam ledger, so this single-family reference cannot represent other markets. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

Iyabo et al. 2015

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-57e4e710d678:12ec898a32f0

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam Cd reference · Yam, as sold

Reference and scope

HMI yam Cd reference · Yam, as sold. Yam, as sold; As sold, as eaten or fresh weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	≤1	1–2.5 (bounded)	10
Alternative weighting	≤2	1–3 (bounded)	10

6 reference units; 1 sampling family. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
WHO GEMS/Food	6	100%

Methods

HMI pools subgroup medians for yam, as sold on a as sold, as eaten or fresh weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

WHO GEMS/Food is the only compatible sampling family for yam, as sold on this basis in the completed yam ledger, so this single-family reference cannot represent other markets. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

WHO GEMS/Food

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-a455ec5c2930:64b51c0409d7

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam Cd reference · Yam, as sold, dry weight

Reference and scope

HMI yam Cd reference · Yam, as sold, dry weight. Yam, as sold; Dry weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	10	75	140
Alternative weighting	10	75	140

2 reference units; 2 sampling families. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
WHO GEMS/Food	1	50%
Iyabo et al. 2015	1	50%

Methods

HMI pools subgroup medians for yam, as sold on a dry weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

2 sampling families with different designs; none is a probability sample of world supply. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-0adddae2d476:d2bea676aa55

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam tAs reference · Yam, as sold

Reference and scope

HMI yam tAs reference · Yam, as sold. Yam, as sold; As sold, as eaten or fresh weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	≤1	≤20	≤85
Alternative weighting	≤10.5	≤52.5	32.5–193 (bounded)

5 reference units; 1 sampling family. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
WHO GEMS/Food	5	100%

Methods

HMI pools subgroup medians for yam, as sold on a as sold, as eaten or fresh weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

WHO GEMS/Food is the only compatible sampling family for yam, as sold on this basis in the completed yam ledger, so this single-family reference cannot represent other markets. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

WHO GEMS/Food

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-5aa01b4d37e6:470d29149d17

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam tHg reference · Yam, as sold

Reference and scope

HMI yam tHg reference · Yam, as sold. Yam, as sold; As sold, as eaten or fresh weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	≤4.2	≤4.2	11
Alternative weighting	≤4.2	5.5–7.6 (bounded)	11

3 reference units; 1 sampling family. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
WHO GEMS/Food	3	100%

Methods

HMI pools subgroup medians for yam, as sold on a as sold, as eaten or fresh weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

WHO GEMS/Food is the only compatible sampling family for yam, as sold on this basis in the completed yam ledger, so this single-family reference cannot represent other markets. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

WHO GEMS/Food

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-69b9283b4701:5ace923e49d8

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam Cu reference · Yam, as sold, dry weight

Reference and scope

HMI yam Cu reference · Yam, as sold, dry weight. Yam, as sold; Dry weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	4500	4500	4500
Alternative weighting	4500	4500	4500

1 reference units; 1 sampling family. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
Iyabo et al. 2015	1	100%

Methods

HMI pools subgroup medians for yam, as sold on a dry weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

Iyabo et al. 2015 is the only compatible sampling family for yam, as sold on this basis in the completed yam ledger, so this single-family reference cannot represent other markets. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

Iyabo et al. 2015

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-dde9955ef75e:bcf71abbd2c4

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam Cu reference · Yam, flour or meal, dry weight

Reference and scope

HMI yam Cu reference · Yam, flour or meal, dry weight. Yam, flour or meal; Dry weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	2150	2150	2150
Alternative weighting	2150	2150	2150

1 reference units; 1 sampling family. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
Iyabo et al. 2015	1	100%

Methods

HMI pools subgroup medians for yam, flour or meal on a dry weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

Iyabo et al. 2015 is the only compatible sampling family for yam, flour or meal on this basis in the completed yam ledger, so this single-family reference cannot represent other markets. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

Iyabo et al. 2015

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-24814095b0ed:75db19431de4

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam Zn reference · Yam, as sold, dry weight

Reference and scope

HMI yam Zn reference · Yam, as sold, dry weight. Yam, as sold; Dry weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	9250	9250	9250
Alternative weighting	9250	9250	9250

1 reference units; 1 sampling family. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
Iyabo et al. 2015	1	100%

Methods

HMI pools subgroup medians for yam, as sold on a dry weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

Iyabo et al. 2015 is the only compatible sampling family for yam, as sold on this basis in the completed yam ledger, so this single-family reference cannot represent other markets. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

Iyabo et al. 2015

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-5a97c34fa2b0:9261cfc0af50

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

HMI yam Zn reference · Yam, flour or meal, dry weight

Reference and scope

HMI yam Zn reference · Yam, flour or meal, dry weight. Yam, flour or meal; Dry weight, µg/kg; no moisture conversion. Distribution of subgroup median concentration values.

Reference (µg/kg)	Q1	Median	Q3
Primary HMI reference	9200	9200	9200
Alternative weighting	9200	9200	9200

1 reference units; 1 sampling family. Counts describe evidence units, not independent studies or certainty.

Contributing family	Reference units	Weight
Iyabo et al. 2015	1	100%

Methods

HMI pools subgroup medians for yam, flour or meal on a dry weight basis: monitoring results summarized as one median per reporting region, sampling type and collection year, total diet composites and printed sample values as single observations, and printed subgroup medians from ordinary farms or markets. Each sampling family has equal total weight. Non-detects stay as zero-to-limit intervals, so quartiles carry lower and upper bounds. Means, ranges and maxima never enter as observations. Other forms, other bases, targeted sampling and results from mining, industrial, wastewater-affected, experimental, fertiliser or manufacturer settings are kept out of this reference.

Inverse weighted empirical CDF; midpoint at exact cumulative-weight boundaries. At least four reference units and a definitely positive Q1 to Q3 spread are required. This is a display eligibility rule, not statistical validation.

Limitations

Iyabo et al. 2015 is the only compatible sampling family for yam, flour or meal on this basis in the completed yam ledger, so this single-family reference cannot represent other markets. Reporting regions and purchase markets are not growing areas. Non-detects with differing limits widen the bounds. A position is descriptive concentration, not a safety or compliance judgment.

Admitted source families

Iyabo et al. 2015

Reference version and interpretation

Frozen evidence selection: 2026-10-22. Method: hmi-pooled-reference-v2.

hmi-pooled-reference-v2:yam-8d94c1e04473:f830672910b3

The reference is computed by HMI from admitted evidence, not copied from a study baseline. It describes the evidence currently in this scope; it is not a worldwide or current-lot benchmark. Source, year and region filters do not change it. Different HMI scopes are not one common ranking.

How metals reach yam

No study in the library compared yam from contaminated and ordinary settings, so the routes by which metals reach it are not measured here.

Which forms and regions measured lower

The HMI reference for lead in yam, as sold pools 13 subgroup units from 1 sampling family, with a median of between 10 and 20 µg/kg and a middle half spanning between 5.15 and 6.2 (lower quartile) and 32.8 µg/kg (upper quartile).^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →} For cadmium in yam, as sold, the reference median was between 1 and 2.5 µg/kg, with a middle half from below 1 to 10 µg/kg across 6 units.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →} For total arsenic in yam, as sold, the reference median was below 20 µg/kg, with a middle half from below 1 to below 85 µg/kg across 5 units.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}

Among GEMS/Food reporting regions, yam, as sold had the lowest lead subgroup median in PAHO (3.7 µg/kg) and the highest in AFRO (125 µg/kg); reporting regions are markets, not growing areas.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →} For cadmium, the lowest regional median was in AFRO (1 µg/kg) and the highest in AFRO (140 µg/kg).^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}

Processing, cooking and preparation

Processed or prepared forms were compared only with unprocessed yam in the same study and group. Yam, flour or meal (tuber group item) had lead higher at 300 µg/kg, against 30 µg/kg for the unprocessed form in the same group (yam, as sold).^{5Iyabo OO, Ogundiran MB, Adebayo OL · 2015Toxic and Essential Metals in Staple Foods Commonly Consumed by Students in Ekiti State, South West, NigeriaInternational Journal of ChemistryRead source →}

Forms differ in water content, so a per-kilogram difference is not by itself a measured removal or gain of metal.

Mitigation for yam

Lot testing against the applicable limit is the check that can be verified.

No measured way to lower metals in this food is in the library yet.

Trade-offs and limits of controls

Metals do not move together, so a lot that passes a lead limit says little about cadmium, arsenic or nickel unless those are tested as well.

Testing yam for metals

Results depend on the method and its reporting limit. Reporting limits for lead ranged from 1 µg/kg (WHO GEMS/Food) to 90 µg/kg (WHO GEMS/Food), so a non-detect from a less sensitive method says much less.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →} Reporting limits for cadmium ranged from 0.3 µg/kg (WHO GEMS/Food) to 10 µg/kg (Adjei-Mensah et al. 2021), so a non-detect from a less sensitive method says much less.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}^{7Adjei-Mensah R, Ofori H, Tortoe C, Johnson PT, Aryee D, Frimpong SK · 2021Effect of home processing methods on the levels of heavy metal contaminants in four food crops grown in and around two mining towns in GhanaToxicology Reports 8 (2021) 1830–1838Read source →} Reporting limits for total arsenic ranged from 1 µg/kg (WHO GEMS/Food) to 300 µg/kg (WHO GEMS/Food), so a non-detect from a less sensitive method says much less.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}

A useful lot result names the form, the basis and a quantification limit well below the limit that applies.

Buying and verifying yam

No maximum level for metals in yam was verified from primary text for this page; buyers should confirm the limit that applies in the destination market.

Exposure from yam

No source in the library converted yam concentrations into a verified estimate of intake for a defined population. Concentrations describe the food, not individual risk.

Evidence review and remaining gaps

Every source record that names yam was decided on its content: 10 occurrence extracted, 10 records in all. The occurrence table renders every extracted result; held values remain visible with their reason.

References identify the sources used in these answers. The Sources index preserves additional discovery links; inclusion there does not mean a source has been reviewed for this assessment. Corrections, completed searches, new direct evidence and changes in requirements should reopen the relevant answer.

Yam FAQs

What heavy metals are found in yam?

The library reports lead, cadmium, total arsenic, total mercury, nickel, chromium, Co, Cu, Fe, Mn and Zn in yam, most often lead, cadmium and total arsenic.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}^{2AuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema, Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · 2023Evaluation of pesticide residues and heavy metalsPeer-reviewed articleRead source →}^{3Guerra F, Trevizam AR, Muraoka T, Marcante NC, Canniatti-Brazaca SG · 2012Heavy metals in vegetables and potential risk for human healthScientia Agricola 69(1):54-60Read source →}^{4Brima EI, Haris PI, Frei M · 2025Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketAfrican Journal of Agriculture and Food ScienceRead source →} WHO GEMS/Food submissions reported lead in yam, as sold from 68 results in 4 reporting regions, with subgroup medians from 3.7 to 125 µg/kg.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}

Which regions report the lowest levels in yam?

Among GEMS/Food reporting regions, yam, as sold had the lowest lead subgroup median in PAHO (3.7 µg/kg) and the highest in AFRO (125 µg/kg); reporting regions are markets, not growing areas.^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →} For cadmium, the lowest regional median was in AFRO (1 µg/kg) and the highest in AFRO (140 µg/kg).^{1World Health Organization · 2026GEMS/Food Contaminants database heavy-metal exportsGEMS/Food Contamination Monitoring and Assessment ProgrammeRead source →}

Does processing change heavy metals in yam?

Only comparisons between forms in the same study are available, not before-and-after measurements of the same yam.^{5Iyabo OO, Ogundiran MB, Adebayo OL · 2015Toxic and Essential Metals in Staple Foods Commonly Consumed by Students in Ekiti State, South West, NigeriaInternational Journal of ChemistryRead source →} Yam, flour or meal (tuber group item) had lead higher at 300 µg/kg, against 30 µg/kg for the unprocessed form in the same group (yam, as sold).^{5Iyabo OO, Ogundiran MB, Adebayo OL · 2015Toxic and Essential Metals in Staple Foods Commonly Consumed by Students in Ekiti State, South West, NigeriaInternational Journal of ChemistryRead source →}

References

Works cited on this page, in citation-number order. See Sources for this page’s source inventory. Each title links to a source record with bibliographic details, reported findings, and document provenance.

GEMS/Food Contaminants database heavy-metal exportsWorld Health Organization · GEMS/Food Contamination Monitoring and Assessment Programme · 2026 · extranet.who.intDataset
Evaluation of pesticide residues and heavy metalsAuthorS: Kingsley O. Omeje in common food tubers from Nigeria Benjamin O. Ezema and Sabinus O.O. Eze AFFILIAtIoNS: Pesticide residues · Peer-reviewed article · 2023 · doi.org/10.17159/sajs.2024/15969Peer-reviewed
Heavy metals in vegetables and potential risk for human healthGuerra F, Trevizam AR, Muraoka T, Marcante NC, and Canniatti-Brazaca SG · Scientia Agricola 69(1):54-60 · 2012 · doi.org/10.1590/s0103-90162012000100008Peer-reviewed
Assessment of Human Health Risk Based on Analysis of Potentially Toxic Elements in African Foods Sold in the UK MarketBrima EI, Haris PI, and Frei M · African Journal of Agriculture and Food Science · 2025 · doi.org/10.52589/AJAFS-TWSMWEGMPeer-reviewed
Toxic and Essential Metals in Staple Foods Commonly Consumed by Students in Ekiti State, South West, NigeriaIyabo OO, Ogundiran MB, and Adebayo OL · International Journal of Chemistry · 2015 · doi.org/10.5539/ijc.v7n1p155Peer-reviewed
Heavy metals health risk assessment for population via consumption of food crops and fruits in Owerri, South Eastern, NigeriaOrisakwe OE, Nduka JK, Amadi CN, Dike DO, and Bede O · Chemistry Central Journal 2012, 6:77 · 2012 · doi.org/10.1186/1752-153X-6-77Peer-reviewed
Effect of home processing methods on the levels of heavy metal contaminants in four food crops grown in and around two mining towns in GhanaAdjei-Mensah R, Ofori H, Tortoe C, Johnson PT, Aryee D, and Frimpong SK · Toxicology Reports 8 (2021) 1830–1838 · 2021 · doi.org/10.1016/j.toxrep.2021.11.001Peer-reviewed

Sources

Browse Yam Sources for sources cited on this page and additional discovery candidates. The searchable index distinguishes verified citation use from discovery relationships whose relevance has not been established.

Update history

22 October 2026: Rebuilt from every yam record in the library: 10 occurrence sources, references by form and basis, same-study contrasts.

Referenced by

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Heavy metals in Yam

Yam overview

What counts as yam

Heavy metal contamination profile of yam

How metals reach yam

Which forms and regions measured lower

Processing, cooking and preparation

Mitigation for yam

Trade-offs and limits of controls

Testing yam for metals

Buying and verifying yam

Exposure from yam

Evidence review and remaining gaps

Yam FAQs

References

Sources

Update history

Related ingredients

Referenced by

Graph View