Geophagic clay consumed during pregnancy carries lead, arsenic, and nickel at concentrations that vary by mining site and by how the clay is processed.
- Metals of concern: Lead, arsenic, nickel, cadmium, and manganese, with very high variation between sites.
- Main drivers: Mining geology, proximity to cities or farms, and whether the clay is baked before sale.
- Practical framing: Measurements exist, but sample counts and method limits are too thin for a pooled estimate.
This page draws on 5 peer-reviewed sources. The complete citation list is at the bottom of the page.
What counts as geophagic clay
Geophagy is the deliberate ingestion of Earth materials, most commonly clay-type soils such as kaolin. The practice occurs globally but is most prevalent in sub-Saharan Africa, where it is documented across countries including Ghana, Nigeria, Cameroon, Kenya, Tanzania, South Africa, Uganda, and Zimbabwe.[^1][^2] Within Africa the highest prevalence rates are reported in pregnant women and young children.[^2]
Consumed materials are diverse. In Ghana, processed kaolin sold ready for consumption is known by names including ayilo (Ga), agatawa (Ewes), and hyire (Akan); in Nigeria it is calabash chalk, ndom, or nzu; in the Congo region it is mabele; Francophone speakers refer to it as craie, poto, or argile.[^1] In Cameroon, kaolin is mined and processed into lumps, oven-baked, and distributed to markets and to sellers who operate through established commercial channels.[^1]
Mineralogically, kaolin is composed predominantly of kaolinite and associated minerals formed from feldspar alteration. Pure kaolin (Table 1 of Bonglaisin et al. 2022) is composed of aluminum oxide (37-39%), silica (45-47%), ferric oxide (0.4-0.5%), titanium oxide (1.9-2.1%), calcium oxide (0.4-0.7%), and sodium oxide (0.6-0.7%), with 12-14% loss on ignition.[^1] Actual consumed clay varies from this composition depending on geological source and admixture with other soil minerals.
Why geophagic clay accumulates metals
Geophagic clay acquires heavy metal contamination through the geological source of the clay deposit and through subsequent handling and distribution pathways.
The primary geological pathway is proximity of the clay deposit to natural or anthropogenic metal sources. Kaolin forms from feldspar alteration in weathering zones, and the residual clay retains whatever metal load was present in the parent rock or in soil solution during formation. Agricultural soils typically contain 1-135 mg/kg lead; urban soils near traffic, industrial sources, and lead-based paint in major African cities (Lagos, Douala) have been documented at more than 1,000 mg/kg.[^1] Kaolin mined from deposits whose drainage crosses cultivated farm fields on a slope above the mine absorbs leached lead from those fields.[^1] Similarly, kaolin near arsenic-rich parent rock or near mining waste from gold and tin extraction can carry elevated arsenic.
The secondary pathway is handling and market distribution. Clay is typically sold in unbaked and baked forms; the baking process reduces but does not eliminate microbial contamination and does not alter the metal content of the clay. Market sampling in Ho municipality, Ghana found comparable metal levels across ore, retail unbaked, retail baked, and market baked categories.[^3]
A third pathway relevant to uptake is gastric chemistry. At stomach pH (1-2), lead and other metals held in kaolin by electrostatic forces are released into ionic form, which is the form available for intestinal absorption.[^1] Bioaccessibility studies using in vitro gastric extraction (PBET protocols) are referenced in Davies 2023 but have not been performed on the specific Ghanaian clay sources measured in Kortei et al. 2019.[^2]
Heavy metal contamination profile
| Analyte | Coverage | Typical (ppb) | Confidence | Key sources |
|---|---|---|---|---|
| Lead (Pb) | n=2 | 530 | low | — |
| Cadmium (Cd) | pending | — | — | — |
| Inorganic arsenic (iAs) | pending | — | — | — |
| Total arsenic (tAs) | n=2 | 1.63 | low | — |
| Total mercury (tHg) | pending | — | — | — |
| Nickel (Ni) | n=1 | 1850 | low | — |
| Aluminum (Al) | pending | — | — | — |
| Chromium (Cr) | — | — | — | — |
| Tin (Sn) | pending | — | — | — |
| Uranium (U) | — | — | — | — |
Lead
Lead in geophagic clay has been documented across multiple West African studies, with concentrations that differ substantially by location and by proximity to industrial or urban lead sources.
Kortei et al. 2019, the only primary measurement study in this deposit, found a mean lead concentration of 0.53 +/- 0.02 mg/kg (530 microg/kg = 530 ppb) in kaolin ore and market samples from Anfoega mining site and the Ho municipality market, Volta Region, Ghana, analyzed by dry ashing and flame atomic absorption spectrophotometry.[^3] The study compared this value with a WHO/FAO PMTDI-derived threshold and concluded it was within permissible levels for a 60-kilogram adult consuming the reported quantities of clay.
However, the same paper cites substantial contradictory evidence from other Ghanaian studies: Nkansah et al. (Kortei ref 38) found lead concentrations of 549-622.92 microg/kg in clay from Kumasi metropolis, and a Cameroon market study (Bonglaisin et al. 2015, cited in Bonglaisin 2022 as ref 92) found high values of lead, cadmium, and mercury in locally traded clay, with lead bio-accumulation in liver reported.[^1]
The Bonglaisin 2022 review notes that published studies have documented lead concentrations in soils near kaolin mines of 1 to 135 mg/kg (median 11 mg/kg) in agricultural zones, rising to more than 1,000 mg/kg in urban soils near major African cities (Lagos, Douala), with one study citing values as high as 50,000 mg/kg in a city-centre location.[^1] Clay drawn from mines whose drainage traverses urban zones or farm fields on a slope would reflect these elevated soil lead levels.
The bioavailability of lead from kaolin depends on the ionic form in which lead is held in the mineral lattice. A rat study referenced in Bonglaisin 2022 found that lead carbonate was 164% bioavailable relative to lead acetate; lead sulfide was 62-67%; lead naphthenate 121%; lead chromate 44%; metallic lead 14%.[^1] The crystalline structure of kaolin holds lead primarily by electrostatic forces; in the acidic stomach (pH 1-2) release into ionic form is the primary absorption pathway.[^1]
What is not yet measured: No study in this deposit reports bioaccessible (IVBA) lead fractions from consumed Ghanaian kaolin, speciated lead forms in the clay mineral lattice, or blood lead levels attributable specifically to clay ingestion in a controlled population.
Arsenic
Arsenic measurements in geophagic clay from Ghana show extreme inter-study variability.
Kortei et al. 2019 measured mean arsenic of 1.63 +/- 0.03 microg/kg (1.63 ppb) in kaolin samples from Anfoega, Ho municipality, Ghana.[^3] This value is about three to five orders of magnitude lower than values cited from other Ghanaian clay studies in the same paper: Nkansah et al. reported 218-271 mg/kg (218,000-271,000 ppb) from Kumasi metropolis clay samples; Doe et al. reported arsenic of 2.7-22.74 microg/g (2.7-22.74 mg/kg, or 2,700-22,740 ppb) in nine clay samples from Greater Accra and Kumasi.[^3]
The source notes that the arsenic values obtained in Kortei et al. 2019 were slightly higher than the finding of 0.0 (nil) mg/kg arsenic reported in an Accra clay study, and that the Doe et al. range of 2.7-22.74 microg/g was substantially above Kortei et al.’s own result.[^3] The disparity likely reflects geological heterogeneity between the Anfoega Volta Region source (a relatively clean kaolin deposit) and the more contaminated urban or peri-urban soils in the Kumasi and Accra catchment areas.
The comparison is further complicated by unit reporting differences across the cited studies (some report mg/kg, some ppm, some microg/g) and by the absence of CRM and recovery data from any of these studies, making cross-calibration uncertain.
Arsenic speciation (inorganic arsenic versus organic arsenic species) is not reported in any source in this deposit. The WHO/FAO PMTDI comparator used by Kortei et al. is for total arsenic; inorganic arsenic, the more toxic species and the form regulated in foods, was not separately determined.
What is not yet measured: Speciation of arsenic in geophagic clay; bioaccessible inorganic arsenic fractions; dose-response data linking geophagic clay ingestion to urinary arsenic markers in pregnant women.
Nickel
Kortei et al. 2019 measured mean nickel of 1.85 +/- 0.3 mg/kg (1,850 ppb) in kaolin samples from Ho municipality, Ghana.[^3] The authors compared this against the WHO/FAO PMTDI of 5.0 microg/kg body weight per day (300 microg/day for a 60-kg person) and found it within permissible ranges at reported intake quantities. No CRM or recovery data are provided.
The Bonglaisin 2022 review lists nickel among the moderately toxic metals in clay, categorized between the strongly toxic group (mercury, uranium, lead, thallium, bismuth) and the slightly toxic group (iron, germanium, selenium, antimony).[^1]
Manganese, copper, zinc, and macro elements
Kortei et al. 2019 measured the following macro and micro nutrients in Ho municipality kaolin: iron (1.38 +/- 1.5 mg/kg), copper (2.40 +/- 1.5 mg/kg), zinc (7.74 +/- 1.5 mg/kg), potassium (4.01 +/- 1.0 mg/kg), magnesium (13.24 +/- 2.2 mg/kg), sodium (13.76 +/- 2.1 mg/kg), manganese (4.72 +/- 0.8 mg/kg).[^3] These are presented in context of RDI values, not as contamination concerns per se. The magnesium and sodium concentrations are of interest because kaolin-associated magnesium has antacid properties that contribute to its appeal as a treatment for nausea and stomach upset during pregnancy.[^1][^2]
Cadmium and mercury
Neither cadmium nor mercury was measured as a primary outcome in Kortei et al. 2019 or in the Davies 2023 review. The Bonglaisin 2022 review cites a companion study (Bonglaisin et al. 2015 from Cameroon) that found high values of cadmium and mercury in market clay in Cameroon, with cadmium and mercury bio-accumulation in the liver documented.[^1] Specific values from that study are not reproduced in Bonglaisin 2022 and require the primary citation for use as evidence.
Ranges by source
The Bonglaisin 2022 review notes that clay from deposits near industrial and urban zones carries substantially higher lead than clay from agricultural zones, and that this urban-proximity effect is a primary driver of inter-site variability.[^1] The review also notes that in Cameroon, kaolin is processed (molded into lumps, oven-baked) and distributed through established commercial channels, while in some settings clay is taken directly from the earth or from riverbank exposures without any processing, with potentially different microbial but similar metal profiles.[^1]
Processing effects
The only source in this deposit that compared multiple distribution channels (Kortei et al. 2019) found that microbial load was higher in unbaked samples from both the Anfoega mining site ore and the Ho Asigame market, while baking reduced but did not eliminate microbial colonies.[^3] Metal concentrations were reported as a combined mean across all sample types rather than stratified by sample category, so no comparison of metal levels by processing step is possible from this study.
Microbial co-exposure
The simultaneous ingestion of pathogens and heavy metals through geophagic clay is a compound exposure pathway that distinguishes clay geophagy from most other dietary heavy metal sources.
Kortei et al. 2019 isolated Bacillus spp. and Pseudomonas spp. from all four sample categories (Anfoega ore, Anfoega retail unbaked, Ho market baked, Ho market unbaked) tested in the study.[^3] Mucor spp. were isolated from Anfoega retail unbaked clay; Aspergillus spp. from Ho market baked clay. Total plate counts ranged from 2.0x10^1 to 9.8x10^2 CFU/g across sample types. No helminths, protozoans, or cysts were identified in the parasitological analysis of this Ghanaian sample set.[^3]
The Bonglaisin 2022 review notes that Clostridium tetani cells are common in soils used for geophagy and can remain inactive in soil for years; children are considered at greater susceptibility to bacterial infection because of their predisposition to soil eating.[^1] E. coli and Salmonella contamination of clay is documented in other settings.[^1] The Davies 2023 review cites studies showing helminth infection (Hookworm, Ascaris, Trichuris) is linked to earth-eating in children in West Africa, though the specific helminth species and infection rates remain unclear in most published studies.[^2]
The Bonglaisin 2022 review also documents the physiological counter-argument: kaolin coats the gastrointestinal tract, potentially protecting against harmful bacteria, and kaolin-based formulations (kaopectate) are used therapeutically for gastrointestinal complaints including diarrhea.[^1] This dual function — pathogen barrier and pathogen vehicle — means the net microbial effect of clay ingestion depends on the specific clay type, preparation method, and microbial load of the source.
Prevalence and exposure population
The primary exposed population documented in the literature indexed on this page is pregnant women in West Africa, particularly in Ghana, Cameroon, Nigeria, and neighboring countries.
Kortei et al. 2019 found a geophagy prevalence of 48.4% among 217 pregnant women attending antenatal clinics in Ho municipality, Volta Region, Ghana (survey conducted 2018-2019).[^3] Of the 177 women (81.6%) who had eaten clay before, 132 (74.6%) consumed clay once daily and 12 (6.8%) consumed four or more pieces per day.[^3] Among 117 women who had cravings to eat clay during pregnancy, 105 (89.7%) acted on those cravings.[^3] The smell (45.8%) and craving (29.4%) of clay were the most common positive motivators; treatment of nausea (29.9%) was the most common therapeutic motivation.[^3]
The Bonglaisin 2022 review estimates that in Cameroon and comparable South American communities, 30-50% of pregnant women consume clay daily in quantities of 100-400 g per day, with some pregnant women consuming 100-400 g daily in communities where geophagy is widely normalized.[^1]
The Medical University of Vienna estimated 30-80% of Africans, especially women, eat clayey soil on a regular basis consuming 100-400 g per day, referenced in Davies 2023.[^2]
Iron and mineral metabolism interactions
Geophagy may impair or supplement mineral nutrition through two opposing mechanisms documented in the literature.
The supplement argument holds that clay provides bioavailable calcium, magnesium, and other minerals absent from the diet, particularly in resource-limited settings where dietary variety is constrained.[^2] The kaolin from Ho municipality contained 13.24 mg/kg magnesium, 13.76 mg/kg sodium, and 7.74 mg/kg zinc (Kortei et al. 2019, Table 4).[^3] At consumption quantities of 100-400 g per day, these represent non-trivial absolute amounts, though without bioaccessibility data their nutritional contribution cannot be quantified.
The impairment argument holds that clay chelates non-haem iron in the gut by forming insoluble iron complexes, reducing total iron absorption, and that clay constituents such as benzoic oxide, aluminum oxide, and magnesium oxide inhibit iron uptake at the intestinal level.[^1] The Bonglaisin 2022 review cites experimental evidence that Fe ions permeate exchangeably with Ca, Mg, Mn, Na, K, and hydrogen ions in clay, forming non-absorbable iron compounds.[^1] This iron-sequestration mechanism is cited as a contributory pathway to the iron deficiency anemia that is frequently associated with geophagy in pregnant women.
The Davies 2023 review notes that this long-standing debate between the micronutrient supplementation theory and the detoxification theory is unresolved; the intensity of causal discussion is diminishing as researchers redirect effort toward in vitro bioavailability studies and the specific knowledge gaps listed in the research priorities section of that paper.[^2]
Ingredient-derivative risk
This page does not cover cosmetic clay or bentonite clay used as processing aids. Those are addressed at Cosmetic clay.
These sources describe clay as it is mined, baked, and sold for eating. They do not describe a concentrate or extract of geophagic clay.
Mitigation options
Baking reduced microbial colonies in the Ho samples and did not provide a separate metal result for baked clay, so it is not evidence that baking lowers lead, arsenic, or nickel.[^3] The lead contrast in the Bonglaisin 2022 review is between urban or industrial deposits and agricultural deposits, which is a difference in where the clay is taken, not a treatment applied after mining.[^1]
Regulatory limits
No paper in this set cites a government maximum level written for geophagic clay as a food. Kortei et al. 2019 compared the Ho means for lead, arsenic, and nickel with WHO/FAO provisional tolerable daily intakes for a 60 kg adult and described those means as within the comparators at the intakes they used.[^3] Inorganic arsenic was not measured, so the arsenic result cannot be set against an inorganic-arsenic food limit.[^3]
What remains uncertain
The contamination profile for geophagic clay cannot be summarized as a reliable central estimate from available evidence. Specific unresolved gaps include the following.
No study in the indexed literature has measured bioaccessible (IVBA) lead or arsenic fractions in Ghanaian kaolin under standardized gastric extraction conditions with certified reference materials. Total-metal values from this deposit are therefore maximum-bound estimates of what is potentially available for absorption, not absorbed doses.
The inter-study range for arsenic in Ghanaian clay spans from 1.63 ppb (Kortei et al. 2019) to roughly 2.7-22.74 microg/g (Doe et al., cited in Kortei), about three to four orders of magnitude, and to 218-271 mg/kg in the Nkansah values cited beside it. This range is not consistent with analytical error and must reflect genuine geological heterogeneity between source deposits, but no study has mapped which deposits produce which metal profiles.
Cadmium and total mercury concentrations are not reported in any primary measurement study in this deposit. The Bonglaisin 2022 review cites their presence in Cameroon market clay in qualitative terms without reproducing specific values.
Arsenic speciation (inorganic versus organic) has not been performed on any geophagic clay sample in the indexed literature, making risk comparison with regulatory limits (which are specific to inorganic arsenic) impossible.
The prevalence data (48.4% in Ho municipality; 30-80% cited by Medical University of Vienna) are not drawn from representative national samples; they may not generalize beyond the specific communities and clinical settings studied.
Sources
Source records associated with this topic. Inclusion does not establish that every finding applies to this product or ingredient. References above identify works cited in the text.
| # | Citation | Year | Type | Used on this page for |
|---|---|---|---|---|
| 1 | Lawluvi et al. 2026. Maternal geophagy in Ghana: a mini review of toxicological, microbial, nutritional, and radiological exposure pathways., Frontiers in Public Health 2026;14:1782963 | 2026 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 2 | Vulla et al. 2026. Geophagy During Pregnancy in Sub-Saharan Africa: A Review of Cultural Practices and Health Implications., Scientifica (2026) 9219293 | 2026 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 3 | Mafe et al. 2025. Geophagia among pregnant women: evaluating the microbiological and toxicological safety of calabash chalk and its implications on maternal health, Environmental Geochemistry and Health (2025) 47:347 | 2025 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 4 | Mensah et al. 2025. Potential Human Health Risks From Ingestion and Dermal Exposure to Geophagic Clays: Applications of Multivariate Analyses (MVA) and Near-Infrared (NIR) Spectroscopy, Journal of Chemistry, Volume 2025, Article ID 2167390, 28 pages | 2025 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 5 | Rukondo et al. 2024. Mineral composition and heavy metal risk assesment of selected geophagic soils from Tanzania, Toxicology Reports 12 (2024) 534-541 | 2024 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 6 | Davies 2023. Current status of research and gaps in knowledge of geophagic practices in Africa, Frontiers in Nutrition | 2023 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 7 | Mouri et al. 2023. Geochemical composition and potential health risks of geophagic materials: an example from a rural area in the Limpopo Province of South Africa, Environmental Geochemistry and Health (2023) 45:6305-6322 | 2023 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 8 | Bonglaisin et al. 2022. Geophagia: Benefits and potential toxicity to human (a review), Frontiers in Public Health | 2022 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 9 | Asowata 2021. Geophagic clay around Uteh-Uzalla near Benin: mineral and trace elements compositions and possible health implications, SN Applied Sciences (2021) 3:569 | 2021 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 10 | Kortei et al. 2020. Potential health risk assessment of toxic metals contamination in clay eaten as pica (geophagia) among pregnant women of Ho in the Volta Region of Ghana, BMC Pregnancy and Childbirth 20 (2020) 160 | 2020 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 11 | Oyebanjo et al. 2020. Health Risk Evaluation of Trace Elements in Geophagic Kaolinitic Clays within Eastern Dahomey and Niger Delta Basins, Nigeria, International Journal of Environmental Research and Public Health 2020, 17, 4813 | 2020 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 12 | Kortei et al. 2019. Elemental minerals and microbial compositions as well as knowledge and perceptions regarding kaolin (clay) consumption by pregnant women in the Ho municipality of Ghana, The Pan African Medical Journal | 2019 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 13 | Coulibaly et al. 2018. Reactivity of Clays Consummated in Côte d’Ivoire in Digestive Conditions: Bioavailability of Mineral Elements, Asian Journal of Applied Sciences, Volume 06, Issue 05, October 2018, pp. 321-332 | 2018 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 14 | Nkansah et al. 2016. Heavy metal content and potential health risk of geophagic white clay from the Kumasi Metropolis in Ghana, Toxicology Reports 3 (2016) 644-651 | 2016 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
| 15 | Ijeoma et al. 2014. Assessment of Heavy Metals in Edible Clays Sold in Onitsha Metropolis of Anambra State, Nigeria, British Journal of Applied Science & Technology 4(14): 2114-2124, 2014 | 2014 | Peer-reviewed | Contribution to this topic remains under review; see the source record for its reported scope. |
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