Abstract

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Nzu clay’ is a geophagious clay consumed in Africa for some medicinal purposes. This study reports the level of accumulated metals in mice that ingested ‘Nzu clay’ for 14 days. Eight female mice (10 ± 2 g) were each fed 0.02 g of ‘Nzu’ mixed with Bendel Plc Feed per day. The ‘Nzu clay’ contained 2.900 mg/kg Pb and 2.143 mg/kg Cd, while the experimental mice accumulated 0.893 mg/kg of Pb and 2.750 mg/kg Cd, but the control accumulated 0.714 mg/kg Pb and 2.250 mg/kg Cd. By extrapolation for 65 kg human weight, 0.014 mg/kg of Cd is anticipated to be accumulated at the end of two weeks. This is 13-fold the WHO tolerable weekly intake of 0.007 mg/kg body weight of human; and 10-fold increase in Pb compared to the WHO tolerable weekly intake. Neutron activation analysis indicated that the clay contained As, Cd and Pb at levels above WHO limits in foods. The accumulated concentration of Al in the mice was four-fold the 120.24 mg/kg in the control, while the accumulated Al concentration was 230-fold the tolerable intake. The accumulated concentration of manganese was 2.05 mg/kg compared to 0.07 mg/kg in the control. ‘Nzu clay’ is rich in K (96.0 mg/kg) and the mice also accumulated 11.5 mg/kg K; the National Academy of Sciences maximum level of daily dietary intake of K is approximately 72 mg/kg. The concentration of As in the clay was 51 mg/kg, which is of health concern. The level of Cr in the experimental mice was significantly elevated (Students’ t-test, P < 0.05) compared to the control. The accumulated level of Cr in the experimental mice was about 36-fold higher than the tolerable intake. The accumulated Fe and Mg in the mice was about 33-fold and 2-fold respectively. This implies that consumption of ‘Nzu clay’ result to bio-accumulation of essential and non-essential metals. Accumulation of heavy metals of health concern at long-term ingestion of the clay call for continuous ban on its consumption.

Keywords: geophagious, Nzu clay, tolerable intake, bio-accumulation, heavy metals, mice, hair