Assessment of Heavy Metals in Edible Clays Sold in Onitsha Metropolis of Anambra State, Nigeria

Aim: To determine and compare the levels of zinc (Zn), lead (Pb), cadmium (Cd), copper (Cu), mercury (Hg), and cobalt (Co) in edible clay samples.
Place and Duration of Study: Department of Chemistry Laboratory, Federal College of Education (Technical), Asaba between June and October 2013.

Methodology: Two species of edible clay (Nzu and Ulo) bought in replicates from four spatially located markets namely Ochanja, Ose, Relief and Okpokoin Onitsha were used for the study. The samples were digested with aqua regia solution and analyzed for heavy metals by atomic absorption spectrophotometry. Mean concentrations were computed from three replicate measurements. Data from the markets were compared by One-Way ANOVA while data between the clay types were analyzed by independent t-test.
Results: Mean concentrations (ppm) of Zn, Pb, Cd, Cu, and Co showed no significant difference [(P =.981, .479, .335, .333 and .613) for Zn, Pb, Cd, Cu, and Co respectively] among markets. The mean concentration (ppm) of Hg (2.335±0.276) in Ochanja market however, differ significantly (P =.045) from those of the other markets, 0.621±0.244, 0.796±0.280 and 0.251±0.190 for Ose, Relief and Okpoko respectively. Statistically reliable differences were found for Zn (P =.000) and Co (P =.003) type 1 and 11 mean concentrations. However, mean concentrations of Pb, Cd, Cu and Hg in type 1 and type 11 clays did not differ significantly [(P =.391, .288, .243, and .613) for Pb, Cd, Cu and Hg respectively]. There were high concentrations of Hg invirtually all samples and Cd in few samples.
Conclusion: The high levels of Cd and Hgin the analyzed edible clays make them unhealthy for human consumption. However, further research is required to validate the reliability of these findings.