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Levels of Essential and Non-Essential Metals in Coffee Beans and Soils of the Three Major Coffee Producing Woredas of Gedeo Zone

Wondimeneh Dubale

The levels of nine essential (K, Ca, Mg, Mn, Cu, Zn, Co, Ni and Cr) and two non-essential (Cd and Pb) metals were determined in coffee beans (from farmer’s farms and washing industries) and soil samples using flame atomic absorption spectroscopy. The samples were collected from the three major coffee producing woredas of Gedeo zone, namely Kochere, Yirgacheffee and Wonago. Effective optimum microwave digestion procedure was developed for coffee bean samples. The efficiency of the optimized procedure was validated by spiking experiment and the percentage recoveries for entire metals lie within the range of 90%-106%. Soil samples were digested with slight modification of EPA 3050B acid digestion method. In all coffee bean samples the concentrations of macroelements were higher than microelements. Among the macroelements, K was determined to be the highest followed by Mg and Ca. On the other hand, among the trace microelements, Cu quantified in the maximum level followed by Mn, Zn, Co, Ni and Cr, respectively. Toxic metals Pb and Cd were not detected in coffee beans of Gedeo zone. Like coffee beans, soil samples also contained highest amount of macroelements than microelements with maximum and minimum concentration of Mg and Cd, respectively. Pb was below method detection limit in all soil samples. The concentrations of metals in coffee beans from farmer’s farms and washing industries were not significantly different at 95% confidence level within a single woreda. The levels of heavy metals in coffee bean samples were found to be below the maximum permissible limits set by FAO/WHO for different food items and herbal plants.