Levels of essential and non-essential metals in edible mushrooms cultivated in Haramaya, Ethiopia

Abstract

Background: Fruiting bodies of two oyster mushroom (Pleurotus ostreatus and Pleurotus florida) species and their respective substrate samples cultivated and collected from the Mushroom Research, Production and Training Laboratory of the Haramaya University, Ethiopia, were analyzed for essential and non-essential metals, viz., Cu, Fe, Zn, Mn, Cd and Pb contents by flame atomic absorption spectrometry after digestion employing dry, wet and microwave digestion techniques. Concentrations of the analyzed metals were expressed on a dry weight basis (mg/kg). Results: The mean metal concentration (mg/kg in dry weight) in the mushroom and respective substrate samples, respectively; for Pleurotus ostreatus were: Cu (51.19, 48.97), Fe (220.87, 299.51), Zn (89.68, 62.55) and Mn (47.55, 58.32). The mean metal concentration (mg/kg in dry weight) in mushroom and the respective substrate samples, respectively, for Pleurotus florida were: Cu (53.56, 51.87), Fe (243.92, 265.23), Zn (95.26, 64.25) and Mn (41.29, 62.55). However, Cd and Pb was not detected in both mushroom and substrate samples. The bio-accumulation factor of the heavy metals was calculated and a highest accumulation of Cu and Zn from substrate was observed for all the analyzed mushrooms samples. The observed results were also compared with the reported results. Conclusions: In this study, the highest concentrations of Cu, Fe, Zn and Mn were confirmed. These elements generally are essential for humans, and may not possibly cause health problems even if mushrooms are consumed regularly. Furthermore, the quantities of the metals found in the samples were within the limits recommended by international organizations like the WHO/FAO Expert Committee on Food Additives. On the other hand, the amounts of Cd and Pb were found to be very low. These elements are toxic to humans, especially at higher doses; however, the concentrations of these non-essential metals were below detectable limit.