Elemental concentration of heavy metals in oyster mushrooms grown on mine polluted soils in Pretoria, South Africa

Issues of food security remains a major subject in ensuring sustainable global development and thus the hazardous effects of heavy metals on food substances call for concern due to the threat on human health and food security at large. Pleurotus ostreatus is an edible mushroom species with a promising nutritional and medicinal values. However, P. ostreatus is quite susceptible to heavy metal contamination from either polluted soil, mining or other anthropogenic activities. Aim at elucidating on the level of contamination and risk associated with the consumption of P. ostreatus from a polluted source, this study examined the amount of heavy metals in the caps and stalks of P. ostreatus grown in a soil sample collected from a mined site. Soil samples were obtained from three different mining areas and P. ostreatus spawns were grown in triplicates on these soils and on unpolluted soil. At maturity, the harvested parts (cap and stalks) were analyzed for heavy metals using Inductively Coupled Plasma Mass Spectrometry (ICP–MS). We found that mean concentration of chromium, manganese, cobalt, nickel, zinc, cadmium, mercury and lead were significantly different (p < 0.05) across the sites. Among the heavy metals investigated, Zn, Cd and Cr topped the permissible values allow for consumption. Though P. ostreatus stalk had higher concentrations of heavy metals than the caps, there was a positive correlation of the metal contents between the two components. The values obtained for the transfer factor pointed to the ability of P. ostreatus to accumulate cobalt, copper, zinc, arsenic, cadmium and lead. Based on hazard quotient (HQ) values obtained for both adults and children, we suggest that there are no possible human carcinogenic risks associated with the consumption of the Oyster mushroom. However, the continuous consumption may result into a serious health hazard owing to the levels of some heavy metals that were above the permissible limit considered safe for human consumption. It can be concluded from the study that P. ostreatus possess the potential to bio-accumulate toxic metals from polluted soils hence we recommend that caution must be taken not to harvest mushroom on polluted soils.