Pattern and concentrations of trace metals in mushrooms harvested from trace metal-polluted soils in Pretoria, South Africa

Consumption of mushrooms is believed to assist in supplying basic nutrients that are required for human growth and well-being maintenance. It has been noted that vegetables and other agricultural crops may uptake trace metals from polluted soils. The present study investigated the pattern and concentrations of trace metals in mushrooms cultivated on polluted soils collected around three mining areas in Brits, South Africa. Spawns of mushroom Agaricus bisporus (white button and crimini varieties) mixed with chicken composted manures sponsored by a certified supplier in Pretoria were spread on polluted soil and allowed to grow to maturity under a controlled environment for mushrooms before harvesting. Harvested mushrooms were separated into caps and stalks and analysed for trace metal contents using inductively coupled plasma mass spectrometry (ICP-MS). The results showed that the concentrations obtained for trace metals in the stalks were more than those recorded for caps, with the exception of copper and zinc. The concentrations of trace metals in the mushrooms were in the ranges of 0.63 ± 0.07 μg/g-370.4 ± 4.71 μg/g Cr, 6.84 ± 0.32 μg/g-492 ± 1.79 μg/g Mn, 0.08 ± 0.03 μg/g-16.37 ± 6.43 μg/g Co, 1.19 ± 0.17 μg/g-54.12 ± 2.70 μg/g Ni, 16.75 ± 0.34 μg/g-51.30 ± 2.91 μg/g Cu, 39.71 ± 0.41 μg/g-257.95 ± 2.38 μg/g Zn and 0.24 ± 0.02 μg/g-4.26 ± 0.09 μg/g Pb. The transfer factor (TF) showed that Cr, Mn, Co and Zn were bio-accumulated from the soil by the mushrooms. Generally, the values obtained for Cr, Zn and Co exceeded the recommended limit for human consumptions. The results proved that mushrooms can bio-accumulate trace metals from the soil hence care should be taken not to cultivate them on polluted soils.