ABSTRACT

 Fruiting bodies of wild Pleurotus ostreatus (Oyster mushroom) and the underlying substrate (dead wood substrate) were collected from forested areas at three different Local Government Areas (LGA) in Abia State and investigated for their contents of cadmium, calcium, copper, iron, lead, magnesium, manganese, nickel, potassium, sodium and zinc using AAS after acid digestion. The potential of the mushrooms to accumulate the metals was assessed by the calculation of their bioconcentration factor (BCF, a quotient of the element content in mushroom fruiting bodies to the element content in substrate). The mushrooms were also investigated for their phytochemical and proximate compositions. For the mushroom, the K, Ca, Mg, Na and Fe contents ranged from 163.00 - 185.00; 26.60 - 44.00, 25.00 - 30.00, 15.00 - 25.00 and 12.60 - 25.00 mg/100g (dry weight) respectively, followed by Zn, Mn, Cu and Ni ranging from 1.63 - 2.64, 0.80 - 2.24, 0.57 - 1.13 and 0.08 - 0.16 mg/100g respectively. The concentrations of the toxic metals Cd and Pb (Cd from 0.03 - 0.14 and Pb from 0.03 - 0.04 mg/100g) were generally low and below the European Union limits for these metals in fungi (10 pg/g dw and 3 pg/g dw respectively), indicating that Pleurotus ostreatus from Abia State forests are safe for human consumption. Analysis of Variance (ANOVA) showed that Cd, Ca and Ni contents of samples from Isuikwuato LGA differed significantly (p<0.05) from the values for the other sites. There was no significant difference (p<0.05) in Cu, K, and Zn contents of the mushroom samples with respect to the sampled sites.The substrate elements contents varied from 115.00 - 123.00, 74.40 - 124.20, 23.40 - 40.10, 11.80 - 19.50 and 47.30-100.80 mg/100g for K, Ca, Mg, Na and Fe respectively, while Zn, Mn, Cu, xiii / Ni, Pb and Cd ranged from 4.01 - 5.56; 1.28 - 13.50, 1.03 - 1.90, 0.53 - 1.04, 0.21 - 0.36 and 0.19-0.32 mg/100g respectively. The BCF were generally <2 (range 0.11 - 1.86) indicating that Pleurotus ostreatus is not a good accumulator of the elements determined. Proximate analysis (%) showed that the mean moisture content ranged from 8.58 - 14.69; ash from 4.22 - 7.04; crude fiber, from 10.66 - 13.47; crude protein from 25.66-28.10; crude fat, 1.66-2.13; and carbohydrate from 36.82 - 46.78. Phytochemical studies (%) showed that mean alkaloids contents ranged from 0.53 - 0.91; flavonoids from 0.22 - 0.38; tannins from 0.43 - 0.62; saponins from 0.19 - 0.36; and phenols from 0.11 - 0.16. The results of this study show that Pleurotus ostreatus which is commonly consumed as a delicacy in most communities in southeastern Nigeria is nutritious, and does not pose health risks to consumers.