Physico-Chemical and Toxicological Profiles of Five Species of Mushroom In Anambra State, Nigeria and Their Potential for Bioremediation of Trace Metal Polluted Soil

Abstract

Five species of Mushroom namely Termitomyces robustus, Agaricus bisporus, Pleurotus tuber-regium, Amanita phalaoides and Amanita verosa were collected from eleven locations in Uke, Abatete, Ideani, Nnobi, Nnewi (Okpuno-egbu), Nnewi (Umudim) and Ozubulu between 2009 and 2012 in Anambra State, Nigeria. They were kept in clean collection bags and identified by a taxonomist. Some of the mushroom samples were later oven dried at 75 0 C for 4 hours and kept for chemical analysis while some were used for cultivation. During cultivation, seeds from matured mushrooms were scrapped from their veils into already compounded substrates/soil from their natural habitats and refuse dump soil (Table 3.2). The seeds were allowed to germinate within 4-5 days, the fruiting bodies/spawns were watered once daily for 14 days. The matured mushrooms were harvested, cleaned and oven dried at 75 0 C for 4 hours. The dried mushroom samples (wild and cultivated respectively) were homogenized into fine powder using blender with titanium blade and stored in pre-cleaned bottles for chemical analysis. These samples were subjected to various chemical analyses using standard methods by Association of Official Analytical Chemist (AOAC). The data were subjected to one way analysis of variance (ANOVA) at 95 % level using Statistical Package for Social Scientists (SPSS) version 16.0. The moisture content (MC) ranged from 81.79 % to 97.84 %, the highest value was from Amanita phalaoides and the least value was from Agaricus bisporus. Dry matter (DM) ranged from 2.63 % to 18.36 % showed an indication of high roughages content of the mushrooms. Crude protein (CP) ranged from 8.16 % to 24.67 % which compared favourably with values of seeds and legumes. Ash contents ranged from 3.26 % to 14.33 % were indications of high mineral elements present in the studied mushroom species. Low values of Lipid (fat/oil) ranged from 1.00 % to 6.68 % gave acceptance of the mushrooms as excellent dietary food for diabetic and coronary heart disease patients. Crude fibre (CF) ranged from 2.62 % to 15.37 %. There were no significant differences at p>0.05 between values of wild and cultivated mushrooms. Carbohydrates contents of 32.00-35.40 %, implied that mushrooms can function effectively in low fat diet such as those required by patients with cardiovascular diseases and diabetes. The vitamin C were detectable at levels ranging from 0.01-0.37 mg/100 g, values determined showed that the studied mushrooms were not good sources of vitamin C, although they could make important contribution to diet. The mean anti-nutritional factors of phytic acid 0.26 mg/100 g, cyanide 0.16 mg/100 g, tannins 0.31 mg/100 g were low when compared with 1.00 mg/100 g found in WHO guideline levels for these toxicants in food. Essential metals concentrations (mg/kg) for wild mushroom samples ranged as follows: Na (152.36 – 777.42), K (166.88 – 933.81), Ca (83.64 -545.00), Mg (476.57–1191.00), Fe (154.68–684.74) while values for cultivated mushroom samples ranged as follows: Na (332.77 – 1061.12), K (196.36 – 844.23), Ca (219.69 – 1841.08), Mg (549.66 – 1566.11) and Fe (401.66 – 777.18) mg/kg. The essential metal concentrations were within WHO guideline values for food. Trace/toxic metal concentrations (mg/kg) for wild mushroom samples ranged as follows: Cd (3.88 – 6.68), Co (0.48 – 1.52), Cr (BDL), Cu (0.12 – 0.72), Mn (8.25 – 24.42), Ni (1.40 – 16.85, Pb (3.60 – 5.03) and Zn (25.00 – 61.17). Values (mg/kg) for cultivated mushroom samples ranged as follows: Cd (4.40 – 9.88), Co (0.49 – 6.04), Cr (BDL), Cu (0.01 – 0.36), Mn (11.60 – 21.72), Ni (2.19 – 22.05), Pb (3.68 – 6.33) and Zn (9.33 - 68.56). There were significant differences at (p < 0.05) between mean trace metal concentrations of wild and cultivated mushrooms. All the soil/substrates samples used for cultivation were polluted with Cd and Cr while 40 % were polluted with Pb. However, Pb showed elevated values in other metals. There were elevated values of Ni in all the mushroom samples. The rest of the metals were below WHO guideline levels. Bioaccumulation factors ranged as follows: Cd (0.14 -1.78), Co (0.06 – 3.01), Cr (BDL), Cu (0.01 – 0.35), Fe (1.17 -2.22), Mn (0.38 – 13.53), Ni (0.08 – 1.95), Pb (0.08 – 1.50) and Zn (0.22 – 10.13). These values were above acceptable limit in food.