Agro-wastes are abundant in both rural and urban areas and when carelessly disposed off to the environment by dumping or burning, they lead to environmental pollution, and consequently to health hazards. Growing of edible mushroom on these wastes can contribute to decrease in environment pollution. This work investigated the growth and yield of Pleurotus ostreatus on different agro-wastes: plantain midrib (PM), corn straw (CS), sugarcane bagasse (SB) and their combinations (PM+CS, PM+SB, CS+SB, CS+PM+SB) with a view to finding the best substrate for the growth of P. ostreatus. The experiment was carried out using completely randomized design with seven treatments and three replications. Results revealed that mycelia growth period and days to pinhead formation were faster in corn straw (7 and 11 days, respectively from the day of inoculation), this was followed by CS+SB (8 and 12 days, respectively) while CS+PM+SB recorded the longest days (13 and 17, respectively). Stipe length ranged from 2.6 cm in PM to 3.3 cm in CS+PM while the pileus diameter was between 3.3 cm in CS and PM and 4.3 cm in PM+SB. Number of fruiting bodies, fresh and dry weights of the mushroom were significantly higher in CS than in the other substrates. The least number of fruiting bodies, fresh and dry weights were recorded in CS+PM+SB.

ABSTRACT. The bioaccumulation of trace metals in mushrooms poses a health risk to consumers. Despite the fact that mushroom eating has been linked to numerous health advantages, little attention has been paid to the relative health risks associated with trace metal build-up in this nutritional source in Nigeria. Pb, Cd, Fe, Hg and As in Pleurotus tuber-regium collected from mechanic workshops in Umuahia were analysed and the associated health risks for the consumers were evaluated. The trace metal contents in the mushroom and its substrates showed a descending order of Fe > Pb > Cd > As > Hg. The heavy metals concentration ranges in fruity body of the Pleurotus tuber-regium were Fe (62.16-98.17 mg kg-1), Pb (0.18-1.21 mg kg-1), Cd (0.05-0.34 mg kg-1), As (0.25-0.51 mg kg-1) and Hg (0.009-0.021 mg kg-1). The estimation of weekly intake values was lower than PTWIs of mushroom species except for Fe. According to the THQ and the HI calculations for trace metal contents in the mushrooms, mercury did not pose any risk on human health; whereas the other determined trace metals gave THQ values of 1 < THQ < 10 and showed the possibility of long-term risk.                     KEY WORDS: Trace metals. Mushroom, Estimated weekly intake, Target hazard quotient, Bioaccumulation   Bull. Chem. Soc. Ethiop. 2021, 35(2), 229-241. DOI: https://dx.doi.org/10.4314/bcse.v35i2.2