This study assessed the quality of mushroom species that grown naturally on the waste cardboard compost at the stage of maturity. Since they were not intentionally cultivated, their characterization became necessary. Physical observation, laboratory analysis and literature search were used to classify the mushrooms. The fruiting bodies of the mushrooms were analyzed in a laboratory for their macro mineral and nutritional contents, using standard method (APHA). At maturity, two species of mushrooms that colonized the compost were Inocybe margaritispora and Corprinus narcoticus. Results of chemical analysis indicated organic carbon (35.35 ± 0.04% and 33.28 ± 0.00%); nitrogen (5.58 ± 0.02% and 33.28 ± 0.00%) and phosphorus (0.33 ± 0.02% and 0.24 ± 0.01%) for the two species respectively. With the exception of potassium, all the parameters were found to be higher in Inocybe margaritispora. Lead and cadmium were (18.35 ± 0.05 mg/kg and 31.30 ± 0.15 mg/kg) and (1.88 ± 0.03 mg/kg and 1.37 ± 0.04 mg/kg) respectively, which exceeded the stipulated international standards. Due to the high levels of heavy metals and lower macro nutrient contents, it is therefore not advisable to utilize them for human consumption. They can, however, find use in some other biotechnology–based functions.
