The site-based data of contaminated and remediated soil samples are presented in Tables S1–S4 in the Supplementary materials .The soil samples collected from gold mining site showed the high est concentrations of Mn and Fe while those from Galvanized Roofing Sheet and ceramic industries had the highest levels of Cu and Zn. The concentration of Ca in the soil samples taken from Cement and Galvanized Roofing Sheet industries was the highest in all the samples analyzed
shows the average values of physical and chemical parameters of the compost, contaminated soil and remediated soil samples (with and without H. cannabinus). Results shown in this section represent the pooled data of analyzed soil (contaminated and remediated) samples collected from the four sampling sites.The compost sample exhibited the highest pH value (8.90 ± 0.02)followed by contaminated soil (8.46 ± 0.69) while the remediated soil sample with Kenaf plant (H. cannabinus) has the lowest pH value (7.63 ± 0.30). The pH of the compost and contaminated soil depicted an alkaline medium. After remediation, the pH decreased to a near neutral condition due to biodegradation activities of microorganisms present in the compost in consistence with previous work [31,32]. During nitrification processes, acidsare generated resulting into low pH environment [31]. Higher pH environment in composting reduces availability of heavy metals[33].
Electrical conductivity followed a similar pattern as pH. EC value decreased in the contaminated soil on introduction of compost by 6% in ‘compost-only’ treated soil and 15% in ‘compost + Kenaf’ treatment. This revealed the positive impact of compost on contaminated soil EC. High EC can affect the microbial activities in soil[34]. Smith and Doran [35] demonstrated that the yield of certain crops (barley, cotton, sugar beet and wheat) decreased as EC value of soil increased beyond the threshold limit. EC of the compost is lower than the threshold limit of 4000 S cm−1, which may be toxic to plant [36].