ASSESSMENT OF HYDROXYAPATITE AND PHOSPHATE SOLUBILISING BACTERIA FOR HEAVY METAL REMEDIATION IN SOIL SAMPLES FROM A MECHANIC WORKSHOP

Heavy metal contamination from mechanic workshops poses a major environmental challenge due to the continuous accumulation of toxic metals in soil, which can affect microbial activities, reduce soil fertility, and pose health risks to humans and other organisms. This study assessed the effectiveness of hydroxyapatite (HAp) and phosphate solubilising bacteria (PSB) (Pseudomonas sp.) in remediating heavy metal contaminated soil collected from a mechanic workshop. The research involved four treatments: soil only (control), soil + PSB, soil + HAp, and soil + PSB + HAp. Microbial counts and heavy metal concentrations (Fe, Cu, and As) were analyzed after incubation. The total heterotrophic bacterial count (THBC) increased from 2.5 × 10⁵ CFU/g in soil treated with PSB alone to 2.75 ± 0.71 × 10⁵ CFU/g in soil treated with both PSB and HAp, indicating enhanced microbial growth due to the combined amendment. The concentrations of iron (Fe) and copper (Cu) decreased significantly in all treated samples compared to the control. Fe reduced from 7561.97 mg/kg in the control to 6197.18 mg/kg in the combined treatment, while Cu decreased from 205.32 mg/kg to 150.19 mg/kg. Percentage reductions of 18.05% (Fe) and 26.85% (Cu) were recorded for the combined treatment, while arsenic (As) was not detected in any sample. These findings demonstrate that hydroxyapatite and Pseudomonas sp. act synergistically to immobilize and reduce heavy metal concentrations in contaminated soils. The combination improves microbial activity, enhances metal precipitation, and reduces the bioavailability of toxic metals. The study concludes that the combined use of hydroxyapatite and phosphate solubilising bacteria is an efficient, low-cost, and environmentally friendly method for remediating heavy metal–polluted soils from mechanic workshops in Nigeria.