HEAVY METAL

This study was carried out in the southwestern part of Nigeria in Ondo State which lies within Latitude 7° 09’ 50.1” and 7° 12’ 20.6”N, and Longitude 5° 13’ 30.5”E and 5° 14’ 30.1”, with the aim of assessing the physical, microbial and chemical parameters of the groundwater. Random sampling technique was employed in obtaining water samples from both the surface and groundwater in the study area. A sterilized one liter plastic bottle was used to collect water samples and were immediately transported to the laboratory for physico-chemical and microbial analysis. A total of ten (10) water samples were collected; seven (7) groundwater samples and three (3) river samples. The physicochemical parameters determined and values obtained are as follows: Electrical conductivity ranged 300 and 960us/cm, Temperature 25.00 to 25.01℃, pH of 6.6-9.2 with a mean value of 6.9, TDS shows a mean valve of 25.69mg/l, COD from 5-18.4 mg/liter with mean value of 10.65mg/liter, Turbidity ranged 1.5 to 6.0 NTU with mean valve of 1.03NTU, Cl- 106.50 to 426.00mg/l, SO42- 0.41 to 2.87 mg/l, TSS shows a mean value of 0.411mg/l, TS 1.33 to 4.33 mg/l, NO3- 23.73 to 41.48mg/l, Mg ranged from 0.42 to 0.67 mg/liter which is within the WHO limit with mean valve of 0.41mg/l, Ca 0.10 to 0.41 mg/l, HCO3- 7.00 to 22.00mg/l, Na ranged from 2.8 to 3.9 mg/liter with mean value of 1.47mg/litre, K 0.41 to 1.20 mg/l, Mn 0.01 to 0.11 mg/l, Fe 0.01 to 0.02 mg/l, Zn 0.01 to 0.65 mg/l, PO4- 0.07 mg/l for all locations. Pb showed a mean value of 0. 011mg/litre. Result of analysis revealed that the ground and surface water in the study area appears to be generally potable, due to concentration of heavy metals being mostly under/within the WHO standard regulation. The pH, salinity and electrical conductivityin the study area was moderate. The colour for some samples were brownish – colourless. The presence of microbial organisms in water is from sewages, septic tanks, and animal faeces. The surface water found within the study area is Ofuso River. The water quality in the study area is generally potable.

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.

The indiscriminate disposal of solid waste and the proliferation of open dumpsites pose serious threats to soil quality, groundwater integrity and plant health. This study evaluated the ecological risk associated with heavy metals in soils collected around open dumpsites in Oluku, Benin City, Edo State, Nigeria. Ten soil samples were randomly collected using an auger and analyzed for heavy metal concentrations using Atomic Absorption Spectrophotometry (AAS). The mean concentrations of the analyzed metals ranged from 1.22 mg/kg for Cu to 3.05 mg/kg for Mn, following the decreasing order: Mn > Cd > Pb > Cr > Ni > Co > Zn > Fe > Cu. The contamination factor (CF) values for Fe, Zn, Cu, Pb, Cd, Mn, Ni, Cr and Co were 1.23, 1.26, 1.22, 1.95, 2.48, 3.05, 1.36, 1.42 and 1.29, respectively, indicating moderate contamination by Cd and considerable contamination by Mn. The ecological risk factor (Eir) of individual metals revealed that Cd (mean = 74.4) contributed the highest ecological risk, followed by Mn (30.58) and Pb (9.77). The overall potential ecological risk index (RI) was 133.92, suggesting a moderate level of ecological risk in the study area. The findings imply that uncontrolled dumping and anthropogenic activities contribute significantly to the accumulation of toxic metals in the soil, which may pose long-term environmental and health risks. Proper waste management strategies and periodic monitoring of soil quality are therefore recommended to mitigate further contamination and safeguard environmental health.