Monitoring of soil pollution with heavy metals using some microbiological parameters

Although heavy metal pollution significantly impacts living organisms, the monitoring biomarkers can guide remediation. This study examined the response of Pb²⁺, Cd²⁺, Cu²⁺, Zn²⁺, Cr⁶⁺, Ni²⁺, and Hg²⁺ to soil microorganisms. Bacterial counts were measured at three metal concentrations (T₁, T₂, and T₃). Results revealed that Hg²⁺-T₁ caused a 91.4% reduction in bacterial counts within 10 days, while the other metals reduced counts by 32.9% to 71.8%. Higher concentrations (T₂ and T₃) of all metals, except Ni²⁺ (48.8%) at T₂, reduced counts by 92.1% to 99.6%. After 40 days, reductions were 74.5% for Hg²⁺-T₁, 97.0% for Cr6+-T2, and 95.2 to 98.0 % for Hg2+, Cr6+, Cu2+ and Zn2+-T3. Intrinsically resistant bacteria were observed after 40 days, constituting 34.2%–71.8% in T₁ of most metals, except Hg²⁺ (25.5%). These percentages decreased in T2 and T3. 55.3% of the initial organic-N was oxidized after 20 days in untreated soil, while Pb²⁺ was the least toxic for ammonification, and Hg²⁺ was the highest. In untreated soil, 67.4% of ammoniacal-N was oxidized after 20 days. Nitrification was unaffected by T₁, except for Hg²⁺. At T₂, Hg²⁺, Ni²⁺, and Cd²⁺ were the most suppressive, while at T₃, Hg²⁺, Zn²⁺, and Cd²⁺ showed the most harmful effects.