Abstract
ABSTRACT 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.
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