Heavy Metal Distribution in Termite Mound Soils of Coptotermes acinaciformis and Nasutitermes walkeri and Adjacent Control Soils in Bauchi State, Nigeria

Abstract

This study evaluated the distribution and ecological implications of iron (Fe), zinc (Zn), lead (Pb), chromium (Cr), manganese (Mn) and cadmium (Cd) in termite mound soils and adjacent control soils across nine communities in Bogoro, Bauchi and Katagum Local Government Areas of Bauchi State, Nigeria. The mound soils were attributed in the field to Coptotermes cf. acinaciformis and Nasutitermes cf. walkeri, although taxonomic confirmation was not undertaken. Soil samples were collected from three communities per Local Government Area, air-dried, ground, sieved and subjected to acid digestion. Metal concentrations were determined by flame atomic absorption spectrophotometry, while one-way analysis of variance and Pearson correlation analysis were used to assess spatial and species-related patterns. Iron recorded the highest concentrations, whereas Cd showed the lowest values across mound and control soils. Reported Fe concentrations ranged from 1.535 to 4.784 mg kg⁻¹, with the highest values observed in Bogoro mound soils. Mound soils generally exhibited higher numerical metal concentrations than adjacent controls, although no statistically significant species-level differences were detected (p > 0.05). Strong positive correlations were observed between Zn and Cr (r = 0.997, p = 0.046) and between Cd and Zn (r = 0.998, p = 0.038). However, these relationships were based on only three Local Government Area-level means and should therefore be interpreted cautiously. The reported Cd, Mn, Cr and Pb concentrations were below the phytotoxic and regulatory comparison thresholds adopted in the study. Nevertheless, the findings do not independently establish ecological or agricultural safety because metal speciation, bioavailability, crop uptake and human exposure pathways were not assessed. Slight Pb enrichment in Bogoro indicates the need for continued site-specific environmental monitoring near roads. Verification of the analytical units, taxonomic identities and near-identical values reported for the two termite taxa is required before termite mound soil can be recommended for agricultural amendment.