INTEGRATED SOIL QUALITY AND MICROBIAL RESPONSE TO CEMENT DEPOT EXPOSURE IN PORT HARCOURT, NIGERIA

Abstract

Cement depot operations pose ecological risks, yet integrated assessments combining physicochemical, microbial, and index-based approaches remain limited in sub-Saharan Africa. This study evaluated soils around four cement depots in Port Harcourt, Nigeria, to assess chemical alterations, microbial diversity, and overall soil quality. Composite topsoil samples (0-15 cm) were collected from Lafarge depots at Rukpokwu and Iriebe, and Dangote depots at Eleme and Eliozu, and a non-depot control. Physicochemical parameters, including pH, bulk density, nutrients, and heavy metals, were analysed using standard protocols. Microbial communities were quantified and identified by culture and biochemical/morphological tests. Soil Quality Index (SQI) was calculated using a weighted additive model, and ANOVA with Tukey’s post hoc test assessed variation across sites. Depot soils were consistently alkaline (pH 8.21-8.55) compared to the control (6.72), with higher bulk density and electrical conductivity. Heavy metals were elevated at depots, especially Eleme, where Pb reached 13.58 mg/kg, Cd 8.18 mg/kg, Cr 26.63 mg/kg, and As 8.25 mg/kg, compared to the control values of 1.62, 0.73, 5.12, and 0.44 mg/kg, respectively. Microbial biomass and viable counts were lower in depot soils, with community shifting toward Serratia, Bacillus, Pseudomonas, Aspergillus, and Fusarium. SQI ranged from 0.565 (Eleme) to 0.606 (Eliozu), all moderate, while the control scored 0.878. ANOVA showed no significant SQI differences (p = 0.431). Cement depot soils are characterised by alkalinity, heavy metal accumulation, and reduced microbial diversity, but retain moderate SQI values due to organic matter and microbial activity. The higher SQI around the control site highlights ecological stress around the depots, with long-term risks if metal buildup persists.