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Microplastic Contamination and Its Impact on Soil Properties Across Different Land Uses in Cross River State, Nigeria
Summary
A survey of soils across four land-use types in southeastern Nigeria found microplastic concentrations up to 12 times higher in commercial areas than in forests, with contamination linked to changes in soil structure, nutrient availability, and water infiltration. This is the first large-scale assessment of microplastic distribution in Nigerian tropical soils, filling a major data gap for sub-Saharan Africa. The findings suggest that heavily contaminated commercial soils may have degraded agricultural and ecological functionality, with consequences for food security in the region.
Background: Microplastic contamination in terrestrial ecosystems represents an emerging environmental threat, yet comprehensive assessments of its distribution and impact on soil properties in tropical African environments remain limited. Objective: This study investigated the spatial distribution of microplastics across four land-use types (forest, agricultural, residential, and commercial) in Cross River State, southeastern Nigeria, and evaluated their effects on soil physical, chemical, and hydrological properties. Methods: A factorial experimental design was employed across 12 locations in three Local Government Areas (Boki, Obubra, and Ikom). Soil samples were collected from 0-10 cm depth, and microplastics were extracted using density separation with saturated saline solution. Comprehensive soil analyses included particle size distribution, chemical properties (pH, organic matter, nutrients, cation exchange capacity), and hydrological characteristics. Results: Microplastic concentrations varied significantly across land uses, with commercial areas exhibiting the highest contamination (12.12 g kg?¹; 150.87 tons ha?¹), followed by residential (5.40 g kg?¹; 70.08 tons ha?¹), agricultural (3.09 g kg?¹; 39.50 tons ha?¹), and forest (1.00 g kg?¹; 10.65 tons ha?¹) sites. Spatial variability was highest in commercial zones (CV = 48.07%). Soil texture was predominantly sandy loam, with pH ranging from moderately acidic to slightly acidic (5.47-5.57). Organic carbon content varied from 0.89% to 3.26%, with forest soils showing significantly higher values. Bulk density ranged from 1.05 to 1.32 g cm?³, with commercial areas demonstrating higher compaction. Cation exchange capacity averaged 9.74 cmol kg?¹ across sites, with commercial areas showing elevated values (14.73 cmol kg?¹). Hydraulic conductivity exhibited substantial variation (15.69-41.57 mm hr?¹), with forest soils maintaining superior infiltration rates. Conclusion: This study provides the first comprehensive assessment of microplastic distribution in Nigerian tropical soils, revealing critical land-use-dependent contamination patterns. Commercial areas represent microplastic hotspots with concentrations exceeding forest baselines by over 1,000%. The contamination correlates with alterations in soil physical structure, nutrient dynamics, and water retention properties, potentially threatening soil ecosystem services and agricultural productivity in the region.