Scholarlink

Purpose <p>Heavy metal accumulation in agricultural soils reflects the interaction of lithogenic background, soil-forming processes, and anthropogenic inputs, with implications for soil quality and environmental sustainability. The objectives of this study were to quantify concentrations of eleven (11) trace elements and evaluate contamination patterns and ecological risk across agroecological zones, elevation gradients, soil types, and land-use systems.</p> Materials and methods <p>Soil samples were collected from agricultural lands across Nigeria using a hierarchical spatial sampling design based on the Soils4Africa field survey protocol. Concentrations of eleven trace elements (V, Hg, Co, Cr, Ni, Cd, As, Cu, Zn, Pb, and Sb) were determined using standardized laboratory procedures, yielding 1,467 valid analytical records for heavy metal assessment. Exceedance frequencies were evaluated relative to FAO guideline values for agricultural soils. Contamination status was assessed using the geoaccumulation index (Igeo), contamination factor (CF), pollution index (PI), contamination degree (CD), and pollution load index (PLI), while ecological risk was evaluated using single-element ecological risk factor (Er) and potential ecological risk index (PERI). Statistical analyses were used to examine variation in metal concentrations and risk indices across agroecological zones, elevation classes, soil types, and land-use categories.</p> Results and discussion <p>Hg showed the highest exceedance frequency, with 45.7% of samples exceeding the FAO guideline, followed by V (18.4%), Cr (3.0%), Co (1.6%), and Ni (0.9%). Cd, As, Cu, Zn, Pb, and Sb remained below their respective guideline values. Spatial visualisation showed broader mapped exceedance patterns for Hg and V than for Cr and Ni. Igeo indicated limited strong geoaccumulation, whereas CF showed moderate enrichment in subsets of samples. Cumulative ecological risk was generally low, with 94.2% of samples classified as low risk and 5.8% as moderate risk.</p> Conclusions <p>This study establishes a harmonised national reference framework for heavy metal assessment in Nigerian agricultural soils. The findings identify Hg and V as priority guideline-exceedance elements, distinguish background enrichment from guideline exceedance and toxicity-weighted risk, and show that cumulative ecological risk is generally low but spatially and element-specifically variable. The framework is relevant for targeted soil quality monitoring in Nigeria and comparable tropical agroecosystems where strong weathering, variable parent materials, land-use intensification, and limited national baseline data complicate heavy metal risk assessment.</p>

错误：搜索内容不能为空，请输入英文关键词
错误：关键词超出字数限制，请精简
高级检索

Heavy metal contamination, enrichment, and ecological risk in Nigerian agricultural soils: A nationwide multi-index assessment

  • 期刊论文

  • 发表日期：

    2026年6月18日

查看全文
  • Samuel Ayodele Mesele,
  • Ekpeno J. Akpan,
  • Jibrin M. Jibrin,
  • Olufunmilayo T. Ande,
  • James O. Jayeoba

摘要

Purpose

Heavy metal accumulation in agricultural soils reflects the interaction of lithogenic background, soil-forming processes, and anthropogenic inputs, with implications for soil quality and environmental sustainability. The objectives of this study were to quantify concentrations of eleven (11) trace elements and evaluate contamination patterns and ecological risk across agroecological zones, elevation gradients, soil types, and land-use systems.

Materials and methods

Soil samples were collected from agricultural lands across Nigeria using a hierarchical spatial sampling design based on the Soils4Africa field survey protocol. Concentrations of eleven trace elements (V, Hg, Co, Cr, Ni, Cd, As, Cu, Zn, Pb, and Sb) were determined using standardized laboratory procedures, yielding 1,467 valid analytical records for heavy metal assessment. Exceedance frequencies were evaluated relative to FAO guideline values for agricultural soils. Contamination status was assessed using the geoaccumulation index (Igeo), contamination factor (CF), pollution index (PI), contamination degree (CD), and pollution load index (PLI), while ecological risk was evaluated using single-element ecological risk factor (Er) and potential ecological risk index (PERI). Statistical analyses were used to examine variation in metal concentrations and risk indices across agroecological zones, elevation classes, soil types, and land-use categories.

Results and discussion

Hg showed the highest exceedance frequency, with 45.7% of samples exceeding the FAO guideline, followed by V (18.4%), Cr (3.0%), Co (1.6%), and Ni (0.9%). Cd, As, Cu, Zn, Pb, and Sb remained below their respective guideline values. Spatial visualisation showed broader mapped exceedance patterns for Hg and V than for Cr and Ni. Igeo indicated limited strong geoaccumulation, whereas CF showed moderate enrichment in subsets of samples. Cumulative ecological risk was generally low, with 94.2% of samples classified as low risk and 5.8% as moderate risk.

Conclusions

This study establishes a harmonised national reference framework for heavy metal assessment in Nigerian agricultural soils. The findings identify Hg and V as priority guideline-exceedance elements, distinguish background enrichment from guideline exceedance and toxicity-weighted risk, and show that cumulative ecological risk is generally low but spatially and element-specifically variable. The framework is relevant for targeted soil quality monitoring in Nigeria and comparable tropical agroecosystems where strong weathering, variable parent materials, land-use intensification, and limited national baseline data complicate heavy metal risk assessment.