Determination of background values and assessment of pollution and ecological risk of heavy metals in urban agricultural soils of Yaoundé, Cameroon

Abstract

Purpose

Presence of heavy metals in urban agriculture is considered a major ecological risk. The aim of this research is to determine concentrations and background values of heavy metals in urban agricultural soils in Yaoundé (Cameroon), in order to assess the degree of soil pollution and to evaluate ecological risk.

Methods

Forty-five composite soil samples were taken from three market garden sites. Heavy metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). Geochemical background threshold values (GBTV) were determined using the robust statistical method of median ± median absolute deviation (MAD). Single (geoaccumulation index and enrichment factor) and complex (pollution load index and Nemerow pollution index) indices of pollution and of ecological risk (potential ecological risk index) were calculated. Significant difference between the three market garden sites was evaluated using the nonparametric test of Kruskal–Wallis.

Results

Median concentrations varied considerably, ranging from the highest to the lowest levels (mg/kg) as Mn 259.0 > Cu 111.2 > Zn 81.9 > Cr 54.6 > Pb 19.3 > Ni 14.9 > Cd 0.1. All median values were below their corresponding geochemical backgrounds, except for Pb. Single pollution indices showed that the study site was contaminated with Pb. Nemerow pollution index showed that 60% of soil samples were in the very high level of pollution. Based on potential ecological risk index, 16% of soil samples were at high risk. The three market garden sites differed significantly regarding their heavy metal contents, except Cd, as well as their pollution and ecological risk indices with the Nkolondom site having, in general, the highest levels.

Conclusions

More than half of the study area is polluted, mainly with Pb, whereas ecological risk is limited to a small part of it. This study can be used as a baseline to develop future long-term risk assessment strategies on the potential migration of heavy metals in urban agricultural soils to vegetables, animals and human beings.

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Data availability

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Acknowledgments

The authors are grateful to the support and cooperation of growers and technicians of the Laboratory of Soil, Plant, Water and Fertilizer (LASPEE) of the Institute of Agricultural Research for Development (IRAD), Yaoundé, Cameroon.

Funding

This work was supported by West and Central African Council for Agricultural Research and Development (WECARD) (Project: Negative externalities of intensification of cultivated soils).

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Contributions

All the authors contributed to the conception of overarching research goals and design of methodology. Verification and validation of the overall activities were done by Souad El Hajjaji, Raymond Charly Birang A Madong and Abdelmalek Dahchour. Management and coordination for the research activity planning and execution on study sites were supervised by Yvette Clarisse Mfopou Mewouo. Amina Aboubakar conducted a research process, specifically material preparation, performing the data collection and laboratory analysis. Analysis and interpretation of data and writing the initial draft of the manuscript were performed by Amina Aboubakar and Ahmed Douaik. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to Ahmed Douaik.

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Aboubakar, A., Douaik, A., Mewouo, Y.C.M. et al. Determination of background values and assessment of pollution and ecological risk of heavy metals in urban agricultural soils of Yaoundé, Cameroon. J Soils Sediments 21, 1437–1454 (2021). https://doi.org/10.1007/s11368-021-02876-4

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Keywords

  • Ecological risk
  • Geochemical background
  • Market garden
  • Heavy metals
  • Urban agricultural soil