Contamination status and toxicity risk assessment of selected potentially toxic elements in surface soils under the influence of different land uses in Midwestern Burkina Faso, West Africa

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Résumé

Background: As land use transitions from rain-fed farming to market gardening and artisanal gold mining in
Burkina Faso, soil contamination with potentially toxic elements (PTEs) has become a major environmental
concern.
Objective: This study investigates the PTE pollution status of highly anthropized soil in Midwestern Burkina Faso.
Methods: A total of 226 topsoil samples were collected, and their PTE concentrations were determined using
inductively coupled plasma mass spectrometry (ICP-MS). Enrichment factors and ecological and toxicity risk
indices were used to evaluate the soil’s contamination status.
Results: The results revealed that artisanal gold mining mainly contributed to Ag, As, Cd, Cu, Ni, and Zn loadings
in the soils, whereas agricultural practices might have partially contributed to Pb concentrations. Based on the
spatial distribution maps of the ecological risk index (RI), the studied soils exhibited low (23–104), moderate
(150 ≤ RI < 300), and very high (RI>600) risk levels. Samples with high toxicity units (ΣTU > 4) and toxicity
risk index (TRI > 20) were clustered around artisanal gold mining sites. The strong spatial and linear correlations
between ΣTU and RI (r² = 0.79), and between RI and TRI (r² = 0.90), suggest that the newly developed toxicity
indices are suitable for assessing PTE toxicity in soils.
Conclusion: The study’s findings demonstrate that, in addition to chemical weathering, uncontrolled artisanal
gold mining activities and, to a lesser degree, agricultural practices are likely to threaten soil functioning and
food security. The study provides valuable insights into the ongoing global discourse on PTE distribution and its
effects on soil environmental quality.

Mots-clés

Land uses Surface soils Potentially toxic element status Ecological risks Toxic risk index