Geochemistry and human health risks of heavy metals in soils from gold mineralized Birimian rocks in Southwestern Burkina Faso

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Résumé

This study aims to identify sources and health risks of a series of heavy metals in topsoil from
Birimian basement rocks in southwestern Burkina Faso. Concentrations of geochemical data of 66
samples were determined using ICP-MS. R-mode factor analysis, Sediment/Soil Quality Guidelines
and ecological and human health risk indices were used to investigate the associations between
the heavy metals and their impacts on the ecosystem and the local population. It can be noted that
78, 83 and 85% of the samples had maximum concentrations of Ni, Cr and As higher than their
respective SQG indices. The mean concentrations of these key contaminants were 42.09, 233.1 and
7.72 mg/kg for Ni, Cr and As, respectively. According to the median effect range mean quotient
(MERMQ), 87.9% (MERMQ >0.11) of the samples had 29% probability of being toxic. In contrast, the
contamination severity indices (CSI) ranged from 0.17 to 2.11, indicating a very low to moderate
probability toxicity. Factor analysis indicated that chemical weathering, with 57% of the total
variance, was the dominant factor controlling the soil geochemistry followed by artisanal gold
mining (10%) and farming (9%). Thus, weathering was the major contributor to heavy metal
loading including Ni, Cr and As. Among heavy metals, only Cr, Ni, As and Ba posed noncancerogenic
(THI >1) and cancerogenic (TCR >1.0 × 10−4) risks to the exposed population with
children being the most vulnerable. In the absence of prior knowledge of the soil geochemical
status, the heavy metals may be redistributed in the soil environment, and thereby compromising
human health.

Mots-clés

Heavy metals; Soil geochemistry; Artisanal gold mining; Chemical weathering; R-mode analysis