Physical Soil Degradation and Geochemical Anomaly at an Artisanal Gold-mining Site in Zanikaha, Northern Côte d’Ivoire

Abstract

Background: Artisanal gold mining can disrupt soil profiles, reduce soil fertility, and redistribute potentially toxic elements, but integrated site-specific information for Zanikaha remains limited. Aim: This study aimed to assess the physical degradation, fertility status, and geochemical quality of soils affected by artisanal gold mining at Zanikaha in northern Côte d’Ivoire. It specifically sought to characterise mining-induced landscape disturbances, determine the main soil physicochemical properties, and identify potential anomalies in trace-element concentrations. Methodology: Field investigations combined a morphopedological survey along a toposequence, the description of two soil profiles, and composite sampling of the 0-30 cm surface layer. Laboratory analyses included particle-size distribution, agronomic parameters, and multi-element geochemical measurements. The survey covered 37.2 ha and documented the major forms of land disturbance associated with artisanal mining activities. Results: The study area showed severe physical degradation, characterised by topsoil stripping, excavations, waste-rock piles, washing sludge, and disrupted surface drainage. The soils were predominantly Ferralsols with plinthic properties and exhibited low organic fertility. Organic matter ranged from 2.41 to 8.62 g kg⁻¹, whereas total nitrogen ranged from 0.4 to 0.6 g kg⁻¹. Available phosphorus locally reached 71.7 mg kg⁻¹. Total arsenic concentrations at Zanikaha ranged from 207.989 to 267.735 mg kg⁻¹, compared with 8.669 mg kg⁻¹ at Gbini, indicating a marked arsenic anomaly. Lead concentrations remained low, while cadmium, mercury, and cyanide were below the reported limits of quantification. Conclusion: The findings demonstrate severe physical soil degradation and a pronounced arsenic anomaly at the Zanikaha artisanal gold-mining site. However, the absence of a matched local reference site, the limited analytical dataset, and the lack of arsenic speciation and bioaccessibility data prevent exclusive attribution of the anomaly to mining activities and do not allow a direct human-health risk assessment. Integrated monitoring of soils, surface water, groundwater, mining residues, dust, and food crops is therefore recommended to clarify contaminant sources, transfer pathways, and potential environmental and health risks.