Assessment of contamination and potential ecological risks of heavy metals in riverine sediments from gold mining and pristine areas in Ghana

Abstract

This study explore the characteristics of heavy metal pollution, contamination levels, and potential ecological risks in riverine sediments found in both gold mining and pristine areas. Such investigations are vital for the ongoing monitoring and preservation of water bodies and overall ecosystem health. In total, 44 composite sediment samples were collected from seven pristine environments and four mining sites. These samples underwent preparation, digestion, and analysis for heavy metal content, utilizing the inductively coupled plasma emission mass spectrometer (ICP-MS). Various tools and models, including the geo-accumulation index, enrichment factor, and degree of contamination, were employed to assess the impact of pollution on the environment. Modified ecological risk index were also used to evaluate potential ecological risks. The average concentrations of heavy metals in pristine sites spanned from 0.01±0.01 (Cd) to 73,753.64 ± 388.15 mgkg⁻¹ (Fe), while in mining sites, they ranged from 0.04±0.02 (Cd) to 56,394.25±400.66 mgkg⁻¹ (Fe). Comparing these concentrations against the USEPA Ecological Screening Values, Mean Shales levels, and the Canadian ISQG, it became evident that Pb, Cd, Zn, Ni, Co, and Mn concentrations generally remained below the recommended guideline values in both pristine and mining areas. However, concentrations of Cr, As, Cu, and Hg exceeded the prescribed threshold limits, particularly in the mining regions. Through Principal Component Analysis (PCA) and Geometrical Analysis for Interactive Aid (GAIA) modeling, two primary sources of heavy metals were identified: anthropogenic-related and geogenic-related. GAIA and PCA together explained 78.53 % and 79.40 % of the total variability in heavy metal concentrations, respectively. Overall, the pollution and ecological risk assessment indicated low to moderate contamination levels, with a notable exception of high arsenic contamination in the Nyam river. The findings of this study hold significance for assessing sediment conditions and river quality in mining communities within Ghana and globally. They also provide empirical data to recommend measures for mitigating water contamination in such communities.