Risk assessment of heavy metal contamination in agricultural sites and river sediments at the Vatukoula gold mine, Fiji Islands

A comprehensive study was conducted to explore the concentration and distribution of heavy metals in farm soils and river sediments around a gold mining area in Fiji with particular emphasis on ecological and human health risks. Representative samples were acquired from farm sites in Matanagata Village and the Nasivi river, both situated around the Vatukoula gold mine limited (VGML), the largest operational gold mine in Fiji. Following aqua regia digestion and analysis by AAS, the average soil concentrations for Cu (110.4 mg kg–1), Cr (136.2 mg kg–1) and Cd (1.7 mg kg–1), and sediment concentrations for Pb (69.31 mg kg–1), Cd (1.82 mg kg–1), Cu (88.95 mg kg–1) and Cr (143.12 mg kg–1) were found to exceed the recommended guideline values. Based on the geo–accumulation index (Igeo) and enrichments factor (EF), the farm soils were moderately contaminated with Cd while the and sediments showed moderate to significant contamination with Pb, Ni and Cr. Ecological risk assessment confirmed moderate to considerable ecological risk in the metal–contaminated samples, with Cd and Pb generally presenting greater risk compared to other metals. Multivariate analyses including principal component analysis pointed to gold mining activities as a potential source for heavy metals in the area. Furthermore, human health risk assessment (HRA) indicated that while adults faced no significant carcinogenic or non–carcinogenic risks from metal exposure (HI < 1), children were at more risk from Co, Mn, Cr and Fe exposure, as well as potential carcinogenic risk from Cd (ILCR = 1.46E–04).

Evolution Assessment of Mining Subsidence Characteristics Using SBAS and PS Interferometry in Sanshandao Gold Mine, China

Ground subsidence is a common geological phenomenon occurring in mining areas. As an important Chinese gold mine, Sanshandao Gold Mine has a mining history of 25 years, with remarkable ground subsidence deformation. Mining development, life security, property security and ecological protection all require comprehension of the ground subsidence characteristics and evolution in the mining area. In this study, the mining subsidence phenomenon of the Sanshandao Gold Mine was investigated and analyzed based on Persistent Scatterer Interferometry (PSI) and small baseline subset (SBAS). The SAR (synthetic aperture radar) images covering the study area were acquired by the Sentinel-1A satellite between 2018 and 2021; 54 images (between 22 February 2018 and 25 May 2021) were processed using the PSI technique and 24 images (between 11 April 2018 and 12 July 2021) were processed using the SBAS technique. In addition, GACOS (generic atmospheric correction online service) data were adopted to eliminate the atmospheric error in both kinds of data processing. The interferometric synthetic aperture radar (InSAR) results showed a basically consistent subsidence area and a similar subsidence pattern. Both InSAR results indicated that the maximum LOS (line of sight) subsidence velocity is about 49 mm/year. The main subsidence zone is situated in the main mining area, extending in the northwest and southeast directions. According to the subsidence displacement of several representative sites in the mining area, we found that the PSI result has a higher subsidence displacement value compared to the SBAS result. Mining activities were accompanied by ground subsidence in the mining area: the ground subsidence phenomenon is exacerbated by the increasing mining quantity. Temporally, the mining subsidence lags behind the increase in mining quantity by about three months. In summary, the mining area has varying degrees of ground subsidence, monitored by two reliable time-series InSAR techniques. Further study of the subsidence mechanism is necessary to forecast ground subsidence and instruct mining activities.

Allergy and Household Living Conditions among Adolescents Living near Gold Mine Tailing Dumps in the Gauteng and North West Provinces of South Africa

This quantitative exploratory baseline study aimed to investigate whether allergy among adolescents was associated with household living conditions, including living near gold mine tailing dumps in South Africa. A questionnaire based on the International Study of Asthma and Allergies was used to collect information on allergy and household risk factors among adolescents (n = 5611). A chi-square test was applied to determine the relationship between community (exposed/unexposed) and confounding variables. Crude and adjusted odds ratios (ORs) and 95% confidence intervals (CI) were calculated using univariate and multiple logistic regression analysis (LRA) to estimate the likelihood of having doctor-diagnosed allergies. The overall prevalence of doctor-diagnosed allergies was 25.5%. The exposed communities had a higher prevalence of doctor-diagnosed allergies (26.97%) compared with the unexposed (22.69%) communities. The study found an association between doctor-diagnosed allergy and having fungus in the house, being female, currently having pets in and around the house, residing in the community for more than three years and living in communities located close to gold mine tailing dumps. Actions to implement buffer zones between gold mine tailing dumps and communities would support Sustainable Development Goals 3 (health) and 11 (sustainable cities and communities), while failing to address the current potential identified risk factors may pose a significant public health challenge. Local policymakers should also apply the precautionary principle to protect the health of children, especially with the location of human settlements relative to air pollution sources.

Biostabilization of Gold Mine Tailings: Co-Inoculation of Cyanobacteria Under Sterile and Non-Sterile Conditions

Cyanobacterial crust formation has attracted attention for stabilizing erosion-susceptible soils in desert regions. However, limited information exists on its application in waste impoundments such as mine tailings. Identifying suitable inoculants with the ability to develop biocrusts in the more toxic conditions of mine tailings represents a challenge for exploiting this biotechnology for such applications. In this study, the performance of two nitrogen-fixing cyanobacteria (Anabaena sp. and Nostoc muscorum), individually and as a consortium, in creating biocrusts over gold mine tailings were investigated under sterile and non-sterile conditions. The results showed that Anabaena sp. and the co-inoculation of the species promoted higher synthesis of chlorophyll-a and total EPS compared to N. muscorum. The inoculated strains also exhibited different responses in the amount of the EPS fractions. The less soluble and more condensed tightly bound EPS represented a higher fraction of total EPS with co-inoculation and N. muscorum. With respect to wind erosion resistance and compressive strength of the biocrusts generated, co-inoculation showed better performance, followed by N. muscorum, while Anabaena sp. appeared to be less effective. The presence of indigenous microbial community within the tailings influenced the biostabilization performance of Anabaena sp., while the influence was insignificant under co-inoculation and N. muscorum. Overall, inoculating the cyanobacteria in a mixture with complementary traits (higher chlorophyll-a synthesis and total EPS secretion of Anabaena sp. vs. higher TB-EPS fraction and filamentous growth of N. muscorum) presented an effective strategy in the development of a resistant biocrust against wind erosion. With this inoculation strategy, the beneficial effects of the individual strains on biocrust formation could be combined, thus a comparatively stronger structure could be formed. Besides chlorophyll-a content, factors such as cyanobacteria morphology and EPS fractions would contribute to the biostabilization process. The results also suggested that sterilization of the tailings would influence the performance of cyanobacteria depending on the inoculant. Thus, the response of inoculants to other microbial communities should be considered prior to field-scale application.

THE GEOLOGICAL STRUCTURE EFFECTS ON SLOPES STABILITY AND TUNNELS OF METAMORPHIC ROCKS AT POBOYA GOLD MINE PALU

Poboya area has many geological structures that result in distribution of strength and stress of rocks not evenly distributed, as a result, the rock mass strength becomes disturbed and slopes become unstable. The objective of the study was to determine the geological structure effect on slope stability and tunnel conditions on metamorphic rocks at the Poboya gold mine. The study was conducted in the Mantikulore sub-district, Palu, Central Sulawesi. Lithology composing study area is metamorphic rocks consisting of gneiss and schist, therefore, the analysis was carried out on both locations which have many geological structures. Numerical analysis was performed applying the finite element method with the RS2 program assistance. The findings show that the safety factor value of the existing slope at gneiss and schist location under static loading is 4.6 and 2.72, if there is an earthquake it becomes 1.07 and 0.77. The safety factor value under static loading with the joint is 4.58 and 2.03, while under dynamic loading with joint, it becomes 0.94 and 0.64. The geological structure effect which represented by the joint gave a big impact with a decrease of safety factor at gneiss about 0.43% under static loading and 80% under dynamic loading. Meanwhile, at schist, safety factor decreased 25% under static loading and 76% under dynamic loading. For tunnel stability, the existence of joint will increase the displacement of 65% at gneiss under static loading and 84% under dynamic loading, while at schist, it increases 25% under static loading and 54% under dynamic loading. This illustrates that geological structures under dynamic loading affect significantly slope stability of Poboya gold mine.