This study focuses on time-dependent microwave-assisted biosynthesis of silver nanoparticles using aqueous peel extracts of Citrus paradisi as a reducing, stabilizing and capping agent with emphasis on its antibacterial property. Optical, structural and morphological properties of the synthesized Citrus paradisi peel extract silver nanoparticle (CPAgNp) were characterized using UV-visible spectrophotometer, transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), Brunauer–Emmett–Teller (BET) and X-ray diffractometer (XRD). The antimicrobial activity was evaluated using the well- and disc-diffusion methods. Characteristic surface plasmon resonance (SPR) wavelength in the range of 420–440 nm at an optimized intensity growth rate typical of silver nanoparticles was obtained. The synthesized CPAgNp are spherical in shape having the size range of 14.84 ± 5 nm and possessing fcc unit phase structure. The Citrus paradisi peel extract mediated AgNp were found to possess a broad-spectrum antimicrobial activity against water-borne pathogenic microbes. GRAPHICAL ABSTRACT

This paper presents a chemical characterization of fine particulate matter in air masses passing through Thohoyandou and further determines their sources. Fine particulate matter (PM2.5) was collected and quantified using gravimetric method. X-ray fluorescence, Smoke stain reflectometer, Optical Transmissometer and Scanning Electron Microscopy- Energy Dispersive X-Ray Spectroscopy were used to determine the chemical and morphological composition of the particulate matter. The source apportionment was done using principal component analysis while the HYSPLIT model was used to depict the long-range transport clusters. The mean of concentrations of PM2.5, soot, black carbon and UVPM were 10.9 μg/m3, 0.69x10-5 m-1, 1.22 μg/m3 and 1.40 μg/m3, respectively. A total of 24 elements were detected in the PM2.5 with Pd, Sn, Sb, Mg, Al and Si being the dominant elements. SEM-EDS have shown the presence of irregular, flat and spherical particles which is associated with crustal material and industrial emissions. Source apportionment analysis revealed six major sources of PM2.5 in Thohoyandou namely, crustal materials, industrial emissions, vehicular emissions, urban emissions, fossil fuel combustion and fugitive-Pd. Air parcels that pass-through Thohoyandou were clustered into four. The major pathways were from the SW Indian Ocean, Atlantic Ocean and inland trajectories. Clusters from the ocean are associated with low concentration, while inland clusters are associated with high concentration of PM2.5. The PM2.5 occasionally exceeds the WHO daily guideline in Thohoyandou and the sources of PM2.5 extend beyond the borders. This study recommends that further studies need to be carried out to assess the health impacts of PM2.5 in Thohoyandou.

A low-cost adsorbent produced from Mn2+-modified bentonite clay was evaluated for groundwater defluoridation. Batch experiments were used to evaluate the effect of contact time at various adsorbent dosages, adsorption isotherms and the effect of pH on fluoride removal. The results showed that the optimum F- uptake occurred within the first 30 min contact time and the percentage removal increased with increasing adsorbent dosage. The data fitted better to pseudo-second-order reaction indicating that Fadsorption occurred via chemisorption. The Weber-Morris model of intra-particle diffusion revealed that both surface and intra-particle diffusion processes were involved during the F- adsorption process. Furthermore, the batch results showed that pH of the solution governed the percentage of fluoride removal with the optimum of 75.2 % fluoride removal achieved at pH 4. The adsorbent chemical stability assessment showed that chemical species were leached at trace concentrations which are within the South African National Standards (SANS) limits. Electrostatic attraction and ion-exchange were established as the major mechanisms responsible for fluoride adsorption at acidic pH and at moderate to alkaline pH levels, respectively. The study demonstrated that Mn2+ intercalated bentonite clay has potential for application in defluoridation of groundwater.

Abandoned gold mine sites are generally characterised by severe environmental problems and physical hazards. Because of socio-economic problems confronting communities around abandoned mine sites, historic and abandoned gold mines have become hot-spots for artisanal and small-scale miners. These mining activities at times thwart the efforts of rehabilitation at these sites. This article details how artisanal mining operations have frustrated rehabilitation efforts of abandoned mine shafts in the Sutherland goldfield. The field investigation of abandoned shafts and analysis of the nature of artisanal mining operations in the Sutherland goldfield revealed that artisanal mining involving digging around collars of sealed shafts is a major threat to the stability of the shafts and their sealing structures. In addition, artisanal mining operations have increased the safety risks of the abandoned shafts in the area. This has also been worsened by the fact that a large number of people, especially women and children, are exposed to the hazards of the abandoned mine sites. This article emphasises an urgent need for the development of holistic and cohesive strategies for dealing with the problems of abandoned gold mine shafts wherever they exist in the country as opposed to simply closing them up.

The present study evaluated the effectiveness of Fe-Mn modified kaolin clay in the uptake of As(V) from the solution. The elemental composition was characterized using X-ray fluorescence (XRF), while the surface morphology was characterized using Scanning Electron Microscopy (SEM). The surface area, pore diameter, and pore volume were determined using Brunauer, Emmett, and Teller (BET) and Barrett-Joyner-Halenda (BJH) techniques. The efficiency of the Arsenic removal of the adsorbent was evaluated using batch experiments. The results showed that the percentage of As(V) removal is optimum at acidic pH and decreased as the solution pH becomes more alkaline. The adsorption kinetics data fitted better to pseudo-second-order compared to the pseudo-first-order of reaction kinetics. The adsorption isotherm data fitted to the Langmuir isotherm model showing a maximum adsorption capacity of 2.44 mg/g, adsorbate concentration range of 1–30 mg/L, and adsorbent dosage of 0.4 g/100 mL. The value of ∆G° of the thermodynamic parameter was found to be negative, while ∆H° and ∆S° were found to be positive. For the regeneration-reuse study, the percentage of removal was found to be >85% after the sixth cycle of reuse. The results obtained from this study showed that Fe-Mn modified kaolin (FMK) is suitable for use in the uptake of As(V) from groundwater.

In the present study, silver nanoparticles (AgNPs) were synthesized using both the chemical and biological methods and conjugated with Pyrenacantha grandiflora extracts. These were then characterized and evaluated for antimicrobial activities against multi-drug resistant pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA), Klebsiella pneumonia, and Escherichia coli. Nanoparticles were analyzed with UV-visible spectrophotometer, transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). Silver nanoparticles, P. grandiflora extracts, and the conjugates were also analyzed with Fourier transform infrared spectroscopy (FTIR). As a result, quasi-sphere-shaped AgNPs with sizes ranging from 5 to 33 nm and spherically shaped AgNPs with sizes ranging from 3 to 25 nm were formed from chemical and biological synthesis, respectively. A well diffusion assay showed that the activity of silver nanoparticles was most improved with acetone extract against all tested bacteria with diameters in the range of 19–24 mm. The lowest MIC value of 0.0063 mg/mL against MRSA was observed when biologically synthesized AgNPs were conjugated with acetone and water extracts. Chemically synthesized silver nanoparticles showed the lowest MIC value of 0.0063 mg/mL against E. coli when conjugated with acetone and methanol extracts. This study indicates that silver nanoparticles conjugated with P. gandiflora tubers extracts exhibit strong antibacterial activities against multi-drug resistant bacterial pathogens. Therefore, biosynthesized conjugates could be utilized as antimicrobial agents for effective disease management due to the synergistic antibacterial activity that was observed.