Abstract
Per- and polyfluoroalkyl substances (PFAS) are persistent pollutants contaminating various environmental media, including air, soil, sediments, surface water, and groundwater, both globally and in Africa. This contamination raises concerns about bio accumulation and adverse health impacts. The widespread use of aqueous film- forming foams (AFFF) containing PFAS in firefighting has led to significant environmental contamination, making fire sites and AFFF application areas potential sources of PFAS exposure. Despite escalating global concerns over PFAS contamination, Africa lacks critical data on the presence, distribution, and impacts of PFAS contamination. To bridge this gap, this study investigates PFAS contamination at fire outbreak sites in Ghana and South Africa, focusing on the detection of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) in soil and surface water samples. By addressing this knowledge deficit, the research aims to inform effective risk assessment, management, and policy development both in Africa and globally. The study seeks to conduct a qualitative and quantitative assessment of PFAS in environmental samples from Ghana and South Africa, evaluate associated risks using the Tolerable Daily Intake (TDI), Hazard Quotient (HQ), and Hazard Index (HI) methods, and to develop a cost-effective, eco-friendly nanocomposite material from palm kernel shells for the photocatalytic remediation of these contaminants.
The first study investigates PFAS contamination levels at selected fire outbreak sites in Ghana, focusing on the detection of PFOA and PFOS in soil and surface water samples. The mean concentrations of PFOA and PFOS were 1.1152 ng/g dry weight (dw) and 1.0632 ng/g dw in soil samples, and 0.9545 ng/L and 1.8715 ng/L in surface water samples, respectively. The independent t-test reveals no significant difference between the concentrations in soil and surface water across all the sites. With the exception of one site, concentrations of PFOA and PFOS in the surface water at all locations exceeded the United States Environmental Protection Agency's (USEPA) health advisory levels of 0.004 ng/L for PFOA and 0.02 ng/L for PFOS. Analysis of HQ and HI values for PFOA and PFOS in surface water revealed elevated levels at sites GR 6W and WR 3W, exceeding the safety threshold of 1 and indicating a significant risk. In contrast, HQ and HI values at other sites were below 1, suggesting minimal risk, although ongoing monitoring is recommended.
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A further study also investigated PFAS contamination levels at selected fire outbreak sites, focusing on PFOA and PFOS detection in soil and surface water samples in South Africa. The findings revealed varying contamination levels across samples. PFOA concentrations in soil varied from 6.16 to 25.50 ng/g dry weight (dw), with a mean concentration of 10.97 ng/g dw. In contrast, PFOS levels in soil were higher, ranging from 6.07 to 32.30 ng/g dw, with a mean concentration of 18.58 ng/g dw. In surface water, PFOA concentrations were lower, ranging from 4.75 to 5.36 ng/L, with a mean concentration of 5.16 ng/L. Similarly, PFOS concentrations in surface water varied from 9.27 to 13.68 ng/L, with a mean concentration of 11.48 ng/L. The soil analysis revealed that 67% of the sampled sites contained detectable levels of PFOA and PFOS within 2 to 5 years following the initial release. Statistical analysis using an independent t-test showed no significant variation in soil and surface water concentrations across the studied sites. The concentrations of PFOA and PFOS in the surface water far exceeded the USEPA health advisory levels. The HQ and HI analysis revealed significant health risks associated with the surface water contamination, indicating that immediate mitigation measures are necessary.
Lastly, this study explored the development of an efficient and cost-effective method for remediating PFOA contamination. A novel photocatalyst was synthesized by combining palm kernel shell activated carbon (PKSAC) with an iron-tin binary oxide (Fe2O3-SnO2). The photocatalyst's structure and properties were characterized using Scanning Electron Micrograph (SEM), Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA), Fourier Transform Infra-red spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and X-Ray Diffraction (XRD) techniques. The photocatalyst's efficacy in degrading PFOA under visible light irradiation was investigated. Optimization studies revealed that a 20 ppm PFOA concentration, 5.0 mg catalyst dosage, and pH 5 yielded the highest degradation efficiency. Under these conditions, PFOA degradation and defluorination rates reached 92.40% and 51.23%, respectively, after 6 hours. Conspicuously, five degradation intermediates with shorter carbon chain lengths were identified: Perfluoroheptanoic acid (PFHpA), Perfluorohexanoic acid (PFHxA), Perfluoropentanoic acid (PFPeA), Perfluorobutanoic acid (PFBA) and Perfluoropropionic acid (PFPrA). These findings demonstrate the potential of the PKSAC - Fe2O3-SnO2 nanocomposite as a highly efficient photocatalyst for PFOA remediation.
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PFAS contamination was detected in Ghana and South Africa, with concentrations at all sites except one exceeding the USEPA health advisory guidelines. Furthermore, the current levels pose significant health risks in surface water at four sites, two in Ghana and two in South Africa. Notably, this study identified a highly effective remediation solution: combining palm PKSAC with iron-tin binary oxide and visible light successfully degrades PFOA pollutants. This breakthrough presents a promising mitigation strategy for addressing PFAS contamination in the affected areas.