A Review on Contaminants of Emerging Concern in the Environment: A Focus on Active Chemicals in Sub-Saharan Africa

Active chemicals are among the contaminants of emerging concern that are rarely covered in regulatory documents in sub-Saharan Africa. These substances are neither in the list of routinely monitored substances nor in the guidelines for routine environmental monitoring activities. This has been of concern to public health officials, toxicologists, communities, and governments, hence the need for risk assessment and regulation of these substances. In this review article, the presence of active chemicals in the sub-Saharan African environment was investigated. The results indicate the availability of few studies in some countries, while in other countries no reports of active chemicals were found, hence the need for further research targeting such countries. It was further observed that mixtures of active chemicals from different therapeutic categories—such as antibiotics and analgesics—were reported. The natural environment is increasingly at risk due to the presence of these substances, their metabolites, and their transformation byproducts. These substances are characterized by persistence as a result of their non-biodegradable nature; hence, they circulate from one environmental compartment to another through the food chain, causing harm along the way. Most studies that evaluated the toxicity of these substances considered the effects of a single drug, but observations indicated the presence of drug mixtures, hence the need for further evaluation of the effects of drug–drug interactions—including synergistic and additive effects—for environmental sustainability. The presence of ACs in several environmental compartments at quantifiable quantities was discovered in this investigation, indicating the potential for ecosystem injury as a result of bioaccumulation, bioconcentration, and biomagnification through the food chain. This necessitates further research on the subject in order to ensure a healthier environment.

Perfluoroalkyl Substances (PFASs) in the Canadian Freshwater Environment.

Per- and polyfluoroalkyl substances (PFASs) are anthropogenic substances that are very stable in the receiving environment. PFASs are persistent and resistant to typical environmental degradation processes and therefore are distributed across all trophic levels and environmental compartments (soil, air, water). Since most uses of PFOS, PFOA and LC-PFCAs are banned in Canada, alternative PFASs have been in use for a number of years. Twenty-nine sites across Canada were sampled for PFASs to determine concentrations and trends. Overall, 13 PFASs were measured in 566 Canadian freshwater samples from 2013- 2020 with a range from below the detection limit of the laboratory to a maximum of 138 ng/L (for PFBS). While PFOS and PFOA concentrations are declining significantly over time, other compounds such as PFPeA and PFBA have increased significantly over 2013-2020. Overall the range of concentrations found in this study were similar to that of other Canadian and international studies. However, this study also found a higher frequency of detections of the replacement PFASs than that of the other, older, Canadian studies.

Polyester Microplastic Fibers affect Soil Physical Properties and Erosion as a Function of Soil Type

Microplastic is recognized as a factor of global change affecting many environmental compartments. Agricultural soils are likely hotspots of microplastic contamination in terrestrial ecosystems and are of particular concern due to their role in food production. Microplastic has already been shown to be able to affect soil properties, but its effect on different soil types is poorly understood. Moreover, no information is available on how the presence of this pollutant can affect soil water erosion processes, which are extremely important issues in many environments. In the light of this, we performed two experiments (a microcosm and a mesocosm study) to investigate how the presence of polyester microplastic fibers affects soil physical and hydrological parameters and processes such as aggregate formation and soil erosion in three different agricultural soil types. Our data show that the effects of polyester microplastic on soil physical parameters (including soil aggregation and erosion) are strongly dependent on soil type. We found that microplastic contamination can decrease the formation of new aggregates but at the same time increase their stability in water, with effects on soil erosion stronger as the intrinsic erodibility of soil increases. Overall, our results highlight the importance of broadly exploring soil properties such as texture, mineralogy, and organic carbon content to better understand how the various soil types respond to microplastic contamination.

Relationships between the Gut Microbiota of Juvenile Black Sea Bream (Acanthopagrus schlegelii) and Associated Environment Compartments in Different Habitats

The fish-gut microbiota play a key role in the physiology, development, and fitness of its host. An understanding of fish-gut microbial communities and the factors influencing community composition is crucial for improving fish performance. In this study, we compared the gut microbiota of juvenile black sea bream Acanthopagrus schlegelii among habitats: (1) wild, (2) offshore cage-culture, and (3) pond-culture. We also explored the relationships between the gut microbiota and host-associated environmental factors. Gut samples and associated environmental compartments were investigated using 16S rRNA gene sequencing. Our results revealed significant habitat-specific differences among the gut microbiota of juvenile A. schlegelii. Wild populations of juvenile A. schlegelii had more diverse gut microbiota than populations cultured in pond habitats due to their omnivorous feeding habits and the corresponding abundance of natural food resources. Significant variations in the composition, core taxa, and diversity of the microbiota were also found between the gut and the environmental compartments. However, no significant differences were observed among the microbiota of the environmental compartments in the relatively isolated pond habitat. Source tracking analysis recovered connections between the fish-gut microbiota and the diet, water and sediment environmental compartments. This connection was especially strong between the microbiota of the fish gut and that of the diet in the pond habitat: the diet microbiota accounted for 33.48 ± 0.21% of the gut microbiota. Results suggested that all A. schlegelii shared a core gut microbiota, regardless of differences in diet and habitat. However, environmental factors associated with both diet and habitat contributed to the significant differences between the gut microbiota of fish living in different habitats. To the authors’ knowledge, this study presents the first comparison of gut microbiota among juvenile A. schlegelii with different diets and habitats. These findings enrich our understanding of the gut microbiota of A. schlegelii and help to clarify the interaction between gut microbiota and environmental factors. Our results may also help to guide and improve fish ecological fitness via the regulation of gut microbiota, thereby increasing the efficacy of stock enhancement programs for this species.

A Study on the Effect of Soil and Sediment Types on the Fugacity Based Multimedia Partitioning of a Contact Fungicide Fluopyram: An Equilibrium Quality Criterion (EQC) Level 1 Approach

Equilibrium Quality Criterion (EQC) Level I calculations have been performed with Standard Equilibrium Quality Criterion (EQC) environment to study the environmental partitioning of a fungicide Fluopyram. Equilibrium Quality Criterion (EQC) Level I calculation assumes no degradation of the chemical, steady-state, and equilibrium conditions between the environmental compartments. The results reveal that the concentration of Fluopyram is expected to be maximum in the sediment compartment, followed by soil and water compartments. The effect of soil and sediment types on partitioning has been studied by systematically varying the densities of these two compartments. In the sediment compartment, the Fluopyram concentration is predicted to be highest if the sediment type is ‘sandy’ and the soil type is ‘clay’.

Microplastic Pollution in The Topsoil of Hot And Dried Areas, Human Exposure and Source Assessment, Aghili Plain, Iran

Although the distribution of microplastic (MPs) has been studied in different environmental compartments during the last decade, there is still a knowledge gap in their distribution and abundances in soil. This study aimed to investigate the abundance, distribution, and type of MPs in the soil of Aghili plain as a hot and dry area in southwest of Iran. In this study, composite soil samples (n=102) were collected from the residential and agricultural areas in Aghili plain, Iran. A combination of visual observations, Scanning Electron Microscopy (SEM) – Energy-dispersive X-ray spectroscopy (EDS), and Raman micro -spectroscopy was conducted to quantify and characterize MPs in soil samples. The intakes of MPs in adults and children were estimated through two exposure EPA scenarios. The total MPs loading in the studies soil was 11.93 ± 0.9 items in Kg-1 of surface soil in Aghili plain. The MPs had various morphology (fiber, pellet, fragment, and spherule shapes), colors (white-transparent, yellow-orange, red-pink, blue-green and black-grey colors), and sizes (<100 µm up to 1000 ≤ µm). Black-grey fibers in size less than 100 μm were dominant MPs in soil samples using a binocular microscope. Trace amounts of C, N, O, Na, P, Si revealed by EDS suggested the organic and inorganic contaminations on the surface of identified MPs. Intake of MPs per day/year through ingestion of polluted soil was calculated. Mean normal and acute exposure was estimated at 0.435 and 0.871 MPs per year through ingestion by children and adults, respectively.

Adsorption of Polycyclic Aromatic Hydrocarbons by Natural, Synthetic and Modified Clays

Polycyclic aromatic hydrocarbons (PAHs) are of major scientific concern owing to their widespread presence in environmental compartments and their potential toxicological effects on humans and biota. In this study, the adsorption capacity of natural (montmorillonite (Mt)), synthetic (Na-Mica-4), and modified (with octadecylamine and octadecyltrimethylamine (ODA-Mt, ODA-Mica-4, and ODTMA-Mt and ODTMA-Mica-4)) clays were assessed and compared for the removal of 16 PAHs. Materials were synthesized and characterized by X-Ray diffraction, Zeta potential, and Fourier-transform infrared spectroscopy. The results showed its correct preparation and the incorporation of PAHs in the structure of the clays after the adsorption tests. The proposed materials were effective PAH adsorbents, with adsorption percentages close to 100%, in particular those using Mt. Mt and Na-Mica-4 presented a better adsorption capacity than their organofunctionalized derivatives, indicating that the adsorption of PAHs may occur both in the surface part and in the interlayer. The proposed adsorbents take the advantage of being a low cost and highly effective. They can be an interesting alternative for wastewater treatment and soil remediation to prevent PAH contamination.

Immobilization of mercury in contaminated soils through the use of new carbon foam amendments

Background Mercury (Hg) is recognized as one of the 10 most toxic elements in nature and is much more persistent in soils than in other environmental compartments. However, an effective, environmentally friendly, economical, and large-scale applicable technology for the remediation of soils contaminated by Hg has not yet been established. This study evaluates the feasibility of a new carbon foam-based product for the remediation of three soils contaminated with Hg, and infers the mobilization or immobilization mechanism through a detailed study of Hg speciation. Results Soil treatment with carbon foams, one of them impregnated with goethite, reduced Hg availability by 75–100%. The proportion of mercury associated to humic acids (Hg–HA) determined the mobility and the availability of Hg when soils were treated with carbon foams. The drop of pH promotes changes in the structure of HA, a consequence of which is that Hg–HA becomes part of the unavailable fraction of the soil along with HgS. The carbon foam impregnated with goethite did not mobilize Fe as occurred with zero valence iron nanoparticles. The presence of acidic groups on the surface of the foam (carboxyl, quinone and phenolic groups) can strongly improve the binding of metal cations, enhancing Fe immobilization. Conclusions A novel carbon foam-based amendment was efficient in immobilizing Hg in all the soils studied. The carbon foam impregnated with goethite, in addition to not mobilizing Fe, had the additional advantage of its low effect on the electrical conductivity of the soil. This novel approach could be considered as a potential amendment for other industrial and/or abandoned mining areas contaminated with Hg and/or other metal(loid)s.