Willis Gwenzi - Academia.edu (original) (raw)

Papers by Willis Gwenzi

Research paper thumbnail of Closing Blank Spots and Illuminating Blind Spots in Research on Emerging Contaminants: The Source–Pathway–Receptor–Impact–Mitigation (SPRIM) Continuum as an Organizing Framework

Water

Emerging contaminants (ECs) include: (1) high-technology rare earth elements, (2) nanomaterials, ... more Emerging contaminants (ECs) include: (1) high-technology rare earth elements, (2) nanomaterials, (3) antibiotic/antimicrobial resistance, (4) microplastics, and (5) synthetic organic chemicals, which are currently unregulated. ECs continue to attract considerable research and public attention due to their potential human and ecological health risks. However, an organizing conceptual framework for framing research on ECs is currently missing. Lacking a conceptual framework, only a few aspects are frequently well-studied (i.e., bandwagon/Matthew effect), while other equally important topics receive only cursory attention. In this Editorial perspective, the Source–Pathway–Receptor–Impact–Mitigation (SPRIM) continuum is proposed as an organizing framework to guide research on ECs. First, a description of the SPRIM continuum and its components is presented. Compared to the prevailing and seemingly ad hoc approach predominant in research on emerging contaminants, the potential novelty of ...

Research paper thumbnail of Ten (10) key research questions on emerging contaminants and novel entities, and their health risks

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of (Micro)plastics in aquatic systems: Current research focal areas, under-studied matrices, and future directions

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of Emerging contaminants in the terrestrial-aquatic-atmosphere continuum: A global perspective

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of Occurrence, human exposure pathways, and health risks of (micro)plastics

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of Ecological health risks of high-technology rare earth elements

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of Defluoridation of drinking water using a ceramic filter decorated with iron oxide‐biochar composites

International Journal of Applied Ceramic Technology, 2021

Research paper thumbnail of Shear strength enhancement by Digitaria setivalva associated with NPK and bio green application on Bungor soil slope

Understanding the chemical constraints to plant growth and their amelioration is critical for ero... more Understanding the chemical constraints to plant growth and their amelioration is critical for erosion control and slope stability on artificial landforms. Limited studies have investigated the effects of chemical amendments on grass growth, and effects on soil physical and chemical characteristics on the slope surface. Digitaria setivalva (Mardi Digit grass) was used as a grass coverage to control erosion on the steep man made slope. The current slope studies (45o-50o) on Bungor soil series to address two objectives; (1) to investigate the effects nitrogen (N)-phosphate (P)-potassium fertilizer (NPK) and Bio Green fertilizer (BG) on above-ground and root growth, and (2) to determine physico-chemical properties and root shear strength after application of treatments. The Bungor series was acidic pH (4.63), moderate soil organic carbon (1.42%), total N (0.12%),available P (12.2 mg kg-1) and potassium (0.44 mg kg-1), indicating low inherent infertility and chemical constraints to plant...

Research paper thumbnail of Metallic Iron for Environmental Remediation: The Fallacy of the Electron Efficiency Concept

Frontiers in Environmental Chemistry, 2021

The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed d... more The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of ...

Research paper thumbnail of Wastewater, waste, and water-based epidemiology (WWW-BE): A novel hypothesis and decision-support tool to unravel COVID-19 in low-income settings?

Science of The Total Environment, 2021

A novel wastewater, waste, and waterbased epidemiology (WWW-BE) is postulated. • The rationale an... more A novel wastewater, waste, and waterbased epidemiology (WWW-BE) is postulated. • The rationale and principles of WWW-BE in low-income countries (LICs) are discussed. • WWW-BE may unravel the distribution, burden and transmission of COVID-19 in LICs. • WWW-BE is a novel decision-support tool for targeting resources and control methods. • Biosafety risks, lack of skills and analytical kits could limit the use of WWW-BE in LICs.

Research paper thumbnail of Recent advances in the polyurethane-based adsorbents for the decontamination of hazardous wastewater pollutants

Journal of Hazardous Materials, 2021

The pollution of aquatic systems with noxious organic and inorganic contaminants is a challenging... more The pollution of aquatic systems with noxious organic and inorganic contaminants is a challenging problem faced by most countries. Water bodies are contaminated with diverse inorganic and organic pollutants originating from various diffuse and point sources, including industrial sectors, agricultural practices, and domestic wastes. Such hazardous water pollutants tend to accumulate in the environmental media including living organisms, thereby posing significant environmental health risks. Therefore, the remediation of wastewater pollutants is a priority. Adsorption is considered as the most efficient technique for the removal of pollutants in aqueous systems, and the deployment of suitable adsorbents plays a vital role for the sustainable application of the technique. The present review gives an overview of polyurethane foam (PUF) as an adsorbent, the synthesis approaches of polyurethane, and characterization aspects. Further emphasis is on the preparation of the various forms of polyurethane adsorbents, and their potential application in the removal of various challenging water pollutants. The removal mechanisms, including adsorption kinetics, isotherms, thermodynamics, and electrostatic and hydrophobic interactions between polyurethane adsorbents and pollutants are discussed. In addition, regeneration, recycling and disposal of spent polyurethane adsorbents are reported. Finally, key knowledge gaps on synthesis, characterization, industrial applications, life cycle analysis, and potential health risks of polyurethane adsorbents are discussed.

Research paper thumbnail of The air-borne antibiotic resistome: Occurrence, health risks, and future directions

Science of The Total Environment, 2021

Antibiotic resistance comprising of antibiotic resistant bacteria (ARB) and antibiotic resistance... more Antibiotic resistance comprising of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is an emerging problem causing global human health risks. Several reviews exist on antibiotic resistance in various environmental compartments excluding the air-borne resistome. An increasing body of recent evidence exists on the air-borne resistome comprising of antibiotic resistance in air-borne bioaerosols from various environmental compartments. However, a comprehensive review on the sources, dissemination, behavior, fate, and human exposure and health risks of the air-borne resistome is still lacking. Therefore, the current review uses the source-pathway-receptor-impact-mitigation framework to investigate the air-borne resistome. The nature and sources of antibiotic resistance in the air-borne resistome are discussed. The dissemination pathways, and environmental and anthropogenic drivers accounting for the transfer of antibiotic resistance from sources to the receptors are highlighted. The human exposure and health risks posed by air-borne resistome are presented. A health risk assessment and mitigation strategy is discussed. Finally, future research directions including key knowledge gaps are summarized.

Research paper thumbnail of Rethinking restoration indicators and end-points for post-mining landscapes in light of novel ecosystems

Geoderma, 2021

Abstract Degraded post-mining landscapes exhibit unique biotic and abiotic components and process... more Abstract Degraded post-mining landscapes exhibit unique biotic and abiotic components and processes relative to pre-disturbance natural ecosystems. Yet the concept of pre-disturbance reference natural ecosystems and their associated soil quality indicators (SQIs) (e.g., pH, soil organic carbon) are prominently used for assessing restoration of post-mining landscapes. Limited reviews exist on the validity, limitations, opportunities and knowledge gaps associated with the application of the concept and SQIs on post-mining landscapes. Hence, evidence was examined to highlight constraints, opportunities and future research directions pertaining to the concept and SQIs. First, as novel, hybrid or designer ecosystems, severely degraded post-mining landscapes lack reference natural ecosystems. The framing of restoration is multi-dimensional, and dependent on spatial and temporal scales. Therefore, short-term data on SQIs often measured at point scale cannot adequately account for the multi-dimensionality and scales. Moreover, evidence linking SQIs to ecosystem functions, goods, values, services, and benefits on degraded post-mining landscapes remains weak. Potential redundancy exists among SQIs, because soil properties exhibit spatial and temporal correlation. The universality of SQIs remains unconfirmed, because data validating the measurement protocols and interpretation of SQIs across various biomes are scarce. A framework is presented proposing: (1) a shift from the concept of reference natural ecosystems to novel and designer ecosystems in restoration ecology, (2) the development of the next generation of hierarchical or ecosystem cascade indicators, and end-points addressing the multi-dimensionality and scale issues, and (3) a decision matrix for integrating novel, hybrid and designer ecosystems. The potential applications of novel tools such as drones, laser-based cameras, genomics, and big data analytics are highlighted. Such novel tools could unravel the complex linkages among biotic and abiotic components, and ecosystem function and services, which are currently difficult to investigate using conventional techniques. Finally, ten tentative hypotheses are presented on the restoration of degraded post-mining landscapes.

Research paper thumbnail of Leaving no stone unturned in light of the COVID-19 faecal-oral hypothesis? A water, sanitation and hygiene (WASH) perspective targeting low-income countries

Science of The Total Environment, 2021

Research paper thumbnail of Development, engineering properties and potential applications of unfired earth bricks reinforced by coal fly ash, lime and wood aggregates

Journal of Building Engineering, 2018

The current study developed and evaluated the engineering properties of improved lowcost UEBs rei... more The current study developed and evaluated the engineering properties of improved lowcost UEBs reinforced with various lime (L)-coal fly ash (F)-wood aggregate (W) mix ratios. The objectives were; (1) to determine the effects of lime-coal fly ash-wood aggregate mixtures on mechanical strength and water resistance properties of UEBs; and (2) to determine the comparative cost of the improved UEBs to that of the control (10% cement). Four UEBs with various lime (L)-coal fly ash (F)-wood aggregates (W) mix ratios (L4%-F16%-W1.5%; L4%-F16%-W3%; L8%-F12%-W3%; L10%-F10%-W1.5%) were fabricated and their engineering properties compared to those of unstabilised (negative control) and 10% cement stabilized Wood aggregates (W)

Research paper thumbnail of Occurrence, behaviour, and human exposure pathways and health risks of toxic geogenic contaminants in serpentinitic ultramafic geological environments (SUGEs): A medical geology perspective

Science of The Total Environment, 2019

h i g h l i g h t s Geogenic contaminants (GCs) in SUGEs include Fe, Cr, Ni, Mn, Zn, Co and chrys... more h i g h l i g h t s Geogenic contaminants (GCs) in SUGEs include Fe, Cr, Ni, Mn, Zn, Co and chrysotile. Human intake occurs via ingestion (foods, water), geophagy, and dust inhalation. Key risk factors predisposing African rural populations to GCs are highlighted. Health risks occur via toxicity of single GCs, and their synergistic interactions. A human risk assessment framework and future research directions are highlighted.

Research paper thumbnail of Antibiotic resistance and class 1 integron gene dynamics along effluent, reclaimed wastewater irrigated soil, crop continua: elucidating potential risks and ecological constraints

Water Research, 2019

Reuse of municipal wastewater is a growing global trend, but currently there is lack of consensus... more Reuse of municipal wastewater is a growing global trend, but currently there is lack of consensus regarding the potential dissemination of antibiotic resistance elements by treated wastewater irrigation. We tracked intI1, a proxy for anthropogenic pollution, and an assemblage of antibiotic resistance genes associated with mobile elements and/or wastewater (bla GES , bla OXA2 , bla OXA10 , bla TEM , bla CTX-M-32 and qnrS) in treated wastewater effluents, effluent stabilization reservoirs, and along irrigation watersoil-crop continua in experimental lysimeters and large-scale commercial fields. While several of the targeted antibiotic resistance genes were profuse in effluents, there was almost no correlation between gene abundance in irrigation water and those detected in soil, and no evidence of systematic gene transfer to irrigated soil or crops. In contrast, soil intI1 abundance correlated strongly to irrigation water levels in lysimeters and sandy field soils, but this was not the case for clay-rich soils or for most of the analyzed crops, suggesting that intI1 may not always be a reliable marker for tracking the impact of treated wastewater irrigation. We hypothesize that "ecological boundaries" expedited by biotic and abiotic factors

Research paper thumbnail of Recurrent Cholera Outbreaks in Sub-Saharan Africa: Moving beyond Epidemiology to Understand the Environmental Reservoirs and Drivers

Challenges, 2019

Recurrent cholera outbreaks in sub-Saharan Africa (SSA) attracted a lot of research interest, rai... more Recurrent cholera outbreaks in sub-Saharan Africa (SSA) attracted a lot of research interest, raising questions about the effectiveness of current prevention and control methods. However, research on cholera and other water-borne diseases in Africa is dominated by epidemiological studies, while investigations on the environmental drivers and reservoirs of cholera remain scarce. The current discourse relating cholera to the environment in SSA is often limited to the rudimentary statement that, “cholera is caused by the consumption of contaminated water and food”. Yet, beyond this simplistic view, literature elsewhere shows that cholera outbreaks are controlled by its complex interactions with environmental drivers and reservoirs. This brings to question whether cholera can be eradicated in SSA without understanding these complex interactions. The current review seeks to (1) highlight the nature and dynamics of recent cholera outbreaks in SSA, (2) discuss the importance of environment...

Research paper thumbnail of Evaluation of the phytotoxicity of coal ash on lettuce (Lactuca sativa L.) germination, growth and metal uptake

Ecotoxicology and Environmental Safety, 2019

Land application of coal ash is considered an environmentally friendly option to improve soil qua... more Land application of coal ash is considered an environmentally friendly option to improve soil quality, but limited information exists on metal bioavailability and phytotoxicity of coal ash to sensitive plant species such as lettuce (Lactuca sativa L.). Germination and pot bioassay experiments were conducted at six coal application rates (0% (control), 5%, 15%, 25%, 50% and 75% v/v) to investigate the hypothesis that, coal ash will have a hormetic effect on germination, growth, metal uptake and biomass yield of lettuce, characterized by stimulatory and phytotoxicity effects at low and high application rates, respectively. Total concentrations (mg/kg) of metals in coal ash spanned several orders of magnitude, and decreased in the order: Fe (5150.5), Mn (326.0), Zn (102.6), Cu (94.7), Ni (74.7) and Pb (11.6). Bioavailable concentrations of metals were very low (0.0-14.1 mg/kg), accounting for less than 2% of the total concentrations. Coal ash had no significant effect on germination indices, but had hormetic effects on radicle elongation, evidenced by stimulatory and phytotoxicity effects at low (5-25%) and high (50-75%) application rates, respectively. Coal ash application at 50% and 75% significantly (p < 0.05) reduced lettuce growth and edible biomass yield, but lower application rates (5-25%) were similar to the unamended soil (control). Fe, Mn, Zn, Cu and Ni bioavailability and plant uptake generally decreased with increasing coal ash application rates particularly at 50% and 75%. Soil pH significantly increased (p < 0.05) from 6.5 for the control to about 8 for 75% coal ash, while electrical conductivity (EC) increased by 2-7 times to about 0.9 and 1.5 dS/m at 50% and 75% coal ash, respectively. Significant inverse linear relationship (p < 0.05; r 2 = 0.80) were observed between edible and total biomass yields and EC, suggesting that increased salinity at high coal ash application rates could account for reduced growth and biomass. Partial elemental balances showed that plant uptake of metals was very low, accounting for just less than 2% of the bioavailable concentrations, while the bulk of the metals (98-99%) remained in the soil. In conclusion, the current findings show that coal ash may have hormetic and phytotoxic effects on sensitive plant species, an observation contrary to the bulk of earlier literature documenting beneficial effects of coal ash application to soils. Long-term field studies are required to confirm the current findings based on laboratory and pot bioassay experiments.

Research paper thumbnail of Synthesis and nutrient release patterns of a biochar-based N–P–K slow-release fertilizer

International Journal of Environmental Science and Technology, 2017

Biochar has excellent solute adsorption capacity, yet few studies have investigated its applicati... more Biochar has excellent solute adsorption capacity, yet few studies have investigated its application as a nutrient carrier in the development of slow-release fertilizers. The current study developed a biochar-based N-P-K fertilizer (BSRF) and evaluated its nutrient release patterns relative to a conventional fertilizer. SEM and EDX analyses confirmed the coarse and highly porous microstructure of the biochar (SBC) that enabled it to effectively sorb NO 3-, PO 4 3-, and K ? and form a nutrient-impregnated BSRF. BSRF had lower NO 3-, PO 4 3-, and K ? release than the conventional chemical fertilizer, demonstrating its low release behavior. BSRF-amended sandy soil had higher water retention capacity than that amended with a conventional chemical fertilizer. BSRF has potential to reduce nutrient leaching, improve water retention, and hence increase crop nutrient and water use efficiencies. Future research should focus on understanding nutrient release mechanisms, synchronization of nutrient release with plant uptake, and applications of the BSRF in environmental remediation.

Research paper thumbnail of Closing Blank Spots and Illuminating Blind Spots in Research on Emerging Contaminants: The Source–Pathway–Receptor–Impact–Mitigation (SPRIM) Continuum as an Organizing Framework

Water

Emerging contaminants (ECs) include: (1) high-technology rare earth elements, (2) nanomaterials, ... more Emerging contaminants (ECs) include: (1) high-technology rare earth elements, (2) nanomaterials, (3) antibiotic/antimicrobial resistance, (4) microplastics, and (5) synthetic organic chemicals, which are currently unregulated. ECs continue to attract considerable research and public attention due to their potential human and ecological health risks. However, an organizing conceptual framework for framing research on ECs is currently missing. Lacking a conceptual framework, only a few aspects are frequently well-studied (i.e., bandwagon/Matthew effect), while other equally important topics receive only cursory attention. In this Editorial perspective, the Source–Pathway–Receptor–Impact–Mitigation (SPRIM) continuum is proposed as an organizing framework to guide research on ECs. First, a description of the SPRIM continuum and its components is presented. Compared to the prevailing and seemingly ad hoc approach predominant in research on emerging contaminants, the potential novelty of ...

Research paper thumbnail of Ten (10) key research questions on emerging contaminants and novel entities, and their health risks

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of (Micro)plastics in aquatic systems: Current research focal areas, under-studied matrices, and future directions

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of Emerging contaminants in the terrestrial-aquatic-atmosphere continuum: A global perspective

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of Occurrence, human exposure pathways, and health risks of (micro)plastics

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of Ecological health risks of high-technology rare earth elements

Emerging Contaminants in the Terrestrial-Aquatic-Atmosphere Continuum:

Research paper thumbnail of Defluoridation of drinking water using a ceramic filter decorated with iron oxide‐biochar composites

International Journal of Applied Ceramic Technology, 2021

Research paper thumbnail of Shear strength enhancement by Digitaria setivalva associated with NPK and bio green application on Bungor soil slope

Understanding the chemical constraints to plant growth and their amelioration is critical for ero... more Understanding the chemical constraints to plant growth and their amelioration is critical for erosion control and slope stability on artificial landforms. Limited studies have investigated the effects of chemical amendments on grass growth, and effects on soil physical and chemical characteristics on the slope surface. Digitaria setivalva (Mardi Digit grass) was used as a grass coverage to control erosion on the steep man made slope. The current slope studies (45o-50o) on Bungor soil series to address two objectives; (1) to investigate the effects nitrogen (N)-phosphate (P)-potassium fertilizer (NPK) and Bio Green fertilizer (BG) on above-ground and root growth, and (2) to determine physico-chemical properties and root shear strength after application of treatments. The Bungor series was acidic pH (4.63), moderate soil organic carbon (1.42%), total N (0.12%),available P (12.2 mg kg-1) and potassium (0.44 mg kg-1), indicating low inherent infertility and chemical constraints to plant...

Research paper thumbnail of Metallic Iron for Environmental Remediation: The Fallacy of the Electron Efficiency Concept

Frontiers in Environmental Chemistry, 2021

The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed d... more The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of ...

Research paper thumbnail of Wastewater, waste, and water-based epidemiology (WWW-BE): A novel hypothesis and decision-support tool to unravel COVID-19 in low-income settings?

Science of The Total Environment, 2021

A novel wastewater, waste, and waterbased epidemiology (WWW-BE) is postulated. • The rationale an... more A novel wastewater, waste, and waterbased epidemiology (WWW-BE) is postulated. • The rationale and principles of WWW-BE in low-income countries (LICs) are discussed. • WWW-BE may unravel the distribution, burden and transmission of COVID-19 in LICs. • WWW-BE is a novel decision-support tool for targeting resources and control methods. • Biosafety risks, lack of skills and analytical kits could limit the use of WWW-BE in LICs.

Research paper thumbnail of Recent advances in the polyurethane-based adsorbents for the decontamination of hazardous wastewater pollutants

Journal of Hazardous Materials, 2021

The pollution of aquatic systems with noxious organic and inorganic contaminants is a challenging... more The pollution of aquatic systems with noxious organic and inorganic contaminants is a challenging problem faced by most countries. Water bodies are contaminated with diverse inorganic and organic pollutants originating from various diffuse and point sources, including industrial sectors, agricultural practices, and domestic wastes. Such hazardous water pollutants tend to accumulate in the environmental media including living organisms, thereby posing significant environmental health risks. Therefore, the remediation of wastewater pollutants is a priority. Adsorption is considered as the most efficient technique for the removal of pollutants in aqueous systems, and the deployment of suitable adsorbents plays a vital role for the sustainable application of the technique. The present review gives an overview of polyurethane foam (PUF) as an adsorbent, the synthesis approaches of polyurethane, and characterization aspects. Further emphasis is on the preparation of the various forms of polyurethane adsorbents, and their potential application in the removal of various challenging water pollutants. The removal mechanisms, including adsorption kinetics, isotherms, thermodynamics, and electrostatic and hydrophobic interactions between polyurethane adsorbents and pollutants are discussed. In addition, regeneration, recycling and disposal of spent polyurethane adsorbents are reported. Finally, key knowledge gaps on synthesis, characterization, industrial applications, life cycle analysis, and potential health risks of polyurethane adsorbents are discussed.

Research paper thumbnail of The air-borne antibiotic resistome: Occurrence, health risks, and future directions

Science of The Total Environment, 2021

Antibiotic resistance comprising of antibiotic resistant bacteria (ARB) and antibiotic resistance... more Antibiotic resistance comprising of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is an emerging problem causing global human health risks. Several reviews exist on antibiotic resistance in various environmental compartments excluding the air-borne resistome. An increasing body of recent evidence exists on the air-borne resistome comprising of antibiotic resistance in air-borne bioaerosols from various environmental compartments. However, a comprehensive review on the sources, dissemination, behavior, fate, and human exposure and health risks of the air-borne resistome is still lacking. Therefore, the current review uses the source-pathway-receptor-impact-mitigation framework to investigate the air-borne resistome. The nature and sources of antibiotic resistance in the air-borne resistome are discussed. The dissemination pathways, and environmental and anthropogenic drivers accounting for the transfer of antibiotic resistance from sources to the receptors are highlighted. The human exposure and health risks posed by air-borne resistome are presented. A health risk assessment and mitigation strategy is discussed. Finally, future research directions including key knowledge gaps are summarized.

Research paper thumbnail of Rethinking restoration indicators and end-points for post-mining landscapes in light of novel ecosystems

Geoderma, 2021

Abstract Degraded post-mining landscapes exhibit unique biotic and abiotic components and process... more Abstract Degraded post-mining landscapes exhibit unique biotic and abiotic components and processes relative to pre-disturbance natural ecosystems. Yet the concept of pre-disturbance reference natural ecosystems and their associated soil quality indicators (SQIs) (e.g., pH, soil organic carbon) are prominently used for assessing restoration of post-mining landscapes. Limited reviews exist on the validity, limitations, opportunities and knowledge gaps associated with the application of the concept and SQIs on post-mining landscapes. Hence, evidence was examined to highlight constraints, opportunities and future research directions pertaining to the concept and SQIs. First, as novel, hybrid or designer ecosystems, severely degraded post-mining landscapes lack reference natural ecosystems. The framing of restoration is multi-dimensional, and dependent on spatial and temporal scales. Therefore, short-term data on SQIs often measured at point scale cannot adequately account for the multi-dimensionality and scales. Moreover, evidence linking SQIs to ecosystem functions, goods, values, services, and benefits on degraded post-mining landscapes remains weak. Potential redundancy exists among SQIs, because soil properties exhibit spatial and temporal correlation. The universality of SQIs remains unconfirmed, because data validating the measurement protocols and interpretation of SQIs across various biomes are scarce. A framework is presented proposing: (1) a shift from the concept of reference natural ecosystems to novel and designer ecosystems in restoration ecology, (2) the development of the next generation of hierarchical or ecosystem cascade indicators, and end-points addressing the multi-dimensionality and scale issues, and (3) a decision matrix for integrating novel, hybrid and designer ecosystems. The potential applications of novel tools such as drones, laser-based cameras, genomics, and big data analytics are highlighted. Such novel tools could unravel the complex linkages among biotic and abiotic components, and ecosystem function and services, which are currently difficult to investigate using conventional techniques. Finally, ten tentative hypotheses are presented on the restoration of degraded post-mining landscapes.

Research paper thumbnail of Leaving no stone unturned in light of the COVID-19 faecal-oral hypothesis? A water, sanitation and hygiene (WASH) perspective targeting low-income countries

Science of The Total Environment, 2021

Research paper thumbnail of Development, engineering properties and potential applications of unfired earth bricks reinforced by coal fly ash, lime and wood aggregates

Journal of Building Engineering, 2018

The current study developed and evaluated the engineering properties of improved lowcost UEBs rei... more The current study developed and evaluated the engineering properties of improved lowcost UEBs reinforced with various lime (L)-coal fly ash (F)-wood aggregate (W) mix ratios. The objectives were; (1) to determine the effects of lime-coal fly ash-wood aggregate mixtures on mechanical strength and water resistance properties of UEBs; and (2) to determine the comparative cost of the improved UEBs to that of the control (10% cement). Four UEBs with various lime (L)-coal fly ash (F)-wood aggregates (W) mix ratios (L4%-F16%-W1.5%; L4%-F16%-W3%; L8%-F12%-W3%; L10%-F10%-W1.5%) were fabricated and their engineering properties compared to those of unstabilised (negative control) and 10% cement stabilized Wood aggregates (W)

Research paper thumbnail of Occurrence, behaviour, and human exposure pathways and health risks of toxic geogenic contaminants in serpentinitic ultramafic geological environments (SUGEs): A medical geology perspective

Science of The Total Environment, 2019

h i g h l i g h t s Geogenic contaminants (GCs) in SUGEs include Fe, Cr, Ni, Mn, Zn, Co and chrys... more h i g h l i g h t s Geogenic contaminants (GCs) in SUGEs include Fe, Cr, Ni, Mn, Zn, Co and chrysotile. Human intake occurs via ingestion (foods, water), geophagy, and dust inhalation. Key risk factors predisposing African rural populations to GCs are highlighted. Health risks occur via toxicity of single GCs, and their synergistic interactions. A human risk assessment framework and future research directions are highlighted.

Research paper thumbnail of Antibiotic resistance and class 1 integron gene dynamics along effluent, reclaimed wastewater irrigated soil, crop continua: elucidating potential risks and ecological constraints

Water Research, 2019

Reuse of municipal wastewater is a growing global trend, but currently there is lack of consensus... more Reuse of municipal wastewater is a growing global trend, but currently there is lack of consensus regarding the potential dissemination of antibiotic resistance elements by treated wastewater irrigation. We tracked intI1, a proxy for anthropogenic pollution, and an assemblage of antibiotic resistance genes associated with mobile elements and/or wastewater (bla GES , bla OXA2 , bla OXA10 , bla TEM , bla CTX-M-32 and qnrS) in treated wastewater effluents, effluent stabilization reservoirs, and along irrigation watersoil-crop continua in experimental lysimeters and large-scale commercial fields. While several of the targeted antibiotic resistance genes were profuse in effluents, there was almost no correlation between gene abundance in irrigation water and those detected in soil, and no evidence of systematic gene transfer to irrigated soil or crops. In contrast, soil intI1 abundance correlated strongly to irrigation water levels in lysimeters and sandy field soils, but this was not the case for clay-rich soils or for most of the analyzed crops, suggesting that intI1 may not always be a reliable marker for tracking the impact of treated wastewater irrigation. We hypothesize that "ecological boundaries" expedited by biotic and abiotic factors

Research paper thumbnail of Recurrent Cholera Outbreaks in Sub-Saharan Africa: Moving beyond Epidemiology to Understand the Environmental Reservoirs and Drivers

Challenges, 2019

Recurrent cholera outbreaks in sub-Saharan Africa (SSA) attracted a lot of research interest, rai... more Recurrent cholera outbreaks in sub-Saharan Africa (SSA) attracted a lot of research interest, raising questions about the effectiveness of current prevention and control methods. However, research on cholera and other water-borne diseases in Africa is dominated by epidemiological studies, while investigations on the environmental drivers and reservoirs of cholera remain scarce. The current discourse relating cholera to the environment in SSA is often limited to the rudimentary statement that, “cholera is caused by the consumption of contaminated water and food”. Yet, beyond this simplistic view, literature elsewhere shows that cholera outbreaks are controlled by its complex interactions with environmental drivers and reservoirs. This brings to question whether cholera can be eradicated in SSA without understanding these complex interactions. The current review seeks to (1) highlight the nature and dynamics of recent cholera outbreaks in SSA, (2) discuss the importance of environment...

Research paper thumbnail of Evaluation of the phytotoxicity of coal ash on lettuce (Lactuca sativa L.) germination, growth and metal uptake

Ecotoxicology and Environmental Safety, 2019

Land application of coal ash is considered an environmentally friendly option to improve soil qua... more Land application of coal ash is considered an environmentally friendly option to improve soil quality, but limited information exists on metal bioavailability and phytotoxicity of coal ash to sensitive plant species such as lettuce (Lactuca sativa L.). Germination and pot bioassay experiments were conducted at six coal application rates (0% (control), 5%, 15%, 25%, 50% and 75% v/v) to investigate the hypothesis that, coal ash will have a hormetic effect on germination, growth, metal uptake and biomass yield of lettuce, characterized by stimulatory and phytotoxicity effects at low and high application rates, respectively. Total concentrations (mg/kg) of metals in coal ash spanned several orders of magnitude, and decreased in the order: Fe (5150.5), Mn (326.0), Zn (102.6), Cu (94.7), Ni (74.7) and Pb (11.6). Bioavailable concentrations of metals were very low (0.0-14.1 mg/kg), accounting for less than 2% of the total concentrations. Coal ash had no significant effect on germination indices, but had hormetic effects on radicle elongation, evidenced by stimulatory and phytotoxicity effects at low (5-25%) and high (50-75%) application rates, respectively. Coal ash application at 50% and 75% significantly (p < 0.05) reduced lettuce growth and edible biomass yield, but lower application rates (5-25%) were similar to the unamended soil (control). Fe, Mn, Zn, Cu and Ni bioavailability and plant uptake generally decreased with increasing coal ash application rates particularly at 50% and 75%. Soil pH significantly increased (p < 0.05) from 6.5 for the control to about 8 for 75% coal ash, while electrical conductivity (EC) increased by 2-7 times to about 0.9 and 1.5 dS/m at 50% and 75% coal ash, respectively. Significant inverse linear relationship (p < 0.05; r 2 = 0.80) were observed between edible and total biomass yields and EC, suggesting that increased salinity at high coal ash application rates could account for reduced growth and biomass. Partial elemental balances showed that plant uptake of metals was very low, accounting for just less than 2% of the bioavailable concentrations, while the bulk of the metals (98-99%) remained in the soil. In conclusion, the current findings show that coal ash may have hormetic and phytotoxic effects on sensitive plant species, an observation contrary to the bulk of earlier literature documenting beneficial effects of coal ash application to soils. Long-term field studies are required to confirm the current findings based on laboratory and pot bioassay experiments.

Research paper thumbnail of Synthesis and nutrient release patterns of a biochar-based N–P–K slow-release fertilizer

International Journal of Environmental Science and Technology, 2017

Biochar has excellent solute adsorption capacity, yet few studies have investigated its applicati... more Biochar has excellent solute adsorption capacity, yet few studies have investigated its application as a nutrient carrier in the development of slow-release fertilizers. The current study developed a biochar-based N-P-K fertilizer (BSRF) and evaluated its nutrient release patterns relative to a conventional fertilizer. SEM and EDX analyses confirmed the coarse and highly porous microstructure of the biochar (SBC) that enabled it to effectively sorb NO 3-, PO 4 3-, and K ? and form a nutrient-impregnated BSRF. BSRF had lower NO 3-, PO 4 3-, and K ? release than the conventional chemical fertilizer, demonstrating its low release behavior. BSRF-amended sandy soil had higher water retention capacity than that amended with a conventional chemical fertilizer. BSRF has potential to reduce nutrient leaching, improve water retention, and hence increase crop nutrient and water use efficiencies. Future research should focus on understanding nutrient release mechanisms, synchronization of nutrient release with plant uptake, and applications of the BSRF in environmental remediation.