1,720,980 research outputs found
Ecological risk modelling of antiretroviral drugs in the aquatic environment
Get PDFDissertation (MSc (Applied Science) Water Utilisation)--University of Pretoria, 2022.The success of antiretroviral therapy (ART) programme's on the management of the Human Immunodeficiency Virus/ Acquired Immunodeficiency Syndrome (HIV/AIDS) in the Sub-Saharan African (SSA) region has inadvertently led to the release of antiretroviral drugs (ARVs) into the environment. This study aimed to model the quantities and risks of ARVs in aquatic environments. Herein, the ecological risks of first regime (efavirenz (EFV), lamivudine (3TC), nevirapine (NVP), zidovudine (AZT) and tenofovir (TDF)), and second regime ARVs (lopinavir (LPV), atazanavir (ATV), ritonavir (RTV), didanosine (DDI) and dolutegravir (DTG)) were investigated. ARV releases and quantification into the aquatic environment were based on Eswatini as a study case country using the material flow analysis (MFA) approach. Quantities of ARVs into the environment were estimated for all ten drugs using the input model parameters, viz.: (number of people living with HIV (PLWHIV), number of people on ARVs, drug dosages, treatment adherence and drug excretion rate). The predicted environmental concentrations (PEC) were then compared to the predicted no effect concentrations (PNEC) to estimate the possible risk (by deriving the risk quotient (RQ). Owing to the dearth of ecotoxicological data for ARVs, Ecological Structure Activity Relationships (ECOSAR) was used to derive the toxicity of each drug for three species: daphnia, algae, and fish. Results indicated quantities of ARVs were three-fold higher in surface water relative to wastewater. For example, in 2017, EFV was 5 671 and 1 853 kg in surface water and wastewater, respectively. Higher flows of ARVs in surface waters were associated with a lack of sanitation services for most Eswatini population, and low wastewater treatment plant (WWTP) performance. Results further showed wide variability of PECs in surface water (0.08–73.2 μg/L) and wastewater (0.02 – 23.1 μg/L). Of the ten ARVs, the risk of DTG was unquantifiable due to a lack of ecotoxicity data even when using the ECOSAR approach. Only DDI had RQs 10) to all three taxa. Further, NVP and AZT presented moderate risk (1 < RQ < 10) to algae, and 3TC and TDF posed minimal risk (RQ < 1) to daphnia. No risk for the ARVs was estimated in wastewater except for TDF due to the lack of their bacterial toxicity data. Results herein make it possible for the first time to quantify the potential environmental risks of ARVs using a modelling approach. The model can be extended to other SSA countries given their limited capabilities to detect and quantify ARVs risks in the environment using costly analytical techniques. Furthermore, the results suggest lack of sanitation services and high HIV/AIDs prevalence in SSA with concomitant high concentrations of ARVs in the environment potentially may trigger antiretroviral drug resistance, with possible negative implications to the ART programme.Chemical EngineeringMSc (Applied Science) Water UtilisationUnrestricte
Mixture effects of metallic nanoparticles, and organic contaminant on Daphnia magna in aqueous media.
Get PDFDissertation (MSc (Chemical Engineering))- -University of Pretoria, 2022.Engineered nanoparticles (ENPs) including silver (n-Ag) and zinc oxide (n-ZnO) are among rapidly increasing contaminants of emerging concern (CECs) globally. Moreover, pesticides (e.g. atrazine (ATZ)) owing to their extensive application are present in variant ecological systems like ground and surface waters, with unintended threats to aquatic life forms. Further, increasing presence of different classes of CECs and persistent organic pollutants (POPs) has led to their co-existence as mixtures in the environmental systems; but with unknown toxicological outcomes to organisms at different biological levels of organization. Herein, freshwater crustacean Daphnia magna was used as a model organism to assess the biological effects of individual ENPs, their binary mixtures with or without ATZ, and ternary mixtures with ATZ. The organisms were exposed to variant concentrations of ENPs and ATZ in ISO medium (standard freshwater), and immobilization was investigated as the endpoint.
Evaluation of the physicochemical characterization of ENPs was carried out to establish plausible link between their properties, and the observed biological outcomes. Aggregation of n-Ag increased with exposure time; whereas that of n-ZnO significantly decreased over time. For the binary mixtures, results revealed irrespective of ENPs type, aggregation size increased in the presence of ATZ due to hetero-aggregation between the compounds. Results of the ternary mixtures indicated aggregation size was four-fold relative to those of ENPs binary mixtures. Dissolution of individual n-Ag and n-ZnO increased and decreased over exposure period of 48 h, respectively. The presence of ATZ enhanced the dissolution of ENPs in the binary mixtures. However, in the ternary system a reduction of the dissolution of both ENPs in the presence of ATZ was observed.
Studies on the toxicity of individual contaminants based on median effective concentration (EC50) values in decreasing order were n-Ag > n-ZnO > ATZ, largely attributed to high dissolution of n-Ag in the exposure medium. For binary mixtures with n-Ag, higher toxicity was apparent, relative to other mixture systems (binary or ternary). For ternary mixtures, no toxicological outcomes were observed irrespective of the exposure concentrations. These findings demonstrated that the toxic silver ions were the primary driver of toxicity towards D. magna. Moreover, co-existence of both nanoscale and macroscale may lead to the chemical transformation of CECs in the exposure medium with marked reduction of individual contaminants toxic effects.Water Research Commission (WRC)Department of Water and Sanitation (DWS)Chemical EngineeringMsc (Chemical Engineering)Unrestricte
Effects of two antiretroviral drugs on the crustacean Daphnia magna in river water
Get PDFSUPPLEMENTARY MATERIALS : TABLE S1: Classes and types of individual Food and Drug Administration-approved ARVs for clinical use; TABLE S2: Global measured
environmental concentrations of ARVs in different matrices [3,22,53,81,82]; TABLE S3: Molecular Formula and physico-chemical properties of ARVs; TABLE S4: Physicochemical parameters of freshwater samples collected from Elands River; TABLE S5: Physicochemical properties of ER water during exposure recorded for the controls, lowest and highest exposure concentrations at 0 and 48 h; TABLE S6: Cumulative immobilization of D. magna exposed to variant concentrations of EFV and TFV.Antiretroviral (ARVs) drugs are used to manage the human immunodeficiency virus
(HIV) disease and are increasingly being detected in the aquatic environment. However, little is
known about their effects on non-target aquatic organisms. Here, Daphnia magna neonates were
exposed to Efavirenz (EFV) and Tenofovir (TFV) ARVs at 62.5–1000 g/L for 48 h in river water. The
endpoints assessed were mortality, immobilization, and biochemical biomarkers (catalase (CAT),
glutathione S-transferase (GST), and malondialdehyde (MDA)). No mortality was observed over
48 h. Concentration- and time-dependent immobilization was observed for both ARVs only at
250–1000 g/L after 48 h, with significant immobilization observed for EFV compared to TFV. Results
for biochemical responses demonstrated that both ARVs induced significant changes in CAT and GST
activities, and MDA levels, with effects higher for EFV compared to TFV. Biochemical responses were
indicative of oxidative stress alterations. Hence, both ARVs could potentially be toxic to D. magna.Water Research Commission (WRC) South Africa.https://www.mdpi.com/journal/toxicsam2023Chemical Engineerin
An integrated approach to waste and energy minimization in the wine industry : a knowledge-based decision methodology
Get PDFThesis (PhD)--University of Stellenbosch, 2004.ENGLISH ABSTRACT: The importance of waste management is growing rapidly for several reasons. These
reasons include the escalating cost of wastewater treatment and cleaning chemicals, an
emerging trend of onerous regulatory regime regarding e uent disposal from governments,
rising public awareness on the adverse e ects of industrial waste as well as drastic reduc-
tion in water resources in the winegrowing regions. In addition, owing to the large energy
demand for refrigeration purposes for high quality wine production and rapidly increasing
energy costs, the challenges of energy management in the wine industry were also inves-
tigated.
In order to address these challenges adequately, the solutions were derived via the
integration of two disciplines: environmental science (waste and energy management)
and computer science (applications of arti cial intelligence). Therefore, the ndings re-
ported from this study seek to advance knowledge through the construction of decision
support systems for waste and energy management in circumstances where conventional
mathematical formalisms are inadequate. In that sense, the dissertation constitutes in-
terdisciplinary research on the application of integrated arti cial intelligence technologies
(expert systems and fuzzy logic) in designing and developing decision tools for waste and
energy management in the wine industry.
The dissertation rst presents the domain of interest, where the scope and breadth of
the problems it addresses are clearly de ned. Critical examination of the domain data-
bases revealed that data, information, and knowledge for waste and energy management
in the wine industry are generally incomplete and lack structure overall. Owing to these
characteristics, a hybrid system approach was proposed for the development of decision
support systems based on fuzzy logic. The integrated decision support systems were de-
veloped based on an object-oriented architecture. This approach facilitated the
exible
design required for waste and energy management-related complex problem-solving.
To illustrate the applicability of the o -line decision tools developed, several case stud-
ies mirroring on actual industrial practices were considered. These systems were found to
be robust and yielded results that were in accordance with actual industrial practices inthe wine industry. Furthermore, they provided intelligent suggestions in scenarios where
there was minimal information, and under certain instances they o ered feasible sugges-
tions in circumstances where a human novice could have problems in making the right
decisions.AFRIKAANSE OPSOMMING: Die belangrikheid van afvalbestuur neem om verskeie redes vinnig toe. Die redes sluit
in die eskalerende koste van afvalwaterbehandeling en skoonmaakmiddels, streng regula-
toriese vereistes van regeringskant met betrekking tot die verwydering van uitvloeisels,
toenemende openbare bewustheid van die nadelinge e ekte van nywerheidsafval, sowel
as die drastiese afname in waterbronne in wynproduserende omgewings. Daarby, a.g.v.
die groot energieverbruik wat deur die verkoeling van hokwaliteitwyn vereis word en die
snelgroeiende energiekoste, is die uitdagings van energiebestuur in die wynbedryf ook on-
dersoek.
Ten einde die uitdagings die hoof te kon bied, is oplossings gevind deur die integrasie
van twee disciplines: omgewingswetenskap (afval- en energiebestuur) en rekenaarweten-
skap (toepassings van kunsmatige intelligensie). Gevolglik is daar deur die bevindinge
van die studie gepoog om kennis te bevorder deur die konstruksie van besluitnemingson-
dersteuningstelsels vir afval- en energiebestuur onder omstandighede waar konvensionele
wiskundige algoritmes ontoereikend sou wees. In die opsig verteenwoordig die proefskrif
interdissiplinre navorsing in die toepassing van gentegreerde kunsmatige intelligensieteg-
nologie (kundige stelsels en wasige logika) in die ontwerp en ontwikkeling van besluitne-
mingshulpmiddels vir afval- en energiebestuur in die wynindustrie.
Die proefskrif baken eers die probleemgebied af, waarna die bestek en omvang van die
probleme waarop die werk gemik is duidelik gede nieer word. Kritiese ondersoek van
die databasisse in die domein het getoon dat die data, informasie en kennis oor afval- en
energiebestuur in die wynbedryf in die algemeen onvolledig en gebrekkig gestruktureer is.
A.g.v. di eienskappe, is 'n hibriede stelselbeandering voorgestel vir die ontwikkeling van
besluitnemingstelsels gegrond op wasige logika. Die gentegreerde besluitnemingsonders-
teuningstelsels is ontwikkel op 'n objek-georinteerde argitektuur. Die benadering het die
daarstelling van 'n buigsame ontwerp wat benodig word vir komplekse probleemoplossing
in afval- en energiebestuur vergemaklik.
Om die toepaslikheid van die a
ynige besluitnemingshulpmiddels wat ontwerp is, te
illustreer, is verskeie gevallestudies wat werklike industrile praktyk uitbeeld beskou. Diestelsels was robuust en het resultate gelewer wat in ooreenstemming was met werklike
industrile praktyke in die wynnywerheid. Die kundige stelsels het verder intelligente
voorstelle gemaak in scenarios waar daar minimale informasie beskikbaar was, en onder
sekere omstandighede het hulle realistiese oplossings voorgestel waar 'n onkundige persoon
probleme sou gehad he tom die regte besluite te kon neem.Doctora
Evaluation of apical and molecular effects of algae Pseudokirchneriella subcapitata to cerium oxide nanoparticles
Get PDFSUPPLEMENTARY MATERIALS: TABLE S1: The composition of 10% BG-11 medium; FIGURE S1: Size characterization of nCeO2 (a) TEM images [36], (b) size distribution; FIGURE S2: Algal growth of P. subcapitata at different concentrations of K2Cr2O7: FIGURE S3: in situ nCeO2 concentration (particles/mL) characterization examined using Nanoparticle Tracking Analysis [92].Cerium oxide engineered nanoparticles (nCeO2) are widely used in various applications
and are, also, increasingly being detected in different environmental matrixes. However, their impacts
on the aquatic environment remain poorly quantified. Hence, there is a need to investigate their
effects on non-target aquatic organisms. Here, we evaluated the cytotoxic and genotoxic effects of
<25 nm uncoated-nCeO2 on algae Pseudokirchneriella subcapitata. Apical (growth and chlorophyll
a (Chl a) content) and genotoxic effects were investigated at 62.5–1000 g/L after 72 and 168 h.
Results demonstrated that nCeO2 induced significant growth inhibition after 72 h and promotion
post 96–168 h. Conversely, nCeO2 induced enhanced Chl a content post 72 h, but no significant
changes were observed between nCeO2–exposed and control samples after 168 h. Hence, the results
indicate P. subcapitata photosynthetic system recovery ability to nCeO2 effects under chronic-exposure
conditions. RAPD-PCR profiles showed the appearance and/or disappearance of normal bands
relative to controls; indicative of DNA damage and/or DNA mutation. Unlike cell recovery observed
post 96 h, DNA damage persisted over 168 h. Thus, sub-lethal nCeO2-induced toxicological effects
may pose a more serious threat to algae than at present anticipated.The South African National Research Foundation—Department of Science and Technology Professional Development Programme Doctoral Grant, the Council for Scientific and Industrial Research (CSIR), South Africa and the Water Research Commission (WRC).https://www.mdpi.com/journal/toxicsam2023Chemical EngineeringNon
Modelling ecological risks of antiretroviral drugs in the environment
Get PDFAPPENDIX A. SUPPLEMENTARY DATA : Supplementary data to this article can be found online at https://DOI.org/10.1016/j.enceco.2023.06.001.The success of the antiretroviral therapy (ART) programme to manage HIV/AIDS in Sub-Saharan Africa (SSA) has inadvertently led to the release of antiretroviral (ARVs) into the environment. Consequently, ARVs have been detected in different countries across the globe, with the highest measured environmental concentrations in the SSA countries. Herein, we quantified ecological risks of ten regimen ARVs (six and four in first and second regimes, respectively) into environmental matrices in four spatial regions in Eswatini, namely: Manzini, Hhohho, Lubombo, and Shiselweni. Ecological risks (expressed as risk quotient (RQ)) were determined for different geographical regions by comparing the predicted environmental concentrations (PECs) to the predicted no effect concentrations (PNECs). PNECs were derived from ecotoxicological data generated using the Ecological Structure Activity Relationships (ECOSAR) model. PECs of ARVs in surfacewater in the Lubombo and Shiselweni regions were three-fold higher compared to those of the Manzini and Hhohho regions with RQs of three ARVs exceeding 10 (RQ > 10) to three taxa (fish, daphnia, and algae). ARVs of concern to the three taxa were ranked in descending order based on both acute and chronic toxicity based on RQ values as efavirenz (EFV) > lopinavir (LPV) > ritonavir (RTV) (all with RQs > 10). Two second regime ARV drugs (RTV and LPV) posed the highest risks to aquatic taxa though they had the least PECs, but were highly toxic with PNECs <1 μg/L. Due to dearth of toxicity data for ARVs on bacteria, their risks in wastewater (with the exception of TDF) could not be established. Results of this study are the first to quantify risks of ARVs in the environment using a modelling approach. The developed model can therefore serve as a first-tier screening tool. In addition, the results raise the need to examine the likelihood of antiviral resistance of ARVs linked to their high environmental concentrations.The Water Research Commission (South Africa).http://www.keaipublishing.com/en/journals/environmental-chemistry-and-ecotoxicology/am2024Chemical EngineeringSDG-03:Good heatlh and well-beingSDG-11:Sustainable cities and communitie
Stability of gold and cerium oxide nanoparticles in aqueous environments, and their effects on Pseudokirchneriella subcapitata and Salvinia minima
Get PDFThesis (PhD)--University of Pretoria, 2019.Engineered nanoparticles (ENPs) are class of emerging environmental pollutants, generally found at low concentrations and are therefore likely to exert sub-lethal effects on aquatic organisms. Among different kinds of NPs, metal and metal oxides NPs are most widely used in consumer products, targeted drug delivery and optical bioimaging. Rapid increasing use and applications of ENPs and their consequent emission into the environments raised the need to understand their potential effects to ecological systems. Yet, currently, the environmental fate, behaviour and potential toxic effects of NPs in the environment are poorly understood. The aquatic environment is at risk of exposure to NPs, as it acts as a final recipient for most environmental contaminants. To address this knowledge gap, the current study seeks to generate data on the fate and behaviour of NPs in aquatic systems and investigates their potential toxic effects on aquatic organisms. Amongst the less studied, but widely produced NPs are gold and cerium oxide NPs, therefore, likely to be released into the environment in high quantities. Algae, Pseudokirchneriella subcapitata and aquatic higher plant, Salvinia minima were selected as models for this study owing to limited nano-ecotoxicity data available.
To investigate the influence of physicochemical properties of NPs and media constituents on the environmental fate and behaviour of NPs; the hydrodynamic diameters and zeta potentials for Au (5, 20 and 40 nm; citrate and branched polyethyleneimine coated) and CeO2 (>25 nm, uncoated) NPs were characterized in de-ionised water (DIW), 10% Hoagland’s medium, dechlorinated tap water and 10% BG-11 algal medium. Findings showed high agglomeration of NPs in biological media compared to DIW due to the low ionic strength of DIW. Instability of NPs in media was size and surface coating dependent, with smaller sized (5 nm) and citrate coated-Au NPs agglomerating rapidly. The much broader particle size distribution observed indicated (i) formation of agglomerates, (ii) instability of Au and CeO2 NPs in ecotoxicological media and (iii) inaccuracy of light scattering techniques in size analysis for non-spherical NPs.
The interaction of Au and CeO2 NPs with S. minima indicated that (i) NPs were not internalized by S. minima irrespective of NP size, coating variant, and type, (ii) NPs can be adsorbed on the roots of S. minima but without inducing morphological level effects such as growth retardation and necrosis and (iii) adsorption was established as mechanism of NPs accumulation in S. minima. Exposure of P. subcapitata to NPs showed that (i) citrate-Au and CeO2 NPs neither inhibited P. subcapitata growth nor affected the cellular chlorophyll content; where slight
growth inhibition was observed at 72 h, algae recovered after 96 h, (ii) genotoxicity assays revealed potential toxicity of NPs to algae at molecular level although no effects observed at morphological level and (iii) algae show an increase in genomic stability under long-term exposure conditions. Overall, the study showed that the behaviour of NPs in aquatic systems and their interactions with aquatic organisms are influenced by their physicochemical characteristics, exposure medium composition and exposure period; also, genotoxicity assays are more sensitive than cytotoxicity assays.GeneticsPhDUnrestricte
Assessment on the occurrence and removal of Triclosan and Triclocarban from a wastewater treatment plant and their potential ecological risks
Get PDFDissertation (MEng (Chemical Engineering))---University of Pretoria, 2022.Increasing use of triclosan (TCS) and triclocarban (TCC) from pharmaceutical and personal care products (PPCPs), personal care products (PCPs), and other industrial applications have resulted in their continuous release into the environment. This is due to their incomplete removal in treated wastewater, and from non–diffuse sources e.g., runoffs. In addition, industrial effluents also release other forms of pollutants into wastewater treatment plants (WWTPs) that are not readily biodegradable in conventional biological treatment plants. In this study, the occurrence and removal of TCS, TCC and other contaminants in the WWTP from domestic and industrial influent (Darvill WWTP, Pietermaritzburg, South Africa) were investigated. The target compounds TCS and TCC were quantitatively analysed using gas chromatography–mass spectrometry (GC–MS), and yielded the measured environmental concentrations (MECs). Conversely, other forms of pollutants were qualitatively assessed using GC–MS in selected ion monitoring (SIM) mode. Both target compounds were detected in the influent and effluent, and, at across different process units. Moreover, using the sales data for the major product sources of TCS and TCC feeding the Darvill WWTP, predicted environmental concentrations (PEC) of the target compounds were determined. Risk quotients (RQs) were calculated to predict the likely risks of both chemicals in the wastewater, freshwater, and soil environmental matrixes.
The MECs obtained for TCS were in the µg/L range, and the highest in the influent in the ranges of 1.02– 3.4 µg/L; whereas in the final effluent (after chlorination) detected values were <LOD–1.1 µg/L. Lower concentrations of TCC levels of two- to three-folds were measured as 0.45–1.1 µg/L and LOD–0.58 µg/L in the effluent (before chlorination) and final effluent (after chlorination), respectively. And, the concentrations showed variability across different treatment processes. The overall removal efficiency was 59% and 45% for TCS and TCC, respectively. Generally, TCS concentrations were higher than TCC concentrations from all treatment units assessed. Other pollutants detected in the influent and effluent were diisoprophylnaphthalenes (DIPNs), 2–Heptyl–4–phenyl–1,3–dioxolane, and polychlorinated biphenyls (PCBs) – hence providing evidence of industrial influent into the Darvill WWTP as these chemicals are mostly used in industrial processes.
Four transformation products (TPs) of TCS and TCC were detected, namely; methyl triclosan (MeTCS), 2,4–dichlorophenol (2,4–DCP), non–chloro carbanilide (NCC), and 4–chloroanaline (4–CA). 2,4–DCP and NCC were detected in all samples analysed at concentration ranges of 0.26–0.4 µg/L and 1.13–2.02 µg/L, respectively. However, MeTCS and 4–CA were not detected above limit of detection in all samples analysed. The formation of TPs, however, was not exclusively due to the TCS and TCC biodegradation along the WWTP alone. This is because both 2,4–DCP and NCC were successfully detected in the influent stream.
The modelled PECs were in good agreement with MECs with average PEC/MEC ratios of 1 and 3 for TCS and TCC, respectively. Hence, indicative of reliability of using PECs as a practical approach to quantify the concentrations of contaminants from household products in the aquatic environment. TCS and TCC RQs for microorganisms were > 1 and < 1, respectively, suggesting possible negative impact of the former to the performance of biological wastewater treatment plants. Results of TCS and TCC showed potential risks to freshwater species irrespective of the tropic level of focus (algae, crustacean, and fish) with RQs obtained exceeding 1. RQ results in terrestrial system were all < 1, indicating low or no risks. All these results taken together, calls for the protection of the freshwater systems by banning incorporation of TCS in products as has been done in other jurisdictions including the USA, European Union, and Canada.Water Research CommissionChemical EngineeringMEng (Chemical Engineering)Unrestricte
Mixtures effects of nanoscale and microscale contaminants to Bacillus subtilis in natural water systems
Get PDFThesis (PhD)--University of Pretoria, 2020.Engineered nanoparticles (ENPs) (e.g. zinc oxide (nZnO) and iron oxide (nFeOx) and organic pollutants (e.g. triclosan (TCS)) are among emerging contaminants (ECs) of environmental concern. However, to date there is limited knowledge on their fate and potential deleterious effects in the ecological systems. Following simultaneous and/or sequential release of ECs in the ecological systems; they co-exist as mixtures defined by complex permutations. As such, toxicological outcomes of individual ECs may be altered as those of mixtures formed may exhibit synergistic, antagonistic or additive effects. Influenced by water physicochemical parameters, chemical interactions between multiple contaminants and the unique properties of ENPs like photoactivity, adsorption capacity and dissolution may alter the toxic outcomes to bacteria. Yet, currently, the environmental fate and toxicity ENPs as mixtures, particularly in natural water are limited.
In this work, Bacillus subtilis was used as a model organism to assess the toxicity of nZnO and maghemite iron oxide (γ-nFe2O3) as individual ENPs, binary mixtures, and ternary mixtures with TCS. Natural water from two river sources, the Elands River (ER) and the Bloubank River (BR) were used to generate environmentally relevant data; and four endpoints were used to evaluate toxicological outcomes (cell viability, cell membrane integrity, ATP production, oxidative stress from reactive oxygen species (ROS). Aggregation of the two ENPs were significantly different between the two river water matrixes with higher aggregates observed in BR water. nZnO induced significant reduction in cell viability and membrane integrity at higher tested concentrations in ER; but none in BR under visible light. A higher decrease in ATP levels was observed in ER than in BR, and ROS production was negligible irrespective of the ENP type and exposure media under visible light. Conversely, γ-nFe2O3 induced no significant effects on B. subtilis on all tested endpoints. nZnO induced concentration-dependent effects on the cell membrane integrity of B. subtilis in both river water samples under solar irradiation.
For binary mixtures of ENPs under solar irradiation, nZnO toxicity was found to be concentration-dependent, with more pronounced effects in ER than BR water due to water chemistry. However, toxic effects were mitigated by γ-nFe2O3 in the binary mixtures, linked to heteroaggregation between the ENPs. Solar irradiation induced ROS had minimal effect on the toxicity of ENPs. For ternary mixtures, toxicity of TCS was more pronounced at the highest concentration. However, the effects were not water chemistry dependent, compared to the observed effects from nZnO. In addition, more distinctive mitigating effects were observed in ternary mixtures, where nZnO dissolution was significantly lower in the presence of TCS. These findings demonstrated that observed differences in the effects of nZnO towards B. subtilis, either in binary or ternary systems were influenced by the nature of interactions (TCS and γ-nFe2O3) as well as water chemistry of natural water in focus. Therefore, the unique physicochemical properties of natural aqueous media were established to be the key determinant attributes in enhancing or inhibiting the effects of ENPs on bacteria, and, the co-existence of ECs of different types and classes may lead to reduction of toxic effects of individual contaminants.Chemical EngineeringPhDUnrestricte
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