Browsing by Author "Thwala, Melusi"
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Item An analysis of engineered nanomaterial characteristics reported in aquatic nanotoxicity studies: 2004-2013(2014-04) Thwala, Melusi; Mahaye, N; Schaefer, Lisa M; Musee, NIn this study, we employed bibliometric techniques to analyse engineered nanomaterials (ENMs) characterization data published in peer-reviewed aquatic nanoecotoxicity hosted in the International Council on Nanotechnology (ICON) and Web of Science databases. Findings reported herein are based on 192 peer reviewed studies from January 2004 to March 2013. From the studies we examined: (1) the extent of reported characterisation properties of ENMs and testing media characteristics in the study data, and (2) the utilisation or application of ENMs characterisation data within a specific study to account for the observed toxicity response on biota. The most reported ENM characteristic was size by 99% of the studies, and surface coating was the least at 30% (Fig. 1). The low reporting of surface area and surface charge by 35% and 34%, respectively, suggests poor understanding on their influence towards reported toxicity. Large percentage of the particle size analysis was undertaken in testing media, rather than relying on data supplied by manufacturers, and suggests a high proportion of the data being credible and scenario relevant. The TEM was the most used technique for size characterisation at 69% (Fig. 2) possibly because it also generates morphology and surface composition characteristics data. Use of more than one size analysis techniques was observed, and hence contributed towards generation of high quality data. The testing media characteristics were poorly reported in the studies as pH, ionic strength, and natural organic matter were reported by 59%, 17%, and 12%, respectively, and need to be improved. Our analysis indicated the effort by the researchers to utilise ENMs characterisation data to a certain degree to account for the observed toxicological responses. Overall, our findings indicates that for future nanoecotoxicity studies, both inherent ENMs characteristics and media chemistry properties should be reported to improve our collective understanding.Item Antibacterial effects of engineered nanomaterials: implications for wastewater treatment plants(Royal Society of Chemistry, 2011-05) Musee, N; Thwala, Melusi; Nota, NNanotechnology is currently at the forefront of scientific research and technological developments that have resulted in the manufacture of novel consumer products and numerous industrial applications using engineered nanomaterials (ENMs). With the increasing number of applications and uses of ENMs comes an increasing likelihood of nanoscale materials posing potential risks to the environment and engineered technical systems such as wastewater treatment plants (WWTPs). Recent scientific data suggests that ENMs that are useful in, for example, medical applications due to their novel physicochemical properties, may also cause adverse effects to the bacterial populations used in wastewater treatment systems. In this review, the toxicological effects of titanium nanoparticles (nTiO2), zinc oxide (nZnO), carbon nanotubes (CNTs), fullerenes (C60) and silver nanoparticles (AgNPs) to bacteria were examined. The results suggest that the potential ENMs risks to bacteria are non-uniform (need to be assessed case-by-case), and are dependent on numerous factors (e.g. size, pH, surface area, natural organic matter). Currently available data are therefore insufficient for evaluating the risks that ENMs pose in WWTPs. To fill these knowledge gaps, we recommend scenario specific studies aimed at improving our understanding on: (i) estimated volumes of ENMs in effluents, (ii) the antibacterial sensitivity of cultures within WWTPs towards selected ENMs, and (iii) processes improving the stability of ENMs in solutions. Two factors that merit consideration for elucidating the potential risks systematically are the toxicity mechanisms of ENMs to bacteria, and the influencing factors based on inherent physicochemical properties and environmental factors. Furthermore, the complexity of behaviour and fate of ENMs in real WWTPs requires case studies for assessing the ENMs risks to bacteria in vivo. The current laboratory results derived using simplified exposure media do not reflect actual environmental conditions.Item Aquatic environment exposure and toxicity of engineered nanomaterials released from nano-enabled products: Current status and data needs(2021-10) Moloi, MS; Lehutso, Raisibe F; Erasmus, M; Oberholster, PJ; Thwala, MelusiRapid commercialisation of nano-enabled products (NEPs) elevates the potential environmental release of engineered nanomaterials (ENMs) along the product life cycle. The current review examined the state of the art literature on aquatic environment exposure and ecotoxicity of product released (PR) engineered nanomaterials (PR–ENMs). Additionally, the data obtained were applied to estimate the risk posed by PR–ENMs to various trophic levels of aquatic biota as a means of identifying priority NEPs cases that may require attention with regards to examining environmental implications. Overall, the PR–ENMs are predominantly associated with the matrix of the respective NEPs, a factor that often hinders proper isolation of nano-driven toxicity effects. Nevertheless, some studies have attributed the toxicity basis of observed adverse effects to a combination of the released ions, ENMs and other components of NEPs. Notwithstanding the limitation of current ecotoxicology data limitations, the risk estimated herein points to an elevated risk towards fish arising from fabrics’ PR–nAg, and the considerable potential effects from sunscreens’ PR–nZnO and PR–nTiO2 to algae, echinoderms, and crustaceans (PR–nZnO), whereas PR–nTiO2 poses no significant risk to echinoderms. Considering that the current data limitations will not be overcome immediately, we recommend the careful application of similar risk estimation to isolate/prioritise cases of NEPs for detailed characterisation of ENMs’ release and effects in aquatic environments.Item Aquatic toxicity effects and risk assessment of ‘Form Specific’ product-released engineered nanomaterials(2021-11) Lehutso, Raisibe F; Wesley-Smith, J; Thwala, MelusiThe study investigated the toxicity effects of ‘form specific’ engineered nanomaterials (ENMs) and ions released from nano-enabled products (NEPs), namely sunscreens, sanitisers, body creams and socks on Pseudokirchneriella subcapitata, Spirodela polyrhiza, and Daphnia magna. Additionally, risk estimation emanating from the exposures was undertaken. The ENMs and the ions released from the products both contributed to the effects to varying extents, with neither being a uniform principal toxicity agent across the exposures; however, the effects were either synergistic or antagonistic. D. magna and S. polyrhiza were the most sensitive and least sensitive test organisms, respectively. The most toxic effects were from ENMs and ions released from sanitisers and sunscreens, whereas body creams and sock counterparts caused negligible effects. The internalisation of the ENMs from the sunscreens could not be established; only adsorption on the biota was evident. It was established that ENMs and ions released from products pose no imminent risk to ecosystems; instead, small to significant adverse effects are expected in the worst-case exposure scenario. The study demonstrates that while ENMs from products may not be considered to pose an imminent risk, increasing nanotechnology commercialization may increase their environmental exposure and risk potential; therefore, priority exposure cases need to be examined.Item Atlas of industrial wastewater reuse potential in South Africa(CSIR, 2021-03) Steyn, Maronel; Walters, Chavon R; Mathye, Salamina M; Ndlela, Luyanda L; Thwala, Melusi; Banoo, Ismail; Tancu, Yolanda; Genthe, BettinaThe South African economy largely depends on mining and other large industries. According to the National Water Resources Strategy 2 (DWA, 2013a), the mining sector, with an estimated demand of about 5% of the country’s available water, is a significant user of water. Coal and Platinum mining in particular is currently expanding into new areas with a projected increase in water demand. Many of these mines are located in water resource scarce catchments (e.g. the Lephalale and Steelpoort areas in the Limpopo province) where the availability of water can become a significant business risk. Water availability should however not be a limiting factor to growth in the country. Water resources management and development should prioritise availability of water to industry. Similarly, implementation of water conservation and water demand management (WC/WDM) measures within the mining sector is required in order to minimise this risk (DWS, 2016).Item Bulk scale industrial effluent reuse potential in South Africa(2021-11) Steyn, Maronel; Walters, Chavon R; Mathye, Salamina M; Thwala, Melusi; Banoo, Ismail; Ndlela, Luyanda L; Tancu, Yolanda; Genthe, BettinaRationale: Water scarcity, increased pollution, unprecedented population growth and climate change are collectively driving the need to reuse water with the aim to enhance water security, sustainability, and resilience. It is clear that South Africa’s already strained water resources will become even more stressed in the near future. The Department of Water and Sanitation predicted that by 2030 water demand will reach 17.7 billion m3, far more than what is available to allocate. Globally, responsible and efficient water management is fast becoming a pressing reality for domestic users, agriculture and industry alike. The challenge is therefore to capitalise on the limited water we currently have. Solution: Bulk-scale reuse of industrial water effluent can play a significant role in water security in a water scarce country, such as South Africa, as it can augment or partially substitute freshwater resources needed for domestic purposes and future development. Water reuse in South Africa is however lagging. Approach: An Atlas for potential industrial bulk scale water reuse was produced from publicly available Natsurv and WARMS data. It highlights the urgent need for water reuse to form an integral part of an integrated water management supply approach in South Africa. While South Africa has progressive legislation to support the implementation of wastewater reuse, it can also be regarded as a barrier in implementing reuse projects, as often water reuse standards and guidelines are far too stringent to allow for cost-effective reuse options to be developed and implemented. Findings: Currently, very little to no data exists regarding wastewater reuse options, treatment options and capabilities, or costs, which can be used for decision making, and much more directed research and information is needed in order to identify wastewater and industrial effluent volume availability, quality and fitness for use in South Africa. A web-based Decision Support System (DSS) tool is being developed to enable municipal and industry partners, and water quality managers to make informed decisions for possible reuse options. The tool aims to directly assist by linking industrial effluent volumes and quality to fitness for use, and linking it with specific industries in the geographical vicinity based on industry specific water quality and quantity requirements. The DSS can be particularly useful in wastewater reuse as it can provide assistance in the evaluation and selection of alternatives for a given reuse application. In addition, the tool will enable engineers and industry partners to collaborate to identify and employ treatment technologies and capabilities to link industrial effluent quality and volumes available to that of potential user requirements in a geographical area.Item Bulk scale industrial effluent reuse potential in South Africa Atlas(2021-10) Steyn, Maronel; Walters, Chavon R; Mathye, Salamina M; Thwala, Melusi; Ndlela, Luyanda L; Tancu, Yolanda; Lehutso, Raisibe F; Banoo, IsmailGlobally, responsible and efficient water management is fast becoming a pressing reality for domestic users, agriculture and industry alike. The challenge is therefore to capitalise on the limited water we currently have. Solution: Bulk-scale reuse of industrial water effluent can play a significant role in water security in a water scarce country, such as South Africa, as it can augment or partially substitute freshwater resources needed for domestic purposes and future development. Water reuse in South Africa is however lagging. Approach: An Atlas for potential industrial bulk scale water reuse was produced from publicly available Natsurv and WARMS data. It highlights the urgent need for water reuse to form an integral part of an integrated water management supply approach in South Africa.Item Characterisation of engineered nanomaterials in nano-enabled products exhibiting priority environmental exposure(2021-03) Lehutso, Raisibe F; Tancu, Yolanda; Maity, Arjun; Thwala, MelusiAnalytical limitations have constrained the determination of nanopollution character from real-world sources such as nano-enabled products (NEPs), thus hindering the development of environmental safety guidelines for engineered nanomaterials (ENMs). This study examined the properties of ENMs in 18 commercial products: sunscreens, personal care products, clothing, and paints—products exhibiting medium to a high potential for environmental nanopollution. It was found that 17 of the products contained ENMs; 9, 3, 3, and 2 were incorporated with nTiO2, nAg, binaries of nZnO + nTiO2, and nTiO2 + nAg, respectively. Commonly, the nTiO2 were elongated or angular, whereas nAg and nZnO were near-spherical and angular in morphology, respectively. The size ranges (width × length) were 7–48 × 14–200, 34–35 × 37–38, and 18–28 nm for nTiO2, nZnO, and nAg respectively. All ENMs were negatively charged. The total concentration of Ti, Zn, and Ag in the NEPs were 2.3 × 10-4–4.3%, 3.4–4.3%, and 1.0 × 10-4–11.3 × 10-3%, respectively. The study determined some key ENM characteristics required for environmental risk assessment; however, challenges persist regarding the accurate determination of the concentration in NEPs. Overall, the study confirmed NEPs as actual sources of nanopollution; hence, scenario-specific efforts are recommended to quantify their loads into water resources.Item Characterisation of titanium oxide nanomaterials in sunscreens obtained by extraction and release exposure scenarios(Springer International Publishing, 2019-04) Nthwane, Yvonne B; Tancu, Yolanda; Maity, Arjun; Thwala, MelusiThe application of titanium oxide engineered nanomaterials (TiO2 (sub 2) ENMs) in products is dominant in sunscreens and can be release into water systems with relative ease during sunscreen use. The current study examined the physico-chemical properties of the TiO2 (sub 2) ENMs extracted from three sunscreens (SUN A, B, and C) and also released during bathing into deionised and tap water. The TiO2 (sub 2) ENMs were identified in all the sunscreen extract samples using scanning and transmitting electron microscopy (SEM and TEM). The mode length of the ENMs measured with SEM were 67.6, 69.8, and 51.8 nm for SUN A, B, and C respectively whereas their width were 31.3, 38.7, and 27.7 nm. From TEM analysis the ENMs length and width mode sizes respectively were 73.9 and 14.5 nm for SUN A, 81.5 and 16.3 nm for SUN B, and 44.7 and 14.0 nm for SUN C. The Ti content of the sunscreens was 1.9, 0.6, and 0.5% w/w respectively for SUN A, B, and C. During bathing TiO2 (sub 2) ENMs were released into wastewater and were in the size range of 47–218, 102–153, and 92–138 nm for SUN A, B, and C respectively in DI wastewater. In tap wastewater they were 100–241, 100–477, and 67–150 nm SUN A, B, and C respectively. The determined environmental concentrations for the ENMs in DI wastewater ranged 0.2–1.16 µg/L, whereas in tap wastewater it was 0.16–0.17 µg/L. The morphologies of the extracted and released ENMs were a mixture of rods, plates, irregular, and near spherical. The released Ti quantity significantly differed between DI and tap wastewater for SUN B and C, indicating the influence of wastewater quality in the exposure profile of ENMs in waterItem Current situation and future prognosis of health, safety and environment risk assessment of nanomaterials in South Africa(2023-01) Gulumian, M; Thwala, Melusi; Makhoba, X; Wepener, VThe commercialisation and everyday use of nanomaterials and nanomaterial-enabled products (NEPs) is rising year-on-year. Responsible development of nanotechnology includes understanding their potential implications on health, safety, and the environment (HSE). The health risk assessment of nanomaterials has therefore become one of the major activities of international agencies including the Organisation for Economic Co-operation and Development and the Environmental Protection Agency for protection of human health and the environment. Nationally, with the foresight and the leadership of the Department of Science and Innovation, a HSE programme was initiated to establish the necessary infrastructure to conduct the tests in the hazard identification and exposure assessment that are needed in the risk assessment of nanomaterials synthesised as well as NEPs available in South Africa. Here we present the advances that have been made in elucidating the different facets that are required when undertaking risk assessments of nanomaterials, i.e. physicochemical characterisation, hazard identification, exposure assessment and effects assessment. These facets are increasingly being considered throughout the nanomaterials present in the life cycles of NEPs. South Africa's research contribution to an international understanding of HSE risks of nanomaterials is highlighted and the future direction to generate the necessary information for effective risk communication and management is provided. This will assist in ensuring safer innovation of nanotechnology in South Africa and support the export of locally manufactured nanomaterials as per international requirements.Item A decision support tool for industrial water reuse in South Africa(2020-08) Steyn, Maronel; Genthe, Bettina; Banoo, Ismail; Thwala, Melusi; Roos, Thomas H; Walters, Chavon R; Ramakhwatho, FWater scarcity, increased pollution, unprecedented population growth and climate change are all driving the need to reuse water to secure the future of the country. It is clear that South Africa’s already strained water resources will become even more stressed in the near future. The Department of Water and Sanitation (DWS) (2017) predicts that by 2030 water demand will reach 17.7 billion m3, far more than what is available to allocate. Responsible and efficient water management is fast becoming a pressing reality for domestic users, agriculture and industry alike. The challenge is therefore to do the most with the little water we currently have.Item The emerging case of nanopollutants in the aquatic environment: analytical challenges for the exposure assessment of silver and zinc oxide nanoparticles(2016-09) Thwala, Melusi; Tancu, YolandaThe growing number of nano-enabled products and technologies suggests likelihood increase of nanopollutants into the environment, a trend that is anticipated to increase further as nanotechnology expands. Nanopollutants are considered a case of emerging environmental contaminants partly due to limited capability to detect and quantify them in environmental matrices. The current paper presents findings from the exposure assessments of silver and zinc oxide nanoparticles (Ag and ZnO NPs) in synthetic and environmental water samples. A suite of commonly used techniques for the determination of size distribution (TEM, zetasizer, NTA), morphology (TEM), stability (UV-vis), dissolution (ICP-MS) and particle concentration (NTA) were applied. For size determination in situ each technique performed fairly well in synthetic media, but all had limitations in river and waste water samples. The presence of background media particles in environmental samples weakened the accuracy of the NTA in deriving both the size distribution and particle number concentration. The determination of soluble metallic forms was influenced by media background concentrations and seperation technique employed. In light of the analytical challenges and the low predicted environmental concentrations of nanopollutants, we propose site specificity for the risk assessment of nano-enabled products.Item Evidence of free radical and antioxidant activity in Spirodela exposed to metallic and metal oxide nanoparticles: potential for protein and lipid damage(2012-04) Thwala, Melusi; Musee, N; Wepener, V; Nota, NThe toxicity of engineered nanoparticles towards macro algae and higher aquatic plants has not been well studied. This knowledge gap challenges the development of nano risk assessment towards water ecosystems. In this study, we investigated free radical activity and oxidation defence activity on Spirodela after exposure to ZnO and Ag ENPs over 96 hours (acute) and 14 days (chronic). Plant specimens were exposed to nanoparricles with concentrations ranging from 0.01-1000 mg/L, and thereafter the quantities of free radicals (H202, total ROS/RNS), antioxidant activity (catalase, superoxide disrnutasc, and total antioxidam capacity) were analyzed. Oxidative stress has been suggested as a significant route of toxicity induction by engineered nanomaterials (ENPs) to biological media.Item Exposure assessment of metal-based nanoparticles in aquatic environments: interactive influence of water chemistry and nanopaticle characteristics(2014-09) Thwala, Melusi; Radebe, N; Tancu, Y; Musee, NTransformation and bioavailability information of engineered nanoparticles (ENPs) in environmental systems impedes assessment of their potential risks to aquatic environments. In aqueous environments ENPs undergo numerous transformation processes; and presently their fate and behaviour are poorly defined. In this study the stability of naked Ag (40-60 nm) and ZnO (10-130 nm) ENPs using standard toxicity testing medium at strengths of 50HM and 100HM to mimic complex environmental water was investigated over 15 days. The ENPs size dynamics were tracked using TEM and NTA whilst ICP-MS quantified dissolution after ultrafiltration. Both Ag and ZnO ENPs underwent remarkable size growth and surface potential variations in the two testing medium strengths, resulting in significant nanoparticles concentration reduction in suspension. At higher ionic strength (100HM) the ENPs were more stabilized relative to the lower one (50HM), such an effect was confirmed by lower dissolution in 100HM. However, following the same test conditions with two sizes of citrate coated Ag ENPs (10 and 40 nm); dissolution between the two sizes varied and ENPs were more stable in 50HM, contradictory to results obtained from naked powder forms where dissolution in 100HM was highly inhibited. These results point to the complex dynamic nature of ENPs transformation in aqueous environments; that in turn determines the hazard potency of nano-pollutants. Our results point to implications for actual aquatic environments receiving nano-pollutants from usage of nano-enabled products at different life cycle phases.Item Exposure media and nanoparticle size influence on the fate, bioaccumulation, and toxicity of silver nanoparticles to higher plant salvinia minima(2021-04) Thwala, Melusi; Klaine, S; Musee, NSilver nanoparticles (AgNPs) are favoured antibacterial agents in nano-enabled products and can be released into water resources where they potentially elicit adverse effects. Herein, interactions of 10 and 40 nm AgNPs (10-AgNPs and 40-AgNPs) with aquatic higher plant Salvinia minima at 600 µg/L in moderately hard water (MHW), MHW of raised calcium (Ca2+), and MHW containing natural organic matter (NOM) were examined. The exposure media variants altered the AgNPs’ surface properties, causing size-dependent agglomeration. The bio-accessibility in the ascending order was: NOM < MHW < Ca2+, was higher in plants exposed to 10-AgNPs, and across all exposures, accumulation was higher in roots compared to fronds. The AgNPs reduced plant growth and the production of chlorophyll pigments a and b; the toxic effects were influenced by exposure media chemistry, and the smaller 10-AgNPs were commonly the most toxic relative to 40-AgNPs. The toxicity pattern was linked to the averagely higher dissolution of 10-AgNPs compared to the larger counterparts. The scanning electron microscopy and X-ray fluorescence analytical techniques were found limited in examining the interaction of the plants with AgNPs at the low exposure concentration used in this study, thus challenging their applicability considering the even lower predicted environmental concentrations AgNPs.Item Fate and behavior of ZnO- and Ag-engineered nanoparticles and a bacterial viability assessment in a simulated wastewater treatment plant(Taylor & Francis, 2014) Musee, N; Zvimba, JN; Schaefer, Lisa M; Nota, N; Sikhwivhilu, LM; Thwala, MelusiThe fate and behaviour assessment of ZnO- and Ag-engineered nanoparticles (ENPs) and bacterial viability in a simulated wastewater treatment plant (WWTP) fed with municipal wastewater was investigated through determination of ENPs stability at varying pH and continuous exposure of ENPs to wastewater, respectively. The ENPs were introduced to a 3-L bioreactor (simulated WWTP) with a hydraulic residence time (HRT) of 6 h at a dose rate of 0.83 mg/min for 240 h. The stability of the ENPs was found to be dependent on their dissolution and aggregation at different pH, where ZnO ENPs exhibited the highest dissolution at low pH compared to Ag ENPs. The results also showed that both ENPs had high affinity for the sewage sludge as they undergo aggregation under typical wastewater conditions. Results of effluent monitored daily showed mean COD removal efficiencies of 71 ± 7% and 74 ± 8% for ZnO and Ag ENPs in test units, respectively. The treated effluent had low mean concentrations of Zn (1.39 ± 0.54 mg/L) and Ag (0.12 ± 0.06 mg/L); however, elevated mean concentrations of Zn (54 ± 39 mg/g dry sludge) and Ag (57 ± 42 mg/g dry sludge) were found in the sludge - suggesting removal of the ENPs from the wastewater by biosorption and biosolid settling mechanisms. Using X-ray diffraction (XRD) and transmission electron microscopy (TEM), the mineral identities of ZnO and Ag ENPs in the sludge from the test units were found comparable to those of commercial ENPs, but larger due to agglomeration. The bacterial viability assessment after exposure to ENPs using the Live/Dead BacLight kit, although not quantitatively assessed, suggested high resilience of the bacteria useful for biodegradation of organic material in the simulated wastewater treatment system.Item From waste to wow – Low cost green technology for domestic wastewater treatment for reuse and beneficiation(The International Water Association (IWA), 2019-09) Steyn, Maronel; Oberholster, Paul; Genthe, Bettina; Thwala, MelusiPhycoremediation makes use of macroalgae or microalgae and can be used to treat wastewater. This technique has the potential to be used as an alternative biomass source for bio-energy production. The current study utilizes a specific consortium of algal species (isolated and cultured in the laboratory) to reduce nutrients and create conditions suitable for effective reduction of pathogens in WWTW as well as reclamation of water in water scarce countries. The aim was firstly to implement a self-sustaining system that is independent of electricity or expensive chemicals and that can be effectively operated within the current financial and capacity constraints of developing countries using existing infrastructure i.e. waste stabilisation pond systems. Secondly, it was to establish the feasibility of algae biomass generated from maturation ponds as bio-energy. This low cost green technology has already been rolled out with great success at two waste water treatment works in South Africa. To date, total phosphate removal efficiencies of 87.1% and nitrogen levels of 56.3% was achieved in final effluent. E.coli numbers were reduced to below Department of water and sanitation guideline levels. Under auspices of the African Development Bank's Africa Climate Technology Centre, the research team recently started a small scale pilot plant for the drying of algae biomass under natural climate conditions at the rural Brandwacht domestic waste water treatment plant. The next step will be to determine the algal biomass that can be generated for bio-energy using a specific consortium of algae under natural drying conditions. If enough algae biomass is generated, the team will explore the possibility of using this algae biomass to generate bio-energy for the small rural town of Brandwacht. Pending a health risk assessment, bio-fertiliser production or pelleting the biomass for animal feed are other products under investigation.Item Genotoxicity of metal based engineered nanoparticles in aquatic organisms: A review(Elsevier, 2017-07) Mahaye, Ntombikayise; Thwala, Melusi; Cowan, DA; Musee, EuniceEngineered nanoparticles (ENPs) are an emerging class of environmental contaminants, but are generally found in very low concentrations and are therefore likely to exert sub-lethal effects on aquatic organisms. In this review, we: (i) highlight key mechanisms of metal-based ENP-induced genotoxicity, (ii) identify key nanoparticle and environmental factors which influence the observed genotoxic effects, and (iii) highlight the challenges involved in interpreting reported data and provide recommendations on how these challenges might be addressed. We review the application of eight different genotoxicity assays, where the Comet Assay is generally preferred due to its capacity to detect low levels of DNA damage. Most ENPs have been shown to cause genotoxic responses; e.g., DNA or/and chromosomal fragmentation, or DNA strand breakage, but at unrealistic high concentrations. The genotoxicity of the ENPs was dependent on the inherent physico-chemical properties (e.g. size, coating, surface chemistry, e.tc.), and the presence of co-pollutants. To enhance the value of published genotoxicity data, the role of environmental processes; e.g., dissolution, aggregation and agglomeration, and adsorption of ENPs when released in aquatic systems, should be included, and assay protocols must be standardized. Such data could be used to model ENP genotoxicity processes in open environmental systems.Item How water chemistry determines the risk of metallic engineered nanoparticles in aquatic ecosystems: nAg and nZnO case study(2013-09) Thwala, Melusi; Musee, N; Sikhwivhilu, L; Wepener, VThe dispersion of nAg and nZnO engineered nanoparticles (ENPs) in water was investigated through the dissolution and agglomeration analysis over a 14 days exposure period. Before testing, the ENPs were in the nanoscale: 40-60 and 10-130 nm for nAg and nZnO respectively. Dynamic light scattering revealed that introduction of ENPs into water resulted in significant particle growth, even reaching um range in certain instances. ICP-OES analysis indicated limited dissolution which was concentration dependent, however more favourable for nZnO. Using a free floating duckweed candidate; we observed induction of oxidative stress following a multiple biomarker endpoint analysis after plants were exposed to the ENPs. Our results siggest a systematic compromise of biological defence mechanisms by ENPs, revealing a crucial toxicity route by ENPs towards higher aquatic plants. We then detail the importance of water abiotic parameters in, (a) influencing the ENPs surface charge potential, (b) driving the ENPs growth, (c) limiting the generation of metal ionic species, and, (d) determining the overall risk by ENPs towards aquatic biota. We suggest that informed understanding or evaluation of ENPs potential harm towards aquatic biota basically lies on detailed and suitable characterisation of both water and ENPs physico-chemical parameters. We close by listing crucial aspects when evaluating nanotechnology risks towards aquatic ecosystems.Item Interactions of metal-based engineered nanoparticles with aquatic higher plants: A review of state of current knowledge(Wiley, 2016-01) Thwala, Melusi; Klaine, SJ; Musee, NThe rising potential for the release of engineered nanoparticles (ENPs) into aquatic environments requires evaluation of risks in order to protect ecological health. The present review examined knowledge pertaining the interactions of metal-based ENPs with aquatic higher plants, identified information gaps and raised considerations for future research to advance knowledge on the subject. The discussion focused on ENPs' (i) bioaccessibility; (ii) uptake, adsorption, translocation and bioaccumulation, and (iii) their toxicity effects on aquatic higher plants. An information deficit surrounds the uptake of ENPs and associated dynamics because the influence of ENP characteristics and water quality conditions has not been well documented. Dissolution appears to be a key mechanism driving bioaccumulation of ENPs, whereas nanoparticulates often adsorb to plant surfaces with minimal internalisation. However, few reports document the internalisation of ENPs by plants, thus the role of nanoparticulates' internalisation in bioaccumulation and toxicity remain unclear, requiring further investigation. The toxicities of metal-based ENPs have mainly been associated with dissolution as a predominant mechanism, although nano toxicity has also been reported. To advance knowledge in this domain, future investigations need to integrate the influence of ENPs' characteristics and water physico-chemical parameters, as their interplay determines ENPs' bioaccessibility and influences their risk to health of aquatic higher plants. Furthermore, harmonisation of test protocols is recommended for fast tracking the generation of comparable data.