Meta-analysis of engineered nanoparticles dynamic aggregation in freshwater-like systems using machine learning techniques.

Predictive algorithms for exposure characterization of engineered nanoparticles (ENPs) in the ecosystems are essential to improve the development of robust nano-safety frameworks. Here, machine learning (ML) techniques were utilised for data mining and prediction of the dynamic aggregation transformation process in aqueous environments using case studies of nZnO and nTiO2. Supervised ML models using input variables of natural organic matter, ionic strength, size, and ENPs concentration showed poor prediction performance based on statistical metric values of root mean square error (RMSE), mean absolute error (MAE), coefficient of determination (R2), and Nash-Sutcliffe efficiency (NSE) for both types of ENP. On the contrary, algorithms developed using model input parameters of zeta potential, pH, and time had good generalisation and high prediction accuracy. Among the five developed ML algorithms, random forest regression, support vector regression, and artificial neural network generated good prediction accuracy for both data sets. Therefore, the use of ML can be valuable in the development of robust nano-safety frameworks to optimise societal benefits, and for proactive long-term ecological protection.

Proteomic evaluation of nanotoxicity in aquatic organisms: A review.

The alteration of organisms protein functions by engineered nanoparticles (ENPs) is dependent on the complex interplay between their inherent physicochemical properties (e.g., size, surface coating, shape) and environmental conditions (e.g., pH, organic matter). To date, there is increasing interest on the use of 'omics' approaches, such as proteomics, genomics, and others, to study ENPs-biomolecules interactions in aquatic organisms. However, although proteomics has recently been applied to investigate effects of ENPs and associated mechanisms in aquatic organisms, its use remain limited. Herein, proteomics techniques widely applied to investigate ENPs-protein interactions in aquatic organisms are reviewed. Data demonstrates that 2DE and mass spectrometry and/or their combination, thereof, are the most suitable techniques to elucidate ENPs-protein interactions. Furthermore, current status on ENPs and protein interactions, and possible mechanisms of nanotoxicity with emphasis on those that exert influence at protein expression levels, and key influencing factors on ENPs-proteins interactions are outlined. Most reported studies were done using synthetic media and essay protocols and had wide variability (not standardized); this may consequently limit data application in actual environmental systems. Therefore, there is a need for studies using realistic environmental concentrations of ENPs, and actual environmental matrixes (e.g., surface water) to aid better model development of ENPs-proteins interactions in aquatic systems.

Exposure Media and Nanoparticle Size Influence on the Fate, Bioaccumulation, and Toxicity of Silver Nanoparticles to Higher Plant Salvinia minima.

Silver 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.

Fate and behavior of ZnO- and Ag-engineered nanoparticles and a bacterial viability assessment in a simulated wastewater treatment plant.

The 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.

Evaluation of Apical and Molecular Effects of Algae Pseudokirchneriella subcapitata to Cerium Oxide Nanoparticles.

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 µg/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.

Effects of Two Antiretroviral Drugs on the Crustacean Daphnia magna in River Water.

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 µg/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 µg/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.

The antibacterial effects of engineered nanomaterials: implications for wastewater treatment plants.

Nanotechnology 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 (nTiO(2)), zinc oxide (nZnO), carbon nanotubes (CNTs), fullerenes (C(60)) 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.

Interactions of Coated-Gold Engineered Nanoparticles with Aquatic Higher Plant Salvinia minima Baker.

The study investigated the interactions of coated-gold engineered nanoparticles (nAu) with the aquatic higher plant Salvinia minima Baker in 2,7, and 14 d. Herein, the nAu concentration of 1000 µg/L was used; as in lower concentrations, analytical limitations persisted but >1000 µg/L were deemed too high and unlikely to be present in the environment. Exposure of S. minima to 1000 µg/L of citrate (cit)- and branched polyethyleneimine (BPEI)-coated nAu (5, 20, and 40 nm) in 10% Hoagland's medium (10 HM) had marginal effect on biomass and growth rate irrespective of nAu size, coating type, or exposure duration. Further, results demonstrated that nAu were adsorbed on the plants' roots irrespective of their size or coating variant; however, no evidence of internalization was apparent, and this was attributed to high agglomeration of nAu in 10 HM. Hence, adsorption was concluded as the basic mechanism of nAu accumulation by S. minima. Overall, the long-term exposure of S. minima to nAu did not inhibit plant biomass and growth rate but agglomerates on plant roots may block cell wall pores, and, in turn, alter uptake of essential macronutrients in plants, thus potentially affecting the overall ecological function.

Cytotoxicity and genotoxicity of coated-gold nanoparticles on freshwater algae Pseudokirchneriella subcapitata.

Gold engineered nanoparticles (nAu) are increasingly detected in ecosystems, and this raises the need to establish their potential effects on aquatic organisms. Herein, cytotoxic and genotoxic effects of branched polyethylenimine (BPEI)- and citrate (cit)-coated nAu (5, 20, and 40 nm) on algae Pseudokirchneriella subcapitata were evaluated. The apical biological endpoints: growth inhibition and chlorophyll a (Chl a) content were investigated at 62.5-1000 µg/L over 168 h. In addition, the apurinic/apyrimidinic (AP) sites, randomly amplified polymorphic deoxyribonucleic acid (RAPD) profiles, and genomic template stability (GTS) were assessed to determine the genotoxic effects of nAu. The results show algal growth inhibition at 5 nm BPEI-nAu up to 96 h, and thereafter cell recovery except at the highest concentration of 1000 µg/L. Insignificant growth reduction for cit-nAu (all sizes), as well as 20 and 40 nm BPEI-nAu, was observed over 96 h, but growth promotion was apparent at all exposures thereafter except for 40 nm BPEI-nAu at 250 µg/L. A decrease in Chl a content following exposure to 5 nm BPEI-nAu at 1000 µg/L corresponded to significant algal growth reduction. In genotoxicity studies, a significant increase in AP sites content was observed relative to the control - an indication of nAu ability to induce genotoxic effects irrespective of their size and coating type. For 5 nm- and 20 nm-sized nAu for both coating types and exposure concentrations no differences in AP sites content were observed after 72 and 168 h. However, a significant reduction in AP sites was observed following algae exposure to 40 nm-sized nAu (irrespective of coating type and exposure concentration) at 168 h compared to 72 h. Thus, AP sites results at 40 nm-size suggest likely DNA damage recovery over a longer exposure period. The findings on AP sites content showed a good correlation with an increase in genome template stability and growth promotion observed after 168 h. In addition, RAPD profiles demonstrated that nAu can induce DNA damage and/or DNA mutation to P. subcapitata as evidenced by the appearance and/or disappearance of normal bands compared to the controls. Therefore, genotoxicity results revealed significant toxicity of nAu to algae at the molecular level although no apparent effects were detectable at the morphological level. Overall, findings herein indicate that long-term exposure of P. subcapitata to low concentrations of nAu may cause undesirable sub-lethal ecological effects.

Occurrence, Fate, Effects, and Risks of Dexamethasone: Ecological Implications Post-COVID-19.

The recent outbreak of respiratory syndrome-coronavirus-2 (SARS-CoV-2), which causes coronavirus disease (COVID-19), has led to the widespread use of therapeutics, including dexamethasone (DEXA). DEXA, a synthetic glucocorticoid, is among the widely administered drugs used to treat hospitalized COVID-19 patients. The global COVID-19 surge in infections, consequent increasing hospitalizations, and other DEXA applications have raised concerns on eminent adverse ecological implications to aquatic ecosystems. Here, we aim to summarize published studies on DEXA occurrence, fate, and effects on organisms in natural and engineered systems as, pre-COVID, the drug has been identified as an emerging environmental contaminant. The results demonstrated a significant reduction of DEXA in wastewater treatment plants, with a small portion, including its transformation products (TPs), being released into downstream waters. Fish and crustaceans are the most susceptible species to DEXA exposure in the parts-per-billion range, suggesting potential deleterious ecological effects. However, there are data deficits on the implications of DEXA to marine and estuarine systems and wildlife. To improve DEXA management, toxicological outcomes of DEXA and formed TPs should entail long-term studies from whole organisms to molecular effects in actual environmental matrices and at realistic exposure concentrations. This can aid in striking a fine balance of saving human lives and protecting ecological integrity.

A model for screening and prioritizing consumer nanoproduct risks: A case study from South Africa.

The potential risks of the increasing variety and volume of engineered nanomaterials (ENMs) entering into the ecosystem remain poorly quantified. In recent years, information essential to evaluate the ecological risks of ENMs has increased. However, the data are highly fragmented, limited, or severely lacking. This limits the usefulness of the information to support holistic screening and prioritization of potentially harmful ENMs. To screen and prioritize ENMs risks, we adopted a two-phased approach. First, a holistic framework model was developed to integrate a diverse set of factors aimed to assess the potential hazard, exposure, and in turn, risk to the ecosystem of ENMs from a given consumer nanoproduct. Secondly, using published literature we created a database of consumer nanoproduct categories, and types based on embedded ENMs type. The database consisted of eight consumer product categories, eleven different types of ENMs, and twenty-three nanoproduct types. The model results indicates the largest quantities of ENMs were released from sunscreens, textiles, cosmetics and paints with dominant ENMs quantities in descending order (based on quantity) as nTiO2>nZnO>nSiO2>nAg, and nFe2O3. In addition, according to the results from this study, nAg from washing machine were found to likely the highest risk to the environment. Overall, our model-derived results based on the case study illustrated: (i) the holistic framework's ability to screen, prioritize, rank, and compare ENMs potential exposure and risks among different nanoproducts categories and types, (ii) the derived risk estimations could support nanowastes classification with likelihood of non-uniformity of nanowastes classes even from the same nanoproduct category (e.g. cosmetics), and (iii) the lack of a mass-based criteria specific for EMNs impedes realistic exposure and risk evaluation in the ecological systems.

Kinetic interpretation of log-logistic dose-time response curves.

A Hill-type time-response curve was derived using a single-step chemical kinetics approximation. The rate expression for the transformation is a differential equation that provides an interpolation formula between the logistic growth curve and second order kinetics. The solution is equivalent to the log-logistic cumulative distribution function with the time constant expressed in terms of a kinetic rate constant. This expression was extended to a full dose-time-response equation by postulating a concentration dependence for the rate constant. This was achieved by invoking a modified form of Haber's law that connects an observed toxic effect with the concentration of the active agent and the elapsed exposure time. Analysis showed that the concept of Concentration Addition corresponds to a special case where the rate constant for the overall transformation rate is proportional to the sum of the rate constants that apply when the agents act individually. Biodiesel "survival" curves were measured and used to test the applicability of the empirical model to describe the effects of inhibitor dosage and binary inhibitor mixtures. Positive results suggest that the proposed dose-response relationship for the toxicity of agents to organisms can be extended to inanimate systems especially in cases where accurate mechanistic models are lacking.

Interactions of metal-based engineered nanoparticles with aquatic higher plants: A review of the state of current knowledge.

The rising potential for the release of engineered nanoparticles (ENPs) into aquatic environments requires evaluation of risks to protect ecological health. The present review examines knowledge pertaining to the interactions of metal-based ENPs with aquatic higher plants, identifies information gaps, and raises considerations for future research to advance knowledge on the subject. The discussion focuses on ENPs' bioaccessibility; uptake, adsorption, translocation, and bioaccumulation; and 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 internalization. However, few reports document the internalization of ENPs by plants; thus, the role of nanoparticulates' internalization in bioaccumulation and toxicity remains unclear, requiring further investigation. The toxicities of metal-based ENPs mainly have 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 ENP characteristics and water physicochemical parameters, as their interplay determines ENP bioaccessibility and influences their risk to health of aquatic higher plants. Furthermore, harmonization of test protocols is recommended for fast tracking the generation of comparable data. Environ Toxicol Chem 2016;35:1677-1694. © 2016 SETAC.

The oxidative toxicity of Ag and ZnO nanoparticles towards the aquatic plant Spirodela punctuta and the role of testing media parameters.

The toxicity effects of silver (nAg) and zinc oxide (nZnO) engineered nanoparticles (ENPs) on the duckweed Spirodela punctuta were studied to investigate the potential risks posed by these ENPs towards higher aquatic plants. The influence of media abiotic factors on the stability of the ENPs was also evaluated. Marked agglomeration of ENPs was observed after introduction into testing media whereby large particles settled out of suspension and accumulated at the bottom of testing vessels. The high ionic strength (IS) promoted agglomeration of ENPs because it reduced the inter-particle repulsion caused by a reduction in their surface charge. Low dissolution was observed for nAg, reaching only 0.015% at 1000 mg L(-1), whilst improved dissolution was observed for nZnO, only falling below analytical quantification at 0.1 mg L(-1) and lower. The quantification of free radicals namely, reactive oxygen and nitrogen species (ROS/RNS) and hydrogen peroxide (H2O2), indicated the induction of oxidative stress in plants exposed to the ENPs. A definite dose influence was observed for ROS/RNS volumes in plants exposed to nZnO for 14 days, a response not always observed. The total antioxidant capacity (TAC) and superoxide dismutase (SOD) activity in plants indicated varying degrees of oxidative toxicity caused by exposure to ENPs. This toxicity was driven mainly by particulates in plants exposed to nAg, whilst dissolved Zn(2+) was the main driver for toxicity in plants exposed to nZnO. Our findings suggest that the toxicity of nAg and nZnO could be caused by both the particulates and ionic forms, as modified by media properties.

Nanotechnology risk assessment from a waste management perspective: are the current tools adequate?

The burgeoning nanotechnology industry is rapidly generating new forms of waste streams generically referred herein as nanowastes. However, little is known about the fate and behavior of these waste streams and their impacts thereof in different ecological systems despite their increasingly widespread dispersion into the environment through production, distribution, handling, and nanomaterials (NMs) incorporation into bulk products processes. In this paper, risk assessment of nanotechnology from a waste management perspective was examined to elucidate potential new forms of challenges nanowastes may likely pose to the current legislative and waste management systems. This was through the identification of several knowledge gaps that merit urgent attention in order to increase our collective understanding of managing nanowastes safely, responsibly, and sustainably. The paper presents the identified gaps and consequently proposes a qualitative risk assessment of nanowastes to address some of the current challenges. The applicability of the proposed model is illustrated through several examples. In addition, the first nanowastes classification protocol presented in this article show that a given nanomaterial may result in generating nanowaste streams of different forms with variant hazard levels ranging from benign to extremely being hazardous waste streams - a dramatic phenomenon from the conventional waste streams due to macroscale chemicals. The study shows that it is in the early days to draw broad generic classification of different nanowastes, and each stream may require their risk profile be assessed on a case-by-case basis. We conclude by presenting several recommendations on what needs to be done in dealing with nanowastes as means of avoiding unintended long-term consequences of nanotechnology.

Simulated environmental risk estimation of engineered nanomaterials: a case of cosmetics in Johannesburg City.

This paper attempts to quantify the potential risks posed by engineered nanomaterials (ENMs) to the aquatic and terrestrial ecosystems from cosmetic-based nanoproducts. The predicted environmental concentrations (PEC) were modelled for the silver (nAg) and titanium dioxide (nTiO(2)) nanoparticles embedded in cosmetic nanoproducts. The Johannesburg Metropolitan City (JHB City), in South Africa, was used as the reference study area. A mathematical model was applied to compute the quantities of ENMs flows from the cosmetic nanoproducts into the JHB City aquatic and terrestrial ecosystems. The risk quotient (RQ) of the nanoscale materials were evaluated as a ratio of PEC to the predicted no effect concentrations (PNEC). RQ values showed wide variance due to factors like; the quantities of ENMs, the fate and pathways of ENMs in the aquatic and terrestrial ecosystems, efficiency of the wastewater treatment plants (WWTP) as well as the economic and demographic data for South Africa and Switzerland. For the aquatic environment, the PEC values of nAg ranged from 2.80 × 10(-3) to 6.19 × 10(-1) µg L(-1) whereas for nTiO(2) the values ranged from 2.7 0 × 10(-3) to 2.70 × 10(-1) µg L(-1) under the realistic dilution factor of 1 with the WWTP functioning at high removal efficiency regime. The RQ values in the aquatic ecosystems were mostly >1, indicating the potential risk of both nAg and nTiO(2) but <<<1 in the terrestrial ecosystems. Our results provide the first quantification of ENMs potential risk into the environment Johannesburg City in a developing country's natural and technical settings.

Engineered inorganic nanoparticles and cosmetics: facts, issues, knowledge gaps and challenges.

The cosmetic industry is among the first adaptors of nanotechnology through the use of engineered nanoparticles (ENPs) to enhance the performance of their products and meet the customers' needs. Recently, there have been increasing concerns from different societal stakeholders (e.g., governments, environmental activist pressure groups, scientists, general public, etc.) concerning the safety and environmental impact of ENPs used in cosmetics. This review paper seeks to address the twin concerns of the safety of cosmetics and the potential environmental impacts due to the constituent chemicals-the ENPs. The safety aspect is addressed by examining recently published scientific data on the possibility of ENPs penetrating human skin. Data indicates that although particular types of ENPs can penetrate into the skin, until now no penetration has been detected beyond the stratum corneum of the ENPs used in cosmetics. Yet, important lessons can be learned from the more recent studies that identify the characteristics of ENPs penetrating into and permeating through human skin. On the part of the environmental impact, the scientific literature has very limited or none existent specific articles addressing the environmental impacts of ENPs owing to the cosmetic products. Therefore, general ecotoxicological data on risk assessment of ENPs has been applied to ascertain if there are potential environmental impacts from cosmetics. Results include some of the first studies on the qualitative and quantitative risk assessment of ENPs from cosmetics and suggest that further research is required as the knowledge is incomplete to make definitive conclusions as is the case with skin penetration. The authors conclude that the cosmetic industry should be more transparent in its use of nanotechnology in cosmetic products to facilitate realistic risk assessments as well as scientists and pressure groups being accurate in their conclusions on the general applicability of their findings. Transparency in cosmetics needs nanotechnology, but nanotechnology in cosmetics also needs transparency...