61 RBCIAMB | v.55 | n.1 | mar 2020 | 61-71 - ISSN 2176-9478 Aline Belem Machado Master’s degree and Ph.D. student in Environmental Quality from Universidade Feevale – Novo Hamburgo (RS), Brazil. Luciane Rosa Feksa Master’s degree and Ph.D. in Biological Sciences from Universidade Federal do Rio Grande do Sul (UFRGS) – Porto Alegre (RS), Brazil. Daniela Montanari Migliavacca Osorio Ph.D. in Ecology from UFRGS – Porto Alegre (RS), Brazil. Daiane Bolzan Berlese Ph.D. in Biochemical Toxicology from Universidade Federal de Santa Maria – Santa Maria (RS), Brazil. Endereço para correspondência: Aline Belem Machado – ERS-239, 2755 – Vila Nova – CEP: 93525-075 – Novo Hamburgo (RS), Brazil – E-mail: linebmachado@hotmail.com Received on: 11/20/2019 Accepted on: 03/09/2020 ABSTRACT Investments in nanotechnology are increasing together with its application in daily products. The use of nanomaterials leads to their release in the environment and the contamination of rivers, which can cause toxicity to the aquatic biota and human beings. Nanomaterials are present in rivers of several countries. However, the detection of nanomaterials in river samples is difficult, so probabilistic methods are being developed to determine their concentration in aquatic environments. Fortunately, water treatments have proven to be effective in removing these nanomaterials. Therefore, the present study aimed to describe the many pathways that nanoparticles can follow from their production to their final destination, along with their possible detection and toxicity, based on the search of manuscripts from ScienceDirect, Wiley Online Library, and Periódicos Capes databases. Keywords: analytical methods; aquatic systems; nanomaterials; toxicity; water treatment. RESUMO Os investimentos em nanotecnologia estão crescendo e, juntamente com eles, sua aplicação em produtos de uso diário. O uso de nanomateriais implica em sua liberação no meio ambiente e na contaminação do rio, o que pode causar toxicidade para a biota aquática e para os seres humanos. A presença de nanomateriais em rios ocorre em diferentes países. Entretanto, a detecção de nanomateriais em amostras de rios é difícil, portanto métodos probabilísticos estão sendo desenvolvidos para determinar a concentração de nanomateriais em ambientes aquáticos. Felizmente, os tratamentos de água estão demonstrando eficácia na remoção desses nanomateriais. Portanto, o objetivo do presente estudo foi descrever os diversos caminhos que as nanopartículas podem ter desde sua produção até seu destino final, juntamente com sua possível detecção e toxicidade, baseado na pesquisa de manuscritos nas bases de dados da Science Direct, Wiley Online Library e Periódicos Capes. Palavras-chave: métodos analíticos; sistemas aquáticos; nanomateriais; toxicidade; tratamento água. DOI: 10.5327/Z2176-947820200625 NANOPARTICLES IN AQUATIC ENVIRONMENTS – FROM PRODUCTION TO WATER TREATMENT: A REVIEW NANOPARTÍCULAS NO AMBIENTE AQUÁTICO – DA PRODUÇÃO AO TRATAMENTO DA ÁGUA: UMA REVISÃO https://orcid.org/0000-0001-5425-6608 https://orcid.org/0000-0001-8063-4713 https://orcid.org/0000-0002-9923-4514 https://orcid.org/0000-0002-5326-8065 Machado, A.B. et al. 62 RBCIAMB | v.55 | n.1 | mar 2020 | 61-71 - ISSN 2176-9478 INTRODUCTION Nanotechnology involves the manipulation of mate- rials within the nanometer size scale between 1 and 100 nm (HANNAH; THOMPSON, 2008; LU; ASTRUC, 2018); however, according to Maurice and Hochella (2008), nanoparticles are those that present at least one nanoparticle with a dimension lower than 100 nm, including spherical, tubular, or irregularly-shaped par- ticles. Nanoparticles have a high surface area to vol- ume ratio and unique physical and chemical properties (GRACA et al., 2018). Due to its great potential, the investments in nano- technology have been increasing together with the worldwide development in scientific and industrial scale (ASZTEMBORSKA et al., 2018). The study of this technology started in 1959 with Richard Feynman’s lec- ture entitled “There’s plenty of room at the bottom” given at the Annual American Physical Society meeting (SAVOLAINEN et al., 2010). Engineered nanomaterials are applicable to different kinds of products and fields, such as cosmetics, medi- cine, engineering, electronics, and environmental pro- tection. However, all these applications result in the release of nanomaterials into the environment and, consequently, in the exposure of organisms to them (QUIK et al., 2010). Moreover, sewage and industrial discharge are the main release pathways of engineered nanoparticles. Thus, wastewater treatment plants are essential for controlling the release of these nanopar- ticles into the environment, such as surface waters through effluent discharge and land through sewage sludge disposal (HOU et al., 2012). Therefore, this review aimed to discuss nanotechnol- ogy from different points of view, including its appli- cation, release, and the consequent impact on the en- vironment and aquatic biota, as well as the different methodologies that can detect it and possibly remove it from water. The present review was based on the investigation of manuscripts about the application, detection, water contamination, toxicity, and water treatment related to the production and use of nanoparticles. The review was performed by searching articles from ScienceDirect, Wiley Online Library, and Periódicos Capes databases, using the following keywords: an- alytical methods, nanomaterials, river basin, toxicity, and water treatment. NANOTECHNOLOGY APPLICATIONS AND CONSEQUENT RELEASE Nanotechnology can be applied to several kinds of products. Some of them — such as fabrics, person- al care items, and food, which contain engineered nanoparticles, including silver (Ag), titanium diox- ide (TiO 2 ), and silica (Si) — can have an easier path to enter the environment, since they can be washed down drains because of their household use (PETERS et al., 2018). In addition to the variety of products that contain engineered nanoparticles, such as those men- tioned above and also sunscreens, detergents, paints, printer inks, and tires, accidental spills during the man- ufacturing and transportation, wear and tear, and their final disposal increase the release of these substances into the environment (NAVARRO et al., 2008). Figure 1 shows the different pathways that nanoparticles can follow from their production to their final destination. Many different types of nanoparticles are widely used in cosmetics and sunscreen products, and their con- sequent disposal into the environment makes rivers and wastewater treatment plants to act as reservoirs of these substances, which can subsequently affect hu- man health through tap water consumption (CHANG et al., 2017). Research performed in 2013 revealed that the pro- duction of different kinds of engineered nanoparticles would reach around 350,000 tons by 2016 (GOSWAMI et al., 2017). This finding can be attested by the increase in products that contain nanoparticles in their compo- sition. In 2005, a website project named Nanotechnol- ogy Consumer Products Inventory (CPI) was created to register products that contain nanotechnology. At first, they listed a total of 54 products, and, by 2014, they had 1,814 products registered (VANCE et al., 2015). In 2019, by the time this article was written, the web- site reported 1946 products with nanotechnology di- vided into eight categories and 37 subcategories (CPI, 2019). Figure 2 presents the number of products avail- able in 2019, according to the main categories. Nanoparticles in aquatic environments – from production to water treatment: a review 63 RBCIAMB | v.55 | n.1 | mar 2020 | 61-71 - ISSN 2176-9478 Green lines: different destinations; yellow lines: consumer consumption and release fate; orange lines: water and sewage treatment and waste incineration; light blue lines: final destination; dark blue lines: final destination from surface water; WWTP: wastewater treatment plant. Source: adapted from Gottschalk et al. (2009) and Peters et al. (2018). Figure 1 – Possible pathways of nanoparticles since their production. ATMOSPHERE LANDFILL SOIL SURFACE WATER SEDIMENTS GROUNDWATER SEWAGE TREATMENT PLANT (STP) WWTP WASTE INCINERATION PLANT (WIP) HOUSEHOLD RECREATIONAL ACTIVITIES ACCIDENTALSPILLSRECYCLING INDUSTRY PRODUCTION, MANUFACTURING Figure 2 – Number of products available in 2019 divided into categories, according to the Consumer Products Inventory. Number of products 908 356 214 142 116 103 69 38 He alth and Fit nes s Ho me and Ga rde n Au tom otiv e Cro ss-C utti ng Foo d a nd Bev era ge Ele ctr oni cs and Co mp ute rs Ap plia nce s Go ods for Ch ildr en Machado, A.B. et al. 64 RBCIAMB | v.55 | n.1 | mar 2020 | 61-71 - ISSN 2176-9478 MEANS OF DETECTION/MODELING Evaluating the potential risks of nanomaterials — de- rived from their production, application, and dispos- al — to the environment and human health requires suitable analytical procedures with reliable results about the fate and pathways of nanomaterials in the environment (LEOPOLD et al., 2016). The detection of nanoparticles in aquatic systems is dif- ficult and scarce. This situation results from the lack of sensitivity and selectivity of analytical methods capa- ble of detecting and characterizing these materials, es- pecially in complex natural matrices in which tradition- al methodologies must be modified in an attempt to detect nanoparticles (VON DER KAMMER et al., 2012). Von der Kammer et al. (2012) conducted an extensive review regarding this issue. However, the analysis of nanomaterials in the environ- ment can be quantified based on their mass, volume, or particle number. Qualitative analysis can sometimes identify the difference between engineered and natu- ral nanoparticles according to their chemical composi- tion and, along with the determination of particle size distribution, is very important for data interpretation (LEOPOLD et al., 2016). Natural nanoparticles are formed by natural processes through chemical, photo-chemical, mechanical, thermal, and biological pathways. Human activities such as mining can also generate them spon- taneously. Engineered as well as natural nanoparticles are formed by the same synthetic principles, which can occur by bottom-up or top-down approaches (SHARMA et al., 2015). The bottom-up principle consists of obtain- ing a final material through its construction from smaller particles (AGHARKAR et al., 2014). On the other hand, the top-down principle involves making a small final ma- terial from something larger (TOUR, 2014). Also, other parameters are relevant to analyze, such as metal spe- ciation, particle shape, surface area, surface charge, sur- face functionality, nature, stability, and coating structure (LEOPOLD et al., 2016). Single particle inductively coupled plasma mass spec- trometry (SP-ICP-MS) has proven to be a reliable method for detecting nanoparticles in aquatic me- dia. Its advantages include the high sensitivity for environmental nanoparticles in relation to their size, size distribution, and dissolved element concentra- tion (DONOVAN et al., 2016). However, analytical methods for detecting nanopar- ticles in water are sometimes difficult to reproduce. Based on this information, some authors (MUELLER & NOWACK, 2008; GOTTSCHALK et al., 2009; DUMONT et al., 2015) created a probabilistic method to deter- mine the concentration of a certain nanoparticle in the environment. This modeling of predicted envi- ronmental concentrations (PEC) is usually necessary and a valuable replacement for measurement studies (GOTTSCHALK et al., 2009). The modeling performed by Gottschalk et al. (2009) was developed based on a probabilistic material flow analysis approach. They used different compartments to calculate better the proba- ble concentration of a certain nanoparticle, including: • environmental: water, air, soil, sediment, and groundwater; • technical: production, manufacturing and consump- tion, sewage treatment plant (STP), waste incinera- tion plant (WIP), landfill, and recycling processes. The derivations of the sizes of air, water, soil, and sedi- ment were also used to calculate the concentrations of engineered nanoparticles in these compartments. This same study took into account the life cycle and the different release pathways of engineered nanoparti- cles and grouped similar life cycles together. Release pathways depend on the engineered nanoparticle-con- taining product, including the following assumptions: • glass and ceramic have all their nanoparticles re- leased into the environment; • cosmetics, coatings, and cleaning agents, as well as dietary supplements present major release of nanoparticles into the environment; • paints have their nanoparticles disposed of in the sewage treatment plant (STP), landfill, soil, and/or surface waters (GOTTSCHALK et al., 2009). In a similar study, Dumont et al. (2015) developed the Global Water Availability Assessment (GWAVA) model, analyzing whether this model was capable of simulating the concentrations of nano silver (Ag-nano) and nano zinc oxide (ZnO-nano) released into surface waters. Un- like the Gottschalk model, Dumont’s also considered space and time; for example, the spatial variability in Nanoparticles in aquatic environments – from production to water treatment: a review 65 RBCIAMB | v.55 | n.1 | mar 2020 | 61-71 - ISSN 2176-9478 population density and temporal variability in river dis- charge. GWAVA simulates the river discharge and the number of some hydrological conditions, such as lake water volumes and human water abstractions. One of the equations includes the area-specific load of engi- neered nanoparticles in surface water through sewage effluent, assuming that households are the only source of Ag-nano and ZnO-nano in the sewage effluent. How- ever, the authors concluded that the estimated con- centrations were lower than those of other studies found in the literature, which can be justified by the differences in modeled regions, assumed production volumes, and market penetration factors. PRESENCE OF NANOPARTICLES IN WATER Population growth and waste disposal from industries have caused a major problem in the aquatic systems (COSTA et al., 2014). The anthropogenic materials, which include nanoparticles, released into aquatic envi- ronments depend on the volume of industrial produc- tion and on how these materials are used (TROESTER; BRAUCH; HOFMANN, 2016). Engineered nanomate- rials can contaminate the environment in any stage of their life cycle, such as production, use, and disposal (PETERS et al., 2018). ZnO and cerium dioxide (CeO2) are two of the most used nanomaterials, being present in items such as personal care products, paints, and cata- lysts. Consequently, they are released into river basins through wastewater or runoff (DONOVAN et al., 2016). Table 1 presents some results of analytical and model determinations of nanoparticle concentrations in rivers. The potential for environmental and human exposure to engineered nanoparticles depends on the amount of these materials in the environment, which in turn have their effect based on their behavior and fate regarding the adsorption, accumulation, persistence, aggrega- tion, and mobility in different environmental media (GAO et al., 2013). The fate of nanomaterials in aque- ous systems is subject to their solubility or dispersibility, interactions between the nanomaterial and natural or Location n-Ag (µg/L) n-CeO 2 (µg/L) n-TiO 2 (µg/L) n-ZnO (µg/L) Method Matrix Reference Netherlands 0.025 0.052 Analytical Surface water PETERS et al., 2018 Netherlands 0.6 Analytical Sludge – WWTP MARKUS et al., 2018 Netherlands 0.13 Analytical Influent – WWTP MARKUS et al., 2018 USA < 0.10* 1.11 Analytical Source water – DWTP DONOVAN et al., 2016 Europe 0.58 – 2.16 0.012 – 0.057 0.008 – 0.055 Model Surface water GOTTSCHALK et al., 2009 USA 0.088 – 0.42 0.002 – 0.010 0.001 – 0.003 Model Surface water GOTTSCHALK et al., 2009 Switzerland 0.555 – 2.63 0.016 – 0.085 0.011 – 0.058 Model Surface water GOTTSCHALK et al., 2009 Switzerland 0.0023 0.36 Model Surface water DUMONT et al., 2015 Table 1 – Summary of nanoparticles analyzed in the environment and the predicted environmental concentration (PEC) found in the literature. µg/L: concentration of nanoparticles in aqueous media; WWTP: wastewater treatment plant; DWTP: drinking water treatment plant; *below the detection limit. Machado, A.B. et al. 66 RBCIAMB | v.55 | n.1 | mar 2020 | 61-71 - ISSN 2176-9478 anthropogenic chemicals in this environment, and bio- logical and abiotic processes (BRAR et al., 2010). Aggregation and dissolution are related to nanoparticle stability in aqueous media and must be considered. Some factors, such as ionic strength, pH, and organic matters, can affect the aggregation and dissolution of nanoparti- cles (DONOVAN et al., 2016). The bioavailability and trans- portation efficiency of nanoparticle aggregates are associ- ated with aggregation and sedimentation when released into the environment. Also, water chemistry strongly in- fluences the stability of nanoparticles (PENG et al., 2017). However, nanoparticles can also be found in different types of water besides river basins. In a study per- formed by Graca et al. (2018), they were able to detect different nanomaterials in seawater from natural sourc- es. They also investigated the influence of seasons on the number of nanoparticles in seawater. The authors identified environmental silica nanofibers of 15 nm, probably from remains of flagellates; manganese and iron oxide nanofibers, possibly from microbes; and py- rite nanospheres of 55 nm, potentially formed in anoxic sediments. Nanoparticles increased in water samples in June compared to November. This fact can be ex- plained by the seasonal variation of flagellates found in the study, in which Summer (June) presents the highest concentration of flagellates in comparison to Autumn (November) (GRACA et al., 2018). The finding demon- strates the effects that different seasons can have on the concentration of nanoparticles. POSSIBLE TOXICITY TO AQUATIC BIOTA Water is an important transfer and fate medium for en- gineered nanoparticles. Human health is related to wa- ter safety, and the potential human impact of metallic nanoparticles leaching into aquatic environments is at- tracting attention (GAO et al., 2013). The toxicity to aquat- ic ecosystems is mainly due to changes in water quantity and quality, as well as in the physical habitat and biologi- cal components, the so-called pressures. Chemicals with nanoparticle size are some of the materials responsible for the toxicity of aquatic organisms (GRIZZETTI et al., 2016). The properties of nanoparticles, such as the high surface area to volume ratio and small size, give them unique characteristics and applications when compared to bulk materials. For this reason, their bioavailability and, consequently, their toxicity can increase (SOUSA; CORNI- CIUC; TEIXEIRA, 2017). Due to the small particle size and corresponding enhanced activity, organisms can have more interaction with engineered nanoparticles than large particles (GOSWAMI et al., 2017). The release of nanoparticles into the environment through water can be very concerning given the po- tential for contamination, as they are capable of cotransporting sorbed contaminants into surface and groundwater, and also because they are nanoparticles themselves (CHEKLI et al., 2015). Some properties, such as the charge of different metal ions (Ag+, Cu2+, and Al3-) and the adsorption efficiency of engineered nanoparticle, can affect the bioavailability of these ma- terials and their consequent eco-toxicological effects (GOSWAMI et al., 2017). An important question concerning nanoparticle toxic- ity is whether this type of material is more dangerous to organisms than the corresponding bulk material. In order to evaluate this toxicity, Xiong et al. (2011) ana- lyzed the acute toxicity of ZnO-nano and TiO 2 -nano on zebrafish (Danio rerio) and compared it to the effects caused by the corresponding bulk materials. The acute toxicity of TiO 2 -nano, ZnO-nano, and bulk ZnO demon- strates a dose dependency. The highest concentration of TiO 2 -nano studied (300 mg/L) was able to cause 100% mortality. However, bulk TiO 2 showed no acute toxicity to zebrafish. The concentration of 30 mg/L of ZnO-nano and bulk ZnO led to 100% mortality. Their results sug- gest that TiO 2 toxicity is subject to particle size; however, ZnO does not exhibit this characteristic, demonstrating that ZnO depends on chemical composition. PRESENCE AND REMOVAL OF NANOPARTICLES IN WATER TREATMENT PLANTS Anthropogenic activities are some of the main pres- sure generators. These pressures can affect the biodi- versity and the status of aquatic systems. Any change in these systems can alter their economic value. Nanoparticles in aquatic environments – from production to water treatment: a review 67 RBCIAMB | v.55 | n.1 | mar 2020 | 61-71 - ISSN 2176-9478 The relationship between these activities and the eco- logical status needs to be understood in order to devise cost-effective measures aimed at achieving good eco- logical status for water bodies (GRIZZETTI et al., 2016). Conventional water treatment consists of coagulation, flocculation, sedimentation, filtration, and disinfection (SOUSA; CORNICIUC; TEIXEIRA, 2017). With the pur- pose of analyzing the removal of TiO 2 -nano with con- ventional drinking water treatment, Sousa, Corniciuc and Teixeira (2017) evaluated four synthetic waters and different concentrations of TiO 2 -nano. They were able to prove that the sedimentation of TiO 2 -nano depends on pH, as at a pH of 5.4, TiO 2 -nano settled faster than in waters with a different pH. This study also revealed that titanium removal efficiency was around 80% when coagulant was not added to water. In conclusion, they proved that TiO 2 -nano can be removed from sur- face water through conventional water treatment. Nanoparticles and biofilms can interact through three different processes: transportation of nanoparticles to the vicinity of the biofilm; deposition of the nanoparti- cle in the biofilm surface; and migration of nanoparticles in the inner area of the biofilm. Nonetheless, different characteristics can interfere with these interactions, such as nanoparticle characteristics, physicochemical and bi- ological composition of the biofilm, and environmental parameters, including water chemistry, flow, and tem- perature (IKUMA; DECHO; LAU, 2015). Besides, different weather conditions can affect the status of nanoparti- cles in wastewater treatment. For example, during dry water conditions, fulvic acids can promote the uptake and bioaccumulation of silver nanoparticles in biofilms, and the sewer biofilm can act as a temporary sink to these nanoparticles and accumulate them. In contrast, during rainy conditions, this biofilm can work as a source of Ag-nano and release it into the environment. There- fore, during these weather conditions, the nanoparticles can bypass the wastewater treatment plant and be re- leased directly into aquatic systems during stormwater discharge (KAEGI et al., 2013). Also, seasons can affect nanoparticles regarding their release into municipal wastewater streams, given that they can be incorporated into functionalized products, which subsequently have their use related to different seasons and their disposal dependent on climate con- ditions. For instance, sunscreen and cosmetics with sun protection factor are used during diurnal solar ra- diation, especially in Summer (CHOI et al., 2018). Season-related changes led Choi et al. (2018) to study the concentration of engineered nanoparticles (TiO2-na- no and ZnO-nano) in a wastewater treatment plant, which included primary clarifier, aeration basin, sec- ondary clarifier, and chlorination, during twelve months aiming at analyzing the relationship between the con- sumption of nanoparticle-containing products and the concentration of nanoparticles in wastewater. They col- lected wastewater samples from influent, effluent, sludge, and sedimentation tanks. The results revealed a higher inflow of TiO2-nano and Zn-nano concentration during Summer and Winter, probably due to the use of personal care products under high or low tempera- tures. Also, the general inflow of TiO2-nano was higher than that of ZnO-nano, indicating greater use of TiO 2 -na- no-related products in comparison to ZnO-nano-related products. In conclusion, the findings demonstrated that nanoparticle concentrations vary seasonally, and that temperature is an important factor for the engineered nanoparticle sorption into sludge particulates. Sometimes, wastewater treatment plants do not fully remove TiO2-nano; thus, a great amount of this sub- stance can reach the environment and natural waters (CHEKLI et al., 2015). However, in the research per- formed by Wang, Westerhoff, and Hristovski (2012), they analyzed the TiO2-nano removal from a waste- water treatment based on sequencing batch reactors with aerated and mixed samples. The reactors were seeded with bacteria culture from the sludge of an ur- ban wastewater treatment plant, which had a reten- tion time of approximately six days. The nanomaterials were added to the feed solution and subsequently to the sequencing batch reactor. The aeration time was approximately 8 hours. They were able to remove around 70% of TiO2-nano from wastewater with the presence of biomass. Therefore, in the absence of bio- mass, these nanoparticles were not removed due to aggregation and sedimentation, factors that belong to the abiotic mechanisms mentioned above. Briefly, they were able to remove TiO2-nano using a biological wastewater treatment plant in lab scale. Another highly studied nanomaterial is Ag-nano. Nu- merous products have this substance, such as clothing, paints, bandages, and food containers. The consump- tion of these products results in the release of these Machado, A.B. et al. 68 RBCIAMB | v.55 | n.1 | mar 2020 | 61-71 - ISSN 2176-9478 nanomaterials into sewer systems and, consequently, into municipal wastewater treatment plants. For this reason, Hou et al. (2012) evaluated the removal of Ag-nano in a wastewater treatment plant from Beijing that uses an activated sludge process involving prima- ry clarification, aeration, secondary clarification, and treatment. The reactors were operated for 15 days, with a hydraulic residence time of 12 hours, and 10 hours of aeration followed by 2 hours of settling. The results demonstrated that, in the primary clarification process with an influent concentration of 269 mg/L of sus- pended solids, most of Ag-nano (94%) remained in the upper layer of wastewater, which means that the first clarification was not able to remove Ag-nano. However, when aeration and secondary clarification processes were implemented, the Ag-nano was completely re- moved from the wastewater. In a similar study performed in field-scale, Kaegi et al. (2013) evaluated the fate of Ag-nano in an urban waste- water system. They found that Ag-nano was transport- ed through the entire distance of 5 km in a sewer sys- tem without deposition. When evaluating efficiency, they verified that nanoparticle removal was around 99%, suggesting that they could be incorporated/attached to flocs of activated sludge. With this result, the authors assumed that a great number of nanoparticles that en- ter the wastewater treatment plant would be incorpo- rated in the sludge and, consequently, removed from the wastewater stream. Nevertheless, the wastewater sludge can still contain nanoparticles after treatment, and if spread to agricultural lands to be used as biosol- ids, it can potentially release nanoparticles into ground- water, subsurface waters, and soil (BRAR et al., 2010). This scenario reveals the anthropogenic contamination of nanomaterials into sewage, which, if not properly treated, can be released into rivers basins and contaminate aquat- ic organisms as well as humans, affecting their health in proportions that sometimes cannot be measured. CONCLUSIONS The production of nanomaterials is growing together with the release of these materials in aquatic environ- ments. Nanomaterials are being detected in rivers, which can result in toxic effects on the biota and hu- man health. 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