Proxy Measures for Simplified Environmental Assessment of Manufactured Nanomaterials

Ecotoxicity Assessment of Graphene Oxides Using Test Organisms from Three Hierarchical Trophic Levels to Evaluate Their Potential Environmental Risk

After more than a decade of studying the ecotoxicity of graphene oxide nanomaterials (nGOs), it has been concluded that there is limited information available regarding the environmental risk of graphene-based materials. Since existing ecotoxicological studies of nanomaterials have produced contradictory results, it is recommended that case-by-case studies should be conducted to evaluate their effects. This can be carried out by employing several methods, testing species from different trophic levels, and conducting community studies. Our goal was to evaluate the toxicity effects of two GOs (AF 96/97 and PM 995) derived from different graphite precursors on various test organisms from diverse trophic levels (bacteria, protozoa, a freshwater microbial community, plants, and invertebrate animals) in aquatic environments. We compared the effects of both nGO types and estimated the predicted no-effect environmental concentration (PNEC) values to determine their potential environmental risk. Our findings demonstrated the need for a complex ecotoxicity toolkit since the ecotoxicity results varied based on the test organism, the selected endpoints, and the test method used. Additionally, we found that toxicity effects were dependent on the concentration and characteristics of the specific nGO type used, as well as the exposure time. We estimated the PNEC values for GO AF 96/97 and GO PM 995 in the aquatic compartment to be 8 ng/L and 4 ng/L, respectively. Even after applying the worst-case scenario approach, the tested nGOs pose no environmental risk.

Current Trends on the Effects of Metal-Based Nanoparticles on Microbial Ecology

The growing field of nanotechnology and its many applications have led to the irregular release of nanoparticles (NPs), with unintended effects on the environment and continued contamination of water bodies. Metallic NPs are used more frequently in extreme environmental conditions due to their higher efficiency, which attracts more attention in various applications. Due to improper pre-treatment of biosolids, inefficient wastewater treatment practices, and other unregulated agricultural practices continue to contaminate the environment. In particular, the uncontrolled use of NPs in various industrial applications has led to damage to the microbial flora and caused irreplaceable damage to animals and plants. This study focuses on the effect of different doses, types, and compositions of NP on the ecosystem. The review also mentions the impact of various metallic NPs on microbial ecology, their interactions with microorganisms, ecotoxicity studies, and dosage evaluation of the NPs, mainly focused on the review article. However, further research is still needed to understand the complexity of interactions between NPs and microbes in soil and aquatic ecosystems.

Fate and effects of graphene oxide alone and with sorbed benzo(a)pyrene in mussels Mytilus galloprovincialis

Graphene oxide (GO) has gained a great scientific and economic interest due to its unique properties. As incorporation of GO in consumer products is rising, it is expected that GO will end up in oceans. Due to its high surface to volume ratio, GO can adsorb persistent organic pollutants (POPs), such as benzo(a)pyrene (BaP), and act as carrier of POPs, increasing their bioavailability to marine organisms. Thus, uptake and effects of GO in marine biota represent a major concern. This work aimed to assess the potential hazards of GO, alone or with sorbed BaP (GO+BaP), and BaP alone in marine mussels after 7 days of exposure. GO was detected through Raman spectroscopy in the lumen of the digestive tract and in feces of mussels exposed to GO and GO+BaP while BaP was bioaccumulated in mussels exposed to GO+BaP, but especially in those exposed to BaP. Overall, GO acted as a carrier of BaP to mussels but GO appeared to protect mussels towards BaP accumulation. Some effects observed in mussels exposed to GO+BaP were due to BaP carried onto GO nanoplatelets. Enhanced toxicity of GO+BaP with respect to GO and/or BaP or to controls were identified for other biological responses, demonstrating the complexity of interactions between GO and BaP.

Theoretical basis and experimental verification for evaluating the distribution of engineered nanoparticles in water-oil system

The distribution of nanoparticles between aqueous and organic phases is universally considered as the starting point in predicting the fate and bioavailability of engineered nanoparticles in the environment. However, the theoretical basis for determining the distribution of nanoparticles in the immiscible water-oil system remains unclear. Here, for the first time, theoretical calculations were conducted to illustrate the underlying mechanism. It was suggested that the distribution of nanoparticles was largely controlled by the surface charge, particle size and surface hydrophobicity, and the water-oil interface was not the favorable phase for nanoparticles until a size threshold (10 nm) was met and the particle surface became amphiphilic. The theoretical results were verified by the experimental approaches of different nanoparticles distributed in the water-octanol mixture. The neutralization of a charged surface led to enhanced distribution into octanol for hydrophobic nanoparticles (e.g., aqueous C₆₀), yet it had little effect on hydrophilic nanoparticles (e.g., fullerol). More nanoparticles were trapped at the water-oil interface when size grew larger (e.g., Ag-CIT and Au-CIT with citrate) and the surface rendered amphiphilic by polymeric coatings (e.g., Ag-PVP with polyvinylpyrrolidone), though larger hydrophobic nanoparticles like aqu-nC₆₀ tended to stay in the octanol. The surface charge and hydrophobicity may have an important impact on the path-dependent distribution of nanoparticles in water- octanol system. The mechanistic insights based on theoretical calculations and experimental approaches will facilitate the accurate prediction of the distribution of engineered nanoparticles in biological and environmental systems.

Insights into eco-corona formation and its role in the biological effects of nanomaterials from a molecular mechanisms perspective

Broad application of nanotechnology inevitably results in the release of nanomaterials (NMs) into the aquatic environment, and the negative effects of NMs on aquatic organisms have received much attention. Notably, in the natural aquatic environment, ubiquitous ecological macromolecules (i.e., natural organic matter, extracellular polymeric substances, proteins, and metabolites) can easily adsorb onto the surfaces of NMs and form an "eco-corona". As most NMs have such an eco-corona modification, the properties of their eco-corona significantly determine the fate and ecotoxicity of NMs in the natural aquatic ecosystem. Therefore, it is of great importance to understand the role of the eco-corona to evaluate the environmental risks NMs pose. However, studies on the mechanism of eco-corona formation and its resulting nanotoxicity on aquatic organisms, especially at molecular levels, are rare. This review systemically summarizes the mechanisms of eco-corona formation by several typical ecological macromolecules. In addition, the similarities and differences in nanotoxicity between pristine and corona-coated NMs to aquatic organisms at different trophic levels were compared. Finally, recent findings about potential mechanisms on how NM coronas act on aquatic organisms are discussed, including cellular internalization, oxidative stress, and genotoxicity. The literature shows that 1) the formation of an eco-corona on NMs and its biological effect highly depend on both the composition and conformation of macromolecules; 2) both feeding behavior and body size of aquatic organisms at different trophic levels result in different responses to corona-coated NMs; 3) genotoxicity can be used as a promising biological endpoint for evaluating the role of eco-coronas in natural waters. This review provides informative insight for a better understanding of the role of eco-corona plays in the nanotoxicity of NMs to aquatic organisms which will aid the safe use of NMs.

Quantitative structure-activity relationship for the photooxidation of aromatic micro-pollutants induced by graphene oxide in water

The photocatalytic degradation behavior of aromatic micro-pollutants (AMPs) exhibits complexity and uncertainty, which mainly depends on the properties of different substituents on benzene. And with similar catalytic reaction substrates, the reaction rate constant could reveal the influence of different characteristics of molecular structure in a specific system. Therefore, the photooxidation pseudo first-order kinetic rate constants (k_obs) of 30 AMPs were experimentally determined in Photo-GO system. A quantitative structure-activity relationship (QSAR) model for predicting the photooxidation reaction of AMPs has been developed by stepwise multiple linear regression (MLR) method, based on the lg k_obs and representative molecule descriptors (20 in total) including physicochemical, quantum chemical and electrostatic descriptors. Afterwards, R_adj², Q_LOO², and Q_ext² were calculated as 0.870, 0.841, and 0.732 respectively, which exhibited the excellent goodness-of-fit, robustness, and predictability of the QSAR model, indicating its great prediction ability for photooxidation behavior of AMPs. Meanwhile, during the photooxidation process of AMPs with GO, the model revealed that the one-electron oxidation potential (E_ox), molecular dipole moment (μ), and number of hydrogen bond donors (#HD) were the most important molecular structural parameters, which showed that the single electron transfer pathway and adsorption were as the significant steps. Additionally, the Hammett correlation showed that photooxidation of AMPs in Photo-GO system is of typical electrophilic reactions, which demonstrated that the electron-donating substituents could promote the photooxidation of AMPs. The QSAR model was constructed and evaluated to perform the prediction of AMPs reaction kinetics, which provided a guidance for the study of the mechanism and selective oxidation of AOPs photooxidation system based on GO.

Analysis of Nanomaterials on Biological and Environmental Systems and New Analytical Methods for Improved Detection

The advancing field of nanoscience has produced lower mass, smaller size, and expanded chemical composition nanoparticles over recent years. These new nanoparticles have challenged traditional analytical methods of qualification and quantification. Such advancements in nanoparticles and nanomaterials have captured the attention of toxicologists with concerns regarding the environment and human health impacts. Given that nanoparticles are only limited by size (1–100 nm), their chemical and physical characteristics can drastically change and thus alter their overall nanotoxicity in unpredictable ways. A significant limitation to the development of nanomaterials is that traditional regulatory and scientific methods used to assess the biological and environmental toxicity of chemicals do not generally apply to the assessment of nanomaterials. Significant research effort has been initiated, but much more is still needed to develop new and improved analytical measurement methods for detecting and quantitating nanomaterials in biological and environmental systems.

In vitro and in silico study of mixtures cytotoxicity of metal oxide nanoparticles to Escherichia coli: a mechanistic approach

Metal oxide nanoparticles (MONPs) are commonly found in the aquatic and terrestrial systems as chemical mixtures. Assessment of cytotoxicity associated with single and combination of MONPs can truly identify the concerned environmental risk. Thus, using Escherichia coli as a test model, in vitro cytotoxicity of 6 single MONPs, 15 binary and 20 tertiary mixtures with equitoxic ratios was evaluated following standard bioassay protocols. Assessment of oxidative stress suggested that the production of reactive oxygen species (ROS) was negligible, and the release of metal zinc ions played an important role in the toxicity of MONP mixtures. From our experimental data points, seven quantitative structure-activity relationships (QSARs) models were developed to model the cytotoxicity of these MONPs, based on our created periodic table-based descriptors and experimentally analyzed Zeta-potential. Two strategic approaches i.e. pharmacological and mathematical hypotheses were considered to identify the mixture descriptors pool for modeling purposes. The stringent validation criteria suggested that the model (Model M4) developed with mixture descriptors generated by square-root mole contribution outperformed the other six models considering validation criteria. While considering the pharmacological approach, the 'independent action' generated descriptor pool offered the best model (Model M2), which firmly confirmed that each MONP in the mixture acts through 'independent action' to induce cytotoxicity to E. coli instead of fostering an additive, antagonistic or synergistic effect among MONPs. The total metal electronegativity in a specific metal oxide relative to the number of oxygen atoms and metal valence was associated with a positive contribution to cytotoxicity. At the same time, the core count, which gives a measure of molecular bulk and Zeta potential, had a negative contribution to cytotoxicity.

Nanowaste: Another Future Waste, Its Sources, Release Mechanism, and Removal Strategies in the Environment

Nanowaste is defined as waste derived from materials with at least one dimension in the 1–100 nm range. The nanomaterials containing products are considered as “nanoproducts” and they can lead to the development of nanomaterial-containing waste, also termed as “nanowaste”. The increased production and consumption of these engineered nanomaterials (ENMs) and nanoproducts that generate enormous amounts of nanowaste have raised serious concerns about their fate, behavior, and ultimate disposal in the environment. It is of the utmost importance that nanowaste is disposed of in an appropriate manner to avoid an adverse impact on human health and the environment. The unique properties of ENMs, combined with an inadequate understanding of appropriate treatment techniques for many forms of nanowaste, makes nanowaste disposal a complex task. Presently, there is a lack of available information on the optimized standards for identifying, monitoring, and managing nanowaste. Therefore, this review highlights concerns about nanowaste as future waste that need to be addressed. The review focuses on ENMs waste (in the form of NP, nanotubes, nanowires, and quantum dots) generated from the manufacture of a wide variety of nanoproducts that end up as nanowaste and adversely affect the environment. Furthermore, the review considers different types of ENMs in waste streams and environmental compartments (i.e., soil, water, and air). Detailed studies are still required to identify data gaps and implement strategies to remove and control this future waste.

Prospective environmental risk screening of seven advanced materials based on production volumes and aquatic ecotoxicity

The number and volume of advanced materials being manufactured is increasing. In order to mitigate future impacts from such materials, assessment methods that can provide early indications of potential environmental risk are required. This paper presents a further development and testing of an environmental risk screening method based on two proxy measures: aquatic ecotoxicity and global annual production volumes. In addition to considering current production volumes, this further developed method considers potential future production volumes, thereby enabling prospective environmental risk screening. The proxy measures are applied to seven advanced materials: graphene, graphene oxide, nanocellulose, nanodiamond, quantum dots, nano-sized molybdenum disulfide, and MXenes. Only MXenes show high aquatic ecotoxicity, though the number of test results is still very limited. While current production volumes are relatively modest for most materials, several of the materials (graphene, graphene oxide, nanocellulose, nano-sized molybdenum disulfide, and MXenes) have the potential to become high-volume materials in the future. For MXenes, with both high aquatic ecotoxicity and high potential future production volumes, more detailed environmental risk assessments should be considered. For the other materials with high potential future production volumes, the recommendation is to continuously monitor their aquatic ecotoxicity data. Based on the application of the proxy measures combined with future scenarios for production volumes, we recommend this environmental risk screening method be used in the early development of advanced materials to prioritize which advanced materials should be subject to more detailed environmental assessments.

Critical review of the characteristics, interactions, and toxicity of micro/nanomaterials pollutants in aquatic environments

A wide range of contaminants of emerging concern such as micro/nanoplastics (MPs/PNPs) and metal-nanoparticles (Me-NPs) from anthropogenic activities have been identified in aquatic environments. The hazardous effects of these micro/nanomaterials as pollutants in organisms and the lack of knowledge about their behavior in aquatic environments have generated growing concern in the scientific community. The nanomaterials have a colloidal-type behavior due to their size range but with differences in their physicochemical properties. This review comprises the behavior of micro/nanomaterials pollutants and the physicochemical interactions between MPs/PNPs and Me-NPs in aquatic environments, and their potential toxicological effects in organisms. Moreover, this article describes the potential use of Me-NPs to remove MPs/PNPs present in the water column due to their photocatalytic and magnetic properties. It also discusses the challenge to determine harmful effects of micro/nanomaterials pollutants in organisms and provides future research directions to improve integrated management strategies to mitigate their environmental impact.

Aquatic Mesocosm Strategies for the Environmental Fate and Risk Assessment of Engineered Nanomaterials

In the past decade, mesocosms have emerged as a useful tool for the environmental study of engineered nanomaterials (ENMs) as they can mimic the relevant exposure scenario of contamination. Herein, we analyzed the scientific outcomes of aquatic mesocosm experiments, with regard to their designs, the ENMs tested, and the end points investigated. Several mesocosm designs were consistently applied in the past decade to virtually mimic various contamination scenarios with regard to ecosystem setting as well as ENMs class, dose, and dosing. Statistical analyses were carried out with the literature data to identify the main parameters driving ENM distribution in the mesocosms and the potential risk posed to benthic and planktonic communities as well as global ecosystem responses. These analyses showed that at the end of the exposure, mesocosm size (water volume), experiment duration, and location indoor/outdoor had major roles in defining the ENMs/metal partitioning. Moreover, a higher exposure of the benthic communities is often observed but did not necessarily translate to a higher risk due to the lower hazard posed by transformed ENMs in the sediments (e.g., aggregated, sulfidized). However, planktonic organisms were generally exposed to lower concentrations of potentially more reactive and toxic ENM species. Hence, mesocosms can be complementary tools to existing standard operational procedures for regulatory purposes and environmental fate and risk assessment of ENMs. To date, the research was markedly unbalanced toward the investigation of metal-based ENMs compared to metalloid- and carbon-based ENMs but also nanoenabled products. Future studies are expected to fill this gap, with special regard to high production volume and potentially hazardous ENMs. Finally, to take full advantage of mesocosms, future studies must be carefully planned to incorporate interdisciplinary approaches and ensure that the large data sets produced are fully exploited.

Release of carbon nanotubes during combustion of polymer nanocomposites in a pilot-scale facility for waste incineration

Nanocomposites, formed by incorporating nanoparticles into a matrix of standard materials, are increasing on the market. Little focus has been directed towards safe disposal and recycling of these new materials even though the disposal has been identified as a phase of the products' life cycle with a high risk of uncontrolled emissions of nanomaterials. In this study, we investigate if the carbon nanotubes (CNTs), when used as a filler in two types of polymers, are fully destructed in a pilot-scale combustion unit designed to mimic the combustion under waste incineration. The two polymer nanocomposites studied, polycarbonate (PC) with CNT and high-density polyethylene (HDPE) with CNT, were incinerated at two temperatures where the lower temperature just about fulfilled the European waste incineration directive while the upper was chosen to be on the safe side of fulfilling the directive. Particles in the flue gas were sampled and analysed with online and offline instrumentation along with samples of the bottom ash. CNTs could be identified in the flue gas in all experiments, although present to a greater extent when the CNTs were introduced in PC as compared to in HDPE. In the case of using PC as polymer matrix, CNTs were identified in 3-10% of the analysed SEM images while for HDPE in only ~0.5% of the images. In the case of PC, the presence of CNTs decreased with increasing bed temperature (from 10% to 3% of the images). The CNTs identified were always in bundles, often coated with remnants of the polymer, forming particles of ~1-4 μm in diameter. No CNTs were identified in the bottom ash, likely explained by the difference in time when the bottom ash and fly ash are exposed to high temperatures (~hours compared to seconds) in the pilot facility. The results suggest that the residence time of the fly ash in the combustion zone is not long enough to allow full oxidation of the CNTs. Thus, the current regulation on waste incineration (requiring a residence time of the flue gas >850 °C during at least 2 s) may not be enough to obtain complete destruction of CNTs in polymer composites. Since several types of CNTs are known to be toxic, we stress the need for further investigation of the fate and toxicity of CNTs in waste treatment processes.

Nanotoxicity of 2D Molybdenum Disulfide, MoS2, Nanosheets on Beneficial Soil Bacteria, Bacillus cereus and Pseudomonas aeruginosa

Concerns arising from accidental and occasional releases of novel industrial nanomaterials to the environment and waterbodies are rapidly increasing as the production and utilization levels of nanomaterials increase every day. In particular, two-dimensional nanosheets are one of the most significant emerging classes of nanomaterials used or considered for use in numerous applications and devices. This study deals with the interactions between 2D molybdenum disulfide (MoS2) nanosheets and beneficial soil bacteria. It was found that the log-reduction in the survival of Gram-positive Bacillus cereus was 2.8 (99.83%) and 4.9 (99.9988%) upon exposure to 16.0 mg/mL bulk MoS2 (macroscale) and 2D MoS2 nanosheets (nanoscale), respectively. For the case of Gram-negative Pseudomonas aeruginosa, the log-reduction values in bacterial survival were 1.9 (98.60%) and 5.4 (99.9996%) for the same concentration of bulk MoS2 and MoS2 nanosheets, respectively. Based on these findings, it is important to consider the potential toxicity of MoS2 nanosheets on beneficial soil bacteria responsible for nitrate reduction and nitrogen fixation, soil formation, decomposition of dead and decayed natural materials, and transformation of toxic compounds into nontoxic compounds to adequately assess the environmental impact of 2D nanosheets and nanomaterials.

Nanomaterials in the environment, human exposure pathway, and health effects: A review

Nanomaterials (NMs), both natural and synthetic, are produced, transformed, and exported into our environment daily. Natural NMs annual flux to the environment is around 97% of the total and is significantly higher than synthetic NMs. However, synthetic NMs are considered to have a detrimental effect on the environment. The extensive usage of synthetic NMs in different fields, including chemical, engineering, electronics, and medicine, makes them susceptible to be discharged into the atmosphere, various water sources, soil, and landfill waste. As ever-larger quantities of NMs end up in our environment and start interacting with the biota, it is crucial to understand their behavior under various environmental conditions, their exposure pathway, and their health effects on human beings. This review paper comprises a large portion of the latest research on NMs and the environment. The article describes the natural and synthetic NMs, covering both incidental and engineered NMs and their behavior in the natural environment. The review includes a brief discussion on sampling strategies and various analytical tools to study NMs in complex environmental matrices. The interaction of NMs in natural environments and their pathway to human exposure has been summarized. The potential of NMs to impact human health has been elaborated. The nanotoxicological effect of NMs based on their inherent properties concerning to human health is also reviewed. The knowledge gaps and future research needs on NMs are reported. The findings in this paper will be a resource for researchers working on NMs all over the world to understand better the challenges associated with NMs in the natural environment and their human health effects.

Evaluating the cytotoxicity of a large pool of metal oxide nanoparticles to Escherichia coli: Mechanistic understanding through In Vitro and In Silico studies

The toxic effect of eight metal oxide nanoparticles (MONPs) on Escherichia coli was experimentally evaluated following standard bioassay protocols. The obtained cytotoxicity ranking of these studied MONPs is Er₂O₃, Gd₂O₃, CeO₂, Co₂O₃, Mn₂O₃, Co₃O₄, Fe₃O₄/WO₃ (in descending order). The computed EC₅₀ values from experimental data suggested that Er₂O₃ and Gd₂O₃ were the most acutely toxic MONPs to E. coli. To identify the mechanism of toxicity of these 8 MONPs along with 17 other MONPs from our previous study, we employed seven classifications and machine learning (ML) algorithms including linear discriminant analysis (LDA), naïve bayes (NB), multinomial logistic regression (MLogitR), sequential minimal optimization (SMO), AdaBoost, J48, and random forest (RF). We also employed 1^st and 2^nd generation periodic table descriptors developed by us (without any sophisticated computing facilities) along with experimentally analyzed Zeta-potential, to model the cytotoxicity of these MONPs. Based on qualitative validation metrics, the LDA model appeared to be the best among the 7 tested models. The core environment of metal defined by the ratio of the number of core electrons to the number of valence electrons and the electronegativity count of oxygen showed a positive impact on toxicity. The identified properties were important for understanding the mechanisms of nanotoxicity and for predicting the potential environmental risk associated with MONPs exposure. The developed models can be utilized for environmental risk assessment of any untested MONP to E. coli, thereby providing a scientific basis for the design and preparation of safe nanomaterials.

Photo-transformation of graphene oxide in the presence of co-existing metal ions regulated its toxicity to freshwater algae

Graphene oxide (GO) sheets are unstable in aqueous environments, and the effect of photo-transformation on GO toxicity to freshwater algae (Chlorella pyrenoidosa) was investigated. Our results demonstrated that GO underwent photo-reduction under 25-day sunlight irradiation, and the transformation was generally completed at Day 8. The toxicological investigation showed that 8-day sunlight irradiation significantly increased growth inhibition of GO (25 mg/L) to algal cells by 11.2%, due to enhanced oxidative stress and stronger membrane damage. Low molecular weight (LMW) species were produced during the 8-day GO transformation, and they were identified as two types of aromatic compounds, which played a crucial role in increasing toxicity. The combined toxicity of GO and Cu²⁺ ions before and after light irradiation was further investigated. Antagonistic effect was observed between the toxicity of pristine GO and co-existing Cu²⁺ ions. After co-irradiation of GO and Cu²⁺ ions for 8 days, their combined toxicity was unexpectedly lower or insignificant in comparison with the treatments of pristine GO, or pristine GO in the presence of Cu²⁺ ions. Two mechanisms were revealed for this finding: (1) Cu²⁺ ions suppressed the photo-transformation of GO; (2) the toxicity of free Cu²⁺ ions was decreased through the adsorption/retention of Cu²⁺ ions and formation of Cu-based nanoparticles (e.g., Cu₂O and Cu₂S) on the photo-transformed GO. The provided data are helpful for better understanding the environmental process and risk of GO under natural conditions.

In the Search for Nanospecific Effects of Dissolution of Metallic Nanoparticles at Freshwater-Like Conditions: A Critical Review

Knowledge on relations between particle properties and dissolution/transformation characteristics of metal and metal oxide nanoparticles (NPs) in freshwater is important for risk assessment and product development. This critical review aims to elucidate nanospecific effects on dissolution of metallic NPs in freshwater and similar media. Dissolution rate constants are compiled and analyzed for NPs of silver (Ag), copper (Cu), copper oxide/hydroxide (CuO, Cu(OH)₂), zinc oxide (ZnO), manganese (Mn), and aluminum (Al), showing largely varying (orders of magnitude) constants when modeled using first order kinetics. An effect of small primary sizes (<15 nm) was observed, leading to increased dissolution rate constants and solubility in some cases. However, the often extensive particle agglomeration can result in reduced nanospecific effects on dissolution and also an increased uncertainty related to the surface area, a parameter that largely influence the extent of dissolution. Promising ways to model surface areas of NPs in solution using fractal dimensions and size distributions are discussed in addition to nanospecific aspects related to other processes such as corrosion, adsorption of natural organic matter (NOM), presence of capping agents, and existence of surface defects. The importance of the experimental design on the results of dissolution experiments of metal and metal oxide NPs is moreover highlighted, including the influence of ionic metal solubility and choice of particle dispersion methodology.