Material Flow Analysis Research Articles

Reassessing tin circularity and criticality

AbstractTin is an important metal for society with a high risk of supply disruptions. It is, therefore, classified as a critical material in many parts of the world. An exception is the European Union, for which tin was classified as a non‐critical material in 2023. However, there are many discrepancies in the literature regarding the definitions and values of the indicators used to determine tin criticality in general, and recycling indicators in particular. Values for end‐of‐life recycling rate (EoL RR) range between 20% and 75%, and values for end‐of‐life recycling input rate (EoL RIR) range between 11% and 32%. In this paper, we critically assess the circularity and criticality indicator values for tin and calculate new values using material flow analysis. The new values for tin recycling indicators are lower than those used in most previous research, with a global EoL RR of 16% and an EoL RIR of 11% in 2017. Based on the updated recycling values, combined with a highly concentrated supply, high import reliance, and difficult substitution, we argue that the European Union should classify tin as a critical material. This reclassification can lead to more policy attention for tin, which can help reduce the impact of future supply disruptions and increase the resilience of the European and global tin supply chains.

An environmentally conscious waste management system in an effort to create a sustainable city (study of waste management systems at Syiah Kuala University)

Final Processing Site (TPA) is a place designated as a final stage waste management location. The increasing accumulation of waste can result in an increase in the volume and discharge of leachate generated through landfill management. Waste management can be implemented, one of which is supported by the existence of waste bank activities. Waste banking is a method implemented through the 3R concept (Reuse, Reduce and Recycle). This research aims to determine the waste management system at the Universitas Syiah Kuala Waste Bank, as well as supporting factors and strategies for increasing waste reduction. Improvements in waste bank management are analyzed using statistical tests, correlations and so on. The method used to determine whether waste bank management has improved is material flow analysis and structural equation modeling (SEM) testing. The results of the material flow analysis show that based on the mass balance the reduction potential of waste that can be managed by the Universitas Syiah Kuala Waste Bank is 45.4%. The results of statistical tests show that the waste management system at the Universitas Syiah Kuala waste bank, Banda Aceh is quite good, seen from the knowledge factor reaching 90.6%, attitude at 88.4% and waste bank behavior at 91.3%.

A dynamic model for estimating the long-term need for repairs and renovations in residential buildings

ABSTRACT Reaching sustainability targets requires a holistic understanding of the different dimensions of residential building stock development. This paper aims to provide a solid and transparent approach for modelling residential building stock development with a focus on the long-term need for repairs and renovations. The modelling approach is based on Dynamic Material Flow Analysis (MFA) and the model is constructed using comprehensive Finnish statistics. Still, it is widely applicable to different geographical locations and modifiable for various purposes. The main contributions to the previous literature are the incorporation of empirical building mortality analysis and rehabilitation degree model in the MFA modelling framework. The model is demonstrated by modelling the development of Finnish residential building stock from 2020 to 2050. The annual average need for renovation from 2020 to 2050 is 4.1 million residential square metres (1.8% percent of the entire housing stock), equalling to annual investments of some 7.8 billion euros. However, the results revealed notable geographical differences between municipality categories. The results also suggest that the proportion of renovations in the total construction market is increasing while the volume of new housing construction is decreasing. The modelled results are in line with the Finnish Long-Term Renovation Strategy 2020–2050.

Material Flow Analysis of Molybdenum in China During 2000–2020

Material Flow Analysis of Molybdenum in China During 2000–2020

Models for Decarbonization in the Chemical Industry.

Various technologies and strategies have been proposed to decarbonize the chemical industry. Assessing the decarbonization, environmental, and economic implications of these technologies and strategies is critical to identifying pathways to a more sustainable industrial future. This study reviews recent advancements and integration of systems analysis models, including process analysis, material flow analysis, life cycle assessment, techno-economic analysis, and machine learning. These models are categorized based on analytical methods and application scales (i.e., micro-, meso-, and macroscale) for promising decarbonization technologies (e.g., carbon capture, storage, and utilization, biomass feedstock, and electrification) and circular economy strategies. Incorporating forward-looking, data-driven approaches into existing models allows for optimizing complex industrial systems and assessing future impacts. Although advances in industrial ecology-, economic-, and planetary boundary-based modeling support a more holistic systems-level assessment, more efforts are needed to consider impacts on ecosystems. Effective applications of these advanced, integrated models require cross-disciplinary collaborations across chemical engineering, industrial ecology, and economics.

Design of modelling and online simulation for energy systems in papermaking mill

This paper presents a general framework of modelling and online simulation for papermaking mill’s energy systems. The energy flow models of thermal power plant, DIP and paper machine for a papermaking mill was designed and implemented an online simulation. The traditional offline, closed and scattered modelling and simulation methods were changed into online, open and integrated forms. Through the analysis of energy systems of papermaking mills, the framework has implemented the followings. The unit (equipment) models were established, it can analyse the energy of energy flow material. The corresponding material flow models library was developed. The craftwork models were designed and the energy flow models library was developed of thermal power plant, DIP and paper machine. The mathematical models of unit (equipment), energy flow, exergy flow, thermal power plant, DIP and paper machine were built. The material properties database was developed. General simulation software architecture and online simulation software architecture were designed. The framework implemented online simulation, analysis, diagnosis and optimization for energy systems of whole papermaking mill. The practical application results are fine when the framework was applied in Guangzhou Paper Group Co., Ltd., and Gold East Paper (Jiangsu) Co., Ltd. The practical application results indicate that the emulation, simulation, analysis, diagnosis and optimization of material flow and energy flow for papermaking mill whole production process can be implemented by online simulation, and the purposes of maximizing the utility efficiency of material and energy resource, reducing resource, reusing and recycling can be achieved.

Participatory modelling of scenarios to restore nitrogen cycles in a nutrient-saturated area

This paper aims to find socially acceptable solutions of circularity as measure to reduce nitrogen (N) losses and prevent environmental damage by combining participatory modelling and scenario Substance Flow Analyses (SFA). A local perspective was taken on the agro-food-waste system in the animal production-dominated German district Cleves. Three scenarios were programmed as Monte Carlo simulation of SFA with stakeholder input regarding crop allocation, livestock composition, livestock reduction, and manure allocation following the elimination of feed imports. The three scenarios either utilized the unaltered stakeholder input (PS), altered crop allocation to satisfy the demand for feed (CBS), or adjusted the livestock numbers to match the locally available feed (LBS). In the reference year (2020) agricultural losses amounted to 68 kg N year−1 ha−1 agricultural land and 116 kg N in feed was imported year−1 ha−1 agricultural land. In the PS feed import elimination led to deficits in feed availability. The LBS showed the biggest reduction of agricultural N losses and improved N use efficiency (+6 %), however agricultural losses were still high (50 kg N year−1 ha−1 agricultural land). The results show a limited effect of feed import elimination on N losses if no further measures are taken, such as reduced consumption of animal-based products. Further, the study shows that it is important to improve stakeholders' knowledge about approaches to circular agro-food-waste systems. The discrepancy between stakeholder visions and N circularity provide policy makers with the recommendation to improve stakeholders' visions of a circular agro-food-waste system.

The environmental impacts of reusable rice packaging: An extended comparative life cycle assessment

Plastic packaging recycling has gained momentum as it can improve the circularity of this typical linear product. However, reuse ranks as a preferred strategy over recycling because product reuse can reduce material usage compared to product recycling and keeps material value higher for a longer time. Such reusable plastic packaging requires, besides a more robust product design, an additional return system. It is crucial to minimize the impact of this product system and ensure that reusable plastic packaging is not only more circular, but also more environmentally friendly than its single-use alternative. For this purpose, understanding the factors contributing to its environmental impact is key. In this paper, a new design of reusable packaging for two kilogram rice is compared with a conventional fully-optimized single-use packaging using a prospective extended life cycle assessment, including a circularity (using material flow analysis and specific circularity indicators, among which the Material Circularity Index), environmental impact (using a life cycle assessment with 16 midpoint indicators) and packaging-related food losses and waste assessment (using the food-to-packaging ratios). On average, the reusable rice packaging could be reused five times, due to losses at the distribution, use, and reuse preparation phase. While the reusable packaging scores better on the circularity indicators (a Material Circularity Index of 91 %, compared with 39 % for single-use packaging), its global warming and fossil resource depletion impact are respectively two and three times higher, considering a functional unit of one kilogram cooked rice to be consumed. The reusability and return rate, providing the retention of reusable packaging at the reuse preparation and use phase, respectively, were identified as the most determinative parameters by the sensitivity analysis. If these parameters could be optimized to a value of 99.75 %, corresponding to a total of 16 uses, the climate change impact of reusable packaging would be lower than its conventional single-use counterpart. The high food-to-packaging ratios (more than 18 for all impact categories) point to the importance of reducing food waste. If the packaging design could reduce food losses in the product system with 0.2 %, the reusable packaged rice would have a lower water use and mineral and metal resource use impact compared to the single-use packaged rice, despite the higher environmental impact of the reusable packaging unit itself. Therefore, this should be prioritized when further optimizing the reusable packaging design.

Techno-Economic Analysis of the Business Potential of Second-Life Batteries in Ostrobothnia, Finland

In an effort to tackle climate change, various sectors, including the transport sector, are turning towards increased electrification. As a result, there has been a swift increase in the sales of electric vehicles (EVs) that use lithium-ion batteries (LIBs). When LIBs reach their end of life in EVs, it may still be possible to use them in other, less demanding applications, giving them a second life. This article describes a case study where the feasibility of a hypothetical business repurposing Tesla Model S/X batteries in the Ostrobothnia region, Finland, is investigated. A material-flow analysis is conducted to estimate the number of batteries becoming available for second-life applications from both the Ostrobothnia region and Finland up to 2035. The cost of repurposing batteries is evaluated for four different scenarios, with the batteries being processed either on the pack, module, or cell level. Three scenarios were found to be feasible, with repurposing costs of 27.2–38.3 EUR/kWh. The last scenario, in which all battery packs are disassembled at the cell level, was found not to be feasible due to the labor intensiveness of disassembly and testing at the cell level. This work gives indications of the potential for repurposing batteries in the Ostrobothnia region and Finland.

Australia's circular economy metrics and indicators

AbstractThis article presents a comprehensive economy‐wide material flow analysis of the Australian economy in 2019, examining the domestic extraction, trade, end‐of‐life flows, and recycling for all materials. The results highlight Australia's role as a natural resource supplier, with metals and fossil fuels being primary contributors. Through material flow analysis, we found that in 2019 Australia extracted 2587 Mt of natural resources, exported a substantial fraction (1459 Mt), and used 917 Mt to fulfill domestic needs. The recycling flows and circularity metrics are also explored, with an end‐of‐life recycling rate of 51.1% and an overall circularity rate of 5.1%. An additional assessment of Australia's consumption‐based material footprint highlights mobility and housing as the dominant material‐using sectors. These results contribute to understanding Australia's material consumption patterns, indicating significant reliance on foreign semifinished and finished products, and provide insights into the potential for enhancing economic circularity.

Characterization of excavated plastic waste from an Indian dumpsite: Investigating extent of degradation and resource recovery potential.

In recent years, the concept of landfill mining has gained a lot of traction in India, and tonnes of plastic waste is being excavated. The present shift towards a circular economy necessitates to explore the use of excavated plastic waste as a source of valuable materials and energy. However, the physicochemical characteristics of plastic waste change due to the degradation and weathering process in landfills, making its valorization difficult. The current study investigates the change in physicochemical characteristics of plastic waste with age from an Indian dumpsite to identify the potential valorization options. In addition, a material and energy flow analysis was performed considering incineration treatment of plastic waste. The plastic waste ranged between 3.6 and 21% in the dumpsite and has almost doubled in recent decades, owing to the increase in plastic waste generation in India. Polyethylene (high- and low-density) accounted for approximately 66% of the excavated plastic waste and had a lot of adhered surface impurities. Mechanical pre-treatment using a shredder was effective in the removal of the adhered impurities with a recovery rate of 50-70% for polyethylene and a higher recovery of 70-90% for other types of plastic. Changes in the surface morphology of plastic waste with aging were observed through Scanning Electron Microscopy. The Fourier Transform Infrared Spectroscopy results confirmed low degradation levels for aged plastic waste, which is also confirmed through the high level of oxygen detected. The material and energy flow analysis revealed that incinerating one tonne of excavated plastic waste could produce approximately 1410 kWh of electricity.

Mapping Chinese plastic flows from 2001 to 2040 based on dynamic probabilistic material flow analysis and scenario projection

Plastic waste management, deeply intertwined with our economy, presents a global challenge. Plastic pollution pervades both aquatic and terrestrial ecosystems worldwide. In a vast country like China, establishing a comprehensive plastic flow regime that accounts for socioeconomic disparities between urban and rural areas is essential for effectively reducing s plastic waste. This study aims to map the life-cycle of China's plastic flows from 2001 to 2040, distinguishing between urban and rural sources, through integrating dynamic probabilistic material flow analysis with scenario analysis. The results indicate that from 2001 to 2020, cumulative plastic waste generation was 1001 ± 14.6 million tonnes (Mt), with a higher proportion originating from urban areas (706 ± 10.3 Mt) compared to rural areas (218 ± 3.2 Mt). The rate of increase in mismanaged plastic wastes (MPWs) in rural areas outpaced that in urban areas, peaking in 2016, five years after the peak in urban areas. Consequently, the cumulative total of rural MPWs, including littering (103.5 ± 2.0 Mt) and open dumping (74.8 ± 1.5 Mt), was higher than that in urban areas (littering: 83.0 ± 4.0 Mt; open dumping: 70.3 ± 1.4 Mt). The scenario analysis forecasts a reduction of 96.5 ± 0.4 % and an 83.0 ± 2.1 % in MPW generations in urban and rural areas by 2040, respectively, if all interventions are implemented. However, strategies like reuse&recycling and reduce&substitute are less effective in rural areas compared to urban areas. Therefore, we recommend establishing a collection system with both penalties and incentives to reduce rural MPWs.

Revealing cradle-to-gate CO2 emissions for steel product producing by different technological pathways based on material flow analysis

Revealing the life-cycle CO2 emissions of steel products is of great significance for mitigating CO2 emissions. However, previous studies did not conduct comparative analysis for steel products produced by different technological pathways, resulting in considerable confusion in the setting of carbon reduction pathways. By using the material flow analysis method, this study revealed the life-cycle CO2 emissions associated with various technological pathways. The results shows that life-cycle CO2 emissions per metric ton of steel are: 3620.78 kg for shaft furnace (SF)-electric furnace (EF) routes, 2598.54 kg for blast furnace (BF)- basic oxygen furnace (BOF), 1868.16 kg for Scrap & Molten Iron-EF and 1330.22 kg for scrap-EF. The energy structure (e.g. coal blending mode, power generation mode) material structure (e.g. iron ore matching mode, matching mode of scrap and molten iron), and transportation mode have a significant impact on CO2 emissions. Undoubtedly, low-carbon or zero-carbon electricity is more effective in reducing CO2 emissions.

Computational Nanotoxicology Models for Environmental Risk Assessment of Engineered Nanomaterials.

Although engineered nanomaterials (ENMs) have tremendous potential to generate technological benefits in numerous sectors, uncertainty on the risks of ENMs for human health and the environment may impede the advancement of novel materials. Traditionally, the risks of ENMs can be evaluated by experimental methods such as environmental field monitoring and animal-based toxicity testing. However, it is time-consuming, expensive, and impractical to evaluate the risk of the increasingly large number of ENMs with the experimental methods. On the contrary, with the advancement of artificial intelligence and machine learning, in silico methods have recently received more attention in the risk assessment of ENMs. This review discusses the key progress of computational nanotoxicology models for assessing the risks of ENMs, including material flow analysis models, multimedia environmental models, physiologically based toxicokinetics models, quantitative nanostructure-activity relationships, and meta-analysis. Several challenges are identified and a perspective is provided regarding how the challenges can be addressed.

Carbon reduction trade-off between pretreatment and anaerobic digestion: A field study of an industrial-scale biogas plant

With the implementation of municipal solid waste source segregation, the enormous sorted biogenic waste has become an issue that needs to be seriously considered. Anaerobic digestion, which can produce biogas and extract floating oil for biodiesel production, is the most prevalent treatment in China for waste management and greenhouse gas (GHG) emissions reduction, in accordance with Sustainable Development Goal 13 of the United Nations. Herein, a large-scale biogas plant with a capacity of 1000 tonnes of biogenic waste (400 tonnes of restaurant biogenic waste and 600 tonnes of kitchen biogenic waste) per day was investigated onsite using material flow analysis, and the parts of the biogas plant were thoroughly analyzed, especially the pretreatment system for biogenic waste impurity removal and homogenization. The results indicated that the loss of the total biodegradable organic matter was 41.8% (w/w) of daily feedstock and the loss of biogas potential was 18.8% (v/v) of daily feedstock. Life cycle assessment revealed that the 100-year GHG emissions were −61.2 kgCO2-eq per tonne biogenic waste. According to the sensitivity analysis, pretreatment efficiency, including biodegradable organic matter recovery and floating oil extraction, considerably affected carbon reduction potential. However, when the pretreatment efficiency deteriorated, GHG benefits of waste source segregation and the subsequent biogenic waste anaerobic digestion would be reduced.

Revealing the long way towards lead-free plastic in China through dynamic material flow analysis of lead salt heat stabilizers in PVC products

The use of lead salt heat stabilizers (LHSs) in plastics are restricted or even prohibited owing to their high toxicity. However, little information is available on its industrial metabolism. A dynamic material flow analysis of LHSs indicates that China consumed 2952 kt LHSs between 1958 and 2020. Moreover, at present, 1020 kt of these is being used in polyvinyl chloride (PVC) products, 1007 kt is in landfills, and 681 kt is in the environment. For China to realize lead-free primary plastics by 2040, 2050, and 2060, the LHSs consumption should be reduced by at least 13 %, 10 %, and 9 % annually, respectively. Certain LHSs would gain new life with PVC recycling. Therefore, approximately 30 years would be required for LHSs to disappear completely after their use is stopped. With improvements in the plastic recycling rate, it is necessary to use chemical recycling and other methods to separate the hazardous additives such as LHSs and reduce the circulation of toxic substances.

Life cycle assessment of hemp-based milk alternative production in Lower Saxony, Germany, based on a material flow analysis of a pilot scale

PurposeRecently, demand for plant-based milk products (PBMP) has increased for multiple reasons, such as the rapid population growth expected to reach 9.7 billion by 2050, health concerns such as lactose intolerance, nutritional aspects, ethical reasons, and environmental concerns. This leads to increased demand for food and competition for natural resources. Hemp-based milk is an emerging dairy alternative, and stakeholders in the supply chain are becoming increasingly interested in learning about the environmental effects of its production. This article aims for a comparative life cycle assessment of hemp-based and bovine milk with fat and protein correction to account for the differences in macronutrient content.MethodsThe cradle-to-factory gate LCA relied on experimental cultivation and milk production in Lower Saxony, Germany. Inventory was based on primary data from fields and the pilot plant of DIL e. V. and on literature and ecoinvent database to develop a life cycle assessment (LCA) model. The LCA was performed using Simapro 9.3 software and IMPACT 2002+ impact assessment method. The life cycle stages include cultivation, harvesting, and milk production. The study compared hemp-based milk to bovine milk based on 1 kg fat and protein-corrected milk (FPCM) as a functional unit (FU). Co-products are taken into consideration using mass-economic allocation.ResultsThe results showed that hemp cultivation accounted for the highest impact (99%) in the production chain of hemp milk production. The GWP of 1 kg of FPCM hemp-based milk is 0.42 kg CO2 eq. The energy consumption for 1 kg of FPCM hemp-based milk is 4.73 MJ (12.26% lower than bovine milk). The other main factors impacting hemp-based milk production were terrestrial ecotoxicity (6.444E2 kg TEG soil) and aquatic ecotoxicity (2.458E2 kg TEG water). Hemp fiber was the co-product with 40% of the allocated impacts. The results are sensitive to the changes in fat-protein contents, functional unit, and system boundaries. The results demonstrated that the impacts of hemp milk production were within the range indicated for other PBMP production and 51.7% lower than bovine milk production in terms of GWP. This range primarily stems from field emissions, fertilizer application, and machinery usage during cultivation and harvest.ConclusionThe results of the comparisons of bovine milk and hemp-based milk were dependable on the FU. The hemp-based milk has the potential to be a more sustainable alternative to bovine milk due to considerably lower impacts in impact categories—land occupation (99% lower than bovine milk), global warming (52% lower than bovine milk), and ionizing radiation (23% lower than bovine milk). It is primarily due to less use of agricultural machinery, less land requirement, and lower NH3 emissions than bovine milk in various stages of milk production.

Mass-Balance-Consistent Geological Stock Accounting: A New Approach toward Sustainable Management of Mineral Resources.

Global resource extraction raises concerns about environmental pressures and the security of mineral supply. Strategies to address these concerns depend on robust information on natural resource endowments, and on suitable methods to monitor and model their changes over time. However, current mineral resources and reserves reporting and accounting workflows are poorly suited for addressing mineral depletion or answering questions about the long-term sustainable supply. Our integrative review finds that the lack of a robust theoretical concept and framework for mass-balance (MB)-consistent geological stock accounting hinders systematic industry-government data integration, resource governance, and strategy development. We evaluate the existing literature on geological stock accounting, identify shortcomings of current monitoring of mine production, and outline a conceptual framework for MB-consistent system integration based on material flow analysis (MFA). Our synthesis shows that recent developments in Earth observation, geoinformation management, and sustainability reporting act as catalysts that make MB-consistent geological stock accounting increasingly feasible. We propose first steps for its implementation and anticipate that our perspective as "resource realists" will facilitate the integration of geological and anthropogenic material systems, help secure future mineral supply, and support the global sustainability transition.

Decreasing resilience of China's coupled nitrogen-phosphorus cycling network requires urgent action.

The coupled nature of the nitrogen (N) and phosphorus (P) cycling networks is of critical importance for sustainable food systems. Here we use material flow and ecological network analysis methods to map the N-P-coupled cycling network in China and evaluate its resilience. Results show a drop in resilience between 1980 and 2020, with further decreases expected by 2060 across different socio-economic pathways. Under a clean energy scenario with additional N and P demand, the resilience of the N-P-coupled cycling network would suffer considerably, especially in the N layer. China's socio-economic system may also see greater N emissions to the environment, thus disturbing the N cycle and amplifying the conflict between energy and food systems given the scarcity of P. Our findings on scenario-specific synergies and trade-offs can aid the management of N- and P-cycling networks in China by reducing chemical fertilizer use and food waste, for example.

Predicting environmental concentrations of nanomaterials for exposure assessment - a review

There have been major advances in the science to predict the likely environmental concentrations of nanomaterials, which is a key component of exposure and subsequent risk assessment. Considerable progress has been since the first Material Flow Analyses (MFAs) in 2008, which were based on very limited information, to more refined current tools that take into account engineered nanoparticle (ENP) size distribution, form, dynamic release, and better-informed release factors. These MFAs provide input for all environmental fate models (EFMs), that generate estimates of particle flows and concentrations in various environmental compartments. While MFA models provide valuable information on the magnitude of ENP release, they do not account for fate processes, such as homo- and heteroaggregation, transformations, dissolution, or corona formation. EFMs account for these processes in differing degrees. EFMs can be divided into multimedia compartment models (e.g., atmosphere, waterbodies and their sediments, soils in various landuses), of which there are currently a handful with varying degrees of complexity and process representation, and spatially-resolved watershed models which focus on the water and sediment compartments. Multimedia models have particular applications for considering predicted environmental concentrations (PECs) in particular regions, or for developing generic “fate factors” (i.e., overall persistence in a given compartment) for life-cycle assessment. Watershed models can track transport and eventual fate of emissions into a flowing river, from multiple sources along the waterway course, providing spatially and temporally resolved PECs. Both types of EFMs can be run with either continuous sources of emissions and environmental conditions, or with dynamic emissions (e.g., temporally varying for example as a new nanomaterial is introduced to the market, or with seasonal applications), to better understand the situations that may lead to peak PECs that are more likely to result in exceedance of a toxicological threshold. In addition, bioaccumulation models have been developed to predict the internal concentrations that may accumulate in exposed organisms, based on the PECs from EFMs. The main challenge for MFA and EFMs is a full validation against observed data. To date there have been no field studies that can provide the kind of dataset(s) needed for a true validation of the PECs. While EFMs have been evaluated against a few observations in a small number of locations, with results that indicate they are in the right order of magnitude, there is a great need for field data. Another major challenge is the input data for the MFAs, which depend on market data to estimate the production of ENPs. The current information has major gaps and large uncertainties. There is also a lack of robust analytical techniques for quantifying ENP properties in complex matrices; machine learning may be able to fill this gap. Nevertheless, there has been major progress in the tools for generating PECs. With the emergence of nano- and microplastics as a leading environmental concern, some EFMs have been adapted to these materials. However, caution is needed, since most nano- and microplastics are not engineered, therefore their characteristics are difficult to generalize, and there are new fate and transport processes to consider.