System Boundaries Research Articles

In recent years, industrial symbiosis (IS) has gained attention as a strategy to enhance circularity and to reduce the environmental impacts of solid waste management through resource reuse and recovery. Life Cycle Assessment (LCA) is increasingly used to evaluate the environmental performance of such inter-industry collaborations. Given the growing diversity of IS practices and LCA models, this updated review serves as a methodological reference, mapping existing approaches and identifying gaps to guide future research on the systematic assessment of circular strategies. Moreover, it investigates the environmental performance of IS approaches in the field, based on the LCA results of the analyzed case studies. We analyzed 48 peer-reviewed studies to examine how LCA has been applied to model and assess the environmental impacts and benefits of IS in the context of waste management. The literature revealed wide methodological variability, including differences in system boundaries, functional units, and impact categories, affecting comparability and consistency. Case studies confirm that IS can contribute to reducing environmental burdens, particularly with regard to climate change and resource depletion, though challenges remain in modelling the complex inter-organizational exchanges and accessing reliable data. Socio-economic aspects are increasingly considered but remain underrepresented. Future research should focus on methodological improvements, such as greater standardization and the better integration of indirect effects, to strengthen LCA in decision-making and to explore a wider range of scenarios reflecting different stakeholders, analytical perspectives, and the evolution of symbiotic systems over time.

Wood and wood-based products are increasingly recognized for their renewability and carbon storage capacity, supporting sustainable development and circular economy goals in the EU. This paper provides a comprehensive review of 42 material flow analysis (MFA) studies on wood resources conducted in the European Union and Switzerland between 2000 and 2024, introducing a five-level data risk classification. It examines how MFA is applied, including system boundaries, data sources, unit consistency, flow representation, and uncertainty handling. Results show that while volume-based units and Sankey diagrams are widely used, there is substantial variation in terminology, data quality, and methodology. The building stage is frequently excluded, limiting the completeness of wood flow assessments. Key challenges include restricted data access, inconsistent spatial and temporal scales, and varying levels of data processing risk. The study recommends harmonized units and terminology, open-access databases, standardization in visualization practices, and ultimately a wood-specific MFA framework to improve data quality, comparability, and policy relevance.

Hydrogen plays a central role in ensuring the fulfillment of the climate and energy goals established in the Paris Agreement. To implement sustainable and resilient hydrogen economies, it is essential to analyze the entire hydrogen value chain, following a Life Cycle Assessment (LCA) methodology. To determine the current methodologies, approaches, and research tendencies adopted when performing LCA of hydrogen energy systems, a systematic literature analysis is carried out in the present study. The choices regarding the “goal and scope definition”, “life cycle inventory analysis”, and “life cycle impact assessment” in 70 scientific papers were assessed. Based on the collected information, it was concluded that there are no similar LCA studies, since specificities introduced in the system boundaries, functional unit, production, storage, transportation, end-use technologies, geographical specifications, and LCA methodological approaches, among others, introduce differences among studies. This lack of harmonization triggers the need to define harmonization protocols that allow for a fair comparison between studies; otherwise, the decision-making process in the hydrogen energy sector may be influenced by methodological choices. Although initial efforts have been made, their adoption remains limited, and greater promotion is needed to encourage wider implementation.

Life cycle assessment of geopolymer materials utilizing construction and demolition waste.

Global environmental pressures from food systems threaten biodiversity and the stability of the Earth system, yet the safe operating space for food systems is unknown. Here we calculate food system boundaries as shares of planetary boundaries, proposing budgets for the food system across nine boundaries. Our results indicate that food systems are a critical driver of planetary boundary transgressions, dominating at least four transgressed boundaries (that is, biosphere integrity, land system change, freshwater change and biogeochemical flows) while strongly contributing to the transgression of two more (that is, climate change and novel entities). Moreover, global food systems are currently beyond all nine food system boundaries; moving to the safe operating space requires reducing related greenhouse gas emissions substantially, halting the conversion of intact nature to agriculture, redistributing fertilizer inputs, limiting pesticide and antibiotic use, and preserving critical freshwater flows without negatively affecting yields.

ABSTRACT Global warming stands as one of the most critical environmental challenges facing humanity today. Among its major contributors, residential buildings account for nearly one‐third of global greenhouse gas emissions and over 40% of global energy consumption. Life Cycle Assessment (LCA) has emerged as a key methodological tool to evaluate the environmental impacts of buildings across their entire life span from material extraction to demolition. This paper presents an updated systematic review of building‐related LCA studies, aiming to highlight current progress, recurring challenges, and potential future directions in the field. The methodology includes a comprehensive analysis of existing literature, emphasizing key LCA parameters such as system boundaries, functional units, life span assumptions, impact characterization methods, and service life considerations. The study identifies common research gaps and inconsistencies in building LCAs and outlines recommendations for improving data reliability and methodological consistency. Furthermore, the review discusses the limitations and assumptions made in prior studies, which can significantly influence LCA outcomes. This paper proposes several future research pathways aimed at addressing these challenges and enhancing the robustness and comparability of building LCA studies. By doing so, it contributes to the development of more sustainable building practices and informed decision‐making in the construction sector.

This article offers a critical sociological-philosophical-communicological review of the Life Cycle Assessment (LCA) method in the context of the food industry. While LCA has been established as a standardized tool for quantifying environmental impacts, this study analyses it not merely as a technical method but as an epistemological construct that actively shapes societal understanding of sustainability. Drawing on the theory of social construction of reality, situated knowledge, and critical theory, the article explores how methodological choices within LCA (e.g., system boundary definition and indicator selection) are not neutral but reflect specific social and political priorities. The findings reveal that standardized LCA approaches often lead to epistemological reductionism by homogenizing complex ecological processes and neglecting local contexts and environmental justice issues. Furthermore, the article examines the instrumentalization of LCA in sustainability communication and green marketing, where quantitative data are frequently used to legitimize existing business models rather than to drive systemic change. The discussion emphasizes the need to transcend instrumental rationality and shift toward transdisciplinary and deliberative approaches. The article advocates for integrating Social Life Cycle Assessment (S-LCA) and broader Life Cycle Sustainability Assessment (LCSA) frameworks to address sustainability challenges in the food industry more holistically, incorporating social justice and cultural sensitivity. Keywords: life cycle assessment (LCA); social construction of reality; situated knowledge; sustainability environmental communication; epistemology of ethics; sociology of responsibility.

Polyvinyl chloride (PVC) is a global plastic commodity with the third-highest rank in production volume after polyethylene and polypropylene. Unfortunately, the chlorine element therein can be detrimental to the environment. Thus, a life cycle assessment (LCA) for the PVC industry becomes important. This study conducted a process-level LCA with a gate-to-gate system boundary of suspension PVC (S-PVC) production in the Indonesian industry using primary industrial data. The results were then compared with the Chinese PVC industry in Anhui Province, as well as the EU27 database from Ecoinvent 3.8. The assessment was carried out using OpenLCA 1.11 software, using the CML-IA baseline method. Following this study, the Indonesian and Chinese PVC industries have a lower impact on marine aquatic ecotoxicity, human toxicity, and freshwater aquatic ecotoxicity compared to the EU27 database. In contrast, the Chinese PVC industry has the highest impact on GWP. This study also demonstrates that chlorine from stripped VCM and PVC dust release is the cause of marine aquatic ecotoxicity, with respective portions of 30.82%, 59.02%, and 23.86% for the Indonesian PVC industry, the Chinese PVC industry, and the EU27 database. The organic additives also add to the impact of human toxicity and freshwater ecotoxicity. In addition, the utilization of refrigerant compounds, as well as CO2 and CH4 emissions during the process, causes GWP. Finally, a ± 5% change in the input amount causes an alteration in marine aquatic ecotoxicity by -7.02% to 12.97% for the Indonesian PVC industry, -26.43% to -18.99% for the Chinese PVC industry, and -11.55% to -9.77% for the EU27 database.

The increase in municipal solid waste (MSW) generation and its inefficient management have caused significant environmental impacts, particularly in developing countries such as Mexico. In the central region, final disposal in uncontrolled sites (UCSs) remains a common practice despite its negative effects on the environment and public health. These impacts have been underestimated due to the scarcity of studies and the lack of technological alternatives aimed at mitigating them. In response to this problem, Life Cycle Assessment (LCA) emerges as a strategic tool to quantify these effects and to guide decision-making toward more sustainable management. The objective of this study was to evaluate the environmental impacts of a UCS using LCA, considering four scenarios: a baseline (E0) representing the current system conditions and three alternative scenarios (E1, E2, and E3) designed to explore potential improvements in environmental performance and to identify a feasible option under the socioeconomic conditions of a municipality in central Mexico. The functional unit was defined as the treatment of one tonne of MSW. The system boundaries included the separation of recyclable inorganic waste (RIW), the treatment of organic waste (OW) through composting and anaerobic digestion (AD), and the final disposal of mixed waste (MW) in UCSs and sanitary landfills. The assessment was performed using SimaPro Analyst v9.6 software and the ReCiPe methodology. The E0 scenario exhibited the highest environmental burdens, whereas E2 and E3 reduced the disposal of MW from 85.92% to 52.57% and emissions by 78.9%. E3 showed the lowest overall impact by integrating mechanical separation, AD, and controlled landfill disposal. E2, which employed composting instead of AD, proved to be a viable alternative for resource-constrained contexts. The results support the closure of uncontrolled sites and encourage the transition toward integrated systems that incorporate valorization technologies, which are urgently needed to achieve the Sustainable Development Goals.

Over the last decade, there has been a significant growth in life cycle assessment (LCA) research on oil palm production around the world, with an emphasis on the stages of the life cycle from oil palm plantation to crude palm oil (CPO). However, there is still a research shortage in the downstream section, which includes CPO and cooking oil production. This study addresses the gap by utilizing LCA to evaluate the environmental impacts using recent field data collected from selected sites in Sumatra. The study aims to examine the environmental impacts associated with the quality of palm cooking oil and compare them with those of other vegetable cooking oils. The system boundary is defined as cradle-to-gate, comprising land preparation, plantation, CPO production, and refinery of cooking oil. The results indicate that higher-quality palm cooking oil with iodine value (IV) 60 is associated with increased environmental impacts across several categories, including global warming, eutrophication, acidification, ozone layer depletion, and marine ecotoxicity. Furthermore, palm cooking oil with IV 56, which represents the most often consumed quality level, has a lower carbon footprint than cooking oils made from rapeseed, sunflower, soybean, peanut, canola, coconut, and maize. These findings provide useful information for consumers, industry, and politicians seeking to reduce the environmental effects of vegetable cooking oil.

Opportunities and limitations of farm-level greenhouse gas accounting tools: An overview based on experience from practice.

Agro-industrial activities require adaptations of technological energy systems to align with the European Sustainable Development Goals, and their highly seasonal and intermittent consumption profiles necessitate precise environmental assessment. This study aims at investigating the photovoltaic (PV) energy in various existing olive mills to assess the reduction in olive oil carbon footprint (CF) when it is supplied by either a rooftop PV system or by PV combined with a battery energy storage system (BESS) to promote the self-consumption of the renewable energy produced, compared to the case when electricity is supplied by the national grid (NG). To this end, an algorithm was developed to optimise a decision-making tool for low-carbon energy systems in agro-industrial activities. An economic assessment was performed to complement the decision-making process. The potential energy self-consumed by the mill ranged between 11% and 18.1%. The renewable energy produced covered between 11% and 84.7% of the mill’s energy consumption. CF reduction resulted between 22% and 119%, depending on the system boundaries considered. The proposed methodology allows for replicability to other industrial activities, having different energy consumption profiles, with seasonal and discontinued consumption paths, since it is based on an hourly energy consumption evaluation.

ABSTRACTResidential buildings play a pivotal role in shaping sustainable development, yet they significantly contribute to environmental degradation throughout their life cycles. With the rapid growth of the global urban population, the need for environmentally responsible housing intensifies, demanding comprehensive tools for evaluating environmental performance. Life Cycle Assessment (LCA) serves as a scientifically robust methodology to quantify environmental impacts across all stages of a building's life span. This study presents a detailed Life Cycle Inventory (LCI) for three residential building case studies located in diverse climatic and socio‐economic contexts in India, assessed using a cradle‐to‐grave system boundary. The inventory includes data collection and quantification for raw material extraction and processing, construction, operational use and maintenance, and end‐of‐life phases, including demolition and disposal. It also accounts for upstream and downstream transportation and secondary material flows. The analysis utilizes both primary and secondary data, supported by regional databases and construction standards specific to Indian conditions. It emphasizes the variability in construction practices, material selection, and maintenance patterns across the case studies. The paper also addresses methodological challenges such as data availability, quality uncertainty, and regional variability. The results lay a strong foundation for environmental impact assessment and inform strategies to reduce the ecological footprint of residential buildings in emerging economies.

Under the constraints of the “dual carbon” goals, accurately depicting the full life cycle carbon footprint of green hydrogen and its derivatives and quantifying the potential for emission reduction is a prerequisite for hydrogen energy policy and investment decisions. This paper constructs a unified life cycle model, covering the entire process from “wind and solar power generation–electrolysis of water to producing hydrogen-synthesis of methanol/ammonia-terminal transportation”, and includes the manufacturing stage of key front-end equipment and the negative carbon effect of CO2 capture within a single system boundary, and also presents an empirical analysis. The results show that the full life cycle carbon emissions of wind power hydrogen production and photovoltaic hydrogen production are 1.43 kgCO2/kgH2 and 3.17 kgCO2/kgH2, respectively, both lower than the 4.9 kg threshold for renewable hydrogen in China. Green hydrogen synthesis of methanol achieves a net negative emission of −0.83 kgCO2/kgCH3OH, and the emission of green hydrogen synthesis of ammonia is 0.57 kgCO2/kgNH3. At the same time, it is predicted that green hydrogen, green ammonia, and green methanol can contribute approximately 1766, 66.62, and 30 million tons of CO2 emission reduction, respectively, by 2060, providing a quantitative basis for the large-scale layout and policy formulation of the hydrogen energy industry.

Corn stover and plastic waste, severely underutilized feedstocks generated in the U.S., could be co-pelletized to produce fuel for cement production. High-density polyethylene bags (0–25% in 5% increments, dry basis) and corn stover were co-pelletized using a flat ring pellet mill with die diameters of 6 and 8 mm. Physical and chemical properties were assessed to determine pellet quality. These results informed techno-economic and life cycle greenhouse gas emissions (GHGe) analyses for a Midwestern plant producing 400,000 metric tons of pellets annually. The system boundary included feedstock acquisition at the pellet plant, size reduction, co-pelletization, and transportation of the pellets to the cement plant by rail. Total resource requirements in terms of raw materials, labor, fuel, equipment, the facility, and utilities were estimated. It was determined that the pellets would be delivered to the cement plant at USD 112.4–138.6/t pellets. The life cycle analysis estimated a total GHGe of 1621.1–1753.1 kg CO2e/t pellets associated with the pellet production, transportation, and combustion. The results suggest that substituting 25% of the thermal energy requirement of a cement plant with a 1.1 million t clinker annual production capacity with plastic–stover pellets would reduce the GHGe by 2.8% compared to 100% of the total energy requirement supplied by coal.

Evaluating the behavioral boundaries of deep learning (DL) systems is crucial for understanding their reliability across diverse, unseen inputs. Existing solutions fall short as they rely on untargeted, random perturbations with limited controlled input variations. In this work, we introduce Mimicry , a novel black-box test generator for fine-grained, targeted exploration of DL system boundaries. Mimicry performs boundary testing by leveraging the probabilistic nature of DL outputs to identify promising directions for exploration. By using style-based GANs to disentangle inputs into content and style components, Mimicry generates boundary test inputs by mimicking features from both source and target classes. We evaluated Mimicry ’s effectiveness in generating boundary inputs for five DL image classification systems, comparing it to two baselines from the literature. Our results show that Mimicry consistently identifies inputs up to \(25\times\) closer to the theoretical decision boundary, outperforming the baselines with statistical significance. Moreover, it generates semantically meaningful boundary test cases that reveal new functional misbehaviors, while the baselines mostly produce corrupted or invalid inputs. Thanks to its enhanced control over latent space manipulations, Mimicry remains effective as dataset complexity grows, resulting in a up to \(36\%\) higher validity rate and competitive diversity, as supported by a comprehensive human assessment.

One size does not fit all: Are there any sustainable alternatives to soybean in chicken systems?

Manure-based anaerobic digestion (AD) systems serve multiple functions, including waste treatment, energy recovery, and nutrient cycling. However, they also entail additional energy consumption and pollutant emissions. Life cycle assessment (LCA) methodology is typically used to holistically quantify the actual environmental impacts of these systems. Nevertheless, comprehensive reviews synthesizing LCA studies in this field remain limited. Following PRISMA guidelines, this study conducted a systematic literature review of LCA studies on manure-based AD systems, focusing on advancements, inconsistencies, and limitations in LCA methodologies and environmental impact results. The findings indicate considerable variability in functional units, allocation methods, system boundaries, and inventory analysis methods across the literature. These methodological discrepancies and the lack of standardized protocols result in remarkable variability in environmental impact potentials. Additionally, there is lack of consensus on the environmental benefits of AD systems compared to traditional manure management, and co-digestion with energy crops or food waste compared to mono-digestion of manure. Consequently, the environmental impacts of manure-based AD systems remain inconclusive due to methodological heterogeneity and data inconsistencies. Future research should develop scientific and standardized approaches and focus on the completeness of system boundaries, selection of key environmental impact categories, environmental load allocation, inventory data quality, and the transparency of the analysis.

Abstract Hydrogen potentially plays a key role in the transportation sector while transitioning to a net-zero emissions economy. Low-carbon hydrogen produced from fossil resources is often viewed as a bridge in the energy transition. This study comparatively evaluates life cycle greenhouse gas emissions of diverse pathways of fossil-based hydrogen production for fuel cell vehicle use. Life cycle emissions of hydrogen production alone vary significantly with production technology and are highly influenced by the supply sources of feedstock and electricity. Reforming and chemical looping with carbon capture and storage (CCS) are competitive to produce low-carbon hydrogen, whereas plasma pyrolysis is not competitive. Using low-carbon hydrogen to replace gasoline and diesel can significantly reduce life cycle emissions for light-duty and heavy-duty vehicles. Low-carbon hydrogen production by steam methane reforming, autothermal reforming, gasification, and chemical looping with CCS accounts for 64% to 78% of the total life cycle emissions associated with hydrogen production, transport, leakage, and vehicle use. Although nominal hydrogen leakage alone has no remarkable effect on life cycle emissions, the expansion of assessment system boundary by including hydrogen transport and utilization can sizably elevate emissions. To secure short-term climate benefits for replacing diesel-fueled heavy-duty trucks and transit buses with hydrogen-fueled vehicles, however, it is necessary to simultaneously limit methane and hydrogen leakage along their supply and utilization chains. These findings imply that economic incentives and policies for a low-carbon hydrogen economy should be developed based on the life cycle emissions of both hydrogen production and utilization.

Abstract The United States (U.S.) is a major beef producing and consuming country and increasing demand for beef is expected to apply additional pressure on non-renewable water resources. Water footprints of beef production are widely documented in the literature and are a contentious issue. The sustainability of water use in beef production is typically assessed through virtual water footprints (VWF) and life cycle assessments (LCAs). However, ongoing debates persist regarding whether water footprints should be volumetric or impact-based assessments. Distinct differences in the methodologies of VWF and LCA introduce challenges for policymakers who aim to redistribute water resources along the beef supply chain to improve sustainability. Here, we summarize the challenges and opportunities associated with water use in the U.S. beef supply chain by synthesizing findings from 71 studies spanning multiple disciplines, including geology, hydrology, water resources, sustainability, livestock production, economics, and policy from 1993 to 2024. The primary challenge identified was the lack of comparability between VWF and LCA studies. Inconsistencies in accounting for green, blue, and grey water footprints, varying functional units, and different system boundaries complicate across-study comparisons. The discrepancies observed between studies are often related to data deficiencies, requiring the implementation of some generalized assumptions. Furthermore, VWF tends to quantify water footprints on a regional or national basis, while LCAs are usually conducted locally. Consequently, resource management initiatives informed by regional-level figures may not have the desired effect on mitigating local water resource stressors. An essential step in addressing these challenges is improved data collection in the form of standardized methodology, functional units, and system boundaries to ensure targeted and meaningful data acquisition. An additional opportunity to address some of the data deficiencies is technology adoption. For example, on-farm camera sensors or stand-alone water monitoring devices can measure direct water consumption. Additionally, the installation of real-time water flow monitoring systems in beef processing plants has the potential to reduce water footprint through improved plant management. The adoption of technologies such as remote sensing and improved irrigation applicators has reduced the water footprint of crop production and, subsequently, the beef water footprint as well due to the impact of irrigation on cattle feed footprints. Continued improvements in water use efficiency and management through technology adoption, as well as the implementation of standardized methods for assessing water footprints, are critical for generating comparable data that can inform policy-making decisions in the U.S. beef industry.