What Do We Know About Metal Recycling Rates?

The recycling of metals is widely viewed as a fruitful sustainability strategy, but little information is available on the degree to which recycling is actually taking place. This article provides an overview on the current knowledge of recycling rates for 60 metals. We propose various recycling metrics, discuss relevant aspects of recycling processes, and present current estimates on global end‐of‐life recycling rates (EOL‐RR; i.e., the percentage of a metal in discards that is actually recycled), recycled content (RC), and old scrap ratios (OSRs; i.e., the share of old scrap in the total scrap flow). Because of increases in metal use over time and long metal in‐use lifetimes, many RC values are low and will remain so for the foreseeable future. Because of relatively low efficiencies in the collection and processing of most discarded products, inherent limitations in recycling processes, and the fact that primary material is often relatively abundant and low‐cost (which thereby keeps down the price of scrap), many EOL‐RRs are very low: Only for 18 metals (silver, aluminum, gold, cobalt, chromium, copper, iron, manganese, niobium, nickel, lead, palladium, platinum, rhenium, rhodium, tin, titanium, and zinc) is the EOL‐RR above 50% at present. Only for niobium, lead, and ruthenium is the RC above 50%, although 16 metals are in the 25% to 50% range. Thirteen metals have an OSR greater than 50%. These estimates may be used in considerations of whether recycling efficiencies can be improved; which metric could best encourage improved effectiveness in recycling; and an improved understanding of the dependence of recycling on economics, technology, and other factors.     

Structural Decomposition Analysis of Raw Material Consumption

The aim of this article is to quantify the drivers for the changes in raw material consumption (domestic material consumption expressed in the form of all materials extracted and used in the production phase) in terms of technology, which refers to the concept of sustainable production; the product structure of final demand, which refers to the concept of sustainable consumption; and the volume of final demand, which is related to economic growth. We also aim to determine to what extent the technological development and a shift in product structure of the final demand compensate for the growth in final consumption volume. Therefore, we apply structural decomposition analysis (SDA) to the change in raw material consumption (RMC) of the Czech Republic between 2000 and 2007. To present the study in a broader context, we also show other material flow indicators for the Czech Republic for 2000 and 2007. Our findings of SDA show that final demand structure has a very limited effect on the change in material flows. The rapid change in final demand volume was not compensated for crude oil, metal ores, construction materials, food crops, and timber. For the material category of non‐iron metal ores, even the change in technology contributes to an increase in material flows. The largest relative increases are reported for non‐iron metal ores (38%) and construction materials (30%). The main changes in material flows related to the Czech Republic are driven by exports and enabled by imports, the main source of these increased material flows. This emphasizes the increasing role of international trade.     

The Everyday Life Context of Increasing Energy Demands: Time Use Survey Data in a Decomposition Analysis

Industrial ecologists have modeled with precision the material foundations of industrial systems, but given less attention to the demand for products and the drivers of structural changes in these systems. This article suggests that time use data complement data on monetary expenditure and can be used to elucidate the everyday life context in which the changes in the economy take place. It builds upon the claim that goods are not direct sources of utility, but enter specific household activities as inputs. A second argument for the proposed approach is that it can be used to introduce and foster human agency in analyses of production systems. The article uses Finnish time use survey data, consumption expenditure data, and data on the sectoral energy intensities of financial output in the Finnish economy. First, a measure of the energy intensity of activities is derived by relating consumer time use and the required direct and indirect energy requirements. Second, the results include a decomposition of changes in the energy requirements of private consumption in Finland during the 1990s. It is shown that although the same activities on average require increasing energy inputs per unit of time, Finns have simultaneously changed the structure of their everyday life toward less energy-intensive activities.     

Protein disulphide isomerase-assisted functionalization of proteinaceous substrates

Protein disulphide isomerase (PDI) is an enzyme that catalyzes thiol-disulphide exchange reactions among a broad spectrum of substrates, including proteins and low-molecular thiols and disulphides. As the first protein-folding catalyst reported, the study of PDI has mainly involved the correct folding of several cysteine-containing proteins. Its application on the functionalization of protein-based materials has not been extensively reported. Herein, we review the applications of PDI on the modification of proteinaceous substrates and discuss its future potential. The mechanism involved in PDI functionalization of fibrous protein substrates is discussed in detail. These approaches allow innovative applications in textile dyeing and finishing, medical textiles, controlled drug delivery systems and hair or skin care products.     

Thidiazuron-induced adventitious shoot regeneration of sweetpotato (Ipomoea batatas)

Adventitious shoots of sweetpotato (Ipomoea batatas L. Lam.) were produced in vitro using a two-stage culture method. Petiole explants were incubated on Murashige and Skoog (MS) medium supplemented with 2,4-dichlorophenoxy acetic acid (0.2 mg·liter^−1) for 3 d, and transferred to MS medium with thidiazuron (0 to 0.4 mg·liter^−1). Shoot regeneration was observed in most explants (78.2%) of genotype PI 318846-3 within 28 days when cultured on thidiazuron at 0.2 mg·liter^−1. Histological studies of cultured petiole explants showed meristematic activity within cells of vascular bundles and throughout the ground tissue. Explants isolated from apical leaves exhibited higher shoot regeneration frequency than those isolated from the basal portion of the shoot. Leaf lamina explants exhibited lower frequency of regeneration than petiole explants. In contrast to thidiazuron, the use of zeatin riboside, and kinetin resulted in a lower frequency of shoot regeneration although more sweetpotato genotypes could be regenerated using either of these two cytokinins. The sweetpotato plants regenerated using thidiazuron grew vigorously and rooted easily when transferred to the greenhouse.     

The impact of hybrids between genetically modified crop plants and their related species: biological models and theoretical perspectives

Forces affecting the rate of spread and increase of hybrids between genetically modified crop plants and their related species remain qualitatively similar, irrespective of whether genetic modification was achieved using traditional methods, those of biotechnology or as a result of the natural evolutionary process. However, the precise magnitude of the forces and, consequently, the likely environmental impact of such hybrids, may depend strongly on the nature of the gene or genes introduced into the native species. While many classes of transgenes are similar to those manipulated by conventional breeding techniques or evolution, biotechnology offers the potential to introduce genes into crops which are novel both from the point of view of function and origin. The qualitative similarity between transgenes and the products of conventional or evolutionary modification suggests that a historical view of the environmental impact of hybrids between traditionally produced crops or exotic species and their relatives would be of use in estimating the probable fate of hybrids containing transgenes in the environment. However, with certain classes of transgenes for which there are no existing analogues, there will need to be greater care in assessing the possible risks associated with release into the environment.     

Assessing the risks of transgene escape through time and crop-wild hybrid persistence

Transgenes introduced into crops can escape in time, as well as space, via the seed bank. For annual plants, especially ruderals, seed bank behaviour may be the most important factor determining population persistence. Crop seeds may exhibit some dormancy and germination cueing in the soil but are expected to be less able to persist than their wild relatives, which often have considerable dormancy and longevity, as well as effective germination cueing responses. Crop-wild hybrids may have seed bank characteristics more suited to persistence, and maternal effects may favour persistence of hybrids having wild plants for their female parent. Escape of transgenes via crop-wild hybrids presents unique concerns not present for crops. Hybrids can undergo natural selection and may back-cross with wild plants. We suggest methods that can be used in conjunction with evaluation of the relative fitness of crop-wild hybrids that will determine the likelihood of back-crossing. Accurate assessment of escape in time and transgene persistence via crop-wild hybrids requires proper plant materials. We emphasize the use of null segregants as controls for transgenic crops and for generating crop-wild hybrid controls for transgenic hybrids. Since good empirical and theoretical understanding of how individual genes influence the fate of plants in different environments is lacking, evaluation of escape in time and the persistence of transgenes via crop-wild hybrids should be on a case-by-case basis.     

Three research priorities for just and sustainable urban systems: Now is the time to refocus

Now is the time to refocus efforts in urban research and design. A changing climate and extreme weather events are presenting unique challenges to urban systems around the world. These challenges illuminate the social barriers that accompany disruptive events such as resource inequities and injustices. In this perspective, we provide three research priorities for just and sustainable urban systems that help to address these matters. The three research priorities are: (1) social equity and justice, (2) circularity, and (3) digital twins. Conceptual context and future research directions are provided for each. For social equity and justice, the future directions are mandatory equity analysis and inclusionary practices, understanding and reconciling historical injustices, and intentional integration with diverse community stakeholders. For circularity applications, they are better metrics for integration, more robust evaluation frameworks, and dynamic modeling at multiple spatial and temporal scales. Future directions for digital twins include developing principles to reduce complexity, integrating model and system components, and reducing barriers to data access. These research priorities are core to meeting several of the United Nations Sustainable Development Goals (i.e., 1—No Poverty, 8—Decent Work and Economic Growth, 10—Reduced Inequalities, and 11—Sustainable Cities and Communities). Useful social and technical matters are discussed throughout, where we highlight the importance of prioritizing localized research efforts, provide guidance for community-engaged research and co-development practices, and explain how these priorities interact to align with the evolving field of industrial ecology.     

A matter of timing: System requirements for repair and their temporal dimensions

Research into repair within the circular economy (CE) typically focuses on technical aspects of design, policy, and markets, and often assumes simplified conditions for the user/owner and the product system to explain the barriers to scaling repair activities. However, factors occurring at pre-use stages of the product's life cycle can significantly influence whether, and to what extent, repair is viable or possible, that is, warranty duration, after-sale service provision, and access to necessities. The passing of time can directly and indirectly affect the ability, difficulty, and thus, the likelihood of repair activities being performed at each stage of the product's life cycle. Drawing from the literature and applying inductive systems-thinking tools, we propose a framework for considering the “System of Repairability.” We delineate how the passing of time (temporal dimensions) affects one's ‘‘ability to repair,’’ as a product progresses through different life cycle phases (i.e., breakdown vs. repair vs. disposal), and the point(s) at which the repair is considered or attempted (i.e., year of usage). By integrating life cycle and temporal (time-based) dimensions into a broad System of Repairability framework, we clarify relevant interconnections, iterations, sequences, and timing of decision points, stakeholders, and necessary conditions to facilitate an outcome of successful repair at the individual level, and thus intervention strategies for scaling repair within CE. We discuss how a policy mix can address the life cycle of products and the repair system more holistically. We conclude with a future outlook on how temporal dimensions can inform policy strategies and future research.     

Analysis of parameters about useful life extension in 70 tools and methods related to eco-design and circular economy

One of the approaches followed by the circular economy (CE) to achieve sustainability through design is product life extension. Extending the life of products to make them useful for as long as possible is a means to reduce waste production and materials consumption, as well as the related impacts. For designers, conceptualizing products in a way that allows them to be used for longer is a challenge, and assessing how well they extend their lifespan can be helpful when it comes to choosing the best proposal. In this paper, 70 tools and methods related to eco-design and circular economy are studied to determine how many of them consider parameters related to life extension and which can be applied in the early stages of design. The results of the analysis show that most of the existing tools and methods are applicable to developed products, and only a few of them take into account parameters related to extending the useful life. Of the 70 tools and methods, only 14 include some parameter related to life extension and are applicable to concepts. CE toolkit, Eco-design PILOT, CE Designer, Circularity Assessment tool, Circularity Potential Indicator and Circular Design Tools take into consideration eight or more parameters to assess life extension in concepts. This will help designers select the most appropriate and will indicate the need for more complete tools to consider useful life extension in the early stages of design and thus enhance the selection of more sustainable products.