Exploratory Data Analysis of the Multilevel Anthropogenic Zinc Cycle

A comprehensive multilevel contemporary cycle for stocks and flows of zinc is analyzed by the tools of exploratory data analysis. The analysis is performed at three discrete organizational levels—country (53 countries and 1 country group that together comprise essentially all anthropogenic stocks and flows of zinc), world region (9 world regions), and the planet as a whole. The results demonstrate the following: (1) Exploratory data analysis provides valuable and otherwise unobtainable information about material flows, especially those across multiple spatial levels. (2) All distributions of countrylevel zinc stock and flow data are highly skewed, a few countries having large magnitudes, many having small magnitudes. Rates of fabrication of zinc-containing products for the countries are poorly correlated with rates of extraction, reflecting the fact that many countries that extract zinc do not fabricate products from zinc to any significant degree, and vice versa. (4) Virtually all countries are adding zinc to stock in the use phase (in galvanizing applications, zinc castings, etc.). These rates of addition are highly correlated with rates of zinc entering use in all regions, and are higher in regions under vigorous development. (5) With weak confidence, the rate of zinc landfilling by countries appears to be highly correlated with the rate of discard. (6) The statistical distributions of regional-level zinc cycle parameters are approximately log normal. (7) The extremes of normalized statistical distributions of zinc flow values are broader at lower spatial levels (country versus region, for example), but regional interquartile ranges for zinc entering use and zinc discards are higher at regional level then at country level.     

The Multilevel Cycle of Anthropogenic Zinc

A comprehensive annual cycle for stocks and flows of zinc, based on data from circa 1994 and incorporating information on extraction, processing, fabrication, use, discard, recycling, and landfilling, was carried out at three discrete governmental unit levels—54 countries and 1 country group (which together comprise essentially all global anthropogenic zinc stocks and flows), nine world regions, and the planet as a whole. All of these cycles are available in an electronic supplement to this article, which thus provides a metadata set on zinc flows for the use of industrial ecology researchers. A "best estimate" global zinc cycle was constructed to resolve aggregation discrepancies. Among the most interesting results are the following: (1) The accumulation ratio, that is, addition to in-use stock as a function of zinc entering use, is positive and large (2/3 of zinc entering use is added to stock) (country, regional, and global levels); (2) secondary input ratios (fractions of input to fabrication that are from recycled zinc) and domestic recycling percentages (fractions of discarded zinc that are recycled) differ among regions by as much as a factor of six (regional level); (3) worldwide, about 40% of the zinc that was discarded in various forms was recovered and reused or recycled (global level); (4) zinc cycles can usefully be characterized by a set of ratios, including, notably, the utilization efficiency (the ratio of manufacturing waste to manufacturing output: 0.090) and the prompt scrap ratio (new scrap as a fraction of manufacturing input: 0.070) (global level). Because capturable discards are a significant fraction of primary zinc inputs, if a larger proportion of discards were recaptured, extraction requirements would decrease significantly (global level). The results provide a framework for complementary studies in resource stocks, industrial resource utilization, energy consumption, waste management, industrial economics, and environmental impacts.     

Explanatory Variables for per Capita Stocks and Flows of Copper and Zinc

A number of potential explanatory variables for the stocks and flows of copper and zinc in contemporary technological societies are co-analyzed with the tools of exploratory data analysis. A one-year analysis (circa 1994) is performed for 50 countries that comprise essentially all anthropogenic stocks and flows of the two metals. The results show that (1) The key explanatory variable for metal use is gross domestic product (GDP) per capita (purchasing power parity, PPP). By itself, GDP explains between one-third and one-half of the variance of per capita copper and zinc use. Other variables that were significantly correlated with copper and zinc use included stock of passenger cars and television sets (per 1, 000 people); two infrastructure variables, wired telephone connections, urban population, and value added inmanufacturing. The results do not provide evidence supporting the Kuznets curve hypothesis for these metals. (2) Metal use per capita can be estimated using multiple regression equations. For copper, the natural logarithm of use is related to the explanatory variables GDP (PPP), value added in manufacturing, and urban population. This model explains 80% of the variance among the different countries (r²= 0.79). The natural logarithm of zinc use is related to GDP (PPP) and value added in manufacturing with an r² of 0.75; (3) For both metals, rates of metal fabrication, use, net addition to stock, and discard in low-and high-income countries differ significantly from each other. Our statistical analyses thus provide a basis for estimating the potential development of metal use, net addition to stock, and discard, using data on explanatory variables that are available at the international level.     

Heavy-Metal Balances, Part II: Management of Cadmium, Copper, Lead, and Zinc in European Agro-Ecosystems

The aim of sustainable heavy-metal management in agroecosystems is to ensure that the soil continues to fulfill its functions: in agricultural production, in environmental processes such as the cycling of elements, and as a habitat of numerous organisms. To understand and manage heavy-metal flows effectively, a consistent approach to modeling the flows is needed within the particular agro-system under study. General aspects of heavy-metal balance studies in agro-ecosystems were described in part I of this study. In this article (part II), several European studies of heavy-metal balances at varying spatial scales and in a variety of agro-ecosystems are reviewed. Sectoral studies at the national and international levels provide information for economic analyses and generic regulations; however, policies implemented at these levels often ignore farm characteristics and individual management options. Field-scale and farm-gate balances give farmers specific feedback on effective options for better heavy-metal management. Heavy-metal balances could be incorporated in an environmental management system of certified farms. In this way, farm certification may well serve as a basis from which to develop policy to address environmental issues in agriculture.     

Estimation of Copper In‐use Stocks in Nanjing,China

Copper (Cu) is an essential but supply‐restricted resource in China. Characterization of in‐use stocks can provide useful instruction for the future recycling of copper. This article attempts to estimate copper in‐use stocks in a Chinese city. To this purpose, an extensive bottom‐up estimate of copper stocks in use in Nanjing in the year 2009 was conducted. The results are a total stock estimate of 295 gigagrams (Gg) of copper or 46.9 kilograms (kg) of copper per capita for 2009. Infrastructure, equipment, and buildings contain 42.0%, 26.1%, and 28.1% of the total stock, respectively, indicating that these three categories are principal potential reservoirs of a secondary copper resource. The copper in transportation amounts to only about 3.7% of the total amount. The per capita stock was compared with similar studies carried out in other regions of the world, and the results show that the Nanjing level is significantly lower than developed countries. On the whole, our results show that electric power transmission and distribution systems, buildings, household durables, and industrial equipment are the four largest potential reservoirs of copper scrap.     

Cadmium Flows Caused by the Worldwide Production of Primary Zinc Metal

Material flows of the economic cycle can contain toxic substances, which enter the economy as impurities in raw materials or are intentionally added as minor or even main constituents during the manufacture of industrial or consumer goods. Cadmium, predominantly associated with zinc minerals, is a by-product of the primary zinc production. Cadmium is generated when zinc is extracted from zinc ores and concentrates, an intermediate product resulting from flotation processing after the zinc ore has been mined and milled. Information on the amount of cadmium generated from zinc extraction is rarely published. In this article, we assess generation and fate of cadmium accumulating worldwide in the production of primary zinc from ores and concentrates. Model calculations for the beginning of the 21st century show that annually about 30,000 tonnes of cadmium were generated, but only approximately 16,000 tonnes were converted to primary cadmium metal, key material for the production of other cadmium compounds (e.g., cadmium oxide), and cadmium-containing goods (e.g., nickel−cadmium batteries). Hence, about 14,000 tonnes of cadmium must have been transferred somewhere else. The fate of about 5,500 tonnes can be plausibly explained, but it is difficult to determine what happens to the rest.     

Future Redistribution of Cadmium to Arable Swedish Soils: A Substance Stock Analysis

This article describes a stock-based methodology designed to analyze the redistribution of substance stocks to environmental compartments. The methodology is then applied to investigate the requirements and possibilities for avoiding undesired future accumulation of cadmium in Swedish arable soils. A prospective decomposition analysis of human cadmium mobilization is thus performed to estimate the potential amounts that can end up in arable soils through different flows from the cadmium stocks identified. The requirements for cadmium abatement to achieve prescribed goals for accumulation limits are determined and compared with past and current achievements and with the varying qualities of possible abatement methods.
A stock-based methodology adds some important information to traditional scenario techniques based on substance flow analysis. The most obvious is that the fact that stocks are limited actually matters for long-term accumulation of cadmium in arable land. The methodology may also contribute certain indicators, for instance, on abatement requirements, which could serve as a complement to regulation and local quality measures on specific flows at an aggregated policy level. The stock perspective also sheds new light on actions such as increased recycling.
Concerning the specific example used in the study, it is possible to achieve a future addition of cadmium in Swedish agricultural soils that is significantly lower than in the past, although the amount depends to a large degree on activities and policies outside Sweden. Considerable uncertainty exists regarding future depositions from air, especially that from distributed small-scale emissions from fuel burning and reemission of already deposited cadmium from natural media. Measures must also be taken to guarantee a continued low addition in the form of mineral phosphorus fertilizers.     

The Temporal Evolution of Anthropogenic Phosphorus Consumption in China and Its Environmental Implications

Modern human activities greatly disturb substance flows in nature and senselessly discard massive amounts of precious resources to natural waste reservoirs; phosphorus (P) is a good example of this. In this article, substance flow analysis is employed to quantify and explore the temporal evolution of China's P consumption in main metabolic nodes from 1984 to 2008, and then the environmental implications for P flows into both surface waters and natural soil are investigated. Results show that the metabolic nodes of human life and animal husbandry have demanded increasingly more P inputs, while disseminating more and more P wastes, with the waste recycling ratios of these processes dropping, respectively, from 65.9% and 66.1% in 1984 to 50.7% and 40.6% by 2008. These change traits were closely related to national polices including the Household Contract Responsibility System and the Shopping Basket Program, as well as the policy vacuum existing between China's agricultural and environmental administration departments. To achieve high crop yield, increasingly more inorganic P fertilizers have been utilized in China, but their use efficiency has decreased by 46.3%. From 2003 to 2008, the total P load into surface waters was stabilized at about 900.0 kilotons (kt), while the total P load into natural soil increased by more than 3.8 times to 3,131.3 kt P in 2008. City life and the intensive breeding of crops are identified as the main targets for further pollution control and nutrient recycling in China. Some suggestions for achieving environmentally sound practices and resource sustainability in China are proposed at the end of this article.     

The Copper Balance of Cities

Material management faces a dual challenge: on the one hand satisfying large and increasing demands for goods and on the other hand accommodating wastes and emissions in sinks. Hence, the characterization of material flows and stocks is relevant for both improving resource efficiency and environmental protection. This article focuses on the urban scale, a dimension rarely investigated in past metal flow studies. We compare the copper (Cu) metabolism of two cities in different economic states, namely, Vienna (Europe) and Taipei (Asia). Substance flow analysis is used to calculate urban Cu balances in a comprehensive and transparent form. The main difference between Cu in the two cities appears to be the stock: Vienna seems close to saturation with 180 kilograms per capita (kg/cap) and a growth rate of 2% per year. In contrast, the Taipei stock of 30 kg/cap grows rapidly by 26% per year. Even though most Cu is recycled in both cities, bottom ash from municipal solid waste incineration represents an unused Cu potential accounting for 1% to 5% of annual demand. Nonpoint emissions are predominant; up to 50% of the loadings into the sewer system are from nonpoint sources. The results of this research are instrumental for the design of the Cu metabolism in each city. The outcomes serve as a base for identification and recovery of recyclables as well as for directing nonrecyclables to appropriate sinks, avoiding sensitive environmental pathways. The methodology applied is well suited for city benchmarking if sufficient data are available.     

Quantitative Evaluation of Data Quality in Regional Material Flow Analysis

A method for quantitative evaluation of data quality in regional material flow analysis (MFA) is presented. The principal idea is that data quality is a multidimensional problem that cannot be judged by individual characteristics such as the data source, given that data from official statistics may not be per se of good quality and expert estimations may not be per se of bad quality, respectively. It appears that MFA data are never totally accurate and may have certain defects that impair the quality of the data in more than one dimension. The concept of MFA information defects is introduced, and these information defects are mathematically formalized as functions of data characteristics. They are quantified on a scale from 0 (no information defect) to 1 (maximum information defect). The proposed method is illustrated in a case study on palladium flows in Austria. A quantitative evaluation of data quality provides opportunities for understanding and assessing MFA results, their a priori information basis, their reliability in decision making, and data uncertainties. It is a formal step toward better reproducibility and more transparency in MFA.     

Global Phosphorus Flows and Environmental Impacts from a Consumption Perspective

Human activities have significantly intensified natural phosphorus cycles, which has resulted in some serious environmental problems that modern societies face today. This article attempts to quantify the global phosphorus flows associated with present day mining, farming, animal feeding, and household consumption. Various physical characteristics of the related phosphorus fluxes as well as their environmental impacts in different economies, including the United States, European countries, and China, are examined. Particular attention is given to the global phosphorus budget in cropland and the movement and transformation of phosphorus in soil, because these phosphorus flows, in association with the farming sector, constitute major fluxes that dominate the anthropogenic phosphorus cycle. The results show that the global input of phosphorus to cropland, in both inorganic and organic forms from various sources, cannot compensate for the removal in harvests and in the losses by erosion and runoff. A net loss of phosphorus from the world's cropland is estimated at about 10.5 million metric tons (MMT) phosphorus each year, nearly one half of the phosphorus extracted yearly.     

Applying Ecological Input-Output Flow Analysis to Material Flows in Industrial Systems: Part I: Tracing Flows

Input-output mathematics, which allows a modeler to fully consider direct and indirect relationships among conserved flows in a system, has a long history in economics with prominent use dating to Leontief in the 1930s. Nearly all previous industrial applications of input-output analysis have been grounded in the monetary flows of an economy. Here however, because of the central nature of physical flows in the environmental impact of industry, we consider physical flows to be a fundamental component of an industrial economy. Hence, we propose an input-output based approach for modeling physical flows in industry independent of their monetary implications.
In this first part of a two-part article, a framework for using input-output mathematics to model material and energy flows is constructed from a foundation laid by previous research in nutrient and energy cycling in natural ecosystems. The mathematics of input-output flow analysis is presented from an ecological perspective, culminating in two core capabilities: tracing of flows with environs (investigated in this article) and characterizing system behavior with flow metrics (presented in the second article). We assert that environ analysis is an effective means for tracing flows through industrial systems while fully considering direct and indirect flow paths. We explore material flows of aluminum and five other metals in depth using environ analysis in this article.     

Lead In-Use Stock

The 20th century was a time of rapidly escalating use of lead (Pb). As a consequence, the standing stock of lead is now substantial. By linking lead extraction and use to estimates of product lifetimes and recycling, we have derived an estimate of the standing stock of lead throughout the century by top-down techniques. We find that the stock of in-use lead is almost entirely made up of batteries (68%), lead sheet (10%), and lead pipe (10%). Globally, about 200 teragrams (Tg) Pb was mined in the 20th century, and about 25 Tg Pb now makes up the in-use stock, so some 87% has been lost over time. Nonetheless, about 11% of all lead entering use was added to in-use stock in 2000, so the stock continues to increase each year. Currently, most of the stock is in Europe (32%), North America (32%), and Asia (24%). On a per capita basis, the global stock is about 5.6 kilograms (kg) Pb, and regional in-use stock ranges from 2.0 kg Pb (Africa) to 19.7 kg Pb (Europe). From a sustainability perspective, we estimate that the global lead resource is around 415 Tg Pb. Were the entire world to receive the services of lead at the level of the developed countries, some 130 Tg Pb would be needed, so there do not appear to be significant long-term limitations to the lead supply.     

Accounting for Fluorine: Production,Use, and Loss

Fluorine is an essential element to human health and to the chemical industry. In spite of our dependence on fluorine and fluorine compounds, we have yet to learn to use them wisely. Our fluorine history, which spans about a hundred years, has had negative effects such as hydrofluoric acid pollution caused by aluminum smelters and ozone depletion due to chlorofluorocarbon (CFC) emissions. More recent concerns center on greenhouse effects from CFCs, hydrofluorocarbons (HFCs), and sulfur hexafluoride (SF6). In this article we note also that fluorine is a nonrenewable resource that is nonsubstitutable for many purposes. This article tracks fluorine from sources through conversion processes to end uses, most of which are dissipative. We present a stock‐flow model of the fluorine system. Based on this model we consider some possible measures that could be taken to increase the degree of recovery. To mention one example, a large percentage of the world demand for fluorspar could be supplied by the phosphate rock (fertilizer) industry, which currently dissipates a great deal of recoverable fluorine in waste phospho‐gypsum.     

Approaches for Quantifying the Metabolism of Physical Economies: A Comparative Survey: Part II: Review of Individual Approaches

This article is the second of a two-part series that describes and compares the essential features of nine "physical economy" approaches for mapping and quantifying the material demands of the human economy upon the natural environ-ment. These approaches are critical tools in the design and implementation of industrial ecology strategies for greater eco-efficiency and reduced environmental impacts of human economic activity. Part I of the series provided an overview, meth-odological classification, and comparison of a selected set of major materials flow analysis (MFA) and related techniques. This sequel includes a convenient reference and overview of the major metabolism measurement approaches in the form of a more detailed summary of the key specific analytical and other features of the approaches introduced in part I. The surveyed physical economy related environmental analysis ap-proaches include total material requirement and output mod-els, bulk MFA (IFF (Department of Social Ecology, Institute for Interdiscplinary Studies of Austrian Universities) material flow balance model variant), physical input-output tables, substance flow analysis, ecological footprint analysis, environmental space, material intensity per unit service, life-cycle assessment (LCA), the sustainable process index, and company-level MFA.     

Planning Biodegradable Waste Management in Stockholm

The environmental impact of the management of biodegradable waste in Stockholm, based mainly on incineration and landfilling, was compared to systems with significant nutrient recycling; large-scale composting, anaerobic digestion, and separate collection and utilization of urine. The systems' emissions, residual products, energy turnover, and resource consumption were evaluated from a life-cycle perspective, using a computerized model, ORWARE (ORganic WAste REsearch model).
Transportation was of relatively low importance to overall environmental impact, even at high rates of nutrient recycling. This is remarkable considering the geographical setting of Stockholm, with high population density and little nearby farmland. Ancillary systems, such as generation of electricity and district heating, were crucial for the overall outcome.
Increased recycling of nutrients in solid biodegradable waste in Stockholm can reduce net environmental impact, whereas separation of human urine to be spread as fertilizer cannot yet be introduced without increased acidification. Increased nutrient recycling from solid biodegradable waste inevitably increases spreading of metals on arable land. Urine is by far the least contaminated residual product. Spreading of all other residuals would be limited by their metal content.     

Full Mode and Attribution Mode in Environmental Analysis

Several tools exist for the analysis of the environmental impacts of chains or networks of processes. These relatively simple tools include materials flow accounting (MFA), substance flow analysis (SFA), life-cycle assessment (LCA), energy analysis, and environmentally extended input-output analysis (IOA), all based on fixed input-output relations. They are characterized by the nature of their flow objects, such as products, materials, energy, substances, or money flows, and by their spatial and temporal characteristics. These characteristics are insufficient for their methodological characterization, and sometimes lead to inappropriate use. More clarity is desirable, both for clearer guidance of applications and for a more consistent methodology development. In addition to the nature of the flow object and to spatial and temporal characteristics, another key feature concerns the way in which processes are included in a system to be analyzed.
The inclusion of processes can be done in two fundamentally different ways: according to a full mode of analysis, with the inclusion of all flows and related processes to their full extent as present in a region in a specific period of time; and according to an attribution mode, taking processes into account insofar as these are required for a given social demand, function, or activity, in principle whenever and wherever these processes take place. This distinction, which cuts across families of tools that traditionally belong together, appears to have significant methodological and practical implications. Thus the distinction between the two modes of analysis, however crucial it may be, strengthens the idea of one coherent family of tools for environmental systems analysis.     

Uncovering the Fate of Critical Metals: Tracking Dissipative Losses along the Product Life Cycle

An increasing number of elements from the periodic table are being used in a growing number of products, enabling new material and product functionalities. Materials of high importance and high supply risks are usually referred to as critical materials. Many materials that are often considered critical are used in ways leading to their dissipative loss along the product life cycle. So far, the issue of material dissipation has been dealt with mainly on a rather aggregated level. Detailed knowledge on the occurrence and amount of dissipative losses in the life cycle of specific products is only scarcely available. Addressing this, a substance flow analysis of different critical metals along the life cycle of selected products is presented in this article. With regard to products used in Germany, the flows of indium and gallium used in copper‐indium‐gallium‐selenide (CIGS) photovoltaic cells, germanium used in polymerization catalysts, and yttrium used in thermal barrier coatings (TBCs) have been analyzed. The results comprise detailed knowledge about the life cycle stages in which dissipative losses occur and about the receiving media. In all case studies, a complete or almost complete dissipative loss can be observed, mainly to landfills and other material flows. In all case studies, material production can be identified as hotspots for dissipative losses. In two case studies fabrication and manufacturing (F&M for CIGS and TBCs) and in one case study end of life (polymerization catalysts) can be identified as further hotspots for dissipative losses. In addition, actions for reducing dissipation along the life cycle are discussed, targeting aspects such as the recovery of critical metals as by‐products, efficiency in F&M processes, and lack of recycling processes. Lack of economic incentives to apply more‐efficient technologies and processes already available is a key aspect in this regard.     

Urban Mining in Times of Raw Material Shortage

The present article investigates to what extent and level of success urban mining—the recovery of resources from anthropogenic stock—has been applied in the past during shortages of primary resources. As a case study, the Austrian economy during World War I—when raw materials indeed had to be substituted from secondary sources—is analyzed here. By means of material flow analysis, the management of copper, an important and relatively scarce metal that is difficult to substitute, is examined. The combination of increased demand for copper (for ammunition) and constraints on supply from sources other than the domestic anthroposphere highlights the importance of planning for and surveying urban mining activities. The results also indicate limitations to extracting a large share of copper from the anthroposphere, even in the face of a critical shortage. Although extreme measures, such as confiscation, were taken, only 1.7 kilograms of copper per capita (kg Cu/cap), amounting to perhaps as little as 10% of the anthropogenic stock, could be made available through the end of the war.     

Particle Flow Analysis

Several authors have highlighted the potential risks of nanoparticles (NPs). Still, little is known about the magnitude of emissions of NPs from society. Here, the method of explorative particle flow analysis (PFA), a modification of the more well‐known substance flow analysis (SFA), is suggested. In explorative PFA, particle number instead of mass is used as flow and stock metric and explorative scenarios are used to account for potential technology diffusion and, consequently, potentially higher emissions. The method has been applied in a case study of the use phase of titanium dioxide (TiO₂) NPs in paint, sunscreen and self‐cleaning cement. The results indicate that the current largest emissions of TiO₂ NPs originate from the use of sunscreen. One scenario implies that, in the future, the largest flows and stocks of TiO₂ NPs could be related to self‐cleaning cement. Gaps in current knowledge are identified and suggestions for future research are given.