An Assessment of the Material Cycle of Cadmium in the U.S

Goal, Scope and Background. In this study, the major flows of cadmium in the U.S. economy are quantified and the primary sinks are identified to gauge the need for additional policy to minimize the potential human health and ecosystem risks associated with these flows. Because of the concurrent occurrence of cadmium and zinc in ore, we also consider the relevant portions of the material cycle of zinc. Methods. We estimated the flows of cadmium through U.S. manufacturing using a mass balance approach with data provided by the U.S. Geological Survey's Minerals Yearbook. Cadmium emissions factors were created using facility specific information found in the U.S. Toxics Release Inventory and were used to model future losses. Data gaps were filled through review of relevant literature. We modeled the import and sales of nickel-cadmium batteries with rechargeable battery usage trends and estimates of market share by battery chemistry. Results and Conclusion. Primary cadmium in the U.S. is almost exclusively produced as a co-product of zinc. Almost all zinc and cadmium mined in the U.S. is exported to foreign smelters as ore concentrate. We estimate that the bulk of cadmium consumed in the U.S. economy (~90%) is imported in the form of nickel-cadmium rechargeable batteries. These batteries can be divided into the larger wet-cells and portable rechargeable batteries (PRB). The collection rate for the recycling of large wet cells was found to be high (80%) while the collection rate for PRBs is low (5–20%). The Rechargeable Battery Recycling Corporation (RBRC) is responsible for the collection of these batteries which are recycled exclusively by the International Materials Reclamation Company (INMETCO). The remaining PRBs are generally disposed of in municipal solid waste (MSW) landfills. This study provides a detailed substance flow analysis of U.S. stocks and flows of cadmium in products, however additional research is needed to better quantify the associated exposures and risks. Recommendation and Perspective. Based on our analysis, we make four recommendations. First we suggest that if cadmium is to be used, it should be used in long-lived products that can be easily collected and recycled with minimal losses. Second, continued cadmium use should be coupled with renewed efforts on the part of policy-makers to encourage the collection and recycling of cadmium-bearing products. At present, consumers do not see the environmental cost associated with the proper disposal of the cadmium content of NiCd batteries. Policy op1 Background, Aim and Scope 1.1 Regulatory context As federal environmental regulation has increased over the past thirty years, cadmium, along with other heavy metals, has received attention from policy-makers due to increasing concern about its environmental and health effects (Smith 1995). Exposure to elevated levels of cadmium is believed to cause lung, kidney and liver malfunction as well as prostate cancer (ATSDR 2004, Ikeda 2000, US EPA 1995). In the most extreme cases, kidney malfunction due to cadmium intake has led to bone decalcification as was the case with the outbreak of Itai-Itai Disease in Japan's industrial Jinzu River Basin.1 This outbreak resulted in Japan's first water quality and industrial discharge control legislation (Ui 1992). In the U.S., industrial facilities have been required under the Emergency Planning and Community Right to Know Act (EPCRA) to report their releases of cadmium since 1987. In 1998 the reporting threshold for cadmium was lowered due to its classification as persistent, bioaccumulative and toxic (PBT). The Clean Air Act of 1990 listed cadmium under its Title III hazardous air pollutants subject to maximum achievable control technology (US EPA 1993). More recently cad1 Chaney (2004) and Reeves (2004) show that human absorption and retention of cadmium in the Jinzu River region may have been increased by deficiencies in zinc, iron and calcium caused by a subsistence rice diet. Metals Closing the Loop on Cadmium Int J LCA 11 (1) 2006 39 mium has been identified as one of the 31 Priority Chemicals for action under the U.S. Environmental Protection Agency's (EPA) National Partnership for Environmental Priorities. Together with lead and mercury, it is one of only three metals selected for this designation (US EPA 2005). Reference human exposure levels for cadmium promulgated by the EPA, Occupational Safety and Health Administration (OSHA) and the Agency for Toxic Substances and Disease Registry (ATSDR) are on the order of 10–4 mg/kg/day for food and water (ATSDR 2004, US EPA 1992) and an eight hour time weighted average of 5 μg/m3 for occupational exposure (OSHA 1992). Regulatory efforts to control the release of cadmium contained in post consumer products have been more modest. The Federal Trade Commission has issued guidelines for the proper labeling of recyclable batteries containing cadmium and other toxic materials. In 1996 congress passed the Mercury Containing and Rechargeable Battery Act (MCRBA) facilitating the recycling of nickel-cadmium NiCd and other rechargeable batteries by standardizing the labeling, collection and disposal requirements previously enforced by state agencies (US EPA 1997). Under the Universal Waste Rule (UWR), 40 CFR 273 (1995), the MCRBA also streamlines the process of returning of NiCd batteries to a recycling facility by relaxing their hazardous waste designation during shipment to a recycling facility. In the European Union, officials have issued the Waste Electrical and Electronic Equipment (WEEE) Directive and Restriction on the use of Hazardous Substances (RoHS) in an effort to address concerns about toxic substances in products. These directives restrict the import and manufacture of products containing a variety of dangerous substances including cadmium, lead, hexavalent chromium, and mercury above threshold values (2002/96/EC, 2002/95/EC). Prior to these directives, policies to control the release of heavy metals in the EU focused on limiting their presence in industrial discharges and requiring facilities to use the best technical means available for the prevention of cadmium discharges (83/513/EC). 1.2 Analytical context Mapping the life cycle material flow of cadmium in an economy allows us to identify opportunities for reducing environmental releases and other 'losses' of this useful, but toxic material. Traditionally, policies intended to reduce exposure to a toxic material focus on a specific exposure route such as industrial emissions. Quantifying the flows of a material through its life cycle can assist in revealing new means of reducing undesirable flows and provide insight into dependencies in the system. van der Voet et al. (2000) have developed models for the flows of heavy metals, including cadmium, through the economy and environment in the Netherlands and found that while environmental regulation has been effective in reducing their emissions from industry over the past few decades, heavy metals are accumulating in the Dutch economy as products and infrastructure. Unless collection patterns change, much of these stocks will enter landfills where their heavy metal contents pose a risk of contaminating leachate, requiring potentially costly management. Their analysis also revealed an important 'hidden' flow of cadmium as a trace element in fertilizers and sludges applied to agricultural soil. Several studies have shown that low level cadmium emissions from a variety of sources contributed to the buildup of cadmium in the Rhine River Basin over the period 1955 to the mid 1990s; these sources included phosphate fertilizers, sewage sludge, corrosion of galvanized zinc, tire wear, fossil fuel combustion, nonferrous smelting and various manufacturing processes (Stigliani et al. 1993, 1994a, 1994b, Anderberg 2000, Klepper 1995). Stigliani points out the role soil plays in buffering ecosystems against cadmium uptake and notes that long-term accumulation of cadmium in soils leads to increasing transport and plant uptake. Today cadmium is used primarily in the manufacture of nickel cadmium (NiCd) rechargeable batteries. Lankey (1998, 2000) assessed the life cycle emissions, energy use and waste generation associated with the use and recycling of rechargeable NiCd batteries and found that the use of recycled materials reduces the energy requirements and environmental emissions associated with the manufacture of rechargeable batteries. She also found that a NiCd battery recycling facility requires a modest payment to make the process profitable. In light of these and other considerations, McMichael and Hendrickson (1998) suggest replacing cadmium and other toxic materials in batteries with efficient, cost-effective alternatives as an ideal while in the meantime regulations are needed to reduce the toxic effects of used portable rechargeable batteries (PRB). Rydh (1999, 2002a) has also performed a material flow and life cycle inventory of NiCd battery recycling in Sweden and concludes that the optimal recycling rate considering all of the environmental impacts is near 100%. In another study, Rydh (2002b) considered the global metal flows arising from PRB use and found that the mass of cadmium extracted for PRB manufacture is roughly four times that of natural cadmium flows (due to weathering and volcanic activity). In this paper we examine the flow of cadmium through the U.S. economy and comment on policy options for reducing environmental emissions and the cadmium contents of municipal solid waste (MSW). Mine concentrates, refined cadmium, products and releases from manufacturing facilities are the primary focus of this analysis. Special attention is given to zinc ore concentrates as they are the only ore for which beneficiation of cadmium metal is currently economical. We included order of magnitude estimates of the flow of cadmium in fertilizers and fossil fuels to allow for comparison, however these flows occur independently from those that comprise the focus of our work and are not part of our dynamic model. 1.3 Cadmium use in the U.S. Environmental regulation has played a role in the decline of the U.S. cadmium industry over the past decade (Plachy 2005). Higher costs associated with emissions control and waste management put economic strain on domestic industries. However, this increased strain has had the effect of Closing the Loop on Cadmium Metals 40 Int J LCA 11 (1) 2006 promoting the search for alternatives to some of the applications for cadmium (US EPA 2000). In 2004, 90% of the zinc mining in the U.S. was done in Alaska. The U.S. exported almost all of the zinc concentrates mined that year and then imported nearly as much refined zinc2. On average from 1993 to 1999, the U.S. exported 70% of its mine production of zinc in concentrates and then imported the same percentage of the refined zinc consumed (Plachy 2004). The International Metals Reclamation Company (INMETCO) located in Ellwood City, Pennsylvania is currently the only facility engaged in the recovery of cadmium in the U.S. Recycling is available for NiCd batteries and electric arc furnace dust resulting from recycling of galvanized steels and alloys. The U.S. Geological Survey (Plachy 2000) estimates that about 15% of all post-consumer cadmium is recycled. Most of this material comes from industrial NiCd batteries which contain 20% of all cadmium used in batteries and are collected at a rate of 80% (Plachy 2003). The remaining cadmium comes from PRBs and electric arc furnace (EAF) dust which are recycled at lower rates. In order to take extended responsibility for their products, manufacturers of NiCd batteries have contributed to formation of the Rechargeable Battery Recycling Corporation (RBRC) which coordinates efforts to collect NiCd PRBs in the U.S. and Canada. Over 30,000 drop off locations in retail stores and public institutions accept batteries which are shipped in boxes provided by RBRC to INMETCO for recycling. INMETCO's cadmium recycling process is capable of recycling 3,000 tonnes of NiCd batteries (NRC 2005) or 500 tonnes cadmium metal3. Although this is enough cadmium to meet the U.S. manufacturing demand of 500 tonnes (USGS 2005a), additional cadmium continues to be extracted along with zinc ore. The increasing use of galvanized steel (Gordon 2003) continues to outstrip the supply of recycled zinc requiring continued extraction of ore. Recovery rates for zinc are low because most zinc is dispersed in products containing low concentrations making it difficult to achieve high recovery rates. In addition to batteries and EAF dust, recovery of cadmium from MSW incineration has been proposed by Brunner (2004). Seventy eight percent of the cadmium used in U.S. manufacturing is used for nickel cadmium batteries while manufacture of pigments (12%), coatings and platings (8%), plastics (1.5%) and nonferrous alloys and other uses (0.5%) consume the remaining material. Over the past four years, consumption of cadmium by U.S. manufacturers has declined by 70% in response to environmental concerns (Plachy 2005). As consumption by U.S. manufacturing continues to decrease, imports of NiCd batteries are an increasingly important source of cadmium in the U.S. An important emerging use for cadmium is thin film photovoltaic (PV) cells which utilize the photoelectric properties of CdS or CdTe to capture a higher percentage of incident solar energy than traditional silicon PV cells. Currently the use of cadmium for PV technologies is very small (less than 0.5%). 1.4 Trace flows of cadmium Significant flows of cadmium also occur due to its presence as a trace element in phosphates, fossil fuels and zinc compounds. The most important of these flows is the cadmium contained in phosphates, estimated to be between 250 and 3,200 tonnes. Most of this material is applied to agricultural soils as phosphate fertilizer. The cadmium content of coal is between 100 and 1,700 tonnes. Three tonnes of this cadmium become air emissions while the majority is concentrated in flu dusts and other combustion by products which are disposed of (70%), used in the manufacture of concrete (10%), used as a fill material (8%), or used for a variety of other purposes. The cadmium in the petroleum consumed in the U.S. is found to be roughly 2 to 200 tonnes. These flows will be discussed in more detail in the following section.