Closing the loop on cadmium - An assessment of the material cycle of cadmium in the US

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 (similar to 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 options for improving recycling rates include collecting deposits and providing rewards for the return of spent batteries, taxing or otherwise discouraging discarding PRBs in municipal solid waste, and providing incentives for extended producer responsibility. Third, we highlight the importance of the connection between zinc mining and the supply of cadmium in designing an effective policy to manage the risks associated with cadmium. Fourth, we recommend that policy measures be taken to provide the necessary data required to improve our understanding of the flow of cadmium into the U.S. in the form of product imports and the amount of cadmium lost or disposed of by recycling processes.