Human health and ecological toxicity potentials due to heavy metal content in waste electronic devices with flat panel displays

Abstract

Display devices such as cathode-ray tube (CRT) televisions and computer monitors are known to contain toxic substances and have consequently been banned from disposal in landfills in the State of California and elsewhere. New types of flat panel display (FPD) devices, millions of which are now purchased each year, also contain toxic substances, but have not previously been systematically studied and compared to assess the potential impact that could result from their ultimate disposal. In the current work, the focus is on the evaluation of end-of-life toxicity potential from the heavy metal content in select FPD devices with the intent to inform material selection and design-for-environment (DfE) decisions. Specifically, the metals antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, lead, mercury, molybdenum, nickel, selenium, silver, vanadium, and zinc in plasma TVs, LCD (liquid crystal display) TVs, LCD computer monitors and laptop computers are considered. The human health and ecotoxicity potentials are evaluated through a life cycle assessment perspective by combining data on the respective heavy metal contents, the characterization factors in the U.S. EPA Tool for the Reduction and Assessment of Chemical and other environmental Impacts (TRACI), and a pathway and impact model. Principal contributors to the toxicity potentials are lead, arsenic, copper, and mercury. Although the heavy metal content in newer flat panel display devices creates less human health toxicity potential than that in CRTs, for ecological toxicity, the new devices are worse, especially because of the mercury in LCD TVs and the copper in plasma TVs.

Introduction

In recent years, there has been a tremendous rate of product re-design and replacement in consumer electronics. The replacement of cathode-ray tube (CRT) televisions (TVs) with flat panel display (FPD) devices such as plasma TVs and liquid crystal display (LCD) TVs, is particularly notable, with millions of new devices now being sold each year, as illustrated in Fig. 1. This rapid replacement is similar to that for CRT computer monitors by LCD monitors and laptop computers, which began several years ago (also shown in Fig. 1). Devices with FPDs are currently the highest volume product within the market for consumer electronic devices [1], [3]. An unintended outcome of this rapid display device replacement is the generation of millions of units of CRT waste [2]. Because of the heavy metal content in CRTs [4], lead (Pb) in particular, the potential for waste CRTs to impact the environment has been studied previously and various waste management initiatives have been put into place. For instance, the leachability of heavy metals has been assessed to simulate the hazard from landfilled electronic devices [5], [6], [7], and the heavy metal content in CRT glass has been characterized to facilitate recycling [4]. The findings from these studies indicate that CRTs contain substantial amounts of Pb, as well as many other heavy metals, and that under standard leaching test procedures, CRTs do indeed represent a potential environmental burden. As a result of these and other findings, the disposal of CRTs in California landfills was banned in 2001 [8]. The U.S. EPA considers CRT glass to be hazardous waste under RCRA (Resource Conservation and Recovery Act, 1976), but in January 2007, implemented policy to streamline management of CRTs if destined for recycling [9].

As LCD computer monitors began to replace CRTs, researchers asked the questions: will these new devices also represent an environmental burden at their end-of-life, and can they be better designed to reduce this potential impact? In the late 1990s, an important study was conducted as part of the U.S. EPA's Design for Environment Program. Called the Computer Display Partnership [10], this effort entailed collaboration between industry and researchers at the University of Tennessee to use life cycle assessment (LCA) methods to analyze the environmental impacts, performance, and cost of both CRT and LCD desktop computer monitors. The results of this endeavor are provided in an extensive U.S. EPA report published in 2001 [11] and summarized in Ref. [12]. The findings of this study indicated that although LCD displays produced less environmental impact potential than the CRTs in almost all impact categories, there were still areas of concern such as potential for aquatic toxicity and eutrophication. Uncertainty related to many aspects of the study, including data sources, were considered in detail. The findings from this study also highlighted the need to better design LCD displays (and other novel devices) to minimize their toxic substance content and reduce their potential for negative environmental impacts throughout the life cycle. Because this study was a comprehensive LCA, the specific effects of material selection in these products is difficult to extract from among the trade-offs that also account for other factors such as energy consumption. Furthermore, this study focused only on CRTs and LCDs, as used for computer desktop displays. Thus, the current work is designed to complement the U.S. EPA study by highlighting the effects of heavy metal content in display technologies and to consider additional display technologies in light of the growing demand for FPD TVs, so as to inform design-for-environment (DfE) decisions. It is recognized that other types of hazardous substances such as brominated flame retardants, liquid crystals, Plexiglas™, polyoxymethylene, polyvinyl chloride, and phthalates are also contained in the devices with FPDs [3], but these are beyond the scope of the present work. The focus of this work is on human health and ecotoxicity potential, rather than the more comprehensive list of impact categories considered in the U.S. EPA study, because this shorter list of impact categories represent those for which the presence of heavy metals have a more direct effect. In addition, the focus is on end-of-life management, because of the large volumes of waste FPDs that will be generated in the future, consideration of which has not been previously studied. Because details on future end-of-life of these devices is highly uncertain, various assumptions are employed and a pathway and impact model is developed to estimate the distribution of the heavy metals in air and water, after the devices are discarded in landfills and/or incinerated. The U.S. EPA Tool for the Reduction and Assessment of Chemical and other environmental Impacts (TRACI) is used as the source of characterization factors, because it is U.S. centric and includes heavy metals in its dataset [13]. It is important to note that this study is, therefore, a comparative evaluation in the context of life cycle assessment, rather than an absolute evaluation in the context of risk assessment [14]. The toxicity potentials over time in the United States are also estimated. This study can contribute to DfE of the devices, to their market-driven improvement by assisting customers in purchasing and insisting upon greener devices [15], and to the development of appropriate e-waste management policy and regulations.