Substance Flow Analysis of Lead for Sustainable Resource Management and Pollution Control

As the biggest producer and the second largest consumer of lead in the world, China is facing serious conflict between rapid economic development and environmental deterioration caused by lead pollution. Our analysis results show that lead poisoning accidents increased sharply since 2005, and there is growing concern that children remain at risk from lead exposure. Accordingly, sustainable resource management and pollution control of lead is of great significance. As the first step, substance flow analysis (abbreviated as SFA) models of lead flows in both economic subsystem and environmental subsystem are established by using top-down approach in this study. Then the situation of production, consumption and emission of lead resources can be revealed. This study provides the most detailed depiction of lead flows within a regional level, and it is essentially important for the future analysis and management of lead resource. Furthermore, environmental simulation models, risk assessment models, Crystalball software and GIS tool are proposed to be integrated on the same platform to recognize the pollution situation, corresponding population risk and major exposure pathways in the study region. This new perspective extends the traditional method of substance flow analysis of lead, not only important for the improvement of lead resource efficiency, but also supporting the pollution prevention policy making. Lead Production and Pollution Lead is an important raw material for industry, which is used widely in lead-acid batteries, bullets and shot, building construction, radiation shield and as part of solders, fusible alloys and pewters. Production and consumption of lead is increasing worldwide continuously. Total annual production is about 10.6 million tonnes in 2012, of which 5.2 million tonnes came from mining [1]. The top lead producing countries are China, Australia, USA, Peru, Canada, Mexico, Sweden, Morocco, South Africa and North Korea [2]. Additionally, China, Australia and the United States account for more than 50% of primary production [3]. However, lead is a highly poisonous metal, affecting almost every organ and system in human body. The main target for lead toxicity is the nervous system, both in adults and children. Previous studies have revealed that past adult lead exposure is associated with longitudinal decline in cognitive function and linked to neurodegeneration measured by brain MRI [4, 5]. Further, children are more vulnerable to lead exposure than adults [6]. Chronic low-level lead exposure during childhood may result in a decreased IQ, attention deficits, reading and learning disabilities, and persistent behavioral problems [7]. Blood lead levels (BLLs) of U.S. children rose sharply between 1900 and 1975 as increased lead emissions caused widespread contamination [8]. Consequently, lead poisoning has been considered as the most important pediatric environmental health problem in the United States [9]. By eliminating leaded gasoline from on-road vehicles, banning the sale of leaded house paint, and prohibiting lead solder in public water systems, plumbing components, and food and drink cans, children’s blood lead concentrations have fallen substantially in a number of countries in the last few decades, including the United States, Australia, Germany, Sweden, Mexico, Poland and the United Kingdom [8, 10-12]. Blood lead concentrations in United Kingdom have fallen substantially since 1984 [13]. By 1999 the geometric mean blood lead for U.S. children 15 years of age had fallen from 15 μg/dL in the late 1970s to 2.0 μg/dL [12]. Moreover, the U.S. government set the Healthy People 2010 objective to eliminate BLLs ≥10 μg/dL [8]. Figure 1 Lead pollution accidents in China Despite the falls in blood lead levels in some countries, childhood lead poisoning continues to be a major public health problem for certain groups of children, especially children in developing countries including China [14-16]. As the largest lead mining country and producer in the world, China is facing lead pollution problem caused by industrial emissions, agricultural activities and lead contaminated products [17]. Serious lead pollutions have been found in the vicinity of mining area, lead-acid battery factory, waste recycling site and even urban street [18-21]. Study results suggested that children's BLLs in China are higher than those of their counterparts in other countries due to its heavy lead pollution [22]. In Wuxi City, China, 27% of children 15 years of age had blood lead levels > 10 μg/dL [23]. Researchers found that 65% of the 11,348 schoolchildren they tested in Shenzhen city in 2002 had concentrations above the safe limit of 10 μg/dL set by the World Health Organization [15]. Since 2005, 40 public reported lead poisoning accidents occurred in 16 provinces (as shown in Fig.1), and children are the main victims. The conflict between rapid economic development and environmental deterioration caused by lead pollution become serious. And there is growing concern that significant numbers of children remain at risk from lead exposure in many regions. Accordingly, sustainable resource management and pollution control of lead is of great significance. Substance Flow Analysis Substance flow analysis (abbreviated as SFA) is one of the main analytical tools in the industrial ecology research field. It is used to identify the causes of the environmental problems and indicate possibilities for a more sustainable management of resource. This method usually describes the flows of one substance in, out and through a system based on the materials balance principle. The system is a physical entity, often representing a geographical area [24]. In most cases, the SFA system is consisted of four parts, including input of resource, manufacture, output of products and waste and emissions (as shown in Fig.2). By tracing the substances introduced into human society, valuable information on emissions to the environment and to waste flows can be obtained. Figure 2 Structure of substance flows Model of Lead Flow Analysis General Model. SFA has become a helpful tool for the study of the industrial metabolism of a certain metal within a regional level.This is because that metals are easy to track, have relatively simple chemistry and processing, and are significant in both material displaced and environmental consequences. As to lead, its flow analysis has been conduct in various industries and processes at both regional and national scale [25, 26]. Figure 3 The main components of lead flow As shown in Fig. 3, the main components of the lead flow processes fall into five categories [24]. Mining and extraction, processes involving extraction of raw lead from the geosphere and transformation into materials that can be used for further production. Production and manufacturing, processes involving the making of products, thereby transforming raw lead into finished products. Trade, processes transporting lead contained goods among different owners or users. Consumption and use, processes involving the consumption or use of lead contained products, thereby transforming them from products into scrap. Waste and emission, represents lead that flows from the economic subsystem to the environmental subsystem. Import of resource and products Industrial Material Processing Export of products