عواقب طولانی مدت جریان های غیرعمدی مواد : مدلسازی جریان های غیرعمدی سرب در سیستم اقتصادی هلندی و ارزیابی پیامدهای محیطی آن ها

Substances may enter the economy and the environment through both intentional and non-intentional flows. These non-intentional flows, including the occurrence of substances as pollutants in mixed primary resources (metal ores, phosphate ores and fossil fuels) and their presence in re-used waste streams from intentional use may have environmental and economic consequences in terms of pollution and resource availability. On the one hand, these non-intentional flows may cause pollution problems. On the other hand, these flows have the potential to be a secondary source of substances. This article aims to quantify and model the non-intentional flows of lead, to evaluate their long-term environmental consequences, and compare these consequences to those of the intentional flows of lead. To meet this goal, the model combines all the sources of non-intentional flows of lead within one model, which also includes the intentional flows. Application of the model shows that the non-intentional flows of lead related to waste streams associated with intentional use are decreasing over time, due to the increased attention given to waste management. However, as contaminants in mixed primary resources application, lead flows are increasing as demand for these applications is increasing.

The chemical and physical properties of heavy metals, such as lead, zinc, cadmium, copper, germanium, gallium and others means that they have many useful and intentional applications within the economy. Non-intentional applications of these metals arise from their natural occurrence in fossil fuels, other metal ores and phosphate ores and, in addition, secondary flows of these metals result from the processing of waste flows of their intentional applications. The consequences of the intentional flows of these substances have been studied extensively and several policies have been implemented to minimize their negative impacts (Van der Voet, 1996). Less attention has been given to the consequences of the non-intentional flows, especially to the long-term consequences. This article seeks to provide an in-depth analysis of the potential problems caused by the non-intentional flows of lead in the Dutch economy. Lead is a highly toxic metal. The US Environmental Protection Agency (US EPA) cites lead as one of the 17 most dangerous chemicals in terms of the threat it poses to human beings and the environment (Wu et al., 2004). Lead can cause behavioral problems and learning disabilities, and can be fatal to children who inhale or ingest it. Moreover, lead can be toxic to plants, diminishing their productivity or biomass, and eliminating some species (Singh et al., 1997, Xiong, 1997 and Patra et al., 2004). Due to its extensive use in the past, large stocks of lead have been built up in the economy and environmental concentrations may still be rising due to continuing emissions (Guinée et al., 1999). Several measures have been taken to reduce the negative impacts of lead. These include end-of-pipe technologies, stimulating recycling and phasing out some applications of lead, such as in water pipes, paint and gasoline. A recent EU directive prevents member states from allowing new electrical and electronic equipment containing lead, mercury, cadmium, chromium VI, and PBB or PBDE to be put on the market (European Commission, 2006). Such measures have been effective in reducing emissions of lead to the environment, reducing human exposure and the subsequent health effects of the intentional applications of lead (Tukker et al., 2001). However, despite effective management of these intentional applications, lead may still threaten human health through indirect routes of non-intentional flows. For example, lead enters the agricultural chain via phosphate fertilizer and accumulates there, leading to significant concentrations in manure (Guinée et al., 1999). The processing of metal ores and the use of fossil fuels leads to emissions of lead to the environment. Both intentional and non-intentional applications of lead may end up in waste streams. Part of this waste is landfilled and part is used as fly ash, bottom ash and slag in construction materials. In addition to direct emissions of lead to the air, water and soil, the accumulated lead in roads, buildings, agricultural soil and landfill sites may leach to the soil or groundwater. Thus, the environmental consequences of non-intentional flows of lead stem from different sources, which might develop differently in the future. For example, the flows of lead in the re-used waste stream from intentional use might decrease in the future due to policies aimed at reducing lead applications, or through increased recycling. On the other hand, flows of lead in fossil fuels, fertilizer or other metals may continue to rise as long as the demand for these applications is increasing. The aim of this article is to evaluate the long-term direct environmental consequences of the non-intentional flows of lead, and compare these with the consequences of the intentional flows of lead. In meeting this goal, a dynamic model for non-intentional flows and stocks of lead is developed. The accumulated secondary flows in roads and buildings can also be seen as secondary sources of lead. The availability of lead in the utilized and landfilled secondary materials (fly ash, bottom ash and slag) generated from the production of other heavy metals, electricity production from coal and the incineration of intentional applications of lead and of the accumulation of lead in buildings, roads and landfill sites will be discussed in a subsequent article. To evaluate the long-term consequences of non-intentional flows of lead and other substances, the sources of these flows need to be combined and the factors determining their long-term development should be identified. Both economic factors related to supply and demand and technological factors describing process efficiency need to be included in the model. The developed model combines functions that describe the long-term development of the main sources of non-intentional flows of lead (electricity production, production of other heavy metal, oil production and fertilizer use), based on statistical approaches and scenarios that describe the demand as a function of socio-economic variables such as GDP, population, price and other specific variables for each application (Burney, 1995, Ranjan and Jain, 1999, Mohamed and Bodger, 2005, Roberts, 1996, Moore et al., 1996, Crompton, 2000, Mergos and Stoforos, 1997 and Bouwman et al., 1997) and technological factors describe that process efficiency, with specific detailed models for the intentional applications of lead (Elshkaki et al., 2004). This article is structured as follows. Section 2 outlines the methodology used in modelling non-intentional flows of lead in the economy and the environment. Section 3 quantifies the model’s relations. Section 4 contains the results of the model’s calculations and Section 5 is dedicated to discussions and conclusions.

In this article the non-intentional flows of lead have been modelled, their direct environmental consequences have been evaluated and a comparison made with the intentional flows of lead. The analysis was conducted using a dynamic model for the non-intentional flows of lead that combines non-intentional flows originating from waste streams from the intentional use of lead together with those originating from mixed primary resources that contain lead as a contaminant. Regression analysis was used to determine the most variables with the greatest influence on the demand for different applications, and the derived equations from the analysis were used to estimate future developments. The main limitation of this approach is the future uncertainty, i.e., the basic assumption that the future relationship will be the same as it has been in the past. This is not always the case, as new developments may change this relationship. The expected explanatory variables, GDP, population, per capita GDP and prices, appeared to adequately explain the trends of production for electricity, oil and metals and the outcome of the regression analysis is comparable to those from other studies for the demand for these products. In the case of phosphate fertilizers, it was not possible to explain the trend of the use of fertilizers by the tested variables, due to the impact of policy. Therefore time was used as the explanatory variable since it was able to capture the influence of other time-related variables on fertilizer use. In some cases, time is used as a proxy for technological change, policy aspects and other time-related variables. This approach is also used in the linear and exponential time models used for the analysis of the intensity of use of metals (Tiltone, 1990, Guzman et al., 2005 and Roberts, 1996). Although these models give good empirical results, they have some limitations, mainly due to the assumption that the net effect of all time-related variables is constant over the time examined (Guzman et al., 2005). Although the used explanatory variables proved to be the most influentional ones in the Dutch case, the model could be improved by including other more case-specific variables, subject to availability of historical data and projections of the future development of these variables. In the case of fertilizers, other case-specific explanatory variables such as the number of animals and agricultural yield could have been used. Other general variables such as the general consumer price index (CPI) and CPI for specific products could also have been used. The overall input of lead into the economy through a combination of direct routes (intentional flows) and indirect routes (non-intentional flows) is expected to increase in the future (Fig. 16). The non-intentional flows of lead originating from the waste streams of intentional applications are expected to decrease over time, due to more effective recycling. However, flows of lead as a contaminant in mixed primary resources appear to be increasing. The only non-intentional inflow related to mixed primary resources that is decreasing over time is the one associated with phosphate fertilizers. This decrease is due to the policy aiming to reduce the use of chemical fertilizers in the Netherlands. The total non-intentional outflow of lead to the air, water, soil and landfill sites is expected to increase in the future. The total emissions of lead to the air from the direct routes and indirect routes are expected to decrease in the future (Fig. 13), while emissions of lead to water are expected to increase (Fig. 14). In terms of pollution, the most important source of emissions of lead is the production of other heavy metals followed by sewage treatment plants. The production of iron and steel accounts for the most emissions of lead to the air (Fig. 13), although these are decreasing due to assumptions about the emission factor. The second largest flow of lead to the air is emissions from coal-fired power plants. The incineration of the waste stream of intentional applications of lead, electricity production from oil and the production of oil make small contributions to atmospheric lead emissions. The largest flow of lead to water originates from sewage treatment plants (Fig. 14), followed by emissions from the production of other heavy metals and then the production of oil. All these flows are increasing over time. The total landfilled stream of lead from the direct and indirect routes is expected to increase in the future due to the increase in the landfilled stream of lead from indirect routes. The main source of lead in landfill sites is the solid waste generated by zinc production, which is increasing over time. The total non-intentional flow of lead in secondary materials will decrease from 2002 to 2010 (Fig. 12). This is due to the declining volumes of streams of fly ash and bottom ash generated by incineration plants, which constitute the largest flows of lead in secondary materials. The other flows of lead in secondary materials (fly ash and bottom ash from coal-fired power plants, lead remains in zinc products, iron and steel slag, sewage sludge) are increasing over time. Bottom and fly ash from incineration are the main source of available lead for possible recovery, followed by fly ash from coal-fired power plants. The environmental and economic consequences of utilizing the secondary materials (fly ash, bottom ash and slag) generated from incineration plants, coal-fired power plants and heavy metals production processes will be investigated in a subsequent article. Lead inputs into the economy through indirect routes (non-intentional flows) account for about 10% of the total input of lead into the economy (Fig. 16). However these flows account for a far higher proportion of lead emissions to the environment (Fig. 17 and Fig. 18): almost half of the emissions to air and water originate from non-intentional flows of lead, and this fraction is expected to rise in the future. Approximately three-fourths of the flow of lead to landfill sites comes from non-intentional applications and this fraction is expected to increase further in the future, to 87% in 2025. Therefore in terms of both waste and emissions, the non-intentional flows are the most important ones. The non-intentional flows of lead originating from mixed primary resource applications, especially those related to the production of zinc, iron and steel and electricity generation from coal, are larger than those originating from the waste streams of intentional applications of lead. Thus particular attention should be given to the management of the residues generated from these processes. In terms of metals, the policy aimed at increasing the incineration of sewage sludge in an attempt to minimize the amount of sludge being used on the soil or landfilled might not be effective if the incineration residues continue to be partly landfilled without the removal of the metals.