Linking Flows And Accumulations Methods Models And Indicators

Frequently applied methods for integral analysis of flows and accumulations of substances through economy and environment are substance flow analysis (SFA) and material flow analysis (MFA). In this chapter the focus is on SFA. For a description of MFA, see Chapter8.

SFA offers a consistent and integral description of material or substance stocks within and flows within and between the economy and the environment in a certain time period, for a certain region. It is based on physical input-output analysis in which the materials balance principle holds for each economic or environmental sector. SFA can be implemented through modeling. Various models of economic flows and stocks have been developed, such as FLUX (Boelens and Olsthoorn 1998; Olsthoorn and Boelens 1998), STOCKHOME (Bergbäck et al. 1998) and a dynamic copper model (Zeltner et al. 1999). Other models focus on modeling environmental flows and stocks such as DYNABOX (Heijungs 2000) and Dynamic (Soil Composition) Balance (D(SC)B) (see Chapter 33).

Bookkeeping, steady state and dynamics are important concepts in modeling (see Chapter 9). In the case study presented below, the steady-state concept is of particular importance. As explained in Chapter 9, the outcome of this type of modeling provides no prediction but an assessment of the long-term sustainability of a certain substance regime compared to the present situation The steady-state situation of, for example, the 1990 flows and stocks of a substance indicates the eventual magnitude of these flows required to maintain the 1990 regime indefinitely.

Material and substance flow analysis (MFA/SFA) studies are designed to support environmental decision making. Although many SFA/MFA case studies have been carried out successfully, the issue of connecting such research with policy has arisen frequently (Brunner and Lahner 1998). Researchers may feel the results of SFA/MFA studies are giving clear messages, but for policy makers the implications are often not quite so self-evident. Several authors have attempted to define indicators in order to bridge this gap (van der Voet 1996; van der Voet et al. 1999; see also Ayres 1996; Azar et al. 1996; Wernick and Ausubel 1995). Possible indicators include the following:

• indicators for the fate of mined heavy metals (total emissions; total landfill; accumulation in the economy; pollution export);

• indicators for the fate of mined heavy metals (total emissions; total landfill; accumulation in the economy; pollution export);

• indicators for evaluation of present management in terms of sustainability (environmental risk ratio (PEC/PNEC) and transition period; human risk ratio (PDI/TDI) and transition period; environmental accumulation; depletion rate);

• indicators for design of a sustainable management regime (technical efficiency; recycling rate; use level; economic dissipation; disturbance rate).

For detailed descriptions, see van der Voet et al. (1999). CASE STUDIES

In this section, we summarize case studies using three of the indicators listed above: the total emissions and two-risk ratio (and transition period) indicators.

1. Total emissions This indicator gives the aggregate emissions (mass/yr) from the economy to the different environmental media (air, water, agricultural and non-agricultural soil). It indicates environmental pressure and it is an early warning for the steady-state risk ratios. It may be compared with emission targets for each medium.

2. Risk ratio and transition period The risk ratio (dimensionless) is calculated for human toxicity and aquatic and terrestrial ecotoxicity, being the daily intake or the environmental concentration in a medium divided by the acceptable/tolerable daily intake or concentration standard, respectively, for that medium. It indicates the potential risk (values > 1) emissions pose to human and ecosystem health. This indicator can be calculated for a base year (for example, 1990) by using empirically measured concentrations, for the steady-state situation by using a steady-state SFA/ environmental fate model or for a year in the future by using a dynamic model: for example, DYNABOX (Heijungs 2000), USES-LCA (Huijbregts 2000) or the Dynamic Soil Composition Balance model (see Chapter 33). 3. Transition period The time it takes for the risk ratio to equal 1.

The contrast between decreasing emissions of the metals cadmium, copper, lead and zinc and continuously increasing input into the economy has been analyzed in three case studies for the Netherlands. The main research questions concerned the fate of the mined metals, the link to environmental risks and ways to render the metals management regime more sustainable. Flows of metals through, and their accumulation within, the economy and the environment were quantified for 1990 in a hypothetical steady-state situation for the Netherlands as a whole, for the Dutch housing sector and for the Dutch agricultural sector. To this end, the SFA method has been applied for copper, zinc, lead and cadmium with the help of several models. See Boelens and Olsthoorn (1998), Olsthoorn and Boelens (1998), Heijungs (2000) and Chapter 33 for detailed descriptions.

The results for the total emission indicators in Figure 30.1 show, for almost all media and all metals, a strong increase of emissions in the steady-state situation compared to the 1990 situation. The increase of air emissions in the steady-state situation compared to the 1990 situation is generally moderate. The increase for cadmium is apparently due to the incineration of spent NiCad batteries. The increase for copper is due to frictional wear from overhead railway wires. Air emissions for zinc for the steady-state decrease compared to 1990, since the amount of zinc used for galvanized iron is decreasing. Besides emissions, transboundary pollution via air from foreign countries is an important source for the total input to air for all four metals; however, this source is not included in the emissions indicator.

For all four metals, the increase of water emissions in the steady-state situation compared to the 1990 situation is due mainly to the corrosion of metals in building materials (for example, zinc gutters, galvanized steel, tapwater heating equipment and bulk materials such as concrete). However, with respect to the total input to water, it is not emissions within the Netherlands but inflow of metals from outside the Netherlands that constitutes the dominant source for all four metals (in some instances over 70 per cent).

The increase of steady-state emissions to agricultural soils compared to 1990 emissions is significant for all metals and is due to increasing flows of organic manure and of source-separated vegetable, fruit and garden waste (the latter being less relevant for lead). The main source for cadmium is the continuous (and constant) inflow of phosphate fertilizer. Main source for copper and zinc is the increasing content of copper and zinc in organic manure. The ultimate source behind these increasing contents of copper and zinc in organic manure is animal fodder. It appears that in the steady-state situation the agricultural soil emissions of copper and zinc are due overwhelmingly (about 80-90 per cent) to the addition of copper and zinc, respectively, to fodder. This is an example of what might be called 'closed loop accumulation' (CLA): copper and zinc are added to fodder, which is imported from abroad and fed to Dutch cattle. The manure produced by the cattle, including its copper and zinc content, is spread on agricultural land as an organic

Cadmium d

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