Stock of metals in Stockholm

The present metal stock in the city of Stockholm, in infrastructure, buildings, vehicles, etc. has developed mainly during the 20th century, but the use of copper for roofing and cladding of buildings and bronze in statues and other objects of art is a very old practice. According to Lohm et al. (1997), electrification (increasing the stock of copper) of the city started at the turn of the century and culminated in 1920-1960; the tapwater system changed in the 1950s basically from iron and zinc piping to copper pipes; applications of stainless steel (Cr and Ni) and galvanised steel (Zn) became common after the Second World War.

Bergbäck et al. (2001) have calculated the metal stock in the anthroposphere of Stockholm for 1995, together with the different exposure conditions of the metals, according to Sörme et al., (2001a), as well as the annual inflows and the outflows from the existing stock of each metal as solid waste and via other routes, Table 3.8. The outflows are defined as metal fluxes from the Stockholm metal stock, either to the "waste" compartment or by means of "goods emissions" or industrial emissions to any of the other three "end stations" considered, sediment, soil or sewage sludge. The goods emissions are further specified in Table 3.9. The outflows from the anthroposphere to the biosphere, as presented by Bergbäck et al. (2001), also included atmospheric deposition and fluxes via food (including drinking water), but since these two fluxes are not directly related to the metal stock in Stockholm, they are not considered as part of a stock modifying mechanism in the following discussion.

Table 3.8. Stock of metals (ktonnes) in the city of Stockholm, the annual amounts of metals in inflows and outflows - with solid waste and via other routes (ktonnes/y) - and the percentages of metals in stock that are protected and exposed to soil, water and air, respectively. After Bergbäck et al., 2001; Sörme et al., 2001a.

Table 3.8. Stock of metals (ktonnes) in the city of Stockholm, the annual amounts of metals in inflows and outflows - with solid waste and via other routes (ktonnes/y) - and the percentages of metals in stock that are protected and exposed to soil, water and air, respectively. After Bergbäck et al., 2001; Sörme et al., 2001a.

Metal

Inflow

Protected Exp.soil

Water

Outflow via: Air Sol. waste Other routes

Cr

0.36

5.6

54

10

11

25 0.1

0.001

Cu

2.30

123

63

14

15

8 0.3

0.012

Ni

0.19

2.5

71

0

9

20 0.03

0.001

Zn

1.9

28

31

0

31

38 0.7

0.024

Table 3.8 clearly shows, first, that the copper stock is by far the biggest of the studied metal stocks and, secondly, that all the four metal stocks were increasing in size at the middle of the 1990s. It was emphasized by the authors (Bergbäck et al., 2001) that there is a relatively wide range of uncertainty in the figures for both existing stocks and outflows with solid waste. Nonetheless, it might be possible to give a broad indication of the rate of change in the stock of the four metals by calculating the percent annual net increase. Thus, it turns out that the nickel stock seems to undergo the fastest increase with 6.4% per year, the zinc and chromium stocks have an intermediate rate of growth (4.3% and 4.6%), while the lowest growth rate was found for the copper stock (1.6% per year).

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