Outflows via other routes eg diffuse emissions from goods

The outflows via other routes, such as industrial and goods emissions, where the goods emissions are largely predominating, have been determined with greater certainty. In this case, it should be noted, however, that these emissions from the anthroposphere are not necessarily ending up in the biosphere. Thus, the metal amounts that eventually will take part in the exposure of sensitive ecosystems only constitute a small fraction of the reported outflows. We shall first examine the outflows from the major goods emission sources in Stockholm, according to data given by Bergbäck et al. (2001) and by Sörme et al. (2001b), see Table 3.9.

The metal fluxes from the road traffic sector (tyres, brakes, petrol och road pavement), especially if car wash is included, are the predominant emissions from goods in Stockholm, at least for chromium and nickel (about 99% of the total), and also for zinc (62%) but less for copper (38%).With the exception of the source "car wash", the metals being released from road traffic activities are primarily spread along the roadsides, where the mainly particle-bound metals are incorporated into the soil and largely immobilized (cf. Gartiser et al., 2003).

Table 3.9. Calculated metal emissions (kg/y) from the major goods emission sources in Stockholm, 1995. After Bergbäck et al., 2001 and Sörme et al., 2001b.

Category Goods Chromium Copper Nickel Zinc

Vehicles Tyres 200 200* 200 10,000

Brakes 6 3,900 8 900

Buildings Roofs/fronts <1 1,000 0.5 2,100

Infrastructure Road pavements 500 400

Aerial lines, galv.goods -- 1,200

1,000 5,000

* according to recent information from tyre producers, very low Cu content is expected in tyres

** car wash contribution to total Cu load taken from later estimate, see Table 3.12

In a recent experiment, where the fate and effect of zinc from tire debris was investigated in roadside soils, it was found that a considerable fraction of zinc was released from the rubber matrix within 1 year, but the parallel increase in soil pH counteracts the increase in quantity of labile zinc in the soil. Thus, no or only marginal increase in zinc levels in pore water or in soil leachates was observed in soils treated with tire debris, and the nitrification rate of the soil was stimulated (Smolders and Degryse, 2002).

In highly urbanized areas with no soil strips along roads, a considerable (however, unknown) fraction of the metals released from road traffic is transported with the surface runoff to the stormwater collectors. From there, in parts of the city with combined sewage and stormwater systems, metals are transported to the sewage treatment plants (STP), where a major fraction is separated and incorporated with the sludge, which in turn is disposed of either on a landfill or on agricultural land. The same fate is waiting for the metals (mainly copper and zinc) being released from tap water and other pipes, and partly also for metals in the runoff from roofs and fronts of buildings. These fluxes will be further described in sections 4.1 and 4.2.

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