Lead and zinc flows from technosphere to biosphere in a city region
By identifying the main product categories and quantifying the pools of metals; the amounts, flows and uses of lead and zinc in the city of Stockholm have been studied. The emissions of metals into different environmental media are estimated. The pools and flows in the biosphere are introduced, and compared with the anthropogenic pools and emissions. Finally, the product emissions are compared with the measured dissipative use, based on the metal concentrations in the sludge at the main waste water treatment plant and in storm water. The amount of lead that is recorded in the waste water treatment plants can mainly be explained by deposition. However, emissions from many of the product categories quantified for lead in Stockholm are not likely to collect at sewage treatment plants. Instead, the emissions are more likely to be noticed in the storm water, the soil and the sediments around the city. In total, about 45 000 tonnes of lead and about 6000 tonnes of metallic zinc are quantified in the study. The product emissions were roughly estimated to be 30 tonnes of lead each year. There are however, large uncertainties in the emission factors. The city can definitely be regarded as a source of zinc pollution. This can be seen in the flows that are registered in the waste water treatment plants, and the estimated storm water flows. From these estimates, the city appears to contribute about 30 tonnes of metallic and biogenic zinc each year to surrounding waters and to sludge. For the product groups and the emission factors used in this study, a zinc emission of about 17 tonnes per year was estimated, with the main contributions coming from street furniture, tyres and buildings.