The use of societal data in environmental research has indicated a need for considering uncertainties of data. Several fundamental conditions for statistical treatment are occasionally not met. The choice is either to use or to ignore the uncertain data. If used, it may impair the quality of the result. If ignored, a possible environmental risk may remain unattended. This article discusses some of the problems encountered with data in urban heavy-metal metabolism, and suggests a methodbased on uncertainty intervals to consider the uncertainties.

The inflow and stock (amount in use) of heavy metals (cadmium (Cd), chromium (Cr),copper (Cu), lead (Pb), mercury (Hg), nickel (Ni) and zinc (Zn)) in goods in 1995 have been quantifiedin the anthroposphere of Stockholm, Sweden. Statistics on national, regional and local levelwere used. Contacts were established with representatives from production and construction in theindustrial sector and with authorities. The results show that the stock of Cd is 0,2 kg per capita. Forthe other heavy metals the corresponding result per capita is: Cr 8, Cu 170, Hg 0,01, Ni 4, Pb 73and Zn 40 kg. The inflow varies between 2–8% of the stock indicating the importance of the stock.The lowest levels are for Cu and Pb. Heavy metal levels in solid waste are high, between 15–45%of the amount in the inflow (Hg excluded), the lowest values were for Cu and Pb. Thus, recycling isincomplete. Long life expectancy goods form the majority of the stock but there is a tendency thatshort life expectancy goods increase their importance in the inflow. Concealed goods are also morefrequent in inflow than in the stock.

The aim of this study was to quantify the diffuse emissions during use of metal containinggoods in the capital of Sweden, Stockholm. The following metals were studied: Cadmium (Cd),Chromium (Cr), Copper (Cu), Lead (Pb), Mercury (Hg), Nickel (Ni) and Zinc (Zn). A major part ofthe metals are found in a protected environment where degrading processes like corrosion are mostlimited. However, during the lifetime of some goods the metal release to the environment is significant.The quantitatively most dominant emissions were found for Cu and Zn. The tap water system androofs/fronts (Cu) represent goods with large exposed areas but with relatively small release rates perunit. In contrast, brake linings, aerial lines and electrical grounding (Cu) and tyres, brake linings andchemicals (Zn) are all goods with high release rates but mostly limited exposed stocks. High yearlyemissions are also found for Pb, ammunition and sinkers dominate the calculated emissions totally.For Cr and Ni, stainless steel represent the major part of the stocks, but corrosion was estimated togive only a minor contribution to the emissions. Potential emission sources, i.e. stabilisers, pigmentsand plated goods dominate the exposed Cd stock. These emissions were not quantified due to lackof data. Hg is currently phased out, but one major source of emission, i.e. the use of amalgam, willbe continuously significant for several decades. The importance of the traffic sector is obvious. Theemissions from brake linings (Cu, Zn and Pb), tyres (Zn, Pb, Cr and Ni) and asphalt wear (Cu, Zn,Cr, Ni and Pb) are all of large importance for the total emission from respectively metal.

The sources of heavy metals to a wastewater treatment plant was investigated. Sources can be actual goods, e.g. runoff from roofs, wear of tires, food, or activities, e.g. large enterprises, car washes. The sources were identified by knowing the metals content in various goods and the emissions from goods to sewage or stormwater. The sources of sewage water and stormwater were categorized to enable comparison with other research and measurements. The categories were households, drainage water, businesses, pipe sediment (all transported in sewage water), atmospheric deposition, traffic, building materials and pipe sediment (transported in stormwater). Results show that it was possible to track the sources of heavy metals for some metals such as Cu and Zn (110 and 100% found, respectively) as well as Ni and Hg (70% found). Other metals sources are still poorly understood or underestimated (Cd 60%, Pb 50%, Cr 20% known). The largest sources of Cu were tap water and roofs. For Zn the largest sources were galvanized material and car washes. In the case of Ni, the largest sources were chemicals used in the WTP and drinking water itself. And finally, for Hg the most dominant emission source was the amalgam in teeth. For Pb, Cr and Cd, where sources were more poorly understood, the largest contributors for all were car washes. Estimated results of sources from this study were compared with previously done measurements. The comparison shows that measured contribution from households is higher than that estimated (except Hg), leading to the conclusion that the sources of sewage water from households are still poorly understood or that known sources are underestimated. In the case of stormwater, the estimated contributions are rather well in agreement with measured contributions, although uncertainties are large for both estimations and measurements. Existing pipe sediments in the plumbing system, which release Hg and Pb, could be one explanation for the missing amount of these metals. Large enterprises were found to make a very small contribution, 4% or less for all metals studied. Smaller enterprises (with the exception of car washes) have been shown to make a small contribution in another city, the contribution in this case study is still unknown. © 2002 Elsevier Science B.V. All rights reserved.

Wastewater treatment sludge contains valuable nutrients, yet represents a residue problem due to the amount of heavy metals, which is one of the factors preventing the use of sludge as fertilizer. In Sweden, the government has a declared aim of closing the ecocycles of nutrients to arable land, while at the same time the existing limit values are among the lowest in the world. This paper focuses on the opportunities for Swedish wastewater utilities (WWUs) to manage and reduce sources of heavy metals in order to get sludge approved and recycled. A case study focusing on sources of the heavy metals Cd, Cu, Hg, Ni, Pb, and Zn and the WWUs ability to influence the source by means of existing regulations was traced and categorized. A substantial fraction of the heavy metals were shown to be caused by diffuse emissions, such as the use of goods and products in society. For most sources discussed in the paper, a WWU can only manage the sources to a limited extent, if at all. This study shows that the WWUs cannot manage both recycling of nutrients and a decrease in heavy metals ending up in sludge. Diffuse emissions of heavy metals must be examined in context, not as a separate phenomenon or an issue for a single actor. The existing environmental legislation does not handle diffuse sources, yet long-term strategies for reducing the emissions to wastewater treatment must involve the reduction of diffuse emissions.