Upstream silver source mapping – a case study in Stockholm, Sweden

Silver (Ag) can be a problem for wastewater treatment plants (WWTP) and their capability to use sewage sludge as a soil fertilizer. Due to a high accumulation rate in soils, the levels of Ag in the incoming water at the WWTP must be reduced. This study aims to identify major diffuse emission sources in the technosphere through a comprehensive substance flow analysis of Ag in Stockholm, Sweden. Large inflows and stocks of Ag were present in electrical and electronic goods and appliances as well as in jewellery and silverware. The total inflow was 3.2 tonnes (4.2 g/person), the total stock was 100 tonnes (140 g/person) and the total outflow was 330 kg (430 mg/person). Major identified Ag sources with emissions ending up in the WWTP (total 26 kg, 34 mg/person) were food, amalgam and beauty products (via urine and faeces, 12 mg/person or 11% of incoming amount), and textiles (via washing, 17 mg/person or 16% of incoming amount). This study explains approximately 35% of the total 80 kg Ag in the incoming water at Henriksdal WWTP in Stockholm. Plastic, photography and beauty products were identified as possible sources of Ag that need to be examined further.