Ecological effects of underwater destruction of detonators in Lake Ormtjärn, Sweden: the impact from lead

After the Second World War, dumping in lakes was a rational way to solve the security problem with the extensive amount of unused, aging ammunition. Most commonly the ammunition was dumped in sealed boxes or as pieces. In some cases the ammunition was deliberately detonated when dumped. In Ormtjarn, a small lake in central Sweden, very high levels of lead (1900 mg/kg dry weight Pb) were detected in the sediments indicating a possible need for remediation. The lead was expected to originate from years of underwater destruction of about 1.5 million detonators containing lead azide. The lake is unique in the sense that the lead levels are among the highest in Sweden, the boundary is well defined and that no other source of pollutant is present in the lake. It is also the only known major site for underwater destruction of detonators in freshwaters in Sweden. The aim of this study was to evaluate the environmental impact from underwater destruction of detonators containing lead azide in this natural forest lake. Samples were taken of sediment, bottom water, surface water, bottom fauna and littoral and was analysed for Pb and physical parameters in order to investigate if a possible effect on biota could be demonstrated from the heavily polluted sediment. Acute toxicity of sediment was determined with a mouse cell assay. Results showed high to very high lead content (1500-2000 mg/kg dry weight) in sediment down to 25 cm depth evenly distributed over the whole lake. Water showed low levels (surface water) to high levels (bottom water) of Pb. Disturbance on bottom fauna was observed for BQI-index but none for O/Cindex. No effect on littoral fauna was found. Acute toxicity was low for bottom