Some ecological effects of underwater self-explosion of ammunition in lake lomtjärn, sweden: the impact from mercury

Abstract

After the Second World War, dumping in lakes was a rational way to solve the security problem with the extensive amount of unreliable or unused ageing ammunition. Most commonly the ammunition was dumped in sealed boxes or as pieces. In some cases the ammunition was deliberately detonated when dumped. In Lake Lomtjärn, a small lake in central Sweden, extremely high levels of mercury (300 mg/kg dry weight Hg) were detected in the sediments. The mercury was expected to originate from years of dumping followed by an underwater self-explosion of ignition capsule containing mercury. The lake is unique in the sense that the mercury levels are among the highest found so far in Sweden and that no other source of pollutant is present in the area. The aim of this study was to evaluate the environmental impact from the underwater explosion. Samples of sediment, bottom water, surface water, bottom fauna, littoral fauna and fi sh (muscle and liver) were analysed for metals as well as physical parameters in order to investigate effects on biota. Acute toxicity of bottom water was determined by Daphnia magna. Results showed very high mercury content (2-338 mg/kg dry weight) in sediment down to 15 cm depth evenly distributed over the whole lake and low levels for other heavy metals (As, Cd, Cu, Pb and Zn). Water showed low levels of mercury (0.02 µg/L in bottom and surface water) as for the other heavy metals (As, Cd, Cu, Pb and Zn). Disturbance of bottom fauna was found for BQI index and O/C index. Disturbance in littoral fauna was seen around the lake (low taxa in six families, ASPT index 5.4. Danish fauna index 4 and acidity index 2). Acute toxicity (Daphnia magna) was high. Levels of mercury in perch were high (muscle 0.6-3.59 mg/kg and liver 1.05-7.64 mg/kg). It was concluded that the underwater detonation of ammunition in Lake Lomtjärn has caused very high levels of mercury in the sediment and a high impact on the ecological chain. In risk assessments aiming to remediation decisions it is recommended early to highlight expected ecological pathways of (mercury) and relevant biomarkers in the ecosystem of concern.