Gimlemoen shooting range – metal levels in water, sediment and fish

Previous monitoring studies have shown considerable leaching of metals and metalloids such as lead (Pb), copper (Cu) and antimony (Sb) in runoff streams from the small-arms shooting range at Gimlemoen in Kristiansand. Lakes in the shooting range are recipients of heavy metals and fish have been exposed to elevated levels of metals, which can cause negative effects. The fish may have accumulated levels of heavy metals that can be harmful to animals and humans who eat the fish. In this study, brown trout (Salmo trutta) was caught from two lakes in the shooting range: Kyrtjønn, a recipient of heavy metals, and Stitjønn, which was not affected by shooting activity. Water and sediment samples were collected from both lakes and analyzed for metals and other elements. The content of Pb, Cu and Sb was measured in the gill, liver, kidney, bone, brain and muscle (fillet) of the fish. The condition of the fish was calculated and ALA-D activity (δaminolevulinic acid dehydratase) was measure in the blood. ALA-D activity is an enzyme, which can indicate exposure to Pb. Fertilized trout eggs were placed in the outlet streams of Kyrtjønn and Stitjønn in order to study survival and metal uptake.

The sediment in Kyrtjønn had high concentrations of Pb, but low concentrations of Cu and Sb. Only a few cm of the top sediment layer was contaminated by Pb, suggesting a low sedimentation rate in the water, and that relatively small amounts of Pb had accumulated in the sediment. Most of the Pb in the sediment was strongly bound to organic matter or to iron (Fe) or manganese (Mn) oxides, and probably not available for uptake by organisms. The water in Kyrtjønn had elevated concentrations of Pb, Cu and Sb. No morphological signs of chronic Pb exposure of the fish was observed, and the fish’s condition seemed good. However, the fish had accumulated high levels of Pb in bone and in organs such as the gill and kidney. In addition, the ALA-D activity was strongly inhibited compared to the fish from Stitjønn. The results imply that adverse long-term effects on adult trout in Kyrtjønn cannot be ruled out. No high metal concentrations were detected in the muscle tissue of the fish, which means that eating the fish should not cause any health hazard.

The mortality of the fertilized eggs in the outlet stream from Kyrtjønn was relatively low, even though the eggs had elevated concentrations of Pb. The Pb in the eggs was mainly (about 90%) bound in the outer eggshell. The trout fry showed high mortality, both in the outlet stream from Kyrtjønn and the reference water Stitjønn. The high mortality of the fry in Kyrtjønn and Stitjønn may be attributed to a relatively low pH and the physical conditions (drought/flood) in the streams. The water in the outlet streams was acidic with a pH around 5. Lead and copper can at low pH and/or low calcium concentration increase the mortality of fry that has just hatched. Both Kyrtjønn and Stitjønn have been limed and added farmed trout. The effect of the liming appeared to be small when this study was conducted. The acidic water probably posed a greater threat to the reproduction of trout in Kyrtjønn than the elevated levels of Pb, but chronic exposure to Pb may have contributed to damage to both fry and adult fish.