Miljøgiftundersøkelser av ørret fra Akerselva og Lysakerelva i 2018

In the period August‐September a total of 90 trout were caught from three stations in River Akerselva and three stations in River Lysakerelva. The fish were dissected, and analysed for selected elements in gill and liver tissue, PAH metabolites in bile as well as microplastics in the digestive channel. The concentration of copper, arsenic, lead, zinc and chromium in trout gills increased down one of or both the rivers, indicating that the levels in trout to some extent were affected by pollution from the densely populated and trafficked lower parts of the rivers’ catchment. The same trend was observed for the PAH metabolite 1‐OH‐pyrene in trout bile. However, the levels of most of the metals as well as arsenic and selenium were similar to what has been found in fish from waters without local pollution sources of significance. Some of the fish from the lower parts of River Akerselva had high levels of lead. Moreover, the zinc level was high in gill samples from all the stations, especially the lowest station in River Lysakerelva. The concentrations of the PAH metabolites 1‐OH‐ phenanthrene and 1‐OH‐pyrene were also higher than what is considered background levels, but was with few exceptions below concentrations considered toxic to marine species of fish. This means that the fish to some extent have been exposed to the PAH substances phenanthrene and pyrene. Traffic and road runoff are potential sources of copper, zinc, and PAH. None of the 90 fish had mercury concentration higher than threshold levels for human consumption. This was probably also the case for cadmium and lead although these were not measured in muscle tissue. Mercury levels was not higher than those usually found in other Norwegian trout of the same size. Microplastic particles were found in the digestive channel of trout from all three stations in River Akerselva and from two of the three stations in River Lysakerelva. The number of microplastic particles varied from 0‐13 per fish. More microplastic particles were found in the trout from Akerselva (0.46 particles/individual) than in those from River Lysakerelva (0.11 particles/individual). These are amounts that can be considered low even if there is little data to compare with. In both rivers 95‐100 % of the microplastic particles were categorised as fibres, and most of them were of blue colour.