Mercury and persistent chlorinated hydrocarbons in owls Strigiformes and birds of prey Falconiformes collected in Norway during the period 1965–1983

Levels of mercury and persistent chlorinated hydrocarbons were determined in the liver of dead birds of prey (n = 568) and owls (n = 310) collected in Norway in 1965–1983. The highest levels of mercury were found in osprey and white-tailed eagle, with median concentrations of 4·7 and 2·4 μg Hg g⁻¹ liver respectively. The levels of DDE and PCB varied considerably, the highest levels of DDE being detected in white-tailed eagle and goshawk which had a median concentration of 2·0 and 1·9 μg DDE g⁻¹ liver respectively. Highest levels of PCB were detected in osprey, gyr falcon and white-tailed eagle (5·0 μg PCB g⁻¹). With a few exceptions the levels of HCB, γ-BHC and dieldrin detected were low. Mercury and organochlorine levels were also determined in unhatched eggs (n = 159) of raptorial birds collected in the same period. The levels of mercury were, with a few exceptions, low. The highest levels of DDE were found in eggs of merlin and sparrow hawk with median concentrations of 30 and 19 μg g⁻¹ respectively, while the highest levels of PCB were found in eggs of white-tailed eagle and goshawk, with median concentrations of 13·9 and 12·3 μg PCB⁻¹, respectively. It was not possible, from the present material, to demonstrate significant changes in contaminant levels over time. Nor was it possible to detect significant geographical differences. Although a very few samples of liver and eggs contained levels of mercury or organochlorines that might be considered toxic, the greater proportion of samples contained levels far below accepted critical limits.