Temporal trends and spatial differences of trace elements in osprey eggs in Finland

Time trends and regional differences of total mercury (THg), methylmercury (MeHg), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), selenium (Se), zinc (Zn), palladium (Pd), platinum (Pt), and rhodium (Rh) concentrations were studied and toxicological significance of the observed levels was assessed in unhatched osprey (Pandion haliaetus) eggs collected by bird ringers in 1972-2005 from 2 to 3 areas in Finland. The study areas were Northern Quark in the Gulf of Bothnia, Baltic Sea, and eutrophic-dystrophic Lake Vanajanselkä, which is affected by industrial emissions. Significant declining trends were found for Pb (average annual decrease 6.9%), Cr (2.8%), MeHg (1.9%), and THg (1.3%), with slightly faster decrease in Northern Quark (7.5%, 3.4%, 3.1%, and 1.8%, respectively) compared to Lake Vanajanselkä (6.9%, 2.6%, 1.2%, and 0.8%, respectively). Metal concentrations in eggs did not exhibit significant regional differences. This pattern aligns with metal concentrations in prey fish from the same areas underscoring the role of long-range atmospheric deposition as the source of exposure. Among the studied metals, only a few eggs with highest THg and Pb concentrations exceeded toxicological thresholds: THg threshold for moderate injury (0.3 µg/g ww) 6.1%, high injury (0.7 µg/g ww) 0.88%, Pb tentative threshold (1.2 µg/g ww) 2.6%. These levels could have contributed to decreased reproductive success. The gradual recovery of the Finnish osprey population during the study period paralleled with declining levels of metals and persistent organic pollutants. This study highlights the value of environmental specimen collections and long-term time series in an apex predator for monitoring aquatic environments.Clinical trial number: not applicable.