Mercury pollution trends in subarctic lakes in the northern Swedish mountains.

Despite many years of research about mercury pollution, data concerning high-latitude regions of Europe are limited, particularly studies of long-term temporal trends. It is not clear whether the mercury load at high latitudes follows the recent decreasing trends in European mercury emissions or whether the load is still high because of continuing global emissions. In this study we use sediments from 12 lakes, located above the Arctic Circle in the Swedish mountains, to assess the past and recent mercury pollution situation, especially for the last 200 y. The mercury load increased clearly in sediment deposited from the late 19th or early 20th century to a peak between 1960 and 1990. This peak represents an enrichment of 1.4 to 4.2 times over background concentrations. This enrichment is comparable with enrichments in sediments from lower latitudes as well as other Arctic regions. Since the 1990s mercury concentration has declined in 8 of the 12 lakes, i.e., similar to emission trends in Europe.

Natural fluctuations of mercury and lead in Greenland lake sediments.

Given the current scenario of increasing global temperatures, it is valuable to assess the potential influence of changing climate on pollution distribution and deposition. In this study we use long-term sediment records from three lakes (spanning ca. 1000, 4800, and 8000 years, respectively) from the Greenland west coast to assess recent and long-term variations in mercury (Hg) and lead (Pb), including stable Pb isotopes (206Pb and 207Pb), in terms of pollution and climate influences. The temporal trends in sediment deposited from about the mid-19th century and forward are in general agreement with the history of industrial emissions at lower latitudes. Therefore, in recent sediment a possible influence from changing climate is difficult to assess. However, by using deeper sediment layers we show that changes in Greenland climate caused changes in the lake influx of material from regional aeolian activity, which resulted in large fluctuations in Hg and Pb concentrations and 206Pb/207Pb ratios. The aeolian material is primarily derived from glacio-fluvial material with low Hg and Pb concentrations and a different isotopic composition. For one of the lakes, the fluctuations in Hg concentrations (10 to 70 ng g(-1)) prior to the 19th century are equal to the anthropogenic increase in the uppermost layers, suggesting that when studying recent concentrations and time trends of pollution in relatively low-contaminated areas such as the Arctic, the early natural fluctuations must be considered.