Coal burning leaves toxic heavy metal legacy in the Arctic

Abstract

Toxic heavy metals emitted by industrial activities in the midlatitudes are transported through the atmosphere and deposited in the polar regions; bioconcentration and biomagnification in the food chain mean that even low levels of atmospheric deposition may threaten human health and Arctic ecosystems. Little is known about sources and long-term trends of most heavy metals before approximately 1980, when modern measurements began, although heavy-metal pollution in the Arctic was widespread during recent decades. Lacking detailed, long-term measurements until now, ecologists, health researchers, and policy makers generally have assumed that contamination was highest during the 1960s and 1970s peak of industrial activity in North America and Europe. We present continuous 1772-2003 monthly and annually averaged deposition records for highly toxic thallium, cadmium, and lead from a Greenland ice core showing that atmospheric deposition was much higher than expected in the early 20th century, with tenfold increases from preindustrial levels by the early 1900s that were two to five times higher than during recent decades. Tracer measurements indicate that coal burning in North America and Europe was the likely source of these metals in the Arctic after 1860. Although these results show that heavy-metal pollution in the North Atlantic sector of the Arctic is substantially lower today than a century ago, contamination of other sectors may be increasing because of the rapid coal-driven growth of Asian economies.

Fig. 1.

Map of Greenland showing the locations of the ACT2 and other ice cores described in Results and Discussion and Methods. The ACT2 ice core was collected ≈55 km west of the ice divide.

Fig. 2.

Monthly (black) and annually (red) averaged concentrations of Tl, Cd, and Pb in central Greenland precipitation from 1772 through 2003.

Fig. 3.

Annual average concentrations of nssS, Tl, Cd, and Pb compared to BC from 1872 to 2003. Heavy lines show 5-year running means.

Fig. 4.

Comparison of monthly averaged Ce, Tl, Cd, and Pb measured in the ACT2 ice core by using two HR-ICP-MS instruments operating in parallel and in real time.

Fig. 5.

Comparison of monthly and annually averaged continuous measurements of Cd in the ACT2 ice core with all 36 previously published discrete measurements of Cd for this time period (filled diamonds) in Greenland ice cores (11, 15). The discrete samples were measured in a core from Summit ≈600 km north of ACT2.

Fig. 6.

Comparisons to other Greenland ice core measurements of Pb. (Upper) Comparison of monthly and annually averaged Pb measurements from ACT2 with previously published discrete measurements [filled circle (11), filled triangle (13), open circle (14)] at Summit ≈600 km north of ACT2. (Lower) Comparison of annually averaged continuous Pb measurements from ACT2 and Summit. Concentrations of Pb at ACT2 are higher than at Summit after industrialization, particularly in the second half of the 20th century.