Trace element contamination in Antarctic ecosystems.

Data concerning trace element concentrations in both abiotic and biotic components of the Antarctic ecosystems are summarized here to be used as a first background database for pollution detection. Antarctic ancient ice and snow cores have been used to assess past and present-day changes in global atmospheric levels of certain trace elements. Concentrations of Pb, Cd, and Hg in the Antarctic tropospheric cell have varied according to glacial and interglacial periods before humans began to contaminate the atmosphere with these metals. Based on data of Pb concentrations in the Antarctic ancient ice cores and samples of recent snow, most of the Pb in Antarctica is anthropogenic. Moreover, this metal has decreased in recent years as a consequence of the reduced use of leaded gasoline in countries of the Southern Hemisphere. Reliable experimental and field data have indicated, however, that human activity in Antarctica contributes significantly to increasing atmospheric Pb levels in this continent, whereas the environmental impact of other metals such as Cd, Zn, or Hg is restricted to the area a few hundreds of meters about the anthropogenic source. Trace element concentrations in Antarctic abiotic matrixes are generally at ultratrace levels, challenging analytical detection limits and increasing the risk of unwanted contamination. Pb and Hg concentrations in Antarctic snow, surficial soil, air, and marine sediment have been considered as the lowest concentrations ever reported. Conversely, concentrations in Antarctic biota, are comparable to those from polar and temperate areas of the Northern Hemisphere, in particular Cd and Hg. Environmental and biological factors favoring a greater metal accumulation by Antarctic biota are discussed. Growth rate of the organisms and detoxification mechanisms (e.g., metallothioneins, molting cycles) are largely affected by the extreme environmental conditions in Antarctica (water supply, temperature regimen, light availability) that probably interfere with uptake, storage, and excretion of trace elements by organisms. On the other hand, environmental factors such as the upwelling of Cd-rich waters and local volcanism undoubtedly increase the bioavailability of metals in the Antarctic environment. In this context, several Antarctic organisms such as fish, mollusks, lichens, and mosses have been proposed as suitable biomonitors, and their trace element concentrations have been suggested as baselines. Structure and dynamics of Antarctic ecosystems as well as quantifying metal point sources and long-range atmospheric transport require in-depth studies to improve the assessment of human impact in Antarctica.