Regional Baseline Concentrations of Persistent Contaminants

Although dry and occult (fog and ice crystals) deposition contributes significantly to the input of contaminants to Antarctica and the Southern Ocean, snow undoubtedly represents the main cleansing mechanism for the Antarctic atmosphere. Snow, firn and ice are the most widespread environmental matrices used to indirectly assess spatio-temporal variations in contaminant deposition throughout the continent. A number of techniques have been introduced for the collection of clean samples and for reliable analytical determinations. However, as discussed in Chapter 5, concentrations of persistent contaminants in Antarctic snow and ice are very low and can be determined in a relatively small number of laboratories. The post-deposition fate of organic chemicals in snow is largely unknown, and variations in snow accumulation over time can determine significant change in its chemical composition, even in the absence of any change in the composition of aerosol over the study area. Snow and ice are thus the only available environmental matrices to study spatio-temporal trends of atmospheric contaminants on the Antarctic plateau and most of the continent. Without better knowledge of their transfer and post-depositional processes, however, the analysis of snow and ice can provide only a qualitative picture of the chemical composition of the overlying atmosphere. Moreover, data on climate change and on contaminant input from other continents in the Southern Hemisphere show that there are considerable differences among various Antarctic regions, and it would not be wise to assign a unique baseline concentration to each persistent contaminant in Antarctic snow or ice. Based on data reported in the previous chapters, it would be opportune to at least differentiate among snow samples collected in the Antarctic Peninsula, West Antarctica, East Antarctica and Victoria Land.

As ice-free areas in Antarctica mainly occur in coastal regions, soils, lake sediments and cryptogams cannot be used to complete environmental surveys throughout the continent. However, most atmospheric deposition occurs on continental fringes, and environmental matrices in ice-free areas receive a large proportion of contaminants deposited on the continent after long-range transport. Although very few data exist on concentrations of chemicals in abiotic and biotic matrices of Antarctic freshwater and terrestrial ecosystems, they could play an important role in regional monitoring programmes. Large-scale surveys in Greenland and other polar regions (e.g. AMAP 1997, 2002) show that freshwater sediments and various species of organisms can be used to detect the deposition of atmospheric contaminants in polar ecosystems. As a rule, the sampling of lake sediments or biota is performed over rather large intervals of time (often 5 years), and contaminant concentrations in these materials are usually some orders of magnitude higher than in snow. These approaches therefore have many advantages and determine much less environmental impact than monitoring surveys based on sampling and analysis of snow or aerosols. As the composition of the latter matrices is extremely variable in space and time, monitoring requires repeated sampling (every few days or weeks) and sophisticated analytical techniques. The determination of very low concentrations of elements or compounds implies errors and large variability of results, and narrow spatio-temporal variations in atmospheric deposition of contaminants often cannot be detected. Furthermore, several countries involved in Antarctic monitoring programmes do not have adequate technical skills, laboratories and instruments for a reliable determination of persistent contaminants in snow and ice.

As discussed in Chapter 5, in ice-free areas of continental Antarctica the chemical weathering of exposed substrata occurs only to a very limited extent, and the environmental biogeochemistry of terrestrial and freshwater ecosystems is largely dominated by elements and compounds in snow and atmospheric dry and occult deposition.As most Antarctic lakes and ponds are located in poorly developed rocky catchments and usually lack outlets, they are the main sink for melting water, solutes and contaminants deposited in the surrounding environment. Preliminary comparative studies in northern Victoria Land (Triulzi et al. 1990; Fuoco et al. 1996), for instance, indicate that lake sediments accumulate higher concentrations of PCBs and 137Cs than soils or marine sediments from the same region. Sediments and algal mats behave as natural integrators of soluble and particulate chemicals deposited in the watershed, and can be important indicators of the impact of local human activity and/or contribute to regional surveys on long-term changes in climatic conditions, biogeochemical cycles or inputs of long-range transported contaminants.

Lichens and mosses are perennial organisms which constitute most of the biomass in Antarctic terrestrial ecosystems (Fig. 49). Due to their slow growth rate, cation exchange capacity and lack of roots, these organisms depend on atmospheric deposition for their metabolism. Together with essential ions, they accumulate persistent atmospheric pollutants from melting snow to levels well above those in snow or aerosols. Several species of cryptogams are

Fig. 49. Lichens and mosses constitute most of the biomass in Antarctic ice-free areas, and these organisms can be used as biomonitors of persistent atmospheric contaminants

Fig. 49. Lichens and mosses constitute most of the biomass in Antarctic ice-free areas, and these organisms can be used as biomonitors of persistent atmospheric contaminants

used worldwide as biomonitors of airborne metals, pesticides and radionuclides, especially for large-scale surveys in remote regions of the Northern Hemisphere. Although Antarctic lichens were found to behave as reliable biomonitors of long-range transported chlorinated hydrocarbons (Bacci et al. 1986), during the last two decades these organisms have mainly been used to biomonitor trace metals, PCBs and PAHs around scientific stations. Some species of Antarctic cryptogams have a circumpolar distribution and could be very useful in establishing long-term biomonitoring networks of persistent atmospheric pollutants in different regions of Antarctica. Predicted changes in temperature and atmospheric precipitation will probably affect the growth rate, colonisation pattern and chemical composition of Antarctic lichens and mosses, and these organisms could constitute an effective early-warning system to detect environmental changes in Antarctic terrestrial ecosystems.

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