Impact of anthropogenic contamination on glacier surface biota

Glaciers are not only ice masses, rather they host different communities and were included, together with ice sheets, in the list of the main terrestrial biomes [1]. Regrettably, by the mid of this century, most of the small glaciers in high mountains will disappear because of global warming [2]. Currently, the research effort on their microbial communities and their relations to biogeochemical processes has markedly increased 3, 4. The most studied glacial ecosystem is the supraglacial zone that is the most biodiverse, spatially heterogeneous, and highly interacts with the surrounding environments [1]. These interactions include the input of materials also from substances that undergo long-range atmospheric transport (LRAT: >1.000 km) before being deposited on glacier surface [5]. Different anthropogenic contaminants can also undergo LRAT: even the Roman Empire’s activity was detected in the Greenland Ice Sheet ice-cores, where lead was found [6]. The deposition of anthropogenic substances is promoted on glaciers because of low temperatures and high precipitation rates, which make the glaciers cold condensers [7]. Once deposited, contaminants cluster in the ice or in the sediment according to their physical–chemical features and they can experience different fates: they can be stored in the ice, released through revolatilization or with melting waters, or degraded through photolysis, hydrolysis, and biodegradation [8].

Hydrophilic compounds are more prone to be released in the melting water, while hydrophobic ones can adsorb on sediments and/or accumulate in the biota in the glacial environment 7, 9. Most of these contaminants are persistent and can interact with the biota for a long time. Many papers have focused on the presence of anthropogenic contaminants and the effect of their release on downstream ecosystems in freshwater and sediments 10, 11. However, recent investigations showed that the bioaccumulation of contaminants in the downvalley waters is very low and it is unlikely that melting waters are major sources of specific contaminants to downstream ecosystems [9]. Hence, it is worth studying the dynamics of contaminants within the glacier environment, because their fate in situ, including their effect on the biota and trophic interactions, may be more important than downvalley. Among the supraglacial environments, cryoconite and cryoconite holes (Box 1) emerged as efficient traps for both organic and inorganic pollutants by adsorption to mineral and organic matter (OM), and, at the same time, are biologically active habitats [12]. Glaciers are important sources of freshwater that billions of people rely on for many uses such as drinking water, energy production, crop irrigation, and animal breeding. They are fragile systems impacted by both direct and indirect human-related activities. Contamination and climate change are interrelated anthropogenic effects that currently have severe consequences on glacier quality. Concomitantly, climate change is causing a rapid decrease of glacial areas worldwide and, in turn, affects the water runoff, alters the biogeochemical cycles, and accelerates the downvalley release of the trapped contaminants. This paper aims at reviewing all the information available so far about the effects of pollutants on the supraglacial biota (SGB), with a focus on persistent organic pollutants (pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs)), whose presence has been extensively documented in cold areas, and on emerging contaminants such as plastic and heavy metals including radionuclides (Figure 1).

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