The researchers found that accelerated glacier melting may account for increased levels of such legacy pollutants in Alpine regions.

• Input fluxes of all organochlorines increased in the 1950s, peaked in the 1960s-1970s, and decreased again to low levels in the 1980s-1990s. This observation reflects the emission history of these compounds and technical improvements and regulations leading to reduced emissions some decades ago.

• The input of synthetic musks remained at a high level in the 1950s-1990s, which is consistent with their relatively constant production throughout the second half of the 20^th century. Since the late 1990s, input of all compound classes into the high-Alpine Lake Oberaar has increased sharply.

• Currently, input fluxes of organochlorines are similar to or even higher than in the 1960s-1970s.

This second peak supports the hypothesis that there is a relevant release of persistent organic chemicals from melting Alpine glaciers. Considering ongoing global warming and accelerated massive glacier melting predicted for the future, our study indicates the potential for dire environmental impacts due to pollutants delivered into pristine mountainous areas.

—Bogdal et al.

The presence of legacy pollutants in the Alps is dangerous for several reasons, including the melting of snow in the spring, use of glacier melt water by consumers and industry, and increased specific exposure of humans and wildlife to hazardous compounds.

When glaciers melt, the accumulated chemicals, deposited years earlier by air currents on to the snow layer and then frozen into the ice, are carried by the runoff water into the nearest glacial lake. There, together with other matter suspended in the melt water, they sink to the bottom of the lake and accumulate in the sediment.

The researchers were able to read the sediment layers in the Oberaarsee reservoir’s sediment samples like tree rings, layer for layer all the way back to 1953, when the dam which created the lake was first built. Reading the rings, the scientists were not only able to distinguish pollutants produced in the 1960s and 1970s, but also see the reduction in chemicals after they were banned.

The increased pollutant levels may be due, in part, to runoff from the Oberaar glacier, which shrank by 120 meters in the last 10 years alone, and could have released a relatively large amount of accumulated toxic substances, they suggest.

Samples from Lake Oberaar were compared to core samples from lakes at lower levels. Sediment from these locations did not exhibit the same increase in legacy pollutants at the end of the 1990s. This finding supported the hypothesis that the increased levels of legacy pollutants in Lake Oberaar resulted from glacier melt.

At this stage, our study indicates that accelerated glacier melting due to global warming may also account for enhanced release of legacy organic pollutants at historically high levels. Since 1999, the 1500 glaciers in the Swiss Alps have shrunk by 12%. A more comprehensive and quantitative evaluation of the relevance of melting glaciers as a secondary source of organohalogens requires, however, additional consideration of glacier dynamics. The recent accelerated mass loss of Alpine glaciers leads to enhanced release of chemical species from surfacial ice layers, which would have been retained much longer in the glacier under stationary climate conditions.

The coupling of glacier dynamics and pollutant cycling is a complex topic and represents a poorly studied research field. Ongoing work in this field may provide additional insight into the fate of persistent organic pollutants in the Alpine environment.

—Bogdal et al.

Resources

• Christian Bogdal, Peter Schmid, Markus Zennegg, Flavio S. Anselmetti, Martin Scheringer and Konrad Hungerbühler (2009) Blast from the Past: Melting Glaciers as a Relevant Source for Persistent Organic Pollutants. Environ. Sci. Technol., Article ASAP doi: 10.1021/es901628x