Persistent organic pollutants are chemicals that can travel long distances in the atmosphere and once deposited can remain in the environment for many years. They accumulate in the food web, affecting the health of living organisms. Examples include PCBs (polychlorinated biphenyls), now banned but previously used in industry, organochlorine pesticides, such as DDT, and synthetic musk compounds used as fragrances in body care products and household detergents.
In the 1950s-1970s, even remote glaciers high in the Swiss Alps were affected by global emissions of persistent organic chemicals. These pollutants have accumulated in the glaciers after being trapped in the surface ice through deposition from the atmosphere.
Lake Oberaar in Switzerland is a remote, hydroelectric reservoir lake, high in the Alpine mountains, fed with meltwater from the Oberaar Glacier. Since 1930, the glacier has retreated by 1.6 km. Swiss researchers analysed core samples taken from the sediment of Lake Oberaar to test for a wide range of contaminants.
Pollutants were deposited in layers in the sediment. The layers were dated from 1953, when the dam was constructed, to 2006, when the samples were taken. Analysis revealed that:
- In the early 1950s, low quantities of chlorine-containing organic chemicals were deposited in the lake sediment, followed by rapid increases in the late 1950s and 1960s, reaching a peak in the 1960s and 1970s. This reflected the wide-spread global use and emissions of these compounds during this time. The input dropped in the 1980s-1990s as a result of improved emission reduction technologies, regulations and the banning of certain chemicals, such as DDT.
- From the 1950s to the 1990s, synthetic musk inputs were high and remained fairly constant as their production was relatively stable.
- In the late 1990s until 2005 (the last year for which data were collected), quantities of all containments rose. Inputs of organic chlorines are similar to, or even higher than, the peaks of 1960s and 1970s. Synthetic musk deposits were higher than in the 1980s, although there was a slight decrease by 2005.
In addition, the researchers compared these results with previous studies on sediment pollutants found in several low-Alpine lakes, including Lake Thun, a rural lake that had not been directly fed with glacial meltwater. Deposit trends of organic pollutants in both lakes were similar up until the late 1990s when inputs to Lake Oberaar increased. This supports the suggestion that the latest peaks in Lake Oberaar have been caused by contaminants released from the melting glacial ice, rather than direct atmospheric deposition in the lakes.
Accelerated glacial melting caused by climate change will release these pollutants and may affect the use of glacial meltwater in irrigation systems, such as drinking water in Alpine huts and in the artificial production of snow. In addition, wildlife and fishermen may be exposed to increased concentrations of these contaminants in the environment.