Sediments in the Spöl, a small river in the very south of the canton Graubünden, are contaminated with PCBs. The chemicals originate from a 50-year-old anti-corrosion coating of a hydroelectric power plant in an upstream dam; they are transported and distributed with the waters of the Spöl - all the way to the Black Sea. Now the river has to be remediated. What is disputed, though, is the extent to which this must be done - and who will pay for it. Analyses by scientists play a central role in this: They show just how much PCB is hidden in which areas of the riverbed.
Luck and misfortune often lie close together in the wilderness of a national park. On 20 September 2020, a park ranger in the Swiss National Park found a dead eagle owl on the edge of a hiking trail next to the little river Spöl. The bird certainly had an unhappy ending: One wing was broken, and the eagle owl was emaciated to 1.3 kilograms, less than half its normal weight, as later examination revealed. That the bird was found at all, on the other hand, was shere luck. Normally, dead animals in the wild are carried off and eaten within hours by foxes or birds of prey.
Now the ball was rolling. The carcass was examined at the Center for Fish and Wildlife Medicine at the University of Bern. To detect any poisonous residues in the bird’s body, the specialists sent the eagle owl’s entrails to Empa. "The sample material was not exactly fresh anymore," recalls Markus Zennegg, a chemist in Empa’s Advanced Analytical Technologies lab. But when Zennegg examined the first samples in the mass spectrometer, he was quite surprised. "The instrument showed concentrations that I would not have thought possible. The load of particularly toxic polychlorinated biphenyls (PCBs) in this bird was 20 micrograms per kilogram of body fat - that’s thousands of times above normal levels for wild animals." Zennegg had to dilute the samples and run them through his instrument one more time to determine the concentration correctly.
The PCB concentrations in the eagle owl from the national park were not entirely unexpected, however. The Spöl, where the bird was found, draws its water from the "Lago di Livigno". The lake is dammed by the "Punt da Gall" dam. And that’s where the problem lies: When the dam was built in the late 1960s, anti-corrosion paint containing PCBs was used, which has since been slowly worn away and contaminates the water at the Spöl.
Here again, luck and misfortune lie close together: In 1970, the dam including the power plant was put into operation. Only two years later, in 1972, Switzerland banned PCB-containing substances in "open systems". But by then, the dam was already finished - and, to a certain extent, brand new. For 50 years, the dam water carried the pollutant slowly downstream and deposited it in sandbanks and floodplains. In some places, PCB pollution reaches as deep as half a meter into the sediment.
It is possible that a first, larger wave of PCBs was distributed in the sediments as early as 2013 during a mud flood in the Spöl. A second incident occurred in 2016: A remediation company stored waste from sandblasting work in the dam wall, which was blown away by a storm and carried into the Spöl. The owner of the dam, the power plant company Engadiner Kraftwerke AG (EKW), reported this accident to the environmental authority. Since then, Empa has been monitoring the case. Markus Zennegg analyzes for instance fish and has developed special, highly sensitive passive samplers that can measure the PCB content in the water of the reservoir. Since 2017, the consumption of fish from the Spöl has been banned: Fish in the Swiss National Park exceed the PCB level permitted for food by a factor of four.
Of course, the eagle owl had no way of knowing this. Like other predators, such as otters, foxes and bears, it is at the top of the food chain. PCBs are fat-soluble pollutants that accumulate in the fatty tissue of fish. If the eagle owl feeds mainly on fish from the Spöl, it becomes a candidate for chronic PCB poisoning.
There are various substances in the group of PCBs. In the dead eagle owl from the Spöl valley, Zennegg detected above all PCB 126, a substance that is only about ten times less toxic than notorious Seveso dioxin TCDD. The substance weakens the immune system and hormone metabolism, damages reproductive organs and can cause cancer.
Humans are also affected by PCB exposure. The chemical virtually does not degrade in the environment and stays there for centuries. The European Food Safety Agency (EFSA) believes that a person should ingest a maximum of two picograms of such dioxin-like PCBs per kilogram of body weight per week. The value is calculated from the sperm quality. Swiss citizens already consume 14 picograms of PCBs per week - seven times above the EFSA recommendation.
So what is to be done? Opinions are divided. All those involved - the power plant company EKW, the environmental office of the canton of Graubünden and the administration of the Swiss National Park - agree that the PCB time bomb in the upper reaches of the Spöl should be defused as soon as possible. After all, the water runs from there into the Inn, then past Innsbruck, Kufstein, Rosenheim and Passau into the Danube - and from there into the Black Sea.
The first 60 meters behind the dam, the stilling basin, had already been rehabilitated in a pilot project in 2016. "They filtered out the fine sand with grain sizes of less than 3 millimeters, burned it out in a gravel plant and then reinstalled it in the basin," explains Ruedi Haller, director of the Swiss National Park. "This method successfully removes about 90 percent of the PCB contamination."
The question remains how many kilometers of the Spöl will have to be remediated in this way. In February 2021, the environmental authority of the canton of Graubünden ordered the remediation of the upper reaches of the Spöl over a length of 2.9 kilometers. The National Park Authority, on the other hand, is demanding remediation of the entire river course over 5.8 kilometers (see info box). Further downstream, the PCB contamination is no longer as serious as in the upper reaches, but still clearly too high for a national park.
National Park Director Haller, in calling for total cleanup, is thinking not only about the water in the rivers, but specifically about wildlife that accumulate the toxin in their bodies. "If animals die, their territories are occupied from other areas, the population is thinning out, and the Spöl valley acts as a population sink. The poisoned Spöl can thus have far-reaching effects if migrating animals carry the PCB over wide areas." But that, he said, is exactly the opposite of what a national park is supposed to be by law: a place where rare species can find an intact habitat and positively impact other populations outside the national park.
A legal dispute has arisen between the power plant company EKW, the Swiss National Park and the environmental office of the canton of Graubünden. EKW had already offered to finance the remediation in advance and settle the dispute over the costs later. Many things are unclear, however: Will the remediation company have to pay for the 2016 accident? Will the case be treated as an industrial contaminated site or under water protection laws? Michael Roth, the director of EKW, sees it this way: "The Spöl case is hardly comparable to any other known environmental pollution incident. Accordingly, authorities cannot refer to other cases, which has a negative impact on legal certainty. It will be inevitable that one or the other question will have to be clarified by the courts."
scientists will continue to monitor the stress on fish and wildlife in the national park with their chemical analyses. A visit to the river is worthwhile sooner rather than later: As soon as the remediation begins, the Spöl will turn into a construction site for two to three years, says National Park Director Haller. "We will stay in the riverbed itself as much as possible with excavators and dumpers to destroy as little of the surrounding area as possible. A mobile gravel plant will travel with the site, filtering out the fine sand from the polluted sediments and burning it out on site so we can put it right back in."
Eventually, the riverbed will be purposefully flooded several times with water from the reservoir to redistribute the clean sand and erase the traces of construction. "A few years later, nature will have reclaimed the landscape - without PCB pollution," says Ruedi Haller. "Then we can pass the national park on to the next generations with a clear conscience."