Poison source in idyll

Luck and misfortune often lie close together in the wilderness of a national park. On September 20, 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 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 toxic residues in the bird's body, the specialists sent the eagle owl's entrails to Empa. "The sample material was already not so fresh," recalls Markus Zennegg, a chemist in the "Advanced Analytical Technologies" department. But when he examined the first samples in the mass spectrometer, he was 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 fat - that's thousands of times above normal levels for wild animals." Zennegg had to dilute the samples again and run them through his machine another time to even determine the concentration correctly.

Pollutants from a hydropower plant

The PCB in the eagle owl from the National Park, however, was not entirely unexpected. The small river Spöl, where the bird was found, draws its water from the Lago di Livigno. The lake is dammed by the Punt da Gall dam, which belongs to Engadiner Kraftwerke AG (EKW). 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 contaminating the water at the Spöl.

Here again, luck and misfortune are close together: In 1970, the dam including the power plant was put into operation. Only two years later, in 1972, substances containing PCBs were banned "in open systems" in Switzerland. But by then, the dam was already finished - and, to a certain extent, brand new. For 50 years, the dam water carried the pollutant very slowly downstream and deposited it in sandbanks and floodplains. In some places, the pollution reaches up to half a meter deep into the sediment.

It is possible that a first, larger wave of PCBs was distributed in the sediments during a mud flood in the Spöl as early as 2013. 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 power plant company reported this accident to the environmental authority. Since then, Empa has been monitoring the case. Markus Zennegg analyzes 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: The fish in the Swiss National Park exceed the PCB level permitted for food by a factor of four.

At the top of the food chain

Of course, the eagle owl could not have known that. 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, then it becomes a candidate for chronic poisoning.

There are various substances in the group of PCBs. Empa detected PCB 126 in particular in the dead eagle owl from Spöltal, 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 pollution. The chemical is practically not degraded in the environment and is on the move 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 more than the EFSA recommendation.

Rehabilitation successfully rehearsed

So what is to be done? Opinions are divided on this. All those involved - the power plant company EKW, the environmental agency 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 little river 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 so-called Tos basin, were already rehabilitated on a trial basis 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 little river Spöl have to be rehabilitated in this way. In February 2021, the environmental authority of the canton of Graubünden decreed a 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 infobox "Legal situation unclear"). Further downstream, the PCB contamination is no longer as serious as in the upper reaches, but is still clearly too high for a national park.

National Park Director Haller, in calling for total cleanup, is thinking not only of the water in the rivers, but of wildlife in particular, which collect the poison in their bodies. "If animals die, their territories are occupied from other areas, the population thins there, 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.

Visit worth - as soon as possible

Empa will continue to monitor the stress on fish and wildlife in the national park with chemical analyses. A visit to the course of the river is worthwhile sooner rather than later: as soon as the cleanup 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."

In the end, the riverbed will be purposefully flooded several times with water from the reservoir to redistribute the clean sand and erase the traces of the construction work. "A few years later, nature will have reclaimed the landscape. But then without PCB pollution," says Ruedi Haller. "Then we can pass the national park on to the next generations with a clear conscience."

Legal situation unclear

A legal dispute arises 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 ordered by the canton in advance and to settle the dispute about the costs later. Many things are unclear: 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 with other known environmental pollution. Accordingly, the authorities cannot refer to other comparable 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."