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Oslo’s wildlife reveals what pollutants we live with

Trosteegg. Foto: Eldbjørg Heimstad, NILU

From NILU’s Annual Report 2020: Red foxes, rats, earthworms, fieldfares, sparrowhawks and tawny owls. All these creatures live in and around the city of Oslo, where they are surrounded by – and affected by – everything humans own, eat, and do.

Every year since 2012, NILU – Norwegian Institute for Air Research, the Norwegian Institute for Nature Research (NINA), and the Norwegian Institute for Water Research (NIVA) have been collecting a variety of samples from several different animals living in and around Oslo, and analysing their content of pollutants, on behalf of the Norwegian Environment Agency.

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Research Director Eldbjørg Heimstad (left) and Senior Scientist Dorte Herzke
Research Director Eldbjørg Heimstad (left) and Senior Scientist Dorte Herzke find a large number of different environmental toxins in samples taken from animals living in and around Oslo. Photo: Linda Hanssen, NILU

The researchers are looking for various pollutants – everything from heavy metals such as lead, to chemicals such as flame retardants and perfluoroalkylated substances (PFAS). The analyses reveal which pollutants end up in the animals’ tissues as a direct result of how we humans influence nature and the environment in the cities we live in.

“We actually know less about pollutants in terrestrial animals than about pollutants in marine ecosystems,” says research director and environmental chemist Eldbjørg Heimstad. “That’s why the Norwegian Environment Agency started this monitoring programme with a focus on animals in cities.”

The researchers’ findings provide vital information for the Environment Agency. The data are used not just within Norway, but also for international pollutant regulations such as REACH and the Stockholm Convention.

The sins of our fathers

Oslo is the largest city in Norway, encompassing both densely populated areas, industrialised zones, and forests. This means that scientists must take samples from soil, air, and animals in both industrial and residential zones, in parks, sporting and recreational areas, water treatment plants, and abandoned landfills to get a complete overview of the situation.

Researchers analyse the samples for hundreds of pollutants, which are then sorted into groups: metals, PCBs, PBDEs, chlorinated paraffins, PFAS, pesticides, etc. For each class of substances, pollutant levels are compared across species and locations. In addition, the researchers assess which groups of substances predominate in the various samples and species, and try to determine where the pollution comes from.

Senior researcher Dorte Herzke says that both the types and the levels of pollutants they find vary greatly from place to place.

“For example, we found the highest concentration of PFAS in the form of PFOS in fieldfare eggs from Grønmo, in earthworms from Alnabru, and in rat liver in general. We have observed this for several years running: the PFOS concentration in fieldfare from Grønmo, for example, is more than ten times higher than the average in other fieldfare eggs. Since Grønmo is an old landfill, and Alnabru is an industrial area, these levels aren’t terribly surprising. These ‘sins of our fathers’ still affect the environment around us.”

Where do the pollutants come from?

In the case of all those rats with excessive PFOS concentrations, identifying a single source is more difficult. The most plausible explanation is that multiple places in the city are polluted by PFAS. But can we assume that the animals take up the pollutants at the sites where they are captured?

“The biologists at NINA have explained that the animals are most likely to get the substances locally,” says Herzke. “Birds can travel long distances, but they metabolise what they eat very quickly – especially the smaller birds. Thus, the chances are that the pollutants we find in their eggs are ingested close to the nesting sites.”

But it isn’t always easy to figure out exactly what has happened. When scientists find rat poison in foxes, they can’t tell whether the fox has fed on poisoned rat bait, or on rats that have eaten poison and become sick and easier to catch. The latter is what researchers call secondary poisoning; it can also be suspected when lead is found in predatory birds and mammals. Did the predators consume the lead directly, or did they get it by eating prey or carrion containing lead shot?

Sunscreen and soap drift away

Heimstad goes on to highlight differences between the air samples they have taken and the other samples. They find completely different levels of some pollutants in the air samples than in the samples from animals, soil, and water.

“Take siloxanes, for example,” she says. “That is a group of pollutants that are widely used in personal care products, such as shampoo, sunscreen, soap, and moisturiser. Siloxanes are very volatile, that is, they evaporate easily. When you shower, they’re washed down the drain, so we find them in air samples from VEAS, Norway’s largest wastewater treatment plant. They also appear in air samples taken in Oslo’s popular Palace Park.”

Thus, the air can tell us something about the substances we city-dwellers surround ourselves with. The researchers also find many other substances that are less volatile, that are resistant to breakdown, and that both humans and animals are exposed to mainly through the food we eat. In most samples from animals, the researchers find that the well-known pollutants PFAS and PCB predominate.

Unique monitoring

At present, no other country runs a similar monitoring programme. Individual studies have been done, but the exceptional feature of this Norwegian programme is that the testing is done repeatedly, and with the same design, over many years. This provides unique insight into developments over time, while offering opportunities to follow up on interesting findings and expand the programme if necessary.

“Investigating local pollution is important,” says Heimstad. “Not only does it reveal old sins; it also exposes new ones. Over the next four years, we will expand the sampling programme to cover additional substances, more locations (such as Marka, the forested zone around Oslo), and new species. Roe deer, bees, bumblebees, snails, nursery web spiders and rowan trees are on the list.

The animals in Norway’s capital live side by side with its human inhabitants – everything humans make, emit, and throw away. This is what leads to the locally high levels of pollutants, because only a fraction of the substances that environmental scientists find in Oslo’s animals occur naturally.

“We study animals and the environment,” says Herzke. “We can’t say for sure what our findings imply for humans, but they can probably serve as an indicator of what we can expect to find in people. Maybe we should be more mindful of that? And of the fact that we have a responsibility to know what chemicals we release, and an obligation to minimise the amounts released to the local environment we share with Oslo’s wildlife?”

The scientists found the highest concentration of PFAS in the form of PFOS in fieldfare eggs from Grønmo (main picture), in earthworms from the industrial area Alnabru, and in rat liver in general. Photo: Eldbjørg S. Heimstad, NILU