When it´s raining on the roads, slops of road dust and contaminants drain into the road trenches. What does it do to wildlife living by the road?

Every day, numerous cars and trucks are wearing on Norway´s almost one hundred thousand kilometers of road: Asphalt wear on the tires, the tires wear on the asphalt, exhaust flows out from the vehicles and all is shrouded by road dust, until a rainfall cleanses the air, leaving all the dust and particles in the ditch. Most places, the dirty rain water is directly discharged into the environment. However, some of the newly built roads have sedimentation dams, where the road runoff rest for some weeks while rubber, soot and dust sink to the bottom, protecting the surrounding environment from road contamination.

Sedimentation dams have caught colleagues Sissel Ranneklev, Merete Grung, and Sondre Meland´s interest. They are all researchers at The Norwegian Institute for Water Research (NIVA), and they have spent the last years doing research on these dams. In a recently published article, they present their findings on the health effects in animals and plants living in sedimentation dams.

From lab to reality

"Sedimentation dams are urban habitats for a range of plants and animals, but it appears these dams also contain high levels of pollutants. Laboratory tests have shown that such contaminants have hazardous effects on for instance fish," Meland explains.

Lab fish that are exposed to the residues of incomplete combustion, so-called polycyclic aromatic hydrocarbons (PAHs), have a higher risk of developing cancer and DNA damage. Ranneklev and Meland wanted to investigate if the effects observed in the lab also occur in sedimentation dams.

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Tunnel wash

With colleagues from NIVA, Norwegian Public Roads Administration, Norwegian University of Life Sciences and University of Copenhagen, Ranneklev and Meland collected plants, frogs, sediments and minnow, a small fish, in a sedimentation dam that protects river Ljanselva at Skullerud, and Sagdammen in river Ljanselva, both in the Oslo area. They also collected minnow in Østmarka southeast of Oslo for comparison. Lastly, they joined the washing of three tunnels and collected a couple of liters with wash water, and brought all samples into the laboratory for analyses. In the lab, they also did an experiment to see if wash water from tunnels affected the protein activity in liver cells, or reduced the growth of an algae called Pseudokirchneriella subcapitata.

Detox proteins and DNA brakes

Half of the minnows living in the sedimentation dam at Skullerud had broken DNA strands. DNA breaks may lead to permanent changes in the genes, at worst causing cancer. But the minnows were trying to fight back; They contained high levels of the detox protein CYP1A. This protein detoxifies toxic compounds, enhancing excretion.

"But the minnow´s detox cure didn´t work a hundred percent. Rather than excreting the PAHs completely, the compounds were instead transformed to PAH metabolites" says Meland, and explains "PAH metabolites are substances that the detox proteins produce from PAHs, and they may be just as toxic as the parent compound."

Unhealthy fish

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The researchers also estimated the effect of contaminated wash water on the fish' condition, a kind of a "fish BMI," expressed at excess energy available for the fish to grow and reproduce. The polluted fish from Skullerud had a lower condition than the unpolluted fish from Østmarka. There might be several explanations to this: Maybe it´s simply because the food availability is better in Østmarka? Or could it be because of the higher concentrations of some compounds? Detox processes are costly, and there might be less energy left for food searching and growth if a lot is spent on detoxification.

Slower growth in wash water

And what about the experiment with liver cells and algae? Correct -"neither of them benefitted from the polluted wash water. Wash water from two of the three tunnels made the algae grow slower, and the liver cells started producing detox proteins.

But why wash water from tunnels, and not roads?

"Tunnels are interesting because they represent only local pollution sources. Other sources, like long range transported compounds, or contaminants transported from other parts of the catchment, can be disregarded," Ranneklev explains.

Several PAH compounds that may be more toxic than those regulated by the authorities, have been detected in tunnel wash water.

More research needed

"Our research reveals some of the consequences of traffic pollution, and underlines the importance of sedimentation dams, where pollutants are trapped before the water is discharged in to the catchments," says Ranneklev.

"More research is needed for a deeper understanding of how pollution from road traffic affects the environment. One important step is to identify the amounts of microplastics that originate from tire wear," says Ranneklev.

This project was part of the R&D program Nordic Road Water, funded by the Norwegian Public Roads Administration. NIVA also contributed to the studies with financial support. The results are published in the scientific journals Chemosphere and Science of the Total Environment.