Pollutant accumulation in road mitigation tunnels for amphibians: A multisite comparison on an ignored but important issue

Underpasses or road tunnels are increasingly installed to reconnect habitats and ensure safe wildlife passage, thus preventing habitat fragmentation caused by roads mortality from collisions with vehicles. In the UK, such underpasses regularly implemented for amphibians especially protected great crested newt, Triturus cristatus . However, also a key source of environmental pollutants including trace metals, salt, petroleum diesel hydrocarbons these might impact mitigation structures where funnelled to, yet extent implications almost never quantified in relation this aspect, despite recognised sensitivity chemical pollutants. Sediments were analysed four amphibian tunnel sites across UK compared natural soil formations at local reference determine whether contaminants indeed accumulating within tunnels. Three potential (copper, lead, total hydrocarbons) found greater concentrations underpass sediments than respective three locations, while one (zinc) was all studied sites. Aggregated sediment pH value significantly study several instances reached values that exceeded thresholds concern. Despite large geographic area covered significant site differences absolute similar sites, suggesting pollution sources pathways. These results suggest ecological could be pathway surfaces it is recommended focussed monitoring maintenance enacted given their short long-term impacts on currently unknown. Potential management options include regular jet-washing underpasses, alternatively, pre- post-implementation modifications designs should aim minimise surfaces.