Identifying pathways of exposure to highway pollutants in great crested newt (Triturus cristatus) road mitigation tunnels

Road mitigation tunnels are increasingly deployed for amphibians but very little is known about chemical pollution in such schemes. We assessed pollution pressures associated with road runoff at a major great crested newt mitigation scheme in England. Sediments and waters in the mitigation system were analysed for major physico‐chemical parameters, trace metals and total petroleum hydrocarbons and compared to a nearby reference site. Seven out of eight tested metals including copper, zinc, lead and iron were in significantly greater concentrations in the tunnels than at a reference site and at environmentally significant concentrations. Water samples also exhibited elevated concentrations of aluminium and chromium and occasionally extreme alkaline pH associated with leaching of portlandite in tunnel cements. High conductivity values in waters and sediments corresponding with seasonal de‐icing salt application were also apparent. The study highlights the potential pollutant pressures for amphibians associated with large‐scale urban development and road mitigation schemes.