A toxic cocktail of damaging chemicals created by road pollution is flowing into England’s rivers and no regulator is monitoring the scale of its impact on wildlife or public health. More than 18,000 outfalls, such as pipes, and about 7,700 soakaways managed by National Highways discharge rainwater potentially contaminated with heavy metals, hydrocarbons, microplastics and other chemicals from the main road network into rivers and on to land. Last month, National Highways reported it had assessed its discharge points and found 1,236 outfalls and soakaways had “a potential high risk of pollution”. Of these, “145 have a verified high risk of pollution and require mitigation” while the remaining 1,091 had a “potential high risk” of “polluting the water environment”. Analysis by the Guardian and Watershed Investigations of hundreds of these sites reveals that about 70 are located in areas that are legally protected for important habitats or wildlife, and about 250 are within 1km (0.6 miles) of a protected site. Hundreds more discharge to rivers and land with no formal protection. Despite urban and transport pollution accounting for 18% of England’s water bodies failing to meet good ecological standards, highways outfalls are not regulated under environmental permitting regulations, which means there is less scrutiny and no monitoring in place. Guy Linley-Adams, a solicitor at the charity Wildfish, said: “The Environment Agency has the power to bring highways drains and discharges under environmental permitting if they involve ‘the discharge or entry to inland freshwaters, coastal waters or relevant territorial waters of any … poisonous, noxious or polluting matter’. “That would certainly appear to be the case here, so the agency must show that it has considered the problem and explain why it has not yet, to our knowledge, required permits that limit pollution of rivers from, at the very least, the higher risk discharges that have been identified by National Highways. “It is no good just saying: ‘We don’t know how big this problem is.’ Put simply, the agency has a duty to find out.” National Highways said it did not routinely monitor runoff because the results varied depending on rainfall and river flows, and because it would not be practical or good value. It had instead developed a predictive tool to determine scenarios where the risk of impacts on water quality were unacceptably high. The lack of monitoring makes it impossible to understand the scale of the pollution but it is also hampered by lack of knowledge over the total number of outfalls across the country. Jo Bradley, a former Environment Agency officer who runs the Stormwater Shepherds not-for-profit, said: “National Highways operates 3% of the road network and they have over 25,000 outfalls and soakaways. Imagine how many there are across the entire road network. The number of these outfalls dwarfs the 15,000 storm sewer overflows, and perhaps the impact of the pollution is worse.” Ten potentially high-risk outfalls drain runoff from the M27 bridge into the River Hamble conservation area, which flows into the Solent. Some of England’s rare and fragile chalk streams are also under threat from runoff; the M1 discharges into the River Colne, near Watford, and runoff from the M3 flows into the River Itchen, in Hampshire, which is home to salmon, brown trout, grayling and otters. A cluster of 24 outfalls surround the River Kennet chalk stream area and its tributaries near Reading. Official data shows the river system has high levels of heavy metals and hydrocarbons, which are associated with road runoff. Charlotte Hitchmough, the director of Action for the River Kennet, said: “The people responsible for highway drainage actively encourage the disposal of polluted rain water straight into the river, even rivers that have the highest levels of legal environmental protection. “Working with the Environment Agency we have measured runoff from the M4 motorway into the River Lambourn causing turbidity to increase 100 times … The riverbed is contaminated with a variety of polyaromatic hydrocarbons (PAHs) from oils and tar as well as heavy metals and microplastics, yet it has been impossible to get any action from National Highways.” Some PAHs are known to be carcinogenic and are classed as priority hazardous substances under the Water Framework Directive. “It’s an incredibly complicated cocktail of 300 or so chemicals,” said Joe Pecorelli, of the Zoological Society of London. “In the summer you get an accumulation of chemicals on the road surfaces … and when the rain comes, all that material – tyre wear, all the metals from brake pads – gets flushed directly into rivers … which causes the reduction of oxygen. In urban areas this is a perennial problem. Every summer we experience fish kills in those rivers where there are fish remaining.” Fish are not the only species under threat. Prof Andrew Johnson, from the Centre for Ecology and Hydrology, said persistent and bioaccumulative chemicals such as PAHs could reach the ocean, “in which case we start to worry about animals such as cetaceans [dolphins, porpoises and whales]”. However, he said the risk was hard to determine because the chemical loads were unknown. An Environment Agency spokesperson said outfalls and road drains were “not directly regulated by the Environment Agency but we do work with the government and partner organisations to reduce pollution from roads. This includes working closely with National Highways to influence their road investment strategy to include pollution mitigating schemes on their priority list of outfalls.” Stephen Elderkin, the director of environmental sustainability at National Highways, said: “We are committed to addressing all of our high-risk water outfalls by 2030 and our water quality plan 2030 sets out a high-level programme of work to achieve this … National Highways has also invested in a programme of research to understand the risk of pollution from microplastics in road runoff.” Under National Highways’ plan, four outfalls have confirmed funding for mitigation this year, and “17 outfalls and soakaways have been identified for potential delivery in 2024-25”. Dr Sue Young, the head of land use planning at the Wildlife Trusts, said it was “hugely concerning that National Highways doesn’t actually know the scale of the problem, and despite having identified over a thousand potentially polluting outfalls, it is mitigating just four of these this year. It’s hard to see, with this snail’s pace of action, how they will resolve this toxic issue by 2030. “Nature is in crisis now, with one in seven species in the UK at risk of extinction. We believe the next road investment strategy should allocate funding to act with greater ambition to stop this pollution now, rather than allowing most sites to continue putting this toxic mix into our most vulnerable rivers and streams until almost the end of the decade.”