Air pollution which plagues the UK threatens the human rights of children, a United Nations expert has warned.
There is an urgent need for the Government to protect children and other at-risk groups from the air pollution "crisis" which causes serious health problems, special rapporteur on hazardous substances and wastes Baskut Tuncak says.
At the end of a visit to the UK at the invitation of the Government, Mr Tuncak also warned that Brexit could put human rights, including the protection from toxic pollution, at risk.
"The forthcoming plan for Brexit should ensure that it does not open a Pandora's Box, freeing the way for deregulation and posing a threat of regression from existing standards of protection," he said.
Despite Government assurances it would maintain current European Union standards on human rights and environmental protections through the Great Repeal Act, the UN expert said he did not find evidence they would be kept in place.
"I was told of a political commitment to maintain standards of environmental and public health protections but nothing in the prime minister's speeches which I heard and saw gave any such indication.
"I was pointed to statements I couldn't find, I was pointed to political commitments that weren't clearly explained."
The UK's pivot towards the US, which does not recognise the same rights, also raises concerns.
Mr Tuncak's visit coincided with record levels of air pollution in London and he warned that paediatricians have described the impact of air pollutants on children's health as a "silent pandemic".
He said: "Children don't only suffer from disabilities and diseases during childhood that may be linked to air pollution, these disabilities and diseases extend into adulthood."
Children, along with other groups such as the elderly and the ill, are particularly vulnerable to the impacts of pollution, which is responsible for 30,000 to 40,000 premature deaths a year in the UK.
But the UN Convention on the Rights of the Child recognises their right to "the highest attainable standard of health", while the UK also has obligations towards other at-risk groups.
The Government has repeatedly been taken to court over its failure to meet EU standards on air pollution and has admitted it might not meet the rules in London and some other cities until 2025, well after Brexit.
"I encourage the UK government to fulfil its human rights obligations on air pollution, protecting the rights of children, women of reproductive age, the elderly and those of poor health who are especially vulnerable to toxic chemicals in developing a new plan to tackle its air pollution crisis," Mr Tuncak said.
Mr Tuncak also said communities fighting fracking had struggled to get information about what was going on in their areas and struggled to access justice because they could not get legal aid or faced other challenges.
He called for stronger measures to ensure they were informed and had "meaningful" opportunities to take part in decisions being made.
Austerity has meant local authorities do not have the resources to monitor and enforce environmental protections, there is a lack of cooperation between levels of government and agencies and Brexit risks further strains on already stretched budgets.
He pointed to local people fighting an open cast mine in Merthyr Tydfil, amid concerns of air pollution, legal loopholes which mean some people are living yards from the fence of the operation and claims of local asthma and cancer clusters.
He said the Welsh Government had put responsibility for investigating the mine's impact on to the company involved and other levels of government.
Mr Tuncak will present his full report to the UN Human Rights Council in September.