John Browne, a lawyer specialising successful concern illness claims astatine Slater and Gordon, said cases involving humanities contamination were hard to analyse - but not impossible.
"Time passing makes cases much hard to prove," helium said.
"Witnesses' memories slice and locating [eye]witnesses becomes progressively challenging and difficult."
However, helium said scientific, aesculapian and forensic grounds could assistance found what happened and whether vulnerability to hazardous substances contributed to illness.
The cardinal question is not simply what the instrumentality was astatine the time, but what was known astir the risks, helium said, adding: "Communities affected by contamination merit transparency and wide answers."
Public Health Wales said its Welsh crab quality and surveillance portion had collected and analysed "every azygous lawsuit of cancer" since the 1970s.
It added: "Based connected the grounds presently available, determination is nary denotation that humanities biology contamination is liable for an accrued hazard of cancer, oregon immoderate different illness oregon illness, successful these areas."
Natural Resources Wales said the Environment Agency, its predecessor, investigated the acerb tar water successful 2006 and 2008 but tests concluded it did not conscionable the ineligible explanation of contaminated land.
"Therefore, work for the tract returned and remains with Wrexham County Council arsenic regulator."
Wrexham assembly said, since these investigations 20 years ago, ongoing monitoring had not identified immoderate important changes and determination was nary statutory request for remediation.
The Welsh authorities said addressing contaminated onshore was 1 of its cardinal priorities.
"A survey of section authorities carried retired by Natural Resources Wales successful 2015 identified much than 9,000 imaginable sites requiring further investigation.
"While not each of these sites volition airs a hazard to quality wellness oregon the environment, this fig demonstrates the standard of the contented facing regulators successful Wales.
"We present mean to make a Wales-wide strategy to progressively reconstruct post-industrial land, truthful that communities are nary longer exposed to imaginable risks."
The UK authorities referred the BBC to the Welsh authorities erstwhile asked to comment.
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