A new BBC programme has discovered that one in 10 of Britain's train carriages dispose toilet waste straight onto railway tracks.
BBC Inside Out sees presenter Mary Rhodes go across the West Midlands to discover the extent of the problem.
The show asked Dr Martin Cox from Coventry University to test random samples from train tracks for analysis, and findings revealed there could be potential to the public and railway worker because of the practice.
It is thought the problem is mainly with older carriages, and, according to the BBC, Ken Usher, from the Rail Maritime and Transport Union (RMT), said more investment was needed to upgrade the coaches.
During the show, Mary Rhodes meets with great-grandmother Susan Leigh, 64, who says human waste from trains routinely splatters into her garden in Shotton, north Wales.
Speaking to the Daily Mail back in February 2014, she said: "I had a new bedding set and I put it on the line - when I came out it was covered everywhere.
"I had to go out with a scarf around my face and plastic bags around my feet and bin the whole lot."
She has now banned her children from playing in the garden because she thinks it's too dangerous.
Arrival Trains Wales told the paper the carriages are old and do not have toilet retention tanks. So the waste is dumped on the railway tracks.
The Rail Delivery Group, which represents Britain's train operating companies, told Inside Out the industry is investing millions of pounds on new trains with sealed toilet tanks, and that they are retro-fitting some older trains.
Inside Out is broadcast on BBC One West Midlands at 7.30pm on Monday, 12 January and nationwide on the iPlayer for 30 days after.