Asbestos has been found in gardens on the site of a former textile mill in a West Yorkshire village.
Tests have shown that four out of 11 gardens on Forest Bank and Springfield Avenue in Gildersome, near Leeds, have the problem.
Soil from the streets' remaining 49 gardens will now be tested. The Environment Agency has given Leeds City Council £50,000 to carry out the work.
The Health Protection Agency said the risk to residents was low.
The houses were built on the site of the former Springfield Mill in the 1970s and 1980s.
Max Rathmell, the council's contaminated land manager, said: "Until we have more information we can only have two theories.
"One is that it was part of the mill itself, because many textile mills did actually weave asbestos into various fabrics that they produced.
"The second sources would be that potentially it was introduced on to the site in topsoil and subsoil that was brought in to make the gardens."
Residents on the two streets have been sent letters informing them of the find and the planned soil sampling work.
Annette Armitage, who has lived in Forest Bank for 18 months, said the letter was very worrying.
She said she was concerned as her young granddaughter often played in the garden.
"It doesn't seem right really, just a letter," she said.
"You think somebody would come visit us to tell you, to come speak to you about it."
Dr Mike Gent, from the Health Protection Agency, said: "The risks appear at the moment to be low.
"Asbestos really affects people when you breathe it in and therefore if it's in the soil then there's less risk of people actually being exposed to this at all."