The housing development at Baiter ( near Poole Quay ) was built on the site of the old Poole Gas works. They " decontaminated " the site prior to development but you're still not allowed / warned against growing veg in the gardens.
They do seem to be able to decontaminate some sites
The place where my wife first worked - known locally as "The BI" made cables
apparently they made the longest cables in the World
but when it closed the land was contaminated - with copper I think
so it wsa said that the land could only be used to commercial purposes
but there are now houses on a part of it but apparently when they were sold there was something about not growing certain things
which I am sure will be passed onto future buyers 20-50 years down the line!!!
(Liverpool also had the factory that used to make the longest ropes in the "World" - Ropeworks down in the docks area
so now you all know something you might not have previously known
you can thank me later!!)