There is plenty of information around on the residual rate of DDT in soil and water, if people are interested I'm sure they can look it up themselves, I would again advise to use other media besides the internet, to research from.
And no, there is no causal effect between polio and DDT, IMO, although, as I said, there is enough correlation for further research to be done.
However, the information that has been posted here, and that I have researched for myself, does not add up. Until further information is available, there is no causal link IMO.
People can do their own research and make their own conclusions.