We've been through this dilema, all the reseach I've read studies high voltage ones, IIRC 11K volts upwards - the big pylons, not the smaller local distribution.
The theroy is that the EM energy from the very high voltage charges pollution particals, making them more reative, these settle on your skin at night and can cause pre-cancerous changes.
So risk decreases with distance, and up-wind is far safer than downwind.
Pretty much anything can cause pre-cancerous changes, and the link is not massively compelling, but it does explain why workers on powerlines don't have higher instances than people who live close.
The trees will help sheild against the particals if you believe this theory, as will the distance, 1000 foot is quite a lot. I'm going out now, but if you want more info PM me and I'll see if I can find the studies - or actually ask the Mrs where she found them
You know all those pictures of Adam and Eve where they have belly button? Think about it..................... take as long as you need........................