If I had to guess one of the possible causes you listed, I would say the lawn chemicals. You could probably do a search on the internet and get more information, but I just recently read in Prevention mag that methoxychlor (got that straight out of the magazine), a pesticide that until recently, was widely used and considered safe, has been banned. Lawn chemicals are amongst the most harmful agents in use today. That little sign that says a lawn has just been chemically treated and no one should walk on it for at least 24 hours? kinda scary. I'm not trying to say lawn chemicals cause cancer, I have absolutely no idea. You did say you worked with them for years, though.
I was diagnosed with CML in 1991. I had worked for 4 years around Benzine. back in the early 90's the prognosis wasnt to good. i was given a survival rate of 3to 5 years. Still doing hanging in there!!!