Hi Ilan, If your father is suffering from PD as a direct result of exposure to an environmental toxin, it would be very worthwhile for him to go on an internal cleansing program using herbs, nutritional therapy and a special diet to get that stuff out of his system. His symptoms will stabalize and most likely improve. He will most likely get better responses to Sinemet as the very least. Check out a Naturopathic Doctor or similar health care person. I have done this myself with very good results.