I have been cruising the neighborhood collecting conveniently bagged organic matter to add to my compost pile, do I need to be concerned as to whether my neighbors debris comes from synthetic yards? Thanks in advance for the advise.

Not really. If you dump it all into your compost pile it should be okay.

Dave's right - but let me add that you need to make sure it gets hot. That helps to eliminate most of the toxins you might have picked up. I'm a "curb shopper" too. But I usually know the neighbors I get the material from and most of them are light on the pesticides, at least.
Kathe