Chemical laden grass clippings safe for compost??

I'm a landscaper and so I've always got tons grass clippings to get rid of. I'd say half of the yards I mow are treated (mistreated) by companies like trugreen, Turf masters, top Turf, and etc. I don't know what all they're treated with. Sometimes they spray and sometimes it's pellets. Every company just about does 7 treatments per year per yard. I'd imagine at least half of those treatments are fertilizer, and one or two treatments of pre and post emergent herbicides. Currently I  pay money to dispose of at dump. But how long do you suppose they'd have to compost for to be chemical free? Think it'd be safe compost to use in food forest after a year or two?

When I adopt a new field that has been treated with mega-ag chemicals, it's not until about the 4th growing season that things start growing normally.

One field for example had a spot where hay was dropped for the horses. Even the weeds didn't grow well in the location until the 4th year.

Are these fields that were previously farmed?