Definitely! There are some really nasty persistent herbicides out there - take clippings from the guy with all the dandelions, not the one with the "picture perfect" golf course lawn!

I'd check with the local/state regulations on which chemicals are allowed/disallowed. There are only a handful of very persistent herbicides and in my area these are banned from homeowner use. Thermophilic composting degrades the common ones pretty well so I don't sweat it. YMMV

Lloyd

At least, ask them what they are using. The active ingredients, not the brand names.

Even if they're banned from homeowner use, couldn't a lawn service still use them? I'd worry about it.

You know what heats up a compost pile really well? Coffee chaff. Just put a garbage bag full in my cubic yard of fall leaves that had been sitting there all winter, within days it was steaming and it has noticeably shrunk. We got a lot of rain this weekend so I have to go turn it (even though it was mostly covered), will let you know how the inside was. I have to get a compost thermometer - my automotive A/C thermometer I use for soil testing is too short.

Here is a link that might be useful: NCSU link on persistent herbicides

Another link - 2011, Imprelis by Scott/Dupont being marketed for home use, seems to be just as persistent as the ag herbicides.

Here is a link that might be useful: Biocycle article

I think there is now a legal requirement that herbicides and pesticides must break down after they are applied. So, chemicals such as DDT are no longer allowed.

The process is called mineralization. Usually it is measured at the site of application; if it is applied to a lawn, the persistence of the chemical is measured in the soil where it was applied. The process of breaking down the chemicals is typically via bacteria, so the presence of organic material that is decomposing affects the rate of decomposition of the chemical.

Composting will, of course, speed the breakdown of these sorts of chemicals. My compost takes about two years to complete.

So it becomes a judgement call. If you are comfortable knowing that lawn chemicals are designed to break down via bacteria, then you might be ok with other people's grass clippings if you compost it for a couple of years.

Obviously, if you use lawn chemicals on your own lawn, you will know when they were last applied. You might want to dispose of the grass clippings right after a chemical application.

I googled and found this link. Somewhat reassuring to hear that Diazinon breaks down more quickly in compost.

Here is a link that might be useful: Study of the minerization of Diazinon

Worried, no; be aware of what is going on, yes.

idaho, thanks for the link.

If the grass is sprayed by a commercial "lawn care" company then, probably, some of the most persistant plant poisons will be applied because those need to be applied by Licensed Pesticide Applicators. Those persistant plant poisons are not available to Joe Homeowner, unless she/he attends that 4 hour class and pays the fee to obtain that license.
Many of the plant poisons that are available to Joe Homeowner are fairly persistant in the environment, but will not cause immediate problems although the use of them is poisoning the water our grandchildren will drinking. Be concerned about those grass clippings only if you care about the world you are leaving your grandchildren.