Scotts weed n feed has two herbacides, 2-4-d and Mecoprop-p. Both are moderately toxic and have relatively short duration, though traces may be found in the soil months later under certain conditions. Both have the potential to leech out of the soil with heavy or repetitive rains (or heavy
irrigation), but 2-4-d more so. In most situations, very little , if any, will be persisting in the top couple inches of soil the following season. I personally have no
experience with these chemicals, and my information came from a pesticide
course I took a few years back. Funny thing, my instructor was anti-herbacides but presented some rather straight forward, seemingly unbiased information.
Both Oregon State and Cornell host Extoxnet information. If you google "Extoxnet", they
should come up. Extoxnet is a good source of info about ag chemicals. Dry reading, but good basic scientific info.
How would I feel about using your grass clippings? Assuming that you mowed your grass several times last year, have had at least 30"-40" of rain or irrigation, and won't be applying anything this spring, I would feel comfortable using the grass clippings in an active compost pile. On my farm, any of my own compost piles that might contain contaminants (for example, I added garbage or orchard waste given to me my friends), I normally inoculate with fungal spore once the pile has cooled. Then I let the fungus work for a couple months before using that compost. Therefore in your scenario, I'd make the compost this spring or early summer, let it sit over the summer, and in the fall till it lightly into the soil just before seeding my winter cover crop. When I lived in NJ, I used to use winter rye as a cover crop. ......That's just one option on what to do with it.