You could wash them in the bathtub or wash tub. ....
Beside the road - make sure there's nothing splashed on them or they were near any parked cars - try the parts behind & protected. I was happy to get these from my friend, as i know he doesn't use pesticides or anything. There are lots of wild grapevines around - maybe you will find some that are more protected, if you're uncertain.
I'd only bake them after you fashion them into a wreath - once dry they are fairly brittle. {I'm not so scientific at the moment about baking - I have the oven on around 250 for about an hour.}

Here's the one Sarah/Jerry gave me/Laker last year - that's small

It had seeds stuck to it & it hangs in Rio's cage.