Gravel Exposed To Rainwater - Safe?

It should be OK with a good wash. It is likely to have dirt, dead leaves, dead petals etc that have been blown into it, and just possibly some sort of creature in there if there's water in the container. We use large plant pot saucers as bird baths and they get insect larvae in them, for example.
But a thorough wash should remove all those.

Thanks both. I did think it'd be fine but really do take every precaution now.
Cheers