I would say it is not likely to be cedar based on a couple points as well as state that it does look truly dry so that all the harmful items should be gone. Location ? I don't think of cedar as being too common in that area but more likely other species. One way to check totally dry is to cut an end off to look for uniform color from outer to inner layers. Wood dry outer to inner so uniform says it is all dry. But then sometimes we don't want to deform a really nice shape so we can go to other thoughts. If the wood is lighter, for it's size, than other wood of the same size, it says dry.
Another big point is how your water is made up. Water with low buffering, will be more prone to changes than hard alkaline water with high buffering qualities. Basic definition of buffering is that it resists change so more buffering lets you get away with more things than soft acidic water with little buffering. General "look and the rounded end in the forth picture looks like it did spend quite a lot of time bouncing around in the water to rub that end round, so I would go with that item without any worry in any water.
But if one were totally wrong, I would expect it to only be a problem with coloring the water like tea, not a real problem for killing fish, etc. as those are not very common. I have hard water and often use old, totally dry cedar.