As the saying goes, "The solution to pollution is dilution." A way to find out is to look and see what amount is used to treat the wood then you might be able to find out what amount is leached out over time.

Personally? I would use them and not give it a 2nd thought.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).