Think before you panic.

Are the chemicals left in the timber soluble in water? I can enviseage a
system whereby a double application of chemicals results in a non-soluble
precipitate being left in the timber.

If they are water soluble, what is probability of more moisture passing from
the timber to the soil in the raised bed rather than from that soil to the
timber?

It would seem to me that more moisture will pass from the soil to the timber
if only because one waters the soil more than the timber.

Ergo, what is the fuss about?

Is it about poisoning gardeners or the environment?

I'm against both but am not going to worry about what I think is a
microscopic risk of being poisoned from the lettuce, leeks, peppers and
asparagus in three of my raised beds.

If anybody is worried about the risk, consider painting the inside of the
timber with bitumastic paint as wold be done on decorative brickwork raised
beds to prevent leaching of salt to the outside of the bricks.

It's very easy to create panic!

Ron