Wood is longer treated with chromated copper chromium arsenate. It's now treated with a copper based preservative without the arsenic (some of the new preservatives actually contain polyquat or something very like it). If it's pitched away from the pool as it should be, I would think a minimal amount of the preservative could be leached into the pool water.

If you regularly treated it with a water repellent sealer that would probably further minimize the leaching.