This past weekend, we went camping, using some boards removed from our house for firewood. In the morning campfire, I noticed that the boards were turning yellow after being burned, and the smoke was covering the other firewood with a yellow coating. Does this indicate the presence of lead (or of something else?)?

P.S. We all inhaled a lot of that smoke the night before. (The kids are 6, 8 and 14.)

Any thoughts?