I imagine that there might be slight contamination from the oil in the exhaust from taxiing and take-offs. I have no idea how much of an oil film the syn/bean oil would leave, but I suspect that it would be negligible.

Just nitpicking. I plan to approach the admins of Walker County Public Lake (a county-owned "fishing" lake) to gain permission to float-fly on the lake, so I've been looking a all aspects in detail. I imagine that their concerns might be that I could annoy fishermen or contaminate the lake.