Plastics in ponds

My new house has a pond, and I have been put a few fish in, and bought
a range of plants to help the pond balance.

Unfortunately the pond is a rectangle, and about a meter deep across
the entire pond. I recently added a plastic shelf unit into my pond,
in order to put some marginals in. I assumed plastic would pose no
problem, and the pond plant containers themselves are plastic. Since
putting the shelf unit in, I have noticed a shiny film on top of the
pond. I am concerned the plastic is leaknig some chemicals into the
pond and will kill the fish.

I'm after some advice on if the plastic is likely to be the problem,
and if it will stop leaking the chemicals. I have a pump and filter
with uv, but not sure is this will clear up the problem with any great
speed. Is there anything I can add to the pond to break down the
greasy film?