Set it up without the ducklings in it, and just give it a sniff. If the plastic is affected, I would think there would be a plastic odor.
If you have a puppy playpen, or a pak-n-play, those can be adapted as brooders. The puppy playpen needs plastic poultry fence or something to keep the littles from just walking through the 2 inch wide spaces till they get a little older.
I used a large Rubbermaid bin the first two weeks - till the Runners outgrew it - and used 16 gauge metal hardware cloth across the top to keep the cats out and suspend the ceramic heat lamps.
I always tried new things out cautiously - either a dry run without the ducklings, or watching closely for half an hour after I changed something. Because the weirdest things can happen with ducklings.