Do seagulls get poisoned when eating garbage at landfills?

haven't seen it yet, but they do eat cardboard (fries container), i tried feeding them the portions with ketchup on it first, and then when i ran out of the ketchup portions, i tried tossing the rest ripped to small pieces and they ate it all.

kind of make sense since cardboard is wood/plant based.

And I have seen lots of them at the garbage dump eating.

I was told that they eat carpet too, (but don't know for sure, haven't seen it).