I remember being told by many people that burning plastic fumes are dangerous or poisonous. I have also heard it depends on the type of plastic.
Before i took on my new job i was a bit worried considering i knew i was PG when i first took it. When reading my contract i read that i will have maternity leave after 12 months (no use to me, but it still kinda indicated that they wont sack me) and then i read in a section that they can not and will not fire me if i am pregnant. You should have a copy of your contract, if you signed one?? But yea, if your permanant/full time they cannot sack you for being pregnant.
Heavy lifting...i wouldnt know how heavy 'heavy' lifting is considered...but i know just picking up 24 packs of 390ml coke bottles i can feel a tad bit of a strain, but thats just me... so Id ask your doc about that one.