Itโs probably plasticisers and other VOCs coming out of the freshly made plastic. Something with degreasing ability will get the surface stuff off (like a kitchen spray, dish soap, windex, etc) but since the smells are embedded in the plastic itself, it may take some time for the smell to dissipate completely. Leave out side to air out for a week.
Test it first, some chemical cleaners can be too strong and โmeltโ plastic. (Not melt but will etch it or make it sticky). However cleaning agents can only ever remove the surface smells. Depending on the type of plastic (ie the ingredients the plastic is made of) it may smell for a shorter/longer time as the smells slowly dissipate. Some plastics can smell years later, some are fairly inert smelling after a few days.
Put them in plastic bags and pop them in the freezer for 48 hours. The cold should kill any bacteria that cause the odours. I used to do this with my boxing gloves and worked quite well.
Generally storage boxes (I'm assuming we're talking about those) are made from thermosetting plastics that should not deform under heat. Don't use boiling water, just hot from the tap and it should be okay. Unless you want to get extra scientific and check the plastic composition.