This opinion article basically states that its perfectly safe.You Californias are crazy. Everything is bad except styrofoam in the soil,
Is It Safe to Use Styrofoam in Planters for Vegetables?. Container gardening lets gardeners grow vegetables in small spaces like balconies and patios. It also gives gardeners the flexibility to move the containers depending on the weather, such as sliding them under an overhang during a...homeguides.sfgate.com
But again it's a opinion piece so taken with a grain of salt imo
I'm genuinely interested if @farmingfisherman has anything specific grow chemical wise that would cause such a large breakdown of styrofoam that it would be leeched up by the plant.