Personally I used to be a chemist working in food migration and I'd stay well away from styrofoam in your garden, but don't take my word for it.

See the txt below from David M Bryant Ph D, University of New Hampshire, Environmental Education Program

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>>I've read this thread with some consternation as a soil scientist.
>>>I know this may sound like recycling of styrofoam but it's really
>>>putting xenobiotics (highly recalcitrant synthetics) into the
>>>soil. I'm not really sure if it would meet your other goal
>>>either. While quantitatively decreasing soil bulk density, as
>>>does soil organic matter (SOM) I doubt that it provides any of the
>>>other benefits of SOM. Styrofoam is a closed cell material, so
>>>even with a high surface area (internally and externally) I doubt
>>>that soil solution or nutrients can interact with these surfaces
>>>to provide cation/anion exchange or enhance soil aeration as the
>>>cells are generally filled with a synthetic gas (previously these
>>>were CFCs).
>>>
>>>Also, there is increasing evidence that plastics release synthetic
>>>compounds, the effects of some are known others unknown.
>>>Moreover, organic chemistry of the SOM and plastics degradation
>>>are not well understood.
>>>
>>>If you have any data or literature on these questions I would be
>>>very interested. In lieu of any evidence of benefits/hazards I
>>>would strongly advise against the practice.
>>>
>>>David
>>>
>>>David M Bryant Ph D
>>>University of New Hampshire
>>>Environmental Education Program
>>>Durham, NH 03824

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