"For instance, the coatings used to make the containers durable for ocean transport also happen to contain a number of harmful chemicals, such as chromate, phosphorous, and lead-based paints. Moreover, wood floors that line the majority of shipping container buildings are infused with hazardous chemical pesticides like arsenic and chromium to keep pests away."
and
"Reusing Containers seems to be a low energy alternative, however, few people factor in the amount of energy required to make the box habitable. The entire structure needs to be sandblasted bare, floors need to be replaced, and openings need to be cut with a torch or fireman’s saw. The average container eventually produces nearly a thousand pounds of hazardous waste before it can be used as a structure."
"About 20 million consignments of all sizes containing radioactive materials are routinely transported worldwide annually on public roads, railways and ships."
http://www.world-nuclear.org/information-library/nuclear-fue...
Note that sprayed on closed cell insulation does little to nothing to mitigate many of the toxins which can be found in shipping containers including mercury - it just makes it poisonous for longer. To use them for a dwelling all wood needs to be removed and they need to be sand or water blasted down to bare metal.
I've been in shipping container buildings before (e.g. Frietag store in Zurich) - they are not really a great size. Many Mobile homes that are comfortable feature pop-out sides. Any plans for expanding them?
Some real positives - fireproof envelope, Envelope can be welded to, several formats available - including ones with side doors can be "racked" can be made airtight (allows you to specify air exchanges, rather than estimate them) portability with the right equipment.