Even "garden soil" and mulch brought in from elsewhere can bring pesticides with it. Kind of a crap shoot out there if it isn't your own organics or someone you know you can trust.
Paul, I he mentioned that the plants were exhibiting a bit of the curl prior to transplanting...which doesn't necessarily rule out pesticides, but makes me wonder. Possibly during hardening off they may have got some pesticide drift while outside. Dunno.
greendream, did you use bought or saved seeds? What was your germinating medium?