"Trace Amount" Studies/Research

Hey there - Can you provide links to any studies supporting the statements that trace amounts of Iodine or Cesium aren't linked to health risks/birth defects?

The only study I've seen on low level radiation/fallout was regarding children in Sweden in utero at time of Chernobyl, and there were measurable effects despite the low dose rate experienced in that country.

It seems that there's actually very little known about the effects of low level fallout exposure...

Thanks