Radiological half-life vs. biological half-life

Can someone explain the difference between radiological and biological
half life?

In another thread discussion xenon, bandstra fromt the BRAWM team said:

http://www.nuc.berkeley.edu/node/2607#comment-2344

"Other elements, such as iodine and cesium, are more chemically active and have very long biological half-lives. Iodine-131 has a biological half-life of 138 days, which is much longer than its radiological half-life of 8 days. So its effective half-life in the body is approximately 8 days -- i.e., essentially all of its radiation is deposited inside the body. Cesium-137 has a biological half-life of 110 days, which is much shorter than its radiological half-life of 30 years, so its effective half-life in the body is 109 days"

A few questions about the above statement:

1. What is the difference between radiological and biological half life?

2. What does "essentially all of its radiation is deposited inside the body" mean?

3. Why would Iodine-131 have a biological half life (138 days) longer than
it's radiological half life (8 days), but Cesium-137 have a biological
half-life (110 days) that is shorter than it's radiological half life (30
years)?