Answer to Question #1952 Submitted to "Ask the Experts"

Q

I do a lot of rockhounding in the Moab Utah and Canyon Lands National Park. I have found many beds of petrified wood and have taken small samples home. I am told that the "pet wood" is very radioactive and can cause harm to my person. Some of the petrified wood I have found is around or near old uranium mines. I can find no information on this issue.

A

It is not unusual for fossils to contain elevated levels of uranium and its associated decay products. This is particularly true for those parts of the country rich in uranium deposits (for example, the Morrison formation). Uranium from the ore will dissolve in the local groundwater and when the latter comes into contact with porous organic material, such as a buried tree trunk or dinosaur bone, the uranium precipitates (the precise chemistry is not something I have information about). Over time, the replacement of the organic material by uranium can become substantial. During the uranium fever of the 1950s, a prospector could make a considerable amount of money from the uranium content in a single petrified tree, and radiation detectors have proven very effective by paleontologists hunting dinosaur remains. The radiation exposure rates associated with these fossils can be high enough (several milliroentgen per hour) that some museums segregate their more radioactive material. However, the small specimens you are probably handling are unlikely to contain sufficient uranium for them to be any cause for concern. While no one has been harmed by handling such fossils, at least to my knowledge, it would still be good practice to wash after handling the material. Just practice good housekeeping. If you are still concerned, you could purchase an inexpensive Geiger Mueller detector. At least then you would have an idea as to the relative activity of your various specimens. To put this in perspective, the real risks associated with your hobby are more likely to be car accidents, trips, falls, snake bites, etc., than any exposure to radiation. And when your remains are laid to rest in a marble orchard, your bones will begin accumulating uranium.

Paul Frame, CHP, PhD