Although actinium is primarily a beta-emitter, it should be classed as a hazardous radioactive poison of high specific alpha-activity along with radium and the trans-uranium elements plutonium, americium and curium.

In the human body, actinium has tendency to accumulate and to be tenaciously retained by the skeleton, in the superficial layers of the bone structure. The elimination rate of actinium from the body is much less than the rate of radioactive decay.