For the most part, concrete in the U.S. is radon free, or nearly so. There are several negative health effects attributed to working with wet concrete that are mainly due to the cement. The most common problem is due to the fact that the cement can dry out your skin and cause it to crack. It does this mainly by removing the protective oils, but can also clog the pores of the skin. A far more serious problem, although fairly rare, involves burning of the skin.
Cement contains calcium hydroxide, a very corrosive compound.
In some people it has caused serious skin burns like those caused by lye. Consider the following example that was printed in the Journal of the American Medical Association. A construction worker had wet concrete spill over the tops of his boots while pouring a foundation. After about 45 minutes, he noticed a burning sensation on his ankles. Despite washing his legs and applying a cream, he went to the emergency room the next day with very painful burns on both ankles.