Why does mercury harm people? I know it's poison, but what makes it that way? Is it radioactive?

Its highly poisonous and that exposure to mercury should be avoided at all costs mercury fillings continueously omit mercury vapor in the filling we get from the dentist it is absorbed into the body in small amounts mercury exposture has been linked to serious medical problems ramging from mental confusion and fogginess to birth defects neurodegeneratives diseases autoimmune diseases and many other illnesses cognitive functions in particular are negatively affected by mercury exposure non-radioactive