Once they enter the body, heavy metals are difficult to expel. The half life of lead in the bones, for instance, is estimated to be more than 20 years. Long-term accumulation must not be ignored.
重金屬進入體內後，不易排除，例如鉛在骨中之半衰期，據估計在廿年以上，其長期累積性不容忽視。