**7. Concluding remarks**

To develop an environmentally sound resource circulation society, it will be essential to implement long-term safety management practices for hazardous substances. The necessity of isolation/sequestration schemes for hazardous heavy metals is described in this chapter in terms of the multi-barrier concept, in which engineering measures, such as pretreatment and solidification technologies, control of landfill conditions, isolation barriers, and geological and artificial barriers, are implemented to attenuate environmental risks. Single artificial engineering measures should always be viewed with skepticism, and multiple barriers are necessary to retard and attenuate the migration of hazardous heavy metals. The multi-barrier concept also considers the (bio) chemical transformation behavior of heavy metals and their effect on migration. A further innovation of measures to isolate/sequester heavy metals may lead to higher levels of safety and more environmentally sound resource circulation.
