In vitro dermal penetration availability of heavy metals in healing earth

摘要

Healing earth (syn. medicinal clay), a fine powder which is obtained from glacial loess deposits, is often topically applied for supportive treatment of acne skin. Being of geogenic origin, healing earth naturally contains toxic heavy metals such as Pb, Cd, As, Ni, Co and V. Healing earth therefore represents a possible source of exposure to heavy metals [1], making a health risk assessment necessary. However, risk evaluation on the basis of total heavy metal contents will significantly overstate the amount of metal Compounds ready for percutaneous absorption, thus overestimating the dermal exposure. In fact, only the bioaccessible fraction of heavy metals in healing earth should be considered for risk assessment purposes, i.e. that fraction being mobilized from the clay by the sweat surface film of the skin. This fraction therefore represents the maximum amount of heavy metals potentially avail-able for percutaneous absorption through the natural bar-rier of the skin [2-4].