On the elimination of extraneous DNA in fossil human teeth with hypochlorite

Elimination of extraneous DNA in fossil specimens is of paramount importance for the successful isolation and analysis of authentic DNA; this is especially true when the specimens are of human origin. Bones and teeth are commonly decontaminated with bleach containing the powerful oxidising hypochlorite ion. The procedures involve either submersion in or wiping with the chlorine agent. Using the radioactive isotope Cl³⁶ we showed that submersion of fossil teeth in solutions of small ions such as Cl⁻ or hypochlorite, ClO⁻, cause that they migrate right into the pulp. This may lead to the unwanted destruction of authentic DNA. However, using pairs of teeth from the remains of four ancient Europeans (1000–2000 YBP) as well as tooth and hair from an Inuit skull (>300 YBP) we provide evidence that at least some endogenous human fossil DNA survives in powdered pulp/dentin that has been submersed in 2% hypochlorite. Further, we show that powdered pulp/dentin deliberately contaminated with huge amounts of a 414 bp PCR product is effectively decontaminated by suspension in 2% hypochlorite for 5 min. Decontamination of fossil material from teeth may therefore be accomplished by a short direct action of hypochlorite on the powdered specimen rather than less controllable and less efficient external treatments of the whole specimen.