Figure 1. A South-American head now housed in Turin’s Museum of Anthropology and Ethnography: (a) The specimen (TSA nu 1); (b) 3D virtual reconstruction of the head showing the fracture of the right maxilla and of the right mandibular condyle. The fractures are not communicating with the oropharinx. By inference it is unlikely that blood from the injury would have entered the trachea and caused death by ‘drowning’. doi:10.1371/journal.pone.0002053.g001 Mummified hair showed irregular cracks easily identifiable on cross-section, not found in contemporaneous hair. On the surface of mummified hair various shaped accretions with numerous holes of different sizes and shapes were identifiable. These accretions and hair shafts were autofluorescent. We propose that these structures represent extra-cellular polymeric substances (EPS) also known as bio-films deposited on the surface of the hair by bacterial metabolism (Figs. 4 & 5). Electron microscopy of hair confirmed the presence of EPS in our specimen. In support of this interpretation we show an electron micrograph obtain from another mummy’s hair showing EPS with one bacterium still in place (Fig. 5). We further examined the hair by Inductively Coupled Plasma/ Mass Spectrometry (ICP/MS) after the usual thorough washing A South-American Head and cleaning to remove surface contaminants (using 0.2% Triton- X and then rinsed several times with double distilled water). ICP/MS showed a lead content of 8680 mcg/g (normal concentrations of lead in hair: 5–29 mcg/g), an arsenic concen- tration of 38 mcg/g (normal concentrations of arsenic in hair: 0.03–3 mcg/g hair) and mercury concentration of 6410 mcg/g (normal concentration of mercury 0.4–1.2 mcg/g hair) (Table 2). Discussion It is well accepted that life is found everywhere even in the most unlikely places such as acid fluids that can dissolve steel and at pressures and temperatures found in hospital autoclaves used to sterilize surgical instruments. These organisms are now known as ‘‘extremophiles’’, they are Archaea that are classed in the ‘‘third domain of life’’, they differ from bacteria, but like bacteria, are single celled; unlike bacteria, however, they are not known to cause disease. Archaea were discovered some 30 years ago and their number keeps on increasing with an accelerating pace of new discoveries [4]. Bacteria have also been found to thrive in places previously thought incompatible with ‘‘normal’’ metabolic processes. Metha- nogenes, for example, get energy from combining hydrogen and carbon dioxide to produce the greenhouse gas methane thought to contribute to global warming. The bacterium Ralstonia mettalidurans is resistant to metals that are highly toxic to other bacteria. It grows in the presence of millimolar concentrations of dissolved silver, cadmium, cobalt, lead, mercury nickel and chromium. This bacterium has also been found to precipitate gold from toxic gold chloride complexes and it continues to grow in AuCl42 after selection for resistance to this toxin [5]. The enormous levels of toxic elements we found in the hair are incompatible with life: they could not have been incorporated by human metabolism into the hair and, by inference, must have been deposited post-mortem. These very high levels also exclude acute poisoning because there would not have been enough time before death for the hair to grow sufficiently to incorporate the toxic elements; human hair grows at approximately 16 cm per year. We set out here to support our hypothesis that the high levels of toxic elements in the hair of our specimen were deposited by soil bacteria. By analogy, the mechanism for the concentration of toxic elements in the hair of our specimen is postulated to be akin to that adopted by Ralstonia mettalidurans concentrating gold complexes in gold mines to produce gold nuggets [5]. Our initial postulate that appropriate imaging of the hair would reveal bio-films secreted by the bacteria to protect themselves from the toxic surroundings was amply confirmed by confocal and electron microscopy. Hair is renewed throughout life; it has also a defined variability in growth. Each hair follicle cycles between three stages: growth, involution and rest. Human hair remains in the growth-stage for 2–8 years to produce long hair. Stable isotope ratios in tissues, including hair, depend on these ratios in food and water. And hair is an ideal material that can be used to study diets of ancient civilizations [6]. Thus stable isotope ratios along the length of hair contain a record of metabolic activity often spanning many years depending on the length of the hair [7]. The analysis of the hydrogen, carbon and nitrogen isotopes in our specimen support the contention that this young man lived in South America around the time of the Spanish conquest and survived on a diet consisting of mainly terrestrial food (C3 plants) with a small marine input. PLoS ONE | www.plosone.org 2 April 2008 | Volume 3 | Issue 4 | e2053