Non-invasive image study of bone bioerosion in Spanish Civil War lime graves

Bacterial bioerosion is a key taphonomic process affecting bone remains in diverse environments. This study presents the anthropological and taphonomic study of two clandestine lime graves from the Spanish Civil War (1936-1939) with two individuals in each burial. These individuals were buried with lime, often used to make bodies disappear in clandestine graves. There is also a popular belief that lime prevents bacterial growth during decomposition and prevent infectious diseases, but we observed that lime does not cause bodies to disappear or mummified, but it dehydrates bone tissue and it did not inhibit the proliferation of microorganism (fungi and bacteria). We reinforced the use of non-invasive techniques in the histotaphonomic study of the ribs of these victims of the Spanish Civil War because not all the cross-sections prepared for SEM analysis consistently revealed microbial attack. However, the bioerosion could be observed along the entire ribs using microCT. Therefore, the shape, distribution and concentration areas of bioerosion were contrasted with both low-vacuum SEM and microCT images. The type and location of bioerosion observed in the ribs of these victims supports endogenous origin of bacteria, which modified bones despite the presence of lime. Bacterial bioerosion is, consequently, a key taphonomic process and potential invaluable forensic criterion of post mortem condition.