Department of Anthropology, Yale University, New Haven, Connecticut, United States of America.
Department of Anthropology, University of Connecticut, Storrs, Connecticut, United States of America.
PLoS One. 2022 Apr 7;17(4):e0266362. doi: 10.1371/journal.pone.0266362. eCollection 2022.
Investigations of organic lithic micro-residues have, over the last decade, shifted from entirely morphological observations using visible-light microscopy to compositional ones using scanning electron microscopy and Fourier-transform infrared microspectroscopy, providing a seemingly objective chemical basis for residue identifications. Contamination, though, remains a problem that can affect these results. Modern contaminants, accumulated during the post-excavation lives of artifacts, are pervasive, subtle, and even "invisible" (unlisted ingredients in common lab products). Ancient contamination is a second issue. The aim of residue analysis is to recognize residues related to use, but other types of residues can also accumulate on artifacts. Caves are subject to various taphonomic forces and organic inputs, and use-related residues can degrade into secondary compounds. This organic "background noise" must be taken into consideration. Here we show that residue contamination is more pervasive than is often appreciated, as revealed by our studies of Middle Palaeolithic artifacts from two sites: Lusakert Cave 1 in Armenia and Crvena Stijena in Montenegro. First, we explain how artifacts from Lusakert Cave 1, despite being handled following specialized protocols, were tainted by a modern-day contaminant from an unanticipated source: a release agent used inside the zip-top bags that are ubiquitous in the field and lab. Second, we document that, when non-artifact "controls" are studied alongside artifacts from Crvena Stijena, comparisons reveal that organic residues are adhered to both, indicating that they are prevalent throughout the sediments and not necessarily related to use. We provide suggestions for reducing contamination and increasing the reliability of residue studies. Ultimately, we propose that archaeologists working in the field of residue studies must start with the null hypothesis that miniscule organic residues reflect contamination, either ancient or modern, and systematically proceed to rule out all possible contaminants before interpreting them as evidence of an artifact's use in the distant past.
过去十年间，对有机石器微残留物的研究已从完全依赖可见光显微镜的形态学观察，转向使用扫描电子显微镜和傅里叶变换红外显微镜光谱学的组成观察，为残留物识别提供了看似客观的化学基础。然而，污染仍然是一个问题，可能会影响这些结果。现代污染物是在人工制品的挖掘后生活中积累的，它们普遍存在、微妙，甚至是“无形的”（常见实验室产品中未列出的成分）。古代污染是第二个问题。残留物分析的目的是识别与使用相关的残留物，但其他类型的残留物也可能在人工制品上积累。洞穴受到各种埋藏因素和有机物质的影响，与使用相关的残留物可能会降解为次生化合物。这种有机“背景噪音”必须加以考虑。在这里，我们通过对来自两个遗址的中石器时代人工制品的研究表明，残留物污染比人们通常认为的更为普遍：亚美尼亚的 Lusakert 洞穴 1 和黑山的 Crvena Stijena。首先，我们解释了 Lusakert 洞穴 1 的人工制品，尽管是按照专门的协议进行处理的，但还是受到了一种来自意想不到来源的现代污染物的污染：一种在野外和实验室中无处不在的拉链袋内使用的脱模剂。其次，我们记录了在对非人工制品“对照物”进行研究的同时，对来自 Crvena Stijena 的人工制品进行研究，比较结果表明，有机残留物附着在两者上，这表明它们普遍存在于沉积物中，不一定与使用有关。我们提供了减少污染和提高残留物研究可靠性的建议。最终，我们建议在残留物研究领域工作的考古学家必须从微小的有机残留物反映污染的零假设开始，无论是古代的还是现代的，并系统地排除所有可能的污染物，然后才能将其解释为人工制品在遥远过去使用的证据。
