Hot Dung: How Well Do Traces of Animal Dung Survive Fire?
A New Study Puts Fecal Biomarkers to the Test
For thousands of years, animal dung has been widely used as a fuel source in many parts of the world due to its availability and long-burning properties, especially in arid and semi-arid regions where firewood is scarce. Even today, dung serves as a free and easy to use alternative fuel source for over 2 billion people, particularly in low-income households and areas with limited access to other types of fuel.
Archaeologist studying ancient settlements often search for traces of burned dung to reconstruct past human activity. One key chemical marker for burned dung is bile acids, compounds produced exclusively by vertebrates that have been used for identifying which animals were present at a site. But how well do these biomarkers withstand exposure to intense heat and fire?
A new study led by researchers at the Max Planck Institute of Geoanthropology aimed to answer these questions. The team burned modern cattle dung under controlled laboratory conditions at varying temperatures and in open-air fire pits. They then extracted and analyzed the bile acids using high-performance liquid chromatography and mass spectrometry.
Their findings show a dramatic degradation of bile acids when exposed to fire, with higher temperatures leading to greater degradation, making species identification from burned remains unreliable. Although some bile acids persisted after burning, their unpredictable concentration changes could lead to wrong identification of species. Nonetheless, the researchers note that bile acids remain a reliable indicator of dung-burning practices.
For archaeologists, this is a valuable insight. By understanding how bile acids break down under heat, researchers can now improve how they interpret burned samples and refine their methods for detecting past human and animal activity. By combining this newly gained understanding with other archaeological methods – such as plant remains analysis – researchers can paint a clearer picture of ancient fuel use, seasonal site occupations, and environmental conditions in past societies.
The team’s next step is to investigate how vegetation types, diet and environmental conditions such as elevation and rainfall affect bile acid abundance and composition across various geographic regions. Through this research, the team aims to investigate whether bile acids can serve as reliable biomarkers for identifying the presence of specific animal species.
