UrbNet discovers unexpected hot spot for heavy-metal contamination in ancient city

10. June 2021

The ancient city of Gerasa in Jordan turns how to be a hot spot for heavy metal contamination even though the usual reasons for pollution in ancient times, such as lead water pipes and mines, have not been documented in the area. This means that other factors play a bigger part in the contamination than previously thought. The results come from analyses of soil and sediment tests done by the team of researchers from the DNRF’s Center of Excellence UrbNet at Aarhus University in collaboration with the Institute for Geoscience and the Aarhus AMS Centre. The study has been published in the scientific journal PLOS ONE.

Udsigt fra Gerasa, hvor man kan se den moderne by Jerash.
View from Gerasa where the modern city Jerash is seen. Photo: The Danish-German Jerash Northwest Quarter Project.

Earlier this week, the DNRF released news about the surprising findings of mercury in the hadal trenches in the Pacific Ocean. Today the news continues in the same vein, but this time on the ground and many millennia back. A new study from UrbNet at Aarhus University, in collaboration with the Institute for Geoscience and the Aarhus AMS Centre, has discovered an unexpected level of heavy-metal contamination in the ancient city of Gerasa in Jordan. The discovery comes from the team of researchers’ examinations of soil and sediment tests from the archaeological material from the Danish-German Jerash Northwest Quarter Project. Dr. Genevieve Holdridge, who was previously a post-doc at UrbNet, is first author on the study, which was published in the scientific journal PLOS ONE.

“By combining pollution data from not only within the ancient city but also from its hinterland and the river valley (called a wadi) up- and down-steam the city, an unexpected pattern became clear. The ancient city was the hot spot of heavy metal pollution that is difficult to explain by ‘the usual suspects’ in ancient pollution studies: lead water pipes and mines,” said Associate Professor Søren Munch Kristiansen from UrbNet, who is a co-author on the study.

New understanding of the distribution of pollution

The sediment tests came back with elevated levels of copper, tin, lead, and arsenic. There are no archaeological findings of mines or evidence of the use of lead pipes in the water management system, factors that usually explain heavy-metal contaminations in ancient cities. Instead, the numbers point to small-scale activities such as coin minting and the production and use of metal objects as the reason behind the high level of heavy metal contamination.

The results of the study showcase how small-scale activities in urban areas should be factored into archeological research in order to fully understand the distribution of pollution in an ancient city since such factors play a bigger role than previously thought.

You can read more about the study at UrbNet here

Read the full study in PLOS ONE here