Found evidence of mercury poisoning in humans more than 5,000 years ago

Red cinnabar powder contains high levels of mercury, which was widely used by ancient people in social ritual activities.

According to the World Health Organization (WHO), exposure to naturally occurring heavy metals can be toxic to the body, including the nervous, digestive and immune systems. That is why WHO considers mercury one of the top 10 chemicals hazardous to human health.

Today, people are often exposed to mercury when they eat certain types of marine fish or shellfish, even though mercury levels are very low, according to the WHO.

How common was mercury exposure by early humans?

To find this out, the researchers analyzed human bones collected from 23 different archaeological sites, including caves, across Spain and Portugal. The skeletons belonged to 370 individuals who lived in different time periods over a period of 5,000 years.

Analysis of several bones, mainly the femur, the humerus bone between the shoulder and the elbow, revealed unusually high levels of mercury with concentrations that were not due to dietary intake or postmortem decay.

The researchers found mercury concentrations of up to 400 parts per million in some of the remains, much higher than the 1 or 2 ppm the WHO considers normal for humans.

The unusually high levels of mercury could be caused by exposure to cinnabar, a toxic mercury sulfide mineral that, when ground into a fine, bright red powder, has been used to make mercury, the researchers say. production of paint pigments in history. One of the largest cinnabar deposits in the world is in Almadén, Spain.

The mining of Almadén's cinnabar treasures began in the Neolithic period, about 7,000 years ago. The highest concentrations of mercury are found in monuments dating from around 2900 to 2300 BC, or from the late Neolithic to the Middle Bronze Age (which is the transition between the Neolithic and Bronze Ages). .

By this time, cinnabar had become a highly symbolic, perhaps sacred, substance that was hunted, traded, and widely used in many social rituals and practices.

In tombs dating from this period found in southern Portugal and Andalusia, cinnabar powder is used to paint chambers, decorate figurines and even sprinkle the dead. According to the team's statement, it's possible that people unintentionally or intentionally, for ritual-related reasons, inhaled or consumed large amounts of mercury-laden cinnabar.