Medieval pottery: beautiful but deadly.
Image credit: Birgitte Svennevig/SDU
Cups and plates glazed with lead oxide were beautiful, easy to clean and in high demand. However, only wealthy people in towns could afford to use them. Unfortunately for them, keeping salty and acidic foods in pots glazed with lead made the surface dissolve, causing lead to leak into the food.
In addition, mercury was involved in preparation of the color cinnabar for use in red ink, which was used for gilding and for medical purposes, especially to treat leprosy - which almost half of the individuals in the study suffered from - and syphilis.
Human exposure to both metals has been revealed by chemical investigations of skeletons from cemeteries in Denmark and Germany.
Associate Prof. Kaare Lund Rasmussen and colleagues from the University of Southern Denmark (SDU) have published a series of chemical and anthropological analyses of 207 skeletons from six cemeteries in northern Germany and Denmark. They tested the skeletons for lead and mercury content.
High levels of lead in townspeople
They found high levels of both metals, especially in the towns.
In Rathaus Markt, Schleswig, Germany, 10 skeletons - or 19% of the individuals surveyed - had lead levels above normal, and 36% had high levels of mercury. In Ole Worms Gade in Horsens (Denmark), all 25 individuals had lead levels above normal levels, and 17% had high mercury levels.
Exposure appears to have been higher and more dangerous in urban communities, but results showed that 30% of rural individuals were in contact with lead, although to a lesser extent.
Rural inhabitants appear to have used glazed pottery more rarely. It would have been expensive and difficult to find. Instead, they used unglazed pottery, and thus unknowingly saved themselves from exposure to the toxic metal.
Prof. Rasmussen says:
"Lead poisoning can be the consequence when ingesting lead, which is a heavy metal. In the Middle Ages you could almost not avoid ingesting lead, if you were wealthy or living in an urban environment. But what is perhaps more severe, is the fact that exposure to lead leads to lower intelligence of children."
Apart from pottery, other sources of lead in towns included coins, stained glass windows and lead tiles on the roofs of important buildings. Drinking water was often collected from the roof, and this may also have been an important source of lead.
Lead is a toxic heavy metal that accumulates in the human body, affecting the nervous system. It was used extensively by the Romans; it is thought that poisoning among the emperors could have contributed to the downfall of the Empire.
Town and country differences
In the Middle Ages, wealthy Danes and Germans mainly lived in towns, while the rural population was generally poorer and more isolated.
The cemeteries in Rathaus Markt and Horsens are both situated on the coast; people buried there were from relatively prosperous medieval towns that had more contact with the outside world than most rural communities.
The measurements of both lead and mercury show that the urban population was more exposed than the rural population. There was almost no lead in the bones of the people who lived in the countryside, compared with high levels in those of townspeople.
Where mercury was used for medical purposes, the effectiveness of treatment appeared to differ between towns. Rasmussen suggests that in some towns, people might have had more medical expertise than in others.
Medical News Today has previously reported on the dangers of lead poisoning for children in the US.