Rosalia Lombardo, the most beautiful mummy in the world and the mystery of formaldehyde
A Jahr100Wissen / 100 years ago interview with the Head of the Department for Physical and Theoretical Chemistry, Prof. Dr. Thorsten Benter
Mummies have always fascinated people. Most of the time, one thinks of the Egyptian Pharaohs, but mummies exist in all continents. However, the best preserved one to date is that of a little girl from Palermo: Rosalia Lombardo. She died 100 years ago at the age of two from the Spanish flu and lies in the catacombs of Palermo. Rosalia seems to sleep in her glass coffin. The embalmer, Alfredo Salafia, who prepared the girl for eternity and thus preserved her perfectly, did not reveal the recipe during his lifetime. In the estate of the doctor, Dario Piombino Mascali of the University of Palermo found a manuscript in which Salafia described the use of formaldehyde. Which substance is this?
Benter: Formaldehyde is a chemical compound consisting of two atoms of hydrogen and one atom each of carbon and oxygen. It is written as H2CO in the "sum notation". The carbon atom is located in the center and is surrounded by the other atoms. The reason is as follows: The bond between two atoms is often associated with a certain reactivity (and a resulting function), especially in organic chemistry. In the formaldehyde molecule, the C=O or carbonyl group (or function) is of particular importance. Molecules that have this function and additionally have another hydrogen atom, or even two hydrogen atoms, as in the special case of formaldehyde, bound to this carbon atom are called aldehydes. Formaldehyde (or methanal, H2CO) is a colorless, gaseous substance at room temperature and normal pressure. The boiling point is about 20°C, the melting point is -117°C. If the gaseous formaldehyde is introduced into water, an aqueous solution is obtained, which is called formalin. Formalin is commercially available from various manufacturers. The formaldehyde concentration of the solution is usually given in mass percent and is sold in various containers. Usual concentrations are 37% formaldehyde. The intended use for these solutions is almost always for sterilization, for fixation of tissues and cells etc. This already gives a clear indication of its mode of action in the human body.
Since Salafia renounced the harmful poisons arsenic and mercury for embalming, all internal organs were preserved. What does formaldehyde do in the human body?
Benter: This question can be viewed from very different angles and can be answered in several ways. The effect of a substance on an organism always depends on the dose of administration or exposure. It is decisive whether this organism is already dead or not. If the organism is alive, let us take a human being as an example, one would hardly administer formalin orally or by infusion, or even expose it to a dense gaseous atmosphere of formaldehyde. Instead, exposure would be kept as minimal as possible. If, on the other hand, one wanted to preserve a dead person, i.e., to preserve his or her appearance as long as possible, one would definitely operate with larger quantities. Since in this case the primary concern is to preserve a mummified human being, we will concentrate on the latter.
The goal of conservation efforts is to keep the body, especially the external appearance, intact for as long as possible. The question then actually is: What processes lead to a dead organism "decomposing", i.e. losing its biological integrity? Since it can quickly become very unappetizing here, we prefer to move within the field of neutral definitions and then roll the whole thing up from behind. The decay of an organism can be roughly divided into two categories: Decay through decompisition and/or decay through putrefaction. The aerobic dissolution processes, i.e. those that take place in the presence of oxygen, are called decompostion. Anaerobic, i.e. processes running under oxygen deficiency or closure are called putrefaction. Dissolution of any kind in this context means the splitting of large molecules into smaller and smaller ones. The dissolution is driven by enzymes which are released by the bacteria and fungi which are always present. The enzymatic dissolution is spontaneous and voluntary, i.e. it takes place under energy release. Enzymes that are still active in the body of the deceased organism (so-called supravital or surviving enzymes) can also drive the dissolution. With these findings we have also found the key to conservation: Bacteria and fungi must be killed. The large, undecomposed organic molecules of the dead organism, such as proteins etc. should be protected from attack by supravital enzymes.
Mercury and arsenic have only a very limited effect here. They would have to penetrate the entire deceased organism in order to then develop their toxicity. And this toxicity is only very limited compared to the protagonists mentioned, especially the enzymes. On the other hand, a formalin solution introduced into the deceased organism, unfolds almost everywhere and non-selectively. This is mainly due to the fact that formaldehyde is a small molecule that can penetrate into almost all areas of the organism and with its distinct molecular functionality finds many molecular targets. In other words: on the one hand, formaldehyde is toxic to bacteria and fungi, on the other hand, it modifies molecular structures in all organs or in the whole body in such a way that an enzymatic attack is hardly or no longer possible. However, the macroscopic integrity of the tissues remains intact. In this context one also speaks of "denaturation", which is accompanied by a macroscopically observable "hardening" of the treated deceased organism.
Formaldehyde occurs in liquid and gaseous form and is considered as an important industrial raw material in the food and pharmaceutical sectors with an annual production of 21 million tons. What is formaldehyde used for today?
Benter: Formaldehyde is an indispensable "basic chemical". In fact, over 40 million tons of formaldehyde are produced worldwide, about half of it in China. The technical production itself is mainly done by catalytic oxidation of methanol. Silver metal (Ag) or metal oxides (often iron oxide, Fe2O3, to which molybdenum and/or vanadium is added) are used as catalysts, each with different synthesis products.
From the chemistry textbook, it can be seen that formaldehyde is one of the most important organic basic materials in the chemical industry. It serves as a starting material for numerous chemical compounds. The largest market share is in urea-formaldehyde resins, phenoplastics, polyoximethylenes and a number of chemical intermediates such as pentaerythritol. Pentaerythritol is also used in the production of resins, plasticizers and emulsifiers, and, how could it be otherwise, in the manufacture of explosives. Formaldehyde is also used in the production of various dyes, pharmaceuticals and in textile finishing.
Nevertheless, formaldehyde is considered carcinogenic. What health damage does this substance cause?
Benter: Formaldehyde is harmful to health, or more succinctly formulated, very toxic. That is why you will find hazard warnings on the containers in which formaldehyde is stored. A statement, which is still valid today and was made by Philippus Aureolus Theophrastus Bombast von Hohenheim, called Paracelsus, is: "All things are poison and nothing without poison; only the dose makes a thing being no poison".
And so there is a whole series of mandatory rules and measures in dealing with formaldehyde. The maximum workplace concentration (MAK value), for example, has been at 0.3 ppmV on an 8-hour average since 2011. In a room with a volume of 30 m³, which corresponds to a room with a ceiling height of 2.5 m and a floor area of 4 x 3 m² , there may only be a maximum of 10 cm³ of gaseous formaldehyde completely distributed in an 8-hour average, which corresponds to half a shot glass of gas. By the way, the MAK value is temporarily reached by smoking 3 cigarettes in this room. Above all, the legally binding classification of formaldehyde in 2015 by the EU, into the category "Probably carcinogenic in humans" stipulates that the exposure must always be kept as low as possible, regardless of limit values.
Formaldehyde is also found in the atmosphere. Your team has even taken measurements. What can you find out with these measurements?
Benter: Here, one must differentiate between measurements in the outside air and in the interior. Indoor air measurements provide an inventory of the air quality. In addition, such measurements can be used to detect obvious or hidden sources of formaldehyde emissions indoors. According to the Federal Environment Agency, there are still a large number of products that contain formaldehyde and can release it into indoor air, despite constant improvements. Wood-based materials, floor coverings, furniture and certain insulating materials are still the main sources, Formaldehyde can also be found in disinfectants, cosmetics and textiles. When released into the ambient air, it is hardly degraded in the gas phase and can therefore accumulate. The formaldehyde concentration can only be lowered by deposition on walls, and of course particularly effectively by regular ventilation. One main reason for the still widespread use is obvious: Whatever can prevent dead organisms from decomposing can certainly also serve very effectively as a preservative for other "things", at a very reasonable price.
The situation is completely different in the outside air, especially in the presence of sunlight. The atmospheric lifetime (a sort of average time a molecule remains in the atmosphere before being "removed" from it) of formaldehyde in this case is only a few hours at most. However, much more important is the removal by chemical reaction, i.e. by transformation into another substance. Compared to the original substance, this new substance often has very different chemical and physical properties. The energy required to trigger such processes is usually supplied by sunlight.
In this context it is also important to note that the atmosphere is an oxidative medium. This is not only caused by the presence of atmospheric oxygen, but especially by the presence of strongly oxidizing trace substances, such as ozone (O3). Although the concentration of these trace substances is small in the atmosphere, their reactivity is even greater. The one ultimately causes the other. The decisive factor is the fact that the reactive trace gases, which are also called atmospheric detergents, are repeatedly reproduced in cycles: The "dirtier" the atmosphere, the higher its concentration, because the cycles "spin" faster and faster. In view of the high number of hours of sunshine per day, it is therefore not surprising that ozone concentrations soar in summer - ultimately, these are an indicator of the increased washing activity of the atmosphere. And so formaldehyde experiences the same fate as many other substances that are introduced in the atmosphere: It is oxidized.
The different time scales on which these reactions occur are of great importance for understanding the chemistry of the atmosphere. Concentration measurements of formaldehyde (and many other substances!), for example, provide a snapshot of the current state of the atmosphere and allow conclusions and projections to be made. In addition to these measurements "in the field", extensive laboratory experiments as well as extensive modelling are necessary to gain an ever better understanding of the chemistry of the atmosphere.
Uwe Blass (Interview on November 11, 2020)
Prof. Dr. Thorsten Benter studied Chemistry at the Christian-Albrechts-University of Kiel from 1982 to 1987 and received his doctorate there in 1993. In 1997, his scientific work took him to the University of California, Irvine for four years. Since 2001, he has been Head of the Department of Physical and Theoretical Chemistry at the University of Wuppertal and represents it in research and teaching.