CTS FOCUS 07 - The Fragrant World of Essential Oils

Biodeterioration processes are widespread in natural environments, and therefore all cultural heritage objects are susceptible to this type of degradation.

Stopping these processes is impossible; slowing them down is the goal. The issue is extremely complex, involving aspects such as the bioreceptivity of different surfaces, the environmental impact on areas surrounding the treatments, effects on operator health, the efficacy and durability of treatments, and more.

Many studies have provided ecological data that helped identify the most common microorganisms, both on monuments and on movable works.

Other studies have focused on methodologies for removing microorganisms, comparing mechanical, physical, and chemical procedures typically used in restoration operations.

Special attention has been given to integrated systems that combine synthetic biocidal molecules with water-repellent protective agents, such as siloxanes and functionalized nanosilicas, as recently described for the development of the Nano Silo Corave (see Focus 4).

In this context, alternative methods based on natural substances have been developed, drawing both from traditional medical knowledge of active compounds extracted from a wide variety of medicinal plants and from rigorous scientific studies that confirm their efficacy using modern control procedures.

The transfer of this knowledge from the medical field to the cultural heritage sector was not simple, and only in recent years has it begun to accelerate: for almost two decades, publications in this area have appeared, among which we highlight the first studies conducted in Italy:

•             The pioneering research carried out during the PhD at the University of Bologna by Oana-Adriana Cuzman, which examined various molecules, including capsaicin (responsible for the spiciness of chili) [1].

•             The applied study on some statues in the Vatican Gardens by the stone sector team of the Vatican Museums, under the supervision of Ulderico Santamaria [2].

•             The fundamental report of the Istituto Centrale del Restauro, authored by Marco Bartolini and Anna Maria Pietrini, which compared some essential oils with well-known synthetic biocides [3].

Application of red thyme essential oil

Red thyme essential oil after one year

In the last decade, studies have multiplied, products have reached the market, and from a commercial standpoint, considerable confusion has also arisen. We now attempt to clarify some points, starting with the most delicate and important.

Essential oils are not non-toxic. Like many other naturally occurring molecules, even a complex mixture that we call “essential oil of…” carries a certain level of toxicity; everything depends on the types of molecules present in the mixture and the amount of product taken—the so-called dose.

Unfortunately, some products have been presented as a “healthy” alternative to harmful synthetic biocides, such as quaternary ammonium salts. It should be noted that during the Covid period, we were heavily exposed to these salts, known bactericides and virucides, present in most hand sanitizers. The use of quaternary ammonium salts (benzalkonium chloride, didecyldimethylammonium chloride, etc.) was recommended by the Istituto Superiore di Sanità (ISS) in Italy, the European Centre for Disease Prevention and Control (ECDC) in Europe, and the WHO globally. As always, the issue of dose applies, excessive use of sanitizing gels is certainly not recommended.

Even regarding essential oils, high doses can cause various problems, so it is necessary to read the hazard statements listed on the corresponding safety data sheets.

For example, cinnamaldehyde, which gives cinnamon its characteristic smell, is used in the preparation of excellent desserts, perfumes, and dietary supplements, and is also found in some medicines. Therefore, we cannot consider it toxic in small doses.

In fact, the safety data sheet for pure cinnamaldehyde states H312 – Harmful in contact with skin and also H317 – May cause an allergic skin reaction. Therefore, some individuals could be affected, from an allergy perspective, by the effects of essential oils, just as some people are allergic to strawberries or almonds.

Another example is carvacrol, found in oregano oil, which can cause severe skin and eye damage (H314) and is harmful if ingested (H302).

Essential oils are not free from adverse effects on nature. Again, it is important to understand the concentration we are using. For instance, in the case of cinnamon, cinnamaldehyde carries the statement H412 – Harmful to aquatic life with long-lasting effects.

Essential oils have differentiated activity on various microorganisms. Just like synthetic products, some essential oils are more active against certain species and may be inactive against others. Some products on the market claim uniform efficacy against all microorganisms, creating unfounded trust.

For these reasons, a careful evaluation of different essential oils was necessary before marketing Biotin Bio, the new CTS product that will be described in the next Focus.

References

1.           Cuzman O.; Tiano P.; Ventura S.; New Control Methods Against Biofilms’ Formation on the Monumental Stones. In: Proceedings of 11th International Congress on Deterioration and Conservation of Stone; Torun, 2008; vol. 2, 837-846

2.           Devreux G, Santamaria U., Morresi F., Rodolfo A., Barbabietola N., Fratini F., Reale R.; Phytoconservation: alternative treatments on stone material works in the Vatican Gardens, in Lo Stato dell’Arte 13, Turin, 22-24 October 2015, pp. 199-206

3.           Bartolini M., Pietrini A.M.; Disinfection of biological patinas on stone artifacts: comparison of chemical and natural biocides, Bollettino ICR New Series n.33, 2016