The Algicidal Potential of Some Volatile Substances on Oil Base: Effect of Structure–Species–Effectivity Relationships

The bio-colonization of building materials by green algae is a widespread problem. To prevent this, it is advisable to use natural substances to avoid environmental damage. This study examined the effectiveness of four essential oils (cinnamon, thyme, oregano and hop) and four oil-based substances (trans-cinnamaldehyde, thymol, carvacrol and β-caryophyllene) in preventing bio-colonization. The effectiveness of these chemicals against three algal species (Haematococcus pluvialis, Chlorella mirabilis and Stichococcus sp.) and a mixture of these species was tested. The tests were carried out under laboratory conditions over a period of 14 days. The concentrations tested were in the range of 3–200 mg/L. Growth densities were assessed spectrometrically as absorbencies at a wavelength of 750 nm. Caryophyllene, thymol, oregano oil, and hop oil did not negatively affect the growth of algal biomass. The algicidal effect increased in the following order for the other chemicals: cinnamon oil and trans-cinnamon aldehyde < thyme oil and carvacrol. Their biocidal effect was influenced by their structure, particularly their molecular weight and solubility in fat (log Kow). H. pluvialis was a less sensitive species than the smaller S. sp and Ch. mirabilis. The artificial biofilm was sensitive to thyme oil and carvacrol, similarly to natural biofilms, as was demonstrated in previously published studies.