ALGAECIDE EFFECT OF NATURAL COMPOUNDS INCORPORATED IN EXTERIOR WATER-BORNE PAINTS

VIERA M.R.; RASTELLI S.E.; GÓMEZ DE SARAVIA S.; BLUSTEIN G.

Río de Janeiro

Simposio; 9 Latin American Biodeterioration and Biodegradation Symposium; 2016

Instituto Nacional de Tecnología; Univ.Fed. do Rio Grande do Sul.

Photosynthetic organisms, such as cyanobacteria and microalgae, are considered the first colonizers of building surfaces. These organisms often develop biofilms on exterior painted surfaces causing colored spots (green, dark brown, black and / or orange) due to the presence of pigments produced by the colonizing species. Microorganisms can cause physical and chemical deterioration of the paints. This is particularly damaging when it occurs on surfaces of great value from the artistic and the historical point of view. Photosynthetic biofilms proliferate especially in walls where atmospheric humidity is high as in La Plata city (Buenos Aires, Argentina) where sampling was performed. To eliminate and prevent the formation of these biofilms, chemicals with biocidal activity are added to paints. These chemicals, in general, also have toxic effects on the environment. Plants synthesize secondary metabolites such as alkaloids, flavonoids, terpenes, coumarins, tannins, etc., which have antimicrobial properties against bacteria, fungi and algae that may be a sustainable alternative to traditional biocides. The aim of this study was to evaluate the algaecide effect of some of these natural compounds incorporated in exterior water borne paints. Biofilms were detached from painted walls with deterioration signs and cultured in BG11 broth and BG11 agar. Algae were taxonomically identified using optic microscopy and specific bibliography. The characteristics of the biofilms and isolated taxa were observed by scanning electron microscopy (SEM) and epifluorescence microscopy. The algaecide effect of four vegetal compounds (anisole, eugenol, guaiacol and thymol) was evaluated using the technique of micro-atmosphere. Different amounts of compound were applied on a piece of filter paper giving 1.25, 2.50, 5.0, 10.0 and 100 μmoles.cm-2. Only anisole did not exert any detrimental effect on any photosynthetic microorganisms assayed. Eugenol, thymol and guaiacol showed a significant decrease or inhibition of the growth of those microorganisms. These three compounds were incorporated (separately) in an exterior latex paint in a concentration of 2% w/w. Pieces of filter paper (2.8 cm x 2.8 cm) were painted with these formulations and then inoculated in spray form with a photosynthetic community or some species isolated from that community. After that, they were placed in Petri dishes with BG11 agar and incubated for 28 days agar under controlled conditions of light, humidity and temperature. These tests were performed in triplicate, and a blank reference was made with latex without biocide. Partial results were recorded weekly. The growth of microalgae in the reference system was observed since the first week. By contrast, paints with the three natural compounds exerted a total inhibition of growth of algae until the end of the trial. These results confirm that these vegetal compounds could provide a sustainable alternative to biocides traditionally used in paints.