Márcia Aiko Shirakawa

Fungal colonization and succession on newly painted buildings and the effect of biocide

This report describes the sequence of fungal colonization and the influence of biocide incorporation on paint films, determined using quantitative methods. Two buildings were painted with an acrylic paint, with and without an experimental biocide formulation containing a carbamate (carbendazin), N-octyl-2H-isothiazolin-3-one and N-(3,4-dichlorophenyl)N,N-dimethyl urea (total biocide concentration 0.25% w/w). One week after painting, the major groups of organisms detected were yeasts and Cladosporium. The yeast population fell to undetectable levels after the third week and this microbial group was not detected again until the 31st week, after which they increased to high levels on the 42nd week. Aureobasidium showed a pattern similar to the yeasts. The main fungal genera detected over the 42-week period were Alternaria, Curvularia, Epicoccum, Helminthosporium, Coelomycetes (mainly Pestalotia/Pestalotiopsis), Monascus, Nigrospora, Aureobasidium and Cladosporium. The latter was the main fungal genus detected at all times. The physiological factors controlling colonization are discussed. Cladosporium, Aureobasidium, Tripospermum and yeasts on the painted surfaces were all able to grow on mineral salts agar containing 10% sodium chloride. This is the first time that the genus Tripospermum has been reported on painted buildings. The fungal population on biocide-containing surfaces was significantly lower than on non-biocide-containing paint after 13 weeks and continued so to 42 weeks after painting, but there was no statistically significant difference in the level of fungal biodiversity.

The development of a method to evaluate bioreceptivity of indoor mortar plastering to fungal growth

The aim of this work was to develop and standardise an accelerated laboratory test for detecting bioreceptivity of indoor mortar to fungal growth. To determine which fungal species were predominant under field conditions, isolation was carried out using mortar samples collected from 41 buildings in two cities of Sao Paulo State in the South East of Brazil. Cladosporium was found to be the genus most frequently recovered from field specimens. Based on the results of laboratory trials strain C. sphaerospermum was chosen as a test microorganism. Four different mortars, two laboratory-manufactured mortars composed of ordinary Portland cement, high calcium hydrated lime and standardised sand, and two different ready-mixed building mortars from the Brazilian market, were investigated for their susceptibility to colonisation by C. sphaerospermum. Several parameters were tested to determine factors influencing fungal bioreceptivity. The type of mortar, degree of carbonation and pH values of mortars, as well as relative humidity of environment effected colonisation of C. sphaerospermum. All except one mortar samples showed significant fungal growth, however, the growth occurred only at 100% relative humidity. Interaction of C. sphaerospermum with mortar specimens was studied using techniques of scanning and environmental scanning electron microscopy combined with energy dispersive X-ray analysis.

Climate as the most important factor determining anti-fungal biocide performance in paint films

The effect of Pigment Volume Content (PVC) on fungal growth on acrylic paint formulations with and without biocide, exposed to weathering in three different climatic regions in Brazil for four years, was studied. Latex paints, with PVC of 30%, 35% and 50%, were applied to autoclaved aerated concrete blocks pre-covered with acrylic sealer and acrylic plaster. They were exposed to equatorial, tropical and temperate climates in north, south-east, and south Brazil. Cladosporium was the most abundant fungal genus detected in the biofilm on the surfaces of all paint formulations at all sites after four years. Heaviest fungal colonization occurred in the tropical south-east and lightest in the temperate south of the country, but more phototrophs, principally cyanobacteria, were detected in the equatorial region. PVC and presence of biocides were shown to be of less importance than environmental conditions (irradiance, humidity and temperature) for biofilm formation and consequent discolouration. These results have important implications for testing of paint formulations.

A conductive polymer based electronic nose for early detection of Penicillium digitatum in post-harvest oranges.

We describe the construction of an electronic nose, comprising four chemiresistive sensors formed by the deposition of thin conductive polymer films onto interdigitated electrodes, attached to a personal computer via a data acquisition board. This e-nose was used to detect biodeterioration of oranges colonized by Penicillium digitatum. Significant responses were obtained after only 24 h of incubation i.e. at an early stage of biodeterioration, enabling remedial measures to be taken in storage facilities and efficiently distinguishing between good and poor quality fruits. The instrument has a very low analysis time of 40 s.

Susceptibility of phosphogypsum to fungal growth and the effect of various biocides

Natural gypsum (NG) and phosphogypsum (PG) were tested for resistance to fungal growth based on standard test ASTM D 3273-86, with the recommended mixture of three fungal species, and using the same test modified by the use of a Cladosporium sp. A, isolated from a gypsum plaster ceiling. In the standard test little growth occurred on any of the test specimens. However, abundant fungal growth was produced by the Cladosporium sp. A on phosphogypsum, which was much more susceptible than natural gypsum. Phosphogypsum heated to 600°C to destroy organic residues was resistant to growth of Cladosporium sp. A, as well as other fungi isolated from phosphogypsum panels stored in the environment for 2 years: Cladosporium sp. B, Aspergillus niger and Trichoderma sp. Phosphogypsum moulded in Petri dishes was susceptible to growth of a wide range of fungi, although Fusarium sp. and Rhizopus sp. caused practically no discoloration of the substrate. Six biocides were separately incorporated into the phosphogypsum at concentrations recommended by the suppliers and test specimens incubated on Sabouraud agar inoculated with various fungal isolates. The biocide 2-N-octyl-4-isothiazolin-3-one was the most efficient compound. It prevented the growth of the fungi most likely to cause health problems in buildings, but not that of Helminthosporium sp., isolated from powdered phosphogypsum in the factory. This was the most resistant fungus showing growth on all biocide-containing specimens.

Statistical analysis of fungicide activity in paint films on two buildings

SummariesFungal growth on external walls of two buildings in São Paulo was quantified over 95 weeks after painting with an acrylic coating with and without a biocide formulation (carbendazim, an N-octyl-isothiazolin-3-one and N-(3,4-dichlorophenyl)N,N-dimethyl urea; concentration 0.25%). Fungal contamination increased exponentially on all sites and was 18 to 25% lower on biocide-containing sites. Simple and multiple regression, the chi-squared and Fisher’s exact tests showed that the biocide was effective throughout the period (p<0.005). The multiple regression equation for both sites was:

Biodeterioration of external architectural paint films – A review

Ln\left( {\frac{{B^ + }}{{\sqrt C }}} \right) = 0.75 + 0.017w

Inhibition of Cladosporium growth on gypsum panels treated with nanosilver particles

where B+=number of colony-forming units (cfu) on biocide-containing sites; C=cfu on control sites; and w=time in weeks.RésuméLa croissance fongique sur les murs externes de deux bâtiments à São Paolo a été quantifiée pendant 95 semaines, les murs ayant été préalablement enduits d’un revêtement acrylique avec et sans une formulation biocide (carbendazim, un N-octyl-izothiazolin-3-one et N-(3,4-dichlorophenyl)N,-N-diméthyl urée; concentration de 0,25%) La contamination fongique a accru exponentiellement sur tous les sites et était plus basse de 18 à 25% sur les sites qui contenaient une biocide. La régression simple, la régression multiple, le chi-carré, et l’épreuve exacte de Fisher ont montré que la biocide était effective tout au long de la période (p<0,005). L’équation de régression multiple pour les deux sites était: