Characterization of Indoor Molds after Ajka Red Mud Spill, Hungary

Abstract

A red mud suspension of ~700,000 m³ was accidentally released from the alumina plant in Ajka, Hungary, on the 4th of October 2010, flooding several buildings in the nearby towns. As there is no information in the literature on the effects of red mud on indoor mold growth, we conducted studies to answer the following question: does the heavy metal content of red mud inhibit fungal colonization in flooded houses? In order to gain knowledge on fungal spectra colonizing surfaces soaked with red mud and on the ability of fungi to grow on them, swabs, tape lifts, and air samples were collected from three case study buildings. A total of 43 fungal taxa were detected. The dominant species were Penicillium spp. on plaster/brick walls, but Aspergillus series Versicolores, Cladosporium, Acremonium, and Scopulariopsis spp. were also present. The level of airborne penicillia was high in all indoor samples. Selected fungal strains were subcultured on 2% MEA with 10^-1 and 10^-4 dilutions of red mud. The growth rate of most of the strains was not significantly reduced by red mud on the artificial media. The consequences of similar industrial flooding on indoor molds are also discussed in this paper.

Keywords: bauxite processing residue; fungal growth; indoor mold; red mud.

Figure 1

(a) A natural-color image of the area surrounding the red mud spill in Hungary. The alumina plant appears along the right edge of the image, with blue and red reservoirs. The red mud forms a red streak running west from the alumina plant. Photo: NASA Earth Observatory. (b) Streets of Devecser after the red mud disaster (aquarelle painting of the author (D. Magyar) based on the aerial photo of Sándor H. Szabó. The artwork was painted with red mud collected in the town after the catastrophe. (c) Flooded buildings (Photo: D. Magyar). (d) Cross-section and (e) floorplan of the investigated buildings. (f) Firewood covered by red mud. (g) Plaster walls covered by red mud in the investigated buildings. (h) Wardomyces inflatus colony in a surface sample. (i) Spores and red mud particles in Psocoptera pellets. Bar = 10 µm.

Figure 2

The effect of red mud, pH, and water activity (a_w) on the colony diameters of fungal strains on special media (MEA + 10^{− 1} red mud concentration, MEA + McIlvain buffer solutions, and YEA + NaCl, respectively) when compared to their growth on the control media (red mud 10⁻¹ control = MEA + red mud 10⁻⁴, pH control = MEA, a_w control = YEA). Ranges of a_w (0.97 ± 0.02) and pH (6.50 ± 0.30) corresponding to MEA with 10⁻¹ red mud concentration are selected. Strains where red mud media had no significant effect are excluded. Significant positive effects are marked with red, orange, and yellow; negative effects are marked with blue. ns = non-significant; nd = no data (not studied). Significant results are marked with ***: p < 0.001, **: p < 0.01, and *: p < 0.05.