ABUNDANCE OF AIRBORNE PENICILLIUM CFU IN RELATION TO URBANIZATION IN MEXICO-CITY

Air was sampled simultaneously at three localities in Mexico City diff ering in urbanization index and air pollution level on 22 days during a period covering both dry and rainy seasons. An Andersen two-stage mi crobial sampler was used for 15 min at 28 liters min-1 to isolate cult urable fungi on malt extract agar. After exposure, plates were incubat ed at 25-degrees-C for 48 to 72 h before colonies were counted and ide ntified to give concentrations of total fungal spores and of Penicilli um spp., expressed as CFU per cubic meter of air. Total fungi numbered 91 to 602 CFU m-3 in Tlalpan Borough (southern area), 40 to 264 CFU m -3 in Cuauhtemoc Borough (downtown), and 26 to 495 CFU m-3 in Gustavo A. Madero Borough (northern area). Although Penicillium spp. were the second most frequently isolated fungal genus, concentrations were smal l, with a maximum of only 133 CFU m-3. Twice as many colonies were iso lated in the southern area, with an urbanization index of 0.25 (arithm etic mean, 41 CFU m-3), as at other sampling stations with greater urb anization indices (arithmetic means, 19 and 20 CFU m-3). In the downto wn area, with an urbanization index of 1.0, Penicillium spp. were more numerous than any other genus and formed 25% of the total fungal coun t compared with 14 and 17% in the other areas. Concentrations of airbo rne Penicillium spp. did not differ significantly.between rainy and dr y seasons. However, their concentration was weakly negatively correlat ed with temperature (r = 0.36, P < 0.01), vapor pressure (r = -0.47, P < 0.001), and relative humidity (r = -0.36, P < 0.001). On average, 7 0% of Penicillium propagules were collected in the small-particle frac tion (considered to be respirable on inhalation, <5-mum aerodynamic di ameter). Of the eight Penicillium species identified, P. aurantiogrise um, P. crustosum, P. chrysogenum, and P. spinulosum were the most comm on. Their small numbers suggest that Penicillium spp. are not importan t outdoor aeroallergens in Mexico City, but total exposure cannot be a ssessed until indoor environments have been sampled.