ALBERT

Notes: Abstract A survey was carried out over a 1-yr period to isolate protozoa suspended in the air of Mexico City and its suburbs. Sampling stations were placed at four cardinal points of the metropolitan area. Selective media were used to culture the protozoa isolated. Specialized taxonomic keys were used for identification and a statistical analysis was performed to determine the correlations between physicochemical and biological parameters. 63 strains were isolated. Species of Kinetoplastida and Chrysomonadida were most abundant, namely species of the genera Bodo, Cercobodo, Monas and Helkesimastix. Amoeboflagellates found included Mastigamoeba and Tetramitus. The only ciliate isolated was Colpoda steini. The greatest number of strains was yielded by Bodo repens and Cercobodo radiatus. Several times during the period of the study SO2, O3, CO, NO, and NO2 exceeded the permissible levels established by the Mexican government. From the results of this study it was concluded that the ability of protozoa to form cysts and cyst size were important factors for their presence, survival, abundance and diversity in the atmosphere. The main source of air-borne protozoa was the soil. Factors that favored the incidence and diversity of the isolates were wind speed and direction, high relative humidity, generation of frequent dust-storms, resuspension of protozoa by vehicular traffic, proximity to garbage dumps and large extensions of bare soil, and temperature (the latter only when it did not favor the production of high levels of O3). Factors that were hostile to the aerial protozoa were industry and their contaminants, and high concentrations of O3 and SO2, especially in winter time when thermal inversions occurred. Soil cover was also associated with a reduction in the incidence and diversity of the aerial protozoa. This study demonstrates that there are viable cysts of protozoa in the atmosphere of Mexico City, that may have potential importance in the case of certain kinds of human allergies and diseases. Further research is needed to find out the aerial presence of viable cysts of obligatory, amphizoic or opportunistic protozoan parasites, and to clarify the qualitative and quantitative effects of the local meteorological and physico-chemical environment on the free-living protozoa present in the atmosphere.