SOURCE BIOAEROSOL CONCENTRATION AND rDNA-BASED IDENTIFICATION OF MICROORGANISMS AEROSOLIZED DURING AGRICULTURAL WASTEWATER REUSE

Reuse of partially treated domestic wastewater for agricultural irrigation is a growing practice in arid regions throughout the world. A field sampling campaign to determine bioaerosol concentration, culturability, and identity at various wind speeds was conducted at a flooded wastewater irrigation site in Mexicali, Baja California, Mexico. Direct fluorescent microscopy measurements for total airborne microorganisms, culture-based assays for eterotrophs and gram-negative enteric bacteria, and small subunit rRNA-based cloning were utilized for microbial characterizations of aerosols and effluent wastewater samples. Bioaerosol results were divided into two wind speed regimes: (i) below 1.9 m/s, average speed 0.5 m/s, and (ii) above 1.9 m/s, average speed 4.5 m/s. Average airborne concentration of total microorganisms, culturable heterotrophs, and gram-negative enteric bacteria were respectively 1.1, 4.3, and 5.3 orders of magnitude greater during the high wind speed regime. Small subunit rDNA encoding gene clone libraries based on samples from air and the irrigation effluent wastewater during a high wind sampling event indicate that the majority of air clone sequences were more than 98% similar to clone sequences retrieved from the effluent wastewater sample. Overall results indicate that wind is a potential aerosolization mechanism of viable wastewater microorganisms at flood irrigation sites.