WORKERS EXPOSURE TO AIRBORNE BACTERIA AND ENDOTOXINS AT INDUSTRIAL WASTE-WATER TREATMENT PLANTS

A study of sewage workers' exposure to airborne culturable bacteria an d inhaled endotoxins was performed at nine wastewater treatment plants that treat mainly industrial effluents. Airborne endotoxins were coll ected on glass fiber filters and analyzed using a chromogenic limulus assay. Endotoxin concentrations measured in the immediate vicinity of the wastewater treatment process varied from 0.1 to 350 ng/m(3). The e ight-hour time weighted average concentrations of endotoxin to which w orkers were exposed exceeded the suggested exposure limit (30 ng/m(3) endotoxin) at four of the plants. Air samples of culturable bacteria c oncentrations varied between 10 and 10(5) colony-forming units/m(3). O f the particles carrying culturable bacteria, 88% had an aerodynamic d iameter of less than 4.7 mu m. The most common genera of airborne gram -negative bacteria were acinetobacter, citrobacter, enterobacter, kleb siella, and pseudomonas. High levels of exposure to bacteria and bacte rial endotoxin usually were related to certain phases of the treatment process. The microbiological contamination of air was highest near th e inlets where incoming wastewater entered the basins, in the sludge t reatment area, and inside the biofilter tower. In these spaces it is n ecessary to control and reduce exposure to airborne bacteria and endot oxin at wastewater plants.