Quantification of Air Contaminants at a Municipal Sewage Sludge Composting Facility

Abstract

In 1993 there were an estimated 4000 employees working at 321 municipal composting facilities in 46 states. This work force may be exposed to dusts of biological origin, various gases, and airborne heavy metals. This study was designed to quantify contaminant concentrations at the Longmont, Colorado, composting facility. Sampling was divided into two phases. Phase I took place from June 12 through June 16, which was the facility's time period for peak volume. Phase II occurred from August 14 through August 18. Total dust concentrations as high as 173.79 mg/m³ were measured. The geometric means of total dust samples on days with screening and sweeping operations were 23.05 and 35.19 mg/m³. The mass median aerodynamic diameter (MMAD) of the aerosol was approximately 4.0 μm. The high dust concentrations coupled with the small MMAD indicate a possible occupational health risk from dust exposure at this municipal composting facility. Endotoxin concentrations varied from 28.9 to 5930.6 ng/m³. Using regression analysis, endotoxin concentrations were compared with total dust concentrations. The coefficient of determination (r²) was 0.71. According to the International Committee on Occupational Health, 21 percent of the collected endotoxin concentrations exceeded levels where organic dust toxic syndrome may be caused, 69 percent exceeded acute bronchoconstriction levels, and 100 percent exceeded the mucous membrane irritation level. These data indicate a potential for occupational exposure to endotoxins during sewage sludge composting. Very low concentrations of silica, gases, and airborne heavy metals were measured at the facility, indicating little potential for occupational overexposures.