Evaluation of Bioaerosol Components, Generation Factors, and Airborne Transport Associated with Lime Treatment of Contaminated Sediment

Abstract

Lime treatment has been used in contaminated sediment management activities for many purposes such as dewatering, improvement of physical properties, and reducing contaminant mobility. Exothermic volatilization of volatile organic compounds from lime-treated sediment is well known, but potential aerosolization of bioaerosol components has not been evaluated. A physical model of a contaminated sediment treatment and airborne transport process and an experimental protocol were developed to identify specific bioaerosol components (bacteria, fungi, cell structural components, and particles) that may be aerosolized and transported. Key reaction variables (amount of lime addition, rate of lime addition, mixing energy supplied) that may affect the aerosolization of bioaerosol components were evaluated. Lime treatment of a sediment contaminated with heavy metals, petroleum-based organics, and microorganisms increased the sediment pH and solids content. Lime treatment reduced the number of water-extractable bacteria and fungi in the sediment from approximately 106 colony-forming units (CFU) · mL-1 to less than the detection limit of 103 CFU • mL-1. This reduction was seen immediately for bacteria and within 21 days for fungi. Lime treatment immediately reduced the amount of endotoxin in the sediment, but the effects of lime treatment on β-D-glucan could not be determined. The temperature of the treated sediment was linearly related to the amount of lime added within the range of 0–25%. Bacteria were aerosolized during the treatment trials, but there was no culturable evidence of aerosolization of fungi, most likely because of either their particular growth stage or relatively larger particle size that reduced their aerosolization potential and their collection into the impingers. Nonbiological particles, endotoxin, and β-D-glucan were not detected in air samples during the treatment trials. The amount of lime added to the reaction beaker and the relative amount of mixing energy supplied to the reaction significantly affected the aerosolization ratio of bacteria (amount of aerosolized bacteria divided by the amount of bacteria in untreated sediment) from the reaction beaker. The rate of lime addition did not significantly affect the aerosolization ratio of bacteria. The aerosolization results suggest that exposure to bacteria is possible with sediment treatment activities, but the hazard level could not be determined because speciation of the aerosolized bacteria for pathogen identification was not performed, and health and safety standards and criteria for bioaerosol components have not been developed. Quantitative scaling analysis and whether the system represents actual environmental conditions were not studied.