An evaluation of the bottom ashes from healthcare waste in a laboratory scale incinerator: Microbiology, mutagenicity and toxicity

Abstract

In this study, experiments of healthcare waste incineration at 500, 600, 700, 800 and 900 degrees C in a lab-scale incinerator were carried out, performing different total bacterial counts for the microorganisms in bottom ashes before and after incineration. However, no data related to Bacillus stearothermophilus bacteria, added as indicator microorganisms to healthcare waste samples before incineration, were available. For the determination of mutagenic activity of waste ashes in a Soxhlet extractor, samples incinerated at 500 and 600 degrees C were extracted with dichloromethane. The extractor dosage, prepared in DMSO, was tested according to the plate incorporation method of Ames Salmonella Microsome test strains of TA98 and TA100, in phase of S9 (-) and S9 (+). The 500 degrees C incineration extract increased the revertant colonies, and might be mutated to be a frame shift. In the second part of the study, cytotoxic effects of healthcare waste incinerations at 500 and 600 degrees C in bottom ashes were tested on NIH3T3 mouse fibroblasts by using MTT assay, which is used for measuring the mitochondrial activity of the cells, and neutral red assay for testing the lysosomal enzyme activities of the cells. While the bottom ash at 500 degrees C time-dependently decreased the mitochondrial activity of NIH3T3 cells, it was shown that lysosomal activity of the cells increased. These data can be related to mutagenic effects of the bottom ash. On the first day, a high cytotoxicity was observed in 600 degrees C bottom ash. On the 4h day of the study, cytotoxic effects of the bottom ash at 600 degrees C were found to be lower, with regard to that of 500 degrees C bottom ash on NIH3T3 fibroblasts. This can be related to temporary cytotoxic effects. As a result, cytotoxic effect of bottom ash at 600 degrees C was found to be lower than that at 500 degrees C. Because none of the animals injected in bottom ashes died at the end of the 48-h period, it can be said that acute lethal effects of bottom ashes were very low.