Particulate emissions from selected combustion sources and their pathological impacts on the lung tissues of male albino mice

Abstract

Particulate emissions and organic volatiles produced by incomplete combustion processes have attracted the attention of many environmental experts. Consequently, increasing concern has been directed towards the study of human health problems caused by carcinogenic and mutagenic soot components such as polycyclic aromatic hydrocarbons (PAHs) and polyenes from various combustion systems. Soot from many combustion systems are well-known precursors for numerous toxicological impacts in the environment as well as biological structures. This study investigated the nature and toxicological effects of soot from simulated forest fire, vehicular exhaust, and tyre burning. Soot from these sources was trapped in the gas phase using gas trapping apparatus and then dissolved in dichloromethane through a porous tube diluter. Volatiles from soot were extracted in dichloromethane for analysis using Gas Chromatography interfaced with a Mass Spectrometer (GC-MS). The energetics of selected PAHs and their corresponding free radicals was explored using high level quantum chemical calculations. Accordingly, the Density Functional Theory (DFT/B3LYP) in conjunction with 6-31G basis set was used in this study. The size distribution analysis and surface morphology of soot was examined using a scanning electron microscopy (SEM). To simulate chronic environmental pollution, 12-week old male albino mice were exposed to particulate emissions at a rate of ~ 250 μg-3day-1 (measured by a gas flow meter) and their lung tissues were extracted for bioassay analyses. Comparisons were made between the lung tissues of mice exposed to the particulate emissions from the three sources, and the control mouse in order to determine the biological impact of particulates on the functioning of the lung tissues. Igor and Image J computational softwares were used to characterize micrograph images. Swelling and shrinking of lung tissue cells was observed as a result of exposure to tyre and diesel exhaust particulate emissions which caused disconnection of tissues and damage to the blood capillaries within the lung alveoli. Organic volatiles detected from tyre and diesel combustion included benzene, benzo[a]pyrene, anthracene, and cyclopentafused PAHs such as fluorene and fluoranthene. The average particulate size of emissions from simulated forest fire using SEM was found to be 11.51 ± 4.91 μm. This study has shown that most of the emissions from simulated forest fire fall under particulate matter of ≤10 μm in size. Simulated forest fire particulates caused minimum damage to the lung tissues whereas particulate emissions from diesel and tyre caused grave damage to the lung system of the mice. These effects may be attributed to toxic organic volatiles as well as particulates which carry with them active radicals and toxic organic intermediates into the respiratory system.