Organic volatiles and particulate emissions from the combustion of tire are believed to contain eco-toxic substances including polycyclic aromatic hydrocarbons (PAHs) and various reactive radical species which may initiate serious respiratory ailments such as asthma and lung tumors. This study investigates the nature and toxicological effects of particulate soot from tire burning. To simulate environmental pollution, 12-week-old male albino mice were exposed to tire particulate emissions at a rate of ~250 μgm ﹣3 ·day ﹣1 and their lung tissues were extracted for bioassay analyses. Comparisons were made between the lung tissues of mice exposed to the particulate emissions, and the control mouse in order to determine the health impact of particulates on the functioning of the lung soft tissue. The thermal degradation profile of tire was also investigated in the temperature range 200℃ - 500℃ and found that the highest mass loss was between 300℃ and 450℃. Organic volatiles were determined using a Gas Chroma tograph coupled to a mass selective detector (MSD). Size distribution of soot particles was determined using Scanning electron microscope (SEM). Evidently, there was swelling and shrinking of lung tissue cells as a result of exposure to tire particulate emissions which caused disconnection of tissues and damage to the blood capillaries within the lung alveoli and microphages. Organic volatiles detected from tire combustion include benzene, anthracene, fluorene and pyrene. Soot particulate average sizes were found to be 16.23 ± 3.36 μm. Tire particulates caused grave damage to the lung tissues of the mice. These effects may be attributed to toxic organic volatiles as well as particulate emissions which may contain reactive active radicals and toxic organic intermediates and thus cause grave damage to the lung tissues of the mice.
The contribution discusses the particulate emissions from tire combustion and their histochemistry on research mice and extrapolates it to the human environment. The disposal of used tires has led to serious environmental health hazards, especially when large stockpiles of tires are burnt [
Histochemistry as the aspect of histology concerned with the identification of chemical components in biological cells and tissues has been used to explain more about soot effects in body organs [
Clean tire samples were obtained from a tire waste yard and used without further treatment. The reagents used in this study were of analytical grade (purity ≥ 99%). All reagents (methanol and dichloromethane) were purchased from Sigma Aldrich, Inc., St. Louis, Missouri, USA. Tire burning was conducted in a quartz reactor of dimensions ~ 1.6 cm3 at 1 atmosphere pressure. The gas phase components were passed over dichloromethane (DCM) and transferred into 2 mL vials for analysis using a GC-MS.
Organic by-products from tire burning was passed through 10 mL dichloromethane solution (DCM), filtered using a filter paper (Whatmann No. 10) and investigated using Agilent 6890 Gas chromatograph connected to an Agilent mass selective detector (MSD), 5890 series. 1 μL of filtered sample was injected into a GC column (DB-5MS, 30 m × 250 μm × 0.5 μm). The temperature of the injector port was set at set at 200˚C to enable the conversion of organic components to the gas-phase prior to MS analysis. Temperature programming was applied at a heating rate of 15˚C for 10 minutes, holding for 1 minute at 200˚C, followed by a heating rate of 25˚C for 4 minutes, and holding for 10 minutes at 300˚C. Electron Impact ionization energy of 70 eV was used [
Soot samples from tire were collected using a clean glass surface and carefully transferred into crimp top amber vials using a special brush free of impurities. Approximately 5 mg of particulate sample was added to 1 mL methanol and gold grids were dipped into the sample. Twisters were used to pick the gold grids from the sample after trapping the particulate sample. The grids were then allowed to dry in air before putting them into the analysis chamber of the SEM (JEOL JMS 7100F) [
All animal studies reported in this work are approved by the Institutional Animal Care and Use Committee and conducted in accordance with the international guidelines established by the Association for Assessment and Accreditation of Laboratory Animal Care [
During exposure periods, the wire-top lid of the mouse cage was replaced with a sealed top and high-efficiency airflow system to deliver gaseous particulates to the mice in their cages at a rate of ~250 μgm−3∙day−1. Mice were exposed to particulates from the different sources continually in order to simulate exposure of PM in the natural environment. This type of exposure protocol can be considered chronic because of the continuous exposure of particulate emissions to the mice. During exposure, the mice were provided with food pellets and water. Pulmonary response to exposure was evaluated after exposure protocol was complete.
Within 2 hours of completing the exposure protocol, control mouse was sacrificed by euthanizing with sodium pentobarbital/chloroform. This was followed by dissection in order to remove and examine the organs of interest (lungs) [
In this study, it was established that the aromatic content of tire emissions were the dominant by-products of tire combustion. In addition, the inhaled particulates may be responsible for the observed pathological effects on the lung tissues of the mice exposed to this type of emissions. Various PAHs were detected from the combustion by-pro- ducts of tire as presented in
Evidently from this study, the intensity of particulate emissions was very high hence it can be concluded that tire burning generates a lot of soot which is hazardous. The detection of cyclopentafused PAHs in the combustion of tire (fluorene) is an indication that tire particulate emissions are very toxic. This is because cyclopentafused PAHs are more bio-active than their analogous PAHs without the cyclopenta moiety [
No | Molecular toxin | Molecular structure | Retention (mins) | Molecular formula mass (g/mol) |
---|---|---|---|---|
i | benzene | 16.12 | 78.05 | |
ii | benzaldehyde | 18.41 | 106.04 | |
iii | propylcyclohexane | 19.35 | 126.14 | |
iv | benzofuran | 20.15 | 118.13 | |
v | fluorene | 20.43 | 166.22 | |
vi | anthracene | 20.51 | 178.08 | |
vii | pyrene | 22.40 | 202.08 |
A few oxygenated compounds also considered xenobiotic and eco-toxicants because of their bio-activity were detected in this investigation. This included benzaldehyde and benzofuran.
It was noted however, that numerous straight chain alkanes such as tetracosane, pentacosane, decaline, nonane, and decane (although of very low intensity) were detected in our experiments. Straight chain alkanes are also well known components of particulate emissions and are conventionally established organic toxicants.
At a magnification of 400×, the particulate emissions of tire were examined using a scanning electron microscope. The micrographs of tire particulates were remarkably interesting as it was quite difficult to obtain a clear image in the whole range of magnification. However, after several attempts a fairly neat image was obtained. Image J was used to measure the sizes of the emission particulates and size distribution was determined using Igor graphical software. The mean diameter of the particulate size of soot from tire burning was quite large (~16.23 ± 3.36 μm),
Since the principal source of airborne fine particles from combustion carry with them free radicals, it is evident that free radicals may induce cellular and alveolar damage and ultimately causing tumors, cancer, and death [
The lowest mass loss from tire combustion was recorded at a temperature of 200˚C and 550˚C. This means that the temperature of 200˚C is not sufficient to effect evolution of organic volatiles. Again at 500˚C most volatiles had been emitted at temperatures between 250˚C and 500˚C. These mass loss effects are well shown in the curve below. In-
itially, there was a slight decrease in percentage char yield at 200˚C and 250˚C. However, between 300˚C and 500˚C there was drastic change in % yield.
The decrease may be associated with high mass loss due to emission of moisture and volatiles especially PAHs such as fluorene and fluoranthene. This observation is in agreement with other results of biomass and tire combustion which indicate high mass loss occurs between 400˚C and 500˚C [
In order to understand the inhalation toxicity of tire particulates, lungs of albino mice were examined by a light microscopy interfaced with a computer to assess the effects on the tissues. After sections of 3 - 4-μm thick were cut and stained with hematoxylin and eosin (H&E), they were examined histologically. One exposure-related major finding we apparent in comparison to the control lung sample (
The alveolar histiocytosis was characterized by slightly increased number of alveolar macrophages that in general were diffusely distributed throughout the lung. The pigmented particulates found in the alveolar macrophages from the recovery animals were more commonly observed in punctate aggregates, possibly reflecting continued cellular processing of the material. Histopathological effects in the lung following exposure to the tire combustion shows that the control mouse exposed to ambient air for 14 days had normal alveolar air spaces and septa (
Air spaces contain scattered pulmonary interstitial macrophages. The mice exposed to tire emissions died after 7 days. Clearly, as observed in
Tire combustion revealed varying concentrations of the various compounds, for exam-
ple, benzaldehyde, fluorene and pyrene had the highest concentrations. These results imply that tire combustion mainly generates PAHs as the major organic volatiles. It is evident therefore from this work that tire combustion by-products are mainly PAHs, some of which have been linked tovarious biological illnesses.
The detection of cyclopentafused PAHs (fluorene and fluoranthene) is an indication that tire particulate emissions are very toxic. This is because cyclopentafused PAHs are more bio-active than their analogous PAHs without the cyclopenta moiety [
PAH have been previously identified in tire combustion and given the negative health impacts associated with them, their concentrations are of considerable interest. However, not all PAHs are of the same toxicity. The structure of a particle and the substituted groups determine harmful properties of PAHs. Many PAHs belong to the group of carcinogens, in particular the unsubstituted PAHs as well as the nitrated and methylated ones, and those containing the carboxylic group. Sulphur based compounds were detected in low concentrations and included phenylmethanethiol and benzenethiol. Nonetheless, we believe a significant amount of sulphur dioxide was evolved during the thermal degradation of tire and this may contribute to some pathological problems observed in the lung tissues of albino mice. This is because; conventionally sulphur is a major component in tire manufacture.
Combustion of tires also generates analogs of cyclic and polycyclic aromatic hydrocarbons that contain heteroatoms [
Oxy-PAHs have been measured in the environment and are detected in particulate matter emitted by combustion sources such as waste incineration, petrol and diesel emissions, bio-mass burning and tire combustion which are inclusive in this study. Oxy-PAHs have also been shown to undergo some reactions (secondary reactions) as a result of parental PAHs combining with atmospheric oxidants like hydroxyl radicals.
The presence of heteroatoms in these polycyclic compounds changes their interactions with biological tissues, giving them different health effects, when compared to PAH. Carbonyl functional groups on PAH do not increase mutagenic properties of these compounds however their oxyl radical can cause serious cellular damage.
Interesting molecular compounds of environmental concern were also identified as minor products, for instance, 2H-benzopyran. This compound is of great interest because of its characteristic behavior to cause serious environmental and biological concerns. At reasonably high temperatures and in presence of small amounts of chlorine and a transition metal such as iron or copper, it can convert into the most toxic class of compounds referred to as benzofurans usually implicated in various poisoning episodes of humans and animals [
Histochemistry is conventionally defined as the study, identification, and distribution of chemical compounds within and between biological cells using histological techniques such as histological stains, indicators, light and electron microscopy. This study proposes that soot emissions alone may not be responsible for the observed effects noticed in
The respiratory tract epithelium which normally begins at the nares and extends to the alveoli and its cellular composition conventionally varies significantly by function and structural site along the respiratory path. Volatiles carried into the respiratory tract are known to pass over epithelial cells in the nares [
This study has demonstrated that tire soot inhalation for a substantial period (i.e. 7 days of particulate exposure) of time aggravates the neutrophilic lung swelling or proinflammatory chemokine expressions related to lung dysfunction. Nevertheless, the lung pathology observed in the mice following the experimental exposures to tire particulate emissions showed significant change in airway epithelial, necrosis, and parenchymal congestion, edema, hemorrhage and inflammation (cf.
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This study has shown that exposure of tire particulates to albino mice have a severe impact on lung tissues. This observation may be extrapolated to higher order animals such as man and may evidently explain the cause of various respiratory problems such as asthma and bronchitis. There is also the production of mutagenic as well as carcinogenic compounds such as PAHs―benzene, anthracene, pyrene, and cyclopentafused PAHs (fluorene) as reported in this study and literature data. These organic toxicants are possible precursors that may disrupt the normal lining of the respiratory tract and cause potential swelling, airway collapse, and respiratory distress. This contribution has also shown that particulates from tire combustion are slightly greater than PM10 particulates.
This study was partially funded by the directorate of research and extension of Egerton University. Miss Anne of Moi Teaching and Referral Hospital (MTRH) is credited for the valuable information included in this work.
Bosire, J., Kibet, J., Kinyanjui, T. and Githaiga, B. (2016) Tire Combustion Emissions and Their Histoche- mical Implications on the Lung Tissues of Albino Mice. Open Access Library Journal, 3: e3076. http://dx.doi.org/10.4236/oalib.1103076