Authored by YN Jolly*
Abstract
This study deals with the determination of the polycyclic aromatic hydrocarbons (PAHs) in the atmospheric particulate matters (PM2.5) at a semi residential site of Gazipur, Dhaka, Bangladesh. Source identification and possible human health impact of polycyclic aromatic hydrocarbon was evaluated as well. A total of 20 samples were collected in six weeks period of time. Polycyclic Aromatic Hydrocarbons (PAH’s) were determined using gas chromatography-mass spectrometry. The average concentration of Anthracene, Phenanthrene, Pyrene, Chrysene, Benzo (a) anthracene, Benzo(a)pyrene, perylene were found to be 0.309, 0.159, 0.227, 2.120, 1.954, 2.269 and 3.373μgm-3 respectively. Two-way ANOVA test revealed that the concentration of different PAHs species (Fcal> Fcrit) are significantly different from each other at a 95% confidence level. The main contributory sources for PAHs were found gasoline exhaust, diesel exhaust, wood burning and brick kilns. The result revealed that these compounds are present in a higher level in the atmosphere when compared with the value of other countries in the world. Concentration of highly carcinogenic Benzo(a) pyrene was in a range where carcinogenic effect is an immediate threat in case of long-time exposure and hence regular monitoring is suggested.
Keyword: Polycyclic Aromatic Hydrocarbon; Air-Metrics Mini-Vol Samplers; Gas Chromatography-Mass Spectrometry; Quartz Filters
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are organic compounds consist of two or more fused benzene rings in a linear or cluster arrangement, typically found as a complex mixtures [1]. They are very stable organic pollutants that are made up of only carbon and hydrogen and occur naturally but, they can be synthesized as individual compounds for research purposes. Furthermore, they have high boiling and melting points with high molec ular weights and are able to survive at high temperatures from the combustion of fuel from automobiles and airplanes engines and most of them have low water solubility [2]. Polycyclic aromatic hydrocarbons (PAHs) are considered ubiquitous in the environment and can be formed from either natural or manmade combustion sources [3]. The dominant sources of PAHs in the environment are thus from human activity: wood-burning and combustion of other bio-fuels etc., and wildfires are another notable source. Dungor crop residues contribute more than half of annual global PAHs emissions, particularly due to bio fuel use in India and China (Anita and Maharaj,2004), industrial processes and the extraction and use of fossil fuels made up slightly more than one quarter of global PAHs emissions, dominating outputs in industrial countries such as the United States. Lower-temperature combustion, such as tobacco smoking tends to generate low molecular weight PAHs, whereas high-temperature industrial processes typically generate PAHs with higher molecular weights [4].
Atmospheric PAHs are distributed (Figure 1) between the gas and particulate phases depending on their physicochemical properties. They can be transported through the atmosphere over long distances. Polycyclic Aromatic hydrocarbons are emitted into the atmosphere either as vapors or associated with primary aerosol particles. Once enters in the atmosphere, the residence times and ultimate fates of these semi volatile chemicals depend upon their distributions among vapor, particle, and droplet phases. The atmospheric chemical and photochemical reactions of PAHs are of great importance because the decomposition product of the PAHs may be more hazardous to human health than the PAHs from which they were derived [5]. A number of experimental studies have demonstrated that many PAHs are susceptible to photochemical and/or chemical oxidation under simulated atmospheric conditions [6]. Nitro PAHs are emitted as a result of incomplete combustion processes.
PAHs have been linked to different cancers in well-established animal model studies [7]. The structure of a PAH influences whether and how the individual compound is carcinogenic [8]. Some carcinogenic PAHs are genotoxic and induce mutations that initiate cancer; others are not genotoxic and instead affect cancer promotion or progression [9] and hence continued research regarding the mutagenic and carcinogenic effects from chronic exposure to PAHs and metabolites is needed. Other than carcinogenic, adult exposure to PAHs has been linked to cardiovascular disease as well [10]. PAHs are among the complex suite of contaminants in tobacco smoke and particulate air pollution and may contribute to cardiovascular disease resulting from such exposures [11]. laboratory experiments, animals exposed to certain PAHs have shown increased development of plaques (atherogenesis) within arteries [12]. Oxidative stress following PAH exposure could also result in cardiovascular disease by causing inflammation, which has been recognized as an important factor in the development of atherosclerosis and cardiovascular disease [13,14]. Biomarkers of exposure to PAHs in humans have been associated with inflammatory biomarkers that are recognized as important predictors of cardiovascular disease, suggesting that oxidative stress resulting from exposure to PAHs may be a mechanism of cardiovascular disease in humans [15]. Multiple epidemiological studies of people living in Europe, the United States, and China have linked in uterus exposure to PAHs, through air pollution or parental occupational exposure, with poor fetal growth, reduced immune function, and poorer neurological development, including lower IQ.
As PAHs are known to have carcinogenic, mutagenic and teratogenic properties, their persistence in the environment have been placed them on the list of priority pollutants by the United States Environmental Protection Agency (US-EPA) and also the European Environment Agency [16]. People from all over the world are concerned more about the air pollution aspects due to the increased rate of mortality and morbidity and also multifarious effects of particulate pollution and we are not out of it. In this regard it is imperative to have a systematic study ascertaining the facts concerning the nature, sources, and trends of the particulate pollution in our beloved city, Dhaka, Bangladesh.
Gazipur area of Dhaka, Bangladesh is known to have moderately dense in population with high traffic and other industrial establishments like garments factories etc. There are several brick kilns in and around the area; more over there is a very busy rail station. Different types of industrial and regular activities are there responsible to contribute a lot carcinogenic aromatic polycyclic hydro carbons in the air of that area that ultimately affects local habitants as well as the visitors. Present study therefore sketched to determine the polycyclic aromatic hydrocarbon concentration in the atmospheric particulate matters collected from Gazipur, Dhaka, Bangladesh, identification of possible sources and human health impact. The main objectives are therefore:
• Determination of the polycyclic aromatic hydro-carbons concentration in the atmospheric particulate matters of Gazipur air
• Identification of the source of the polycyclic aromatic hydrocarbon in the atmosphere.
• Understanding the possible human health impact of polycyclic aromatic hydrocarbon.
Materials and Methods
Sampling site
Air samples were collected from Gazipur area of Dhaka, Bangladesh, which is a residential area of moderate population density. The sampling location is within 20 m from a local road and about 200m from a secondary roadwith moderate traffic density. The highway of Joydeb puris a very busy traffic point, which is about 5 km west to the studied site. Joydebpur rail station, through which daily 60 trains pass away, is about 100m away from the sampling location. At “Konabari” and “Kodda” which are about 5 to 7 km to the north-west of the sampling site, more than 100 brick kilns are there in production using kindle wood. There are also many garments and other industrial units at 4 to 7 km distance from this site (Figure 2).
Samples collection and preparation
PM2.5 (particulate matter) sampling was started from 13 January 2014 by Air-Metrics Mini-Vol samplers at Joydebpur (Gazipur), Dhaka, Bangladesh. And the samplers were placed on the flat roof of the continuous air monitoring station (CAMS-4) site of Clean Air and Sustainable Environment (CASE) project, Gazipur city corporation central symmetry, at 20 feet height from the ground level. The amount of air passed was maintained at 7.2m3.PM2.5 was collected simultaneously for every 24 hours (from 10 a.m. to 10 a.m. of the next day) at the sampling site. The pre-weighted conditioned clean filters (quartz) were loaded to respective filter holder assembly at the conditioning room of CAMS. After sampling, filter holder assemblies (keeping the exposed filters inside) were brought to the conditioning room of the Atomic Energy Centre (AEC), Dhaka, directly from the sampling site for conditioning and PM filter retrieval. Special care was taken in transporting the exposed filter holder assemblies, so that there should be no PM loss.PM2.5 masses were measured in the Atmospheric and Environmental Chemistry Laboratory of Chemistry Division of the Atomic Energy Centre (AECD), Dhaka and preserved under 4°C temperatures. The aerosol sample having PM2.5 was determined by weighing filter before and after exposure using a micro balance. The difference in weights for each filter was calculated and the mass of each PM2.5 sample thus determined.
Extraction of Samples
The particulate PAHs containing sample was weighed and taken into the volumetric flask, then about 30 ml dichloromethane (DCM solvent solution) was added to dissolve the PAHs, kept for 24 hours then sonicated. After sanitations the extract was filtered through what man filter paper and collected in a clean volumetric flask. Special attention was given to avoid loss of extract. Silica clean up column was prepared and the samples were passed through the column and collected. The total solution was concentrated using liquid nitrogen gas to 1-2 ml and transferred into a GC vial for analysis.
Preparation of standard PAHs solution
A known amount of PAHs was dissolved in definite amount of solvent (dichloromethane) to prepare 5 ppm PAHs standard solution of Phenanthrene, Anthracene, Pyrene, Chrysene, 1.2-benzanthracene, Perylene, Benzo-a-pyrene, marked with individual identification number and was stored in the refrigerator. The quantitative determination of PAHs has been done by external calibration curve method. The calibration curve of each compound is prepared with known concentrations of the compound prepared and run through GC-MS. Standard curve for each compound is generated by plotting the area vs. the concentration range for corresponding samples. Over this concentration range, the linear regression analysis of peak areas (y) in function of concentration (x), calculated by least square method. Calibration curve for each compound is presented in (Figure 3).
Chromatogram of a standard PAHs solution
The GC column temperature program employed was 400C to 2800C, started from 400C with holding time 1 min and then raised to 1600C at 100C min-1 ramping and finally the temperature raised to 2800C at 150C min-1 ramping. The injector and detector temperature were 2500C and 2800C respectively. The difference in the chemical properties between different molecules in a mixture and their relative affinity for the stationary phase of the column will promote separation of the molecules as the sample travels the length of the column. The molecules are retained by the column and then elute come off from the column at different time (called the retention time), and this allows the mass spectrometer downstream to capture, ionize, accelerate, deflect, and detect the ionized molecules separately. The mass spectrometer does this by breaking each molecule into ionized fragments and detecting these fragments using their mass-to-charge ratio. So, the components have been separated and detected through their retention time and quantified the area through their charge to mass ratio. The retention time of standard solution is 21.59, 21.75, 25.79, 29.40, 29.51, 33.23 and 33.45 min for Phenanthrene, Anthracene, Pyrene, Chrysene, Benz[a]anthracene, Perylene, Benzo[a]pyrene respectively.
Result and Discussion
Analysis of different PAHs in PM2.5 samples
Distribution of different PAHs revealed that the concentrations vary from time to time depending on the trend of air flow. In general, concentration of total PAHs is easily affected by location and seasonal variation. Besides local sources of PAHs, in both urban and rural areas, transport of PAHs through atmosphere can play a large role. The highly carcinogenic benzo[a]pyrene was normally found in the range of 1-20 ng/m3 in Europe, and around 1 ng/m3 in the USA. For other PAHs, individual concentrations were generally in the range of 1-50 ng/m3 in Europe, 0.1-1 in North and South America and in Australia, 1-10 in Japan, and 10-100 in two towns in India and New Zealand [17]. The measured concentration of Phenanthrene, Anthracene, Pyrene, Chrysene, 1,2- Benzanthracene, Perylene, Benzo-a-Pyrene are presented in (Table 1).
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