135
Heavy Metal Contamination of Airborne Dust in the Environment of Two Main Cities in the Eastern Province
of Saudi Arabia
Moetaz Mahmoud El-Sergany and Mahmoud Fathy El-Sharkawy Environmental Health Department, College of Applied Medical Sciences,
Dammam University, Kingdom of Saudi Arabia
Abstract. Amounts and chemical components of airborne dust in urban city centers are important environmental pollution indicators. High concentrations of heavy metals in the environment result in health hazards including adverse effects on the nervous, blood forming, cardiovascular, renal and reproductive systems. The aim of the present study was to assess the heavy metals contamination of street and ambient airborne dust in two main cities in the Eastern Province of Saudi Arabia. Dust samples were collected from street environment and ambient air at different sites in the selected two cities. The metal composition of dust samples was quantitatively determined by inductively coupled plasma-atomic emission spectrometer. The average concentrations of ambient airborne dust were below the Saudi's air quality criteria of 150µg/m3, while the average levels of street airborne dust were exceeding the air quality standards of 150 – 350 µg/m3. Metal concentrations in the street airborne dust were much higher than those of the ambient type. Aluminum (Al) is considered as an index of mineral dust, and during this study, values of metal/Al ratios for street airborne dust were much higher than those of the ambient type. This reflects the high contribution of man-made sources, particularly motor vehicles, in metal composition. Banning of leaded petrol helped in the general decrease of lead (Pb) concentrations in the KSA Eastern Province atmosphere.
Keywords: street airborne dust, total suspended particulate, metal composition, air quality criteria, motor vehicles, and atmosphere.
Introduction
Airborne dust (or total suspended particulate, TSP) within the urban environment is attributed to a number of both natural and anthropogenic sources, including the increase in motor vehicles, urban construction, heating installation and industrial combustion. Relatively little data are available for dust chemical composition (Peachey et al., 2009 and Caoa et al., 2009).
The chemical components and quantities of roadway and airborne dust in urban city centers are important environmental pollution indicators (Harrison et al., 2004 and Yongming et al., 2006). In recent decades, there have been numerous studies on the extent of heavy metal contamination in roadway and airborne dust and source identification in different countries of the world (Banerjee et al., 2003; Azimi et al., 2005; Ahmed et al., 2006; Tokalıog˘lu and Kartal, 2006; Al-Khashman et al., 2007; Preciado et al., 2007 and Lu et al., 2009).
Heavy metals are often associated with high traffic densities (Allen et al., 2001; Harrison et al., 2003; Riga-Karandinos et al., 2004 and Wahlin et al., 2006). Previous studies indicated that road traffic can contribute to airborne metals through different pathways, e.g., combustion products from fuel, wear products from tires, brake linings and road construction materials, and re-suspension of road dust (Young et al., 2002; Abu-Allaban et al., 2003, and Furusjo¨ et al., 2007). The most common heavy metals released from vehicles on road are cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), iron (Fe), and zinc (Zn) (Sezgin et al., 2003; Al-Khashman et al., 2004, and Han et al., 2007).
Street dust investigation is of particular importance for two main reasons. First, street dust is freely being inhaled by those traversing the streets and those residing within the vicinity of the streets. The more the dusts on such streets become contaminated with heavy metals, the more such people are exposed to the health hazards associated with such metals. Second, when rains are received, dust usually gets discharged in the adjoining marine environment, and could seriously pollute water and concentrates in the surface sediments of the coastal areas. This might prove toxic to marine life, and at worst it may contaminate fish or shellfish, which could have adverse direct impacts on the health of individuals that consume seafood (Chirenje et al., 2006). In general, high concentrations of heavy metals in the environment result in health
hazards such as adversely affecting the nervous, blood forming, cardiovascular, renal and reproductive systems. Other includes reduced intelligence, attention deficit and behavioral abnormality (Inyang and Bae, 2006).
In recent years, there is a growing concern for the potential contribution of ingested dust to metal toxicity in humans. Some trace metals (such as Cu and Zn) at small amounts are harmless, but some (mainly Pb, As, Hg and Cd) even at extremely low concentrations are toxic and are potential cofactors, initiators or promoters in many diseases and cancer (Willers et al., 2005). Young children are more likely to ingest significant quantities of dust than adults because of the behavior of mouthing non-food objects and repetitive hand/finger sucking. In addition, children have a much higher absorption rate of heavy metals from digestion system and higher hemoglobin sensitivity to heavy metals than adults (Ferreira-Baptista and Miguel, 2005; Ahmed et al., 2006;
Schwarze, 2006; Duong and Lee, 2009 and Faiz et al., 2009). Metals are also an important and emergent class of carcinogens (Seoane and Dulout, 2001). They induce DNA damage and have varied genotoxic effects (Mouron et al., 2001).
The Kingdom of Saudi Arabia (KSA) is one of the developing countries that have rapid improvement in commercial and industrial activities. The number of cars in the Kingdom of Saudi Arabia has been increased from 100,000 in 1979 to approximately 7 million in 2004 (Al- Rajhy, 2004). The Eastern Province is considered one of the most important sectors in KSA. Presence of seaport, a large number of industries and several universities encourage migration of people to this region for getting job, studying, and recreational activities. Hence, air pollutant levels, particularly airborne dust, are expected to be high in its atmosphere. The combination of high population density, rapid industrialization and dense traffic activity in the Eastern Province, has inevitably led to increased dust levels in its environment. Very limited information is available on heavy metals in the urban dusts of developing countries, including KSA. Moreover, limited attention has been focused on other trace metals which have adverse effects on human health, as well as on the environment. The aim of the present study was to assess the heavy metals contamination of street and ambient airborne dust in two main cities in the Eastern Province of Saudi Arabia; Dammam and
Khobar. Similar studies have not been previously conducted in this region.
Materials and Methods Study Areas
Two areas with completely different pattern of traffic activity were selected for this study: King Fahd Road representing a very heavy traffic activity, and King Faisal University (KFU) campus representing a light or moderate traffic area. These two different areas were selected to study the effect of traffic activity on dust levels and its heavy metal constituents in the environment of urban areas.
King Fahd Road is one of the most important roads in the Eastern Province. It connects between the two largest cities in this area, Dammam (the capital) and Khobar. It is surrounded by all types of human activities (industrial, commercial, residential, recreational, educational, etc) and thus, it is crowded with heavy traffic activity most of the day. Two locations were selected as sampling stations in this road.
These two locations had nearly the same characteristics, one of them was near Dammam city and the other near Khobar. Samples of street airborne dust were simultaneously collected from the locations.
King Faisal University (KFU) campus lies between Dammam and Khobar Cities far from the King Fahd Road by more than five kilometers.
It is located near Dammam seaport and is surrounded from the north by Saudi Naval Institute (light traffic activity), from the east by the main coastal road (moderate traffic road), from the south by Al-Rakh district and from the west by a residential area with very low traffic activity.
Inside the Campus, two similar locations were selected as sampling stations; the first was located at the northern wall of the campus, while the second was located at the eastern wall. Samples of ambient airborne dust were collected from the two stations at the same time.
Collection of Dust Samples
This study was conducted during the spring season (February-May) of the academic year 2008-2009. This period was characterized by nearly constant weather conditions; with atmospheric temperature of 25-30°C, relative humidity of 45-50% and steady wind speeds.
Samples of ambient airborne dust were collected for about eight hours per day on Staplex® No. TFAQ810 quartz fiber filters (8 x 10 inch) by the Staplex® High Volume Air Samplers at a flow rate of 1.7- 1.9 m3/min for each sample at a height of about 1.5m. Street airborne dust samples were collected for about eight hours during the day on 60 mm quartz fiber filters by the MUNRO L5-10 Portable Air Sampler at a flow rate of 10 L/min. Samples were taken at 1.5m height. Sampling of both types of dust was conducted during three days of the week for continuously for four months. A total number of 100 samples was collected for each type.
All filters were conditioned at a constant temperature (23 ± 3 ºC) and at a constant humidity (45 ± 5 %). Concentrations of the two types of particulate matter were calculated gravimetrically. The weight difference of each filter, before and after sampling, was calculated and then divided by the collected sample air volume to obtain the corresponding concentrations in microgram of dust per cubic meter of air (µg/m3) (Inter Society Committee, 2000).
Sample Analysis
Heavy metals in dust samples were digested at a temperature of 75–
90 ºC with 5 ml of concentrated metal grade hydraulic acid and 0.5ml of concentrated metal grade nitric acid (Kuo et al., 2009). After completions of the digestion process, digested samples were filtered using glass fiber filters (Whatman grade 934AH) under vacuum. Filtrate was transferred quantitatively and diluted to 25 milliliter with deionized water (Inter Society Committee, 2000). A blank was prepared in the same way with unexposed fresh filter paper.
Analysis of the elements was carried out using inductively coupled plasma-atomic emission spectrometer (ICP-AES) – (ICAP 6000 Thermo). The wavelength calibration was performed using internal calibration, by a mercury vapor lamp. The standardization for the different elements was carried out using multi element standards. The measurements for emission were carried out at the optimum wavelengths in nm – Cr (205.55); Mn (257.61); Fe (238.20); Cu (324.75); Zn (213.86); Cd (214.44); Pb (220.35); Al (194.23). Proper quality assurance procedures were followed in site selection, sampling preservation, and analysis (Rahn, 1976; Rastogi and Sarin, 2009;
Jayasekher, 2009; and Godoy et al., 2009).
Quality Assurance of Sampling and Analysis
Dust samplers were calibrated before sampling. Filter paper used for sample collection was given utmost care to protect from external contamination. A blank filter paper was employed exactly with the same extraction and analytical procedure in order to examine the background concentration. All glassware and filter assembly used for extraction and analysis were acid washed and oven dried to avoid contamination. Trace element analyses were done using well-calibrated ICP-AES. Laboratory and field blank samples were also measured for internal quality assurance. All samples were analyzed in triplicate to get the concordant value. The measured concentrations were compared with those given in literature for other places around the world. The pollution level of every metal has been evaluated and discussed.
Data Handling and Analysis
Data entry and analysis were conducted using Microsoft Office Excel Program. Measures of central tendency and measures of dispersion were calculated and graphs were designed and drawn using the same program. Test of significance (independent t-test) was performed using SPSS-16 Package.
Results and Discussion Dust Concentration
Table 1 summarizes the daily average concentration of ambient dust levels and its metal composition at the two selected sites inside KFU campus. The daily average dust concentrations at station 1, which is located near the low-traffic road, were in the range of 31.4 – 120.8 µg/m3, with an average concentration of 85.2 ± 31.4 µg/m3. At station 2, the daily average concentration was in the range of 59.2 – 140.5, with an average concentration of 94.8 ± 30.8 µg/m3. The higher levels of ambient dust at this station compared with station 1 (which is located at the end of campus near from low traffic movement), indicates the main role of motor vehicles in the magnitude of air pollution problem in the urban atmospheres rather than other sources (industrial, commercial and residential). The averages of both stations (89.7 ± 30.4 µg/m3) were below the Saudi's air quality criteria of 150 µg/m3.
Table 1. Concentrations of airborne dust and their metal constituent levels in µg/m3 in the environment of King Faisal University Campus.
Pollutant Station 1 Station 2 Sig. (t-test)
TSP 85.2 ± 31.4 94.8 ± 30.8 0.562
Al 0.74 ± 0.57 0.76 ± 0.61 0.964
Cd* 0.15 ± 0.07 0.14 ± 0.04 0.626
Cr* 1.81 ± 0.95 1.81 ± 1.1 0.998
Cu 0.034 ± 0.03 0.049 ± 0.033 0.369
Fe 0.41 ± 0.27 0.41 ± 0.28 0.999
Mn 0.014 ± 0.005 0.013 ± 0.005 0.545
Pb 0.021 ± 0.01 0.021 ± 0.011 0.820
Zn 0.23 ± 0.24 0.104 ± 0.068 0.198
*ng/m3
Table 2 represents the daily average concentration of street airborne dust and its chemical components in Dammam and Khobar cities. The concentration of the street airborne dust ranged from 83.3 to 1166.7 µg/m3 with an overall mean level of 463.5 ± 216.8 µg/m3 for all locations during this study. The average level of street airborne dust in Dammam city (695.5 ± 303.7 µg/m3) was much higher than that in Khobar City (213.5 ± 130.0 µg/m3). This can be explained by the high traffic density and road reconstruction projects in Dammam compared to Khobar. In addition, the average levels of street airborne dust (463.5 ± 216.8 µg/m3) were found to exceed the air quality standards (150 – 350 µg/m3) of total suspended particulates for different countries in the world (Kilbride et al, 2006). On the other hand, the mean level of street airborne dust during the morning periods in Dammam (798.2 ± 278.2 µg/m3) was higher than that of the evening periods (592.8 ± 316.5 µg/m3). This finding confirms the serious effect of traffic activity in polluting the urban atmosphere by different contaminants, particularly dust or particulate matter.
Table 2. Concentrations of airborne dust and their metal constituent levels in µg/m3 in the street environment of a main road in KSA.
Pollutant Dammam Khobar Sig. (t-test)
TSP 695.5 ± 303.7 213.5 ± 130.0 0.000
Al 1.39 ± 2.92 6.93 ± 4.73 0.001
Cd* 9.4 ± 15.0 7.4 ± 7.8 0.657
Cr* 907.2 ± 467.3 1120 ± 1630 0.647
Cu 1.67 ± 1.03 0.88 ± 0.53 0.022
Fe 10.2 ± 6.7 4.71 ± 5.35 0.026
Mn 0.33 ± 0.26 0.18 ± 0.22 0.147
Pb 0.04 ± 0.07 0.047 ± 0.06 0.765
Zn 63.0 ± 72.0 46.9 ± 68.7 0.559
*ng/m3
Statistical analysis of dust results using independent t-test (Tables 1,2 and 3) shows significant differences (p < 0.05) between the levels of ambient and street airborne dust and between street dust levels in Dammam and Khobar cities, while there is no statistical differences between levels of ambient airborne dust for the two university campus stations.
Table 3. Independent t-test value for ambient and street airborne dust and their metal constituent levels during this study.
Correlation Sig. (t-test)
Ambient & Street dust 0.000
Elemental compositions:
Al 0.009 Cd* 0.009 Cr* 0.002 Cu 0.000 Fe 0.000 Mn 0.000 Pb 0.198 Zn 0.004
Elemental Compositions
As shown in Tables (1-3), concentrations of the eight measured metals (Al, Cd, Cr, Cu, Fe, Mn, Pb and Zn) in the street airborne particulate matter were much higher compared to the ambient type.
Comparing between metal compositions of ambient airborne dust samples, only the two sampling stations inside the university campus indicated that the levels of three metals (Al, Cu and Zn) at station 2 (the nearest to road traffic) were higher than those at station 1, while levels of the other metals were nearly the same. This can be attributed to the impact of motor vehicle emissions on the surrounding atmosphere as mentioned before. For this type of dust, there is no significant difference for all elements between the two selected stations.
For the street airborne dust, significant differences between Dammam and Khobar for Al, Cu and Fe were found. The statistical correlation between the metal compositions of the two types of dust showed high significant differences (p < 0.01) for all elements, except for Pb. Traffic speed and traffic volume are the important factors that can influence the differences of metal concentrations in the urban atmosphere (Kuo et al., 2009). Road conditions (e.g., gradient, curve, branch roads, road surface damage, etc.) can affect the traffic speed (Kuo et al., 2009).
Although there were no branch roads or road surface damage at the sampling sites, the difference in road design (traffic lights, bridges or tunnels) at these sites might have led to the wide variability in airborne metal concentrations. Additionally, driving conditions (stop and go or free cruising conditions, brake or acceleration maneuvers) can also influence the differences of metal concentrations among these sites (Kuo et al., 2009). On the other hand, there was no significant difference between Pb concentrations at all sampling points in Dammam and Khobar cities. Until a decade ago, one of the major sources of Pb to atmosphere was vehicular emission (gasoline combustion), but with the ban on leaded petrol, a general decrease is expected in its atmospheric abundance. However, atmospheric concentration of Pb over the Eastern Province of Saudi Arabia Kingdom was higher than some of the reported data in literature (Kocak et al., 2004 and Farinha et al., 2009); but lower than that over heavily polluted sites such as India (Venkataraman, 2004).
According to Rahn (1976) and Rastogi and Sarin (2009), Al is considered as an index of mineral dust. In order to characterize the mineral dust over the studied region, we have calculated the ratio of concentrations of different elements to that of Al measured in both types of particulate matters (Table 4). Values of all metal/Al ratios, except Pb, for street airborne dust are higher than those of the ambient type. This reflects the high contribution of man-made sources, particularly motor vehicles, in metal composition of the KSA Eastern Province atmosphere. In contrast, the higher ratio of Pb/Al for the ambient airborne dust than the street type confirms the above conclusion of the negligible role of motor vehicle emission in polluting the atmosphere with Pb after using the unleaded gasoline in the KSA Eastern Province. Table (5) shows values of metal/Al ratios in the ambient airborne dust in the present study compared with other studies in different cities of the world. It is evident that values of all ratios, except Zn/Al, during the present study were nearly similar or very close to values of the other studies. The Zn/Al ratio of the present study is higher than the other studies. Sources of Zn in the atmosphere were reported to be non-ferrous metal production, iron and steel manufacturing, coal and wood combustions (Pacyna et al., 1984;
Nriagu et al., 1988 and Aziz et al., 2006). The Eastern Province of Saudi Arabia is characterized by the presence of different industrial sectors (e.g. Jubail and Dammam) including large number of industries of different activities that represent another main source of metals in the
atmosphere. Furthermore, the deposition of dust derived from the study region to various aquatic systems (oceans/lakes) will have different effect than that due to mineral dust having Upper Continental Crust (UCC) composition. These characteristics can also be utilized in tracing the long-range transport of dust from continent to ocean or continent to continent.
Table 4. Metal/Al ratios of ambient and street airborne dust.
Ratio Cd/Al Cr/Al Cu/Al Fe/Al Mn/Al Pb/Al Zn/Al
Ambient
airborne dust 0.192 0.002 0.055 0.542 0.018 0.028 0.230 Street airborne
dust 2.033 0.242 0.307 1.820 0.063 0.010 13.273
Table 5. Metal/Al ratios in ambient dust of this study compared with other studies.
Ratio Present study
Ahmedabad (India)
Mumbai (India)
ZBT (China)
Erdemli
(Turkey) UCC
Fe/Al 0.54 0.59 1.23 0.59 0.68 0.44
Pb/Al 0.028 0.0154 - 0.025 0.0423 0.0002
Mn/Al 0.0178 0.0138 0.079 0.015 0.0135 0.0075
Zn/Al 0.23 0.018 0.185 0.035 0.0251 0.0009
Conclusions
Metal composition of the KSA Eastern Province atmosphere was characterized by high metal contents of the street airborne dust compared with the ambient airborne dust. Values of metal/Al ratios street airborne dust were higher than those of the ambient type, which reflects the high contribution of man-made sources, particularly motor vehicles, in this sector. In addition, banning of leaded petrol, helped in the general decrease of Pb concentrations in the Kingdom atmosphere.
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