Determination of some polycyclic aromatic hydrocarbons ( PAHs ) associated with airborne particulate matter by high performance liquid chromatography ( HPLC ) method

In this study, polycyclic aromatic hydrocarbons (PAHs) associated with airborne particulate pollutants of aerodynamic size 10 μm (PM10) were studied for three months, from October to December 2010 in the Vanderbijlpark area. Some PAHs are highly carcinogenic and could be more harmful when combined with inhalable PM10. A dual E-Sampler which combines the light scatter and the gravimetric filter methods was used. A 10 mg/L standard stock solution that contained naphthalene (Naph), 2-methyl naphthalene (2-MNaph), phenanthrene (Phe), anthracene (Anth), benzo(b)fluoranthene (BbFl), benzo(k)fluoranthene (BkFl), benzo(a)pyrene (BaPy) and dibenzo(a,h)anthracene (DiBahAn) was prepared, compounds were indentified and quantified with an Agilent high performance liquid chromatography (HPLC). A dichloromethane (DCM) and n-hexane (1:1) extraction mixture was used to extract the pollutants from both exposed and unexposed (blank) filters. Detection limits obtained ranged from 0.001 to 0.0305 mg/L and R-values ranged from 0.996 – 0.999. Very good percentage recoveries were obtained with the lowest 97.63% and highest 101.57% associated with DiBahFl and 2-MNaph, respectively. Total concentration of 2-MNaph obtained per month were 325.2 ng/L (October 2010), 162.4 ng/L (November 2010) and 381.2 ng/L (December 2010). Relatively high levels of 2-MNaph were detected consistently when compared with other pollutants in the three months. Concentration ranges of other PAH compounds were Anth (7.2 14.76 ng/L), BbFl (6.7 13.6 ng/L), BaPy (6.8 13.0 ng/L) and BkFl (6.7 10.8 ng/L). Daily and monthly mass concentration levels obtained were lower than the strict regional daily limit of 0.075 μg/m, as well as national and international daily limits of 0.150 μg/m. These results could be used as the basis for undertaking a comprehensive study on the status of these organic compounds from the heavily industrialized Vaal Triangle region.


INTRODUCTION
Polycyclic aromatic hydrocarbons (PAHs) are a class of organic pollutants which are known to be carcinogenic to animals (Hailin et al., 1998;Menzie et al., 1992).They are lipophilic and present in the atmosphere due to emissions from vehicles, residents heating systems that utilize coal, wood, gas and industrial processes (Söderström et al., 2005).PAHs are composed of carbon and hydrogen atoms arranged in the form of fused benzene ring as cluster, linear or angular (Maliszewska-Kordybach, 1999).They exist in the atmosphere in both vapor and particulate phase (Guo et al., 2003;Van Jaarsveld et al., 1997).PAHs with low molecular weight have propensity to be more concentrated in the vaporphase whereas those with higher molecular weight are often associated with particulates (Maliszewska-Kordybach, 1999;Guo et al., 2003).When in air, PAHs can be transported over a long distance before they are deposited with atmospheric precipitation on soils, vegetation, sea and inland (Wania and Mackay, 1996;Wild and Jones, 1995).PAHs have been associated with adverse health effects in the human population (Halsall et al., 1994;IARC, 1987).They are linked to morphological, physiological and developmental abnormalities in test animals, increased allergic immune responses in human at low levels and may act synergically with other air toxics to cause adverse health effects (Li et al., 2005;ATSDR, 1995;Diaz-Sanchez et al., 1996;Harvey, 1991).Estimated potential doses of carcinogenic PAHs by inhalation to range is between about 0.02 and 3 µg/day with a median value of 0.16 µg/day, which is about 20 times more than the calculated food dose and about 25 times more than the potential dose with drinkable water (Menzie et al., 1992).
Vanderbijlpark city is located close to anthropogenic pollution sources such as mining, a coal power station, steel manufacturing companies, an oil refinery, major roads and fossil fuel burning residential areas.This city has been identified as one of the national air pollution hot spots according to the National Environment Management Air Quality Act 2004 (Act No. 39 of 2004) of South Africa (Vaal Environmental News, 2011).A number of reports exist on the general environmental pollution by PAHs within this city and the surrounding areas, however, not much if any has been reported on airborne pollution by PAHs.
The aim of this study was to evaluate the levels of PAHs associated with airborne PM10 particles from the Vanderbijlpark.Cities of Vanderbijlpark, Sasolburg and Meyerton form the Vaal Triangle region.These cities are also close to townships such as Sebokeng, Evaton and Sharpville.

Sample collection
A particulates E-Sampler from Met One Instruments Inc, Oregon Moja et al. 211 United States of America, was used to collect PM10 samples (Figure 1).The E-sampler is a dual technology instrument that combines the real time measurement of the light scatter method and the gravimetric filter method where particles are preconcentrated.An internal rotary vane pump draws air at the rate of 2 L per minute (LPM) into the visible laser light sensing chamber used for measuring the number of particles in a particular volume of air.The instrument is capable of making 40 measurements per second and averaging them to get a representative particulate data per hour, day or month.Rugged state of the art electronics measure the intensity of the focused light and output a signal to the central processing unit (CPU).The E-Sampler was placed in the backyard of a suburban house (26°42′01′′S, 27°51′15′′E) and sampling occurred in three consecutive months from October to December 2010.Continuous daily samples were averaged every 30 min and then arranged per month.Data measured on the day which experienced the highest PM10 loading was further arranged per hour to study the diurnal distribution.High purity quartz filters (20 x 25 cm Whatmann 41, Whatman Corp, USA) were used and dried in a desiccator overnight.A mass of filter paper was weighed before and after exposure to attain the total particulate mass loading per sampling period on a Mettler Toledo AG245 analytical balance.

Standard and sample preparation
A 1.0 mg/L standard stock solution was prepared by dissolving 1.0 mg of each of Naph, 2-MNaph, Phe, Anth, BbFl, BkFl, BaPy and DiBahFl PAH compounds (Dr.Ehrenstorfer Reference Materials, Atlanta, U.S.A.) in 1000.0 ml acetonitrile solvent.All solvents used were of analytical grade and were obtained from Sigma-Aldrich, Johannesburg, S.A.A series of calibration standard solutions ranging between 0.01 and 1.0 mg/L were prepared from the stock solution.
A benchmark method for the extraction of PAHs from soils and sediments (was adopted during this study (Lau et al., 2010).The soxhlet extraction apparatus were cleaned by evaporating methanol at 180°C in a rotaevaporator three times, followed by three times evaporation of the extraction mixture of dichloromethane (DCM) and n-hexane (1:1) for an hour.The fourth extract of the extraction solvent mixture was collected from the receiving flask for analysis.PAH compounds were extracted from both unexposed and exposed filters with the prepared extraction mixture for an hour at 180°C in the rotaevaporator.Extracts were analyzed on the same day or stored in amber sample bottles in a fridge at below 4 °C temperatures.About 20.0 μl of sample were injected five times per sample in a high performance liquid chromatographic (HPLC) instrument.
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PM10 mass concentration
Average daily and monthly PM10 mass concentrations for three months are shown in Table 1.The highest mass concentration data per month were: 0.048 mg/m 3 (20 th ), 0.03554 mg/m 3 (6 th ), 0.02283 mg/m 3 (4 th ) and 0.02196 mg/m 3 (29 nth ) in October; 0.02754 mg/m 3 (28 th ); 0.02046 mg/m 3 (13 th ) in November and the December data were all below 0.02 mg/m 3 .These results are also in agreement with those obtained in summer seasons as reported (Moja et al., 2012).Average daily mass concentrations were below the stringent Vaal Triangle regional standard of 0.075 mg/m 3 .Department of Environmental Affairs (DEA's) national daily limit together with international EPA's standard and WHO's guidelines of 0.150 mg/m 3 were also not exceeded (NAAQS, 2009;Annergan and Scorgie, 2002).The highest daily PM10 loading was obtained on the 20 th October.Hourly distribution of this data is shown in Figure 2, with the largest peak starting from 2:00 (0.0001 mg/m 3 ) and ending at 16:00 (0.0011 mg/m 3 ) with a peak maxima occurring at 13:00 (0.0043 mg/m 3 ).A smaller peak was measured from 18:00 (0.0011 mg/m 3 ) to 22:00 (0.001 mg/m 3 ) with a peak maxima at 19:00 (0.0021 mg/m 3 ).Similar PM10 diurnal distribution pattern within this study area was previously reported (Moja et al., 2012).This distribution pattern resemble the morning traffic flow to work, as well as the optimized industrial activities at around midday.

Concentrations of PAHs
Detection limits for the instrument were taken as three times the standard deviation of the lowest detectable concentration of PAHs from the mean of triplicate analyses and ranged from 0.001 to 0.0305 mg/L (   times are listed in the same order.Figure 6a   levels of 2-MNaph were detected consistently when compared with other pollutants in the three months of this study (Figure 7).Concentration ranges of other PAH compounds were Anth (7.2 -14.76 ng/L, BbFl (6.7 -13.6 ng/L), BaPy (6.8 -13.0 ng/L and BkFl (6.7 -10.8 ng/L).2-MNaph is formed through the distillation of methylnaphthalene, where 1-methylnaphthalene is removed leaving behind 2-MNaph (ATSDR, 1995).Mixtures containing 2-MNaph are used in the formulation of alkyl-naphthalenesulfonates (used for detergents and textile wetting agents), chlorinated naphthalenes, and hydronaphthalenes (used as solvents).Pure 2methylnaphthalene is a component used in the manufacture of vitamin K and the insecticide carbaryl (1naphthyl-N-methylcarbamate) (HSDB, 2002).Possible PAH sources within the study area would include combustion activities from a coal power station, coal using steel manufacturing companies, an oil refinery and diesel and petrol powered vehicles or informal burning of solid waste.Another possible source could be insecticides used at a nearby farm area.
This study successfully evaluated the levels of some PAHs association with airborne PM10 particles within the Vanderbijlpark study area.Based on these results and the outcome of other similar studies (Liu et al., 2006), airborne PAHs and PM10 pollutants could be used as indicators of urban air pollution.

Conclusion
Average daily and monthly mass concentration levels obtained were lower than the strict regional daily limit, as well as national and international daily limits.
The presence and wide distribution of some PAHs within the Vanderbijilpark environment is a major challenge Moja et al. (2013) reported the presence of some carcinogenic compounds such as BbFl and InPy in water samples used for domestic and agricultural purposes in the same study area.The current study also reports the existence in the atmosphere of PAH compounds that could cause adverse human health effects, for example, Anth, BbFl, BkFl and BaPy.The association of respirable fraction of airborne particles with toxic PAHs elevates local air to dangerous levels.These results could be used as the basis for undertaking a comprehensive study on the status of these organic

Figure 1 .
Figure 1.Filter loading area of the E-Sampler (Model 9800 Rev G).

Figure 3 .
Figure 3. Chromatogram of PAHs from the prepared extracting solvent mixture.

Figure 4 .
Figure 4. Chromatogram of PAHs extracted from an unexposed filter paper.

Figure 5 .
Figure 5.A chromatogram of standard PAHs mixture.

Figure 6 .
Figure 6.Chromatograms of (a) October sample, (b) November sample and (c) December sample.

Table 1 .
Average daily and monthly PM10 mass concentration results levels (mg/m 3 ).