Contamination of Environment with Polycyclic Aromatic Hydrocarbons in India ()
1. Introduction
Polycyclic aromatic hydrocarbons (PAHs) are a large group of chemical compounds, I, with a similar structure comprising two or more joined aromatic carbon rings [1] . The compounds are formed by combustion of fuels, biomass and waste materials [2] . Polycyclic aromatic compounds are carcinogenic and mutagenic compounds, causing irreversible changes in the structure and functioning of living organisms [3] . There are thousands of PAH compounds in the environment but 13 compounds i.e. naphthalene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benz (a) anthracene, benzo (b) fluoranthene, benzo (k) fluoranthene, benzo (a) pyrene, benzo (ghi) perylene, dibenz (ah) anthracene, indeno1,2,3-(cd) pyrene and coronene of the increased environmental and health interests. These compounds differ substantially in their physical, chemical and toxicological properties and therefore, their quantification in the environment is needed. The most potent carcinogens have been shown to be benzo [a] anthracene, benzo [a] pyrene and dibenz [ah] anthracene. They are multimedia contaminants, reported at elevated levels in several environmental samples i.e. dust, particulate matter, sludge and sewage of various region of the World [4] - [26] .
2. Methods and Materials
2.1. Selection of Sampling Sites
Raipur (21˚23'N, 81˚63'E) is the capital city of the Chhattisgarh state with population of »2 million. The Raipur city is now becoming an important regional commercial and industrial destination for the coal, power, steel and aluminum industries. Several steel rolling mills, sponge iron plants, steel plants, agro-industries, thermal power plants and vehicles (>1.0 × 105) are emitting effluents in and around the city.
2.2. Collection of Samples
The road dust, sludge and sewage samples were collected using a stainless-steel scoop from 13 locations of Raipur city in February 2010, Figure 1. They were kept in 250-mL glass bottle and dried at 30˚C in an oven for overnight. The samples were crushed into fine particles by mortar and sieved out the particles of mesh size < 0.1 mm. The samples were stored in aluminum foil.
The coarse particulate matter (PM10) and fine particulate matter (PM2.5) were collected by using Partisol Model 2300 Sequential speciation air sampler. The sampler was installed at the roof of the building, »10 m above from the ground level at residential site: Dagania, Raipur. Both PM2.5 and PM10 were collected simultaneously over 47 mm quartz fiber filters housed in molded filter cassette. The sampler was run for 24 hrs (6.00 am - 6.00 am) at flow rate of 10 L/min. One sample blank was used for collection of both PM10 and PM2.5. The loaded filters were dismounted, brought to laboratory, and heated up to 30˚C for 6 hrs to remove the moisture contents. The filters were transferred into the desiccator, and finally weighted to record the particulate contents.
2.3. Analysis of Carbons
The CHNSO-IRMS Analyzer by SV Instruments Analytica Pvt Ltd. was used for analysis of the total carbon (TC). Three carbons i.e. elemental carbon (EC), organic carbon (OC) and carbonate carbon (CC) were analyzed in the samples. The total carbn (TC) sample was oxidized with O2 at 1020˚C with constant helium flow by measuring the resulting CO2 with thermal conductivity detector. The CC content was analyzed by treating the sample with HCl acid in the CO2 free atmosphere. The resulting CO2 was measured by coulometric titration method. The OC content was analyzed by titration method using K2Cr2O7 as oxidant, and the excess of K2Cr2O7 was determined by titration with the FeSO4・7H2O solution. The EC content was evaluated by using following equation.
2.4. Analysis of PAHs
The PAH samples were analyzed by capillary gas chromatography (Varian STAR 3400 CX) using temperature programmable splitless injection, a fused silica RTX5-MS column and ion trap mass spectrometric detection [27] .
3. Results and Discussion
3.1. Carbon Concentration
All samples are colored, ranging from brown to black, depending on the EC content. The content of EC, OC and
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Figure 1. Representation of sampling locations.
CC in the 16 environmental shown in Table 1. Relatively high content of EC in all samples was achieved, ranging from 6.5% - 13.5% with mean value of 8.4% ± 1.1%. Very low content of OC and CC was observed in the dust, sludge and sewage samples unlikely to PM samples may be due to their degradation and water solubility, Figure 1. The EC content with the OC and CC had good relation (r = 0.94 - 0.96), indicating origin from the similar sources.
3.2. PAHs Concentration
The chemical characteristics of 13 PAHs i.e. phenanthrene (Phe), anthracene (Ant), fluoranthene (Fla), pyrene (Pyr), benz [a] anthracene (Baa), chrysene (Cry), benzo [b] fluoranthene (Bbf), benzo [k] fluoranthene (Bkf), benzo [a] pyrene (Bap), benzo [ghi] perylene (Bgh), dibenz [a,h] anthracene (Dba), indeno [1,2,3-cd] pyrene (Ind) and coronene is summarized in Table 2. The content of 13 PAHs in 16 environmental samples is presented in Table 3. The sum of total concentration of PAHs (SPAH13) in the road dust of Raipur city (n = 8) was ranged from 10,427 - 26,031 µg/kg with mean value of 15,282 ± 3377 µg/kg. The highest concentration of the SPAH13 was observed at site no 5 (i.e. Birgaon) due to higher industrial and traffic emissions, Figure 2. Similarly, the concentration of SPAH13 in the SL, MW, AW and TPPW was found to be 7980, 9669, 10,570 and 8326 µg/kg, respectively. No signal for Cor was detected in the environmental samples i.e. RD, SL, MW, AW and TPPW samples. The major fraction of PAHs in the RD, AW and TPPW samples was contributed by three compounds i.e. Phe, Fla and Pyr, Figure 3. A different distribution pattern of PAHs in the SL and MW samples was observed, dominated by Pyr and Bgh contents, Figure 3. The concentration of SPAHs in the PM10 and PM2.5 was strongly enriched, >25-folds higher than the road dust with appearing of strong Cor signal. The PM2.5 sample
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Table 1. Chemical characteristics of PAHs.
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Table 2. Concentration of carbons and polycyclic aromatic hydrocarbons in environmental samples.
RD, SL, MW, TPPW, AW, PM10 and PM2.5 represent road dust, sludge, municipal/sewage waste, thermal power plant waste, agricultural waste, coarse particulate matter and fine particulate matter, respectively.
was dominated by higher PAHs i.e. Bbf, Bgh and Ind, Figure 4. Whereas, the PM10 sample was dominated by PAHs i.e. Fla, Pyr, Bgh and Ind, Figure 4. The PAHs content in the dust was negatively and fairly correlated with particle size (r = −0.89), Figure 5. The concentration of the PAHs in the environmental samples of studied area was found to be comparable to the other parts of the country and World [4] - [25] .
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Figure 2. Spatial distribution of PAHs in the road dust.
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Figure 3. Distribution of PAHs in dust (RD), thermal power plant ash (TPPA), agricultural waste (AW), sludge (SL) and municipal waste (MW).
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Figure 4. Distribution of PAHs in the PM10 and PM2.5.
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Figure 5. Correlation of PAHs content in the sample with particle size.
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Table 3. Concentration of PAHs in environmental samples, µg/kg.
* = 103.
3.3. Vertical Distribution of PAHs
The vertical distribution of the PAHs from 0 - 30 cm in the sludge samples was studied, and presented in Figure 6. The åPAHs content was strongly increased with increase of the sludge depth profile from 0 - 30 cm, may be due to their poor adsorption with the geo-media. Among them, extremely high vertical distribution of compounds i.e. Fla, Pyr, Bbf and Bap was observed.
3.4. Toxicities
The toxicities of PAHs increases as the mass number increases, and seven PAHs (i.e. Pyr, Baa, Bbf, Bkf, Bap, Dba and Ind) are considered to be more toxic, may bedue to higher thermal stability and delocalization of
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Figure 6. Vertical distribution of PAHs in the sludge, SL1 = 0 - 10 cm, SL2 = 10 - 20 cm, SL3 = 20 - 30 cm.
π-electrons. The carcinogenic potentiality of Pyr, Baa, Bbf, Bkf, Bpa, Dba and Ind reported was 0.01, 0.1, 0.1, 0.1, 0.1, 1.0 and 0.1, respectively [28] . The benzo [a] pyrene equivalent (BapE) value was computed by using the following equation:
where, Ci and TEFi are the concentration and the corresponding toxic equivalent factor (TEF) value of PAHs.
The BapE value for RD, SL, MW, AW, TPPW, PM10 and PM2.5 was found to be 1108, 1135, 1237, 846, 475, 52,000 and 138,500 µg/kg in the term of Bap. The carcinogenic fraction of PAHs in RD, SL, MW, AW, TPPW, PM10 and PM2.5 samples was ranged from 5.7% - 15.7% with significantly higher value for SL, MW and PM samples, Figure 7. The concentration of PAHs in the environmental samples was found to be several folds higher than recommended value of 1000 µg/kg [29] .
3.5. Correlation and Sources
The correlation matrix of the carbons and PAHs are summarized in Table 4. The PAHs had fair correlation with the BC, OC and CC contents (r = 0.70 - 0.96), indicating their origin from the burning processes. The lower PAHs (i.e. Phe, Ant, Fla and Pyr) among themselves had fair correlation, may be due to existence of their larger fractions in the gaseous forms, Table 4. The higher PAHs (i.e. Baa, Cry, Bbf, Bkf, Bap, Bgh and Ind except Dba) among themselves had good correlation, indicating origin from the burning processes, Table 4.
The diagnosis ratios: Phe/Antand [Fla]/[Fla + Pyr] were used to find out the sources of PAHs in the studied samples [30] [31] . The Phe/Ant ratio for TPPW, RD, AW, SL, MW, PM10 and PM2.5 was found to be 27, 10.2, 9.6, 3.4, 3.9, 5.0 and 3.9, respectively, suggesting the domination of petrogenic PAHs in the TPPW, RD and AW samples, Figure 8. The [Fla]/[Fla + Pyr] ratio of >0.5, 0.5 - >0.4 and <0.4 was used as signature for PAHs emission from combustion of grass, wood/ coal, petroleum and diesel, respectively [31] . The [Fla]/[Fla + Pyr] ratio was ranged from 0.36 - 0.52, indicating domination of biomass or coal origin PAHs in the RD, TPPW and PM10 samples, Figure 8.
4. Conclusion
The light PAHs (3 - 4 ring) was found to be dominated in the RD, TPPW, AW and PM10 samples unlikely to SL, MW and PM2.5 samples. Their origins were largely pyrogenic, emitted by combustion of biomass, coal and diesel. The higher PAHs (5 - 6 ring) was found to extremely enrich in the PM2.5 sample due to origin by the combustion processes. The PHAs concentration was remarkably increased vertically and might be due to poor adsorption by the geo-media. The PAHs content in the environmental samples of the studied area was found to be several folds higher than recommended value of 1000 µg/kg.
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Figure 7. Percentage of carcinogenic PAHs in environmental samples.
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Figure 8. Diagnostic ratio for source determination of PAHs.
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Table 4. Correlation matrix of PAHs in the road dust.
Acknowledgements
We are thankful the CCOST, Raipur for granting research support for doing this work.
NOTES
*Corresponding author.