Comparison of PAHs Extracted from Lichens and Atmospheric

Environ. Sci. Technol. 2006, 40, 6384-6391

Use of Lichens as Pollution Biomonitors in Remote Areas: Comparison of PAHs Extracted from Lichens and Atmospheric Particles Sampled in and Around the Somport Tunnel (Pyrenees) M A R IÄ A B L A S C O , C E L I A D O M E N ˜ O, AND C R I S T I N A N E R IÄ N * Grupo GUIA-Instituto de Investigacioń de Ingenierıá en Aragoń (I3A), Centro Superior de Ingenieros (CPS), Marıá de Luna 3, 50018 Zaragoza, Spain

Lichens of the species Parmelia sulcata were collected from sites on both sides of the Somport tunnel (which links France and Spain) and atmospheric particles were collected by air samplers installed within and on either side of the tunnel. Polycyclic aromatic hydrocarbons (PAHs) in the lichen and particle samples were then extracted, identified, quantified, and compared to evaluate the potential utility of lichens as pollution biomonitors in remote areas. The origin of the PAHs was also assessed using the Phe/Ant, Flu/Pyr, Ant/Ant+Phe, Flu/Flu+Pyr, and BaA/BaA+Chr concentration ratios. The total concentration of 16 priority PAHs ranged from 6.79 to 23.3 µg/g in particles outside the tunnel, from 18.3 to 265.2 µg/g in particles inside the tunnel, and from 0.91 to 1.92 µg/g in the lichen samples. The PAH ratios found in the lichens and particulate matter indicate that they were of pyrogenic origin and that road traffic was a major contributor. Results from the lichen samples suggest that they may be excellent biomonitors of pollution in remote areas.

1. Introduction A large number of air pollutants pose significant potential health and environmental risks at varying spatial scales, ranging from highly localized to regional or even global. Thus, there is increasing interest in monitoring the levels and dispersal of contaminants. Such monitoring programs implicitly involve sampling the atmosphere, but this is often hampered by problems associated with sampling air in remote areas. One potentially useful approach is to use biomonitors such as lichens, which concentrate a variety of pollutants in their tissues (1-4). Thus, lichen data can be used to identify areas that may require more intensive or quantitative monitoring using devices that sample specific atmospheric fractions and/ or groups of compounds in known volumes of air. The partitioning of specific pollutants between various atmospheric phases (e.g., the purely gaseous phase, aerosols, soot, soil, and other particulates) is strongly influenced by weather conditions, and different pollutants are removed from the atmosphere at widely diverging rates by various chemical processes and deposition, both wet and dry. For * Corresponding author phone: 34 976 76 1873; fax: 34 976 76 2388; e-mail: [email protected]. 6384

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these reasons, the relative amounts of different pollutants collected by air samplers are influenced by both the collection procedures employed and the weather conditions before and during the sampling periods. However, lichens absorb contaminants and nutrients into their biological matrix from both wet and dry precipitation more or less constantly throughout their lifecycles. Thus, lichens in remote areas tend to reflect integrated, background levels of trace contaminants originating from long-range transport, while particulate samples tend to reflect pollution directly emitted in the area during (and shortly before) the sampling period. A further difference is that concentrations of substances present in atmospheric phases collected by air samplers can be directly related to unit volumes of air, but concentrations found in lichens can only be qualitatively related to the surrounding air masses. Therefore, combining biomonitoring with sampling atmospheric particulates can provide valuable complementary information for assessing and evaluating the air quality in remote regions (5). To date, most studies on the accumulation of air pollutants by lichens have focused on their uptake of heavy metals (6-9). Their ability to accumulate other pollutants has been much less thoroughly investigated. In the study reported here, therefore, we assessed their potential utility as biomonitors of polycyclic aromatic hydrocarbons (PAHs), by comparing PAH levels and ratios in lichens with those in particulates collected by air samplers. Sixteen PAHs are included among the persistent organic pollutants (POPs) designated in the “Convention on Longrange Transboundary Air Pollution” adopted by the United Nations Economic Commission for Europe. PAHs were also identified as high-priority chemicals for Region VII (Central and North East Asia) in the “Regionally-based Assessment of Persistent Toxic Substances” jointly conducted by the United Nations Environment Programme and Global Environmental Fund (10). The U.S. Environmental Protection Agency (EPA) has also identified 16 PAHs as priority pollutants. These compounds have been shown to have mutagenic and/or carcinogenic properties, and to pose significant health risks (11). PAHs (12) occur in both gaseous forms and as adsorbents on particles in the atmosphere, with their partitioning between these phases depending, inter alia, on the volatility of the PAH species. Highly condensed molecules with four or more rings tend to be largely particle-bound, whereas smaller PAHs mainly remain in the gas phase. PAHs tend to persist for relatively long periods in the environment due to their comparatively stable molecular structure and slow rates of photochemical decomposition and biodegradation (13). For these reasons concentrations of PAHs in lichens could provide relatively stable indicators of pollution levels in their respective environments. Anthropogenic sources of PAH emissions to the atmosphere include traffic, domestic heating and industrial processes (14, 15). However, identifying the sources of PAHs in lichen tissues is not straightforward because, as mentioned above, once PAHs are emitted they redistribute between the gas and particle phases and are removed by oxidative and photolytic reactions and by both dry and wet deposition (16). Deposited PAHs can also be re-emitted (through volatilization) if the temperature increases. To mitigate the adverse health and environmental effects (17) of PAHs it is essential to identify their sources, which in turn requires the identification and quantification of PAHs present in the affected area. Previous studies have found that lichens can accumulate considerable concentrations of 10.1021/es0601484 CCC: $33.50

 2006 American Chemical Society Published on Web 09/06/2006

FIGURE 2. Schematic diagram of the air samplers built in-house: 1, filter holders and glass fiber filters; 2, moisture traps; 3, gas meters; 4, pump. lichens were collected in and around the Somport tunnel in the Pyrenees. The Somport tunnel was opened in 2003, linking the Spanish road N-330 with the French road N-134. It is 8608 m long: 5759 m on the Spanish side and 2849 m on the French side. After the tunnel opened the levels of traffic on the linked roads increased, which may be of environmental concern, from 665 automobiles and 154 trucks per day in 2002 to 924 and 255, respectively (19). Several air samplers were installed at both sides of the tunnel and a large number of lichen samples of the species Parmelia sulcata were collected. PAHs were analyzed in all the particulate and lichen samples and the PAH profiles and concentrations in the two sets of samples were then compared.

2. Experimental Section

FIGURE 1. Map of the study area showing locations of the air samplers (Fusileros and Peilhou) and lichen sampling points (1 to 6). PAHs, and that their PAH concentrations may be directly correlated with levels of vehicular traffic in the surrounding area (18). To evaluate the contribution of traffic to the PAH load in remote areas, air can be sampled in a road tunnel, where the contribution of traffic is likely to be strongest, and the PAH profiles and concentrations found in the samples can be compared with those obtained from air samples and lichens collected at other sites in the area. This strategy was adopted in the study reported here, in which samples and

2.1. Reagents. The polycyclic aromatic hydrocarbons naphthalene, acenaphtylene, acenaphthene, fluorene, anthracene, phenanthrene, dibenzofurane, chrysene, pyrene, benzo(a)pyrene, fluoranthene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)anthracene, dibenzo(a,h)anthracene, and benzo(g,h,i)perylene were supplied as certified standards by the U.S. EPA. Normal non-deuterated standards were used in all cases. All the solvents used in the extractionsshexane, cyclohexane, dichloromethane, methanol and tolueneswere from Scharlab S.L. (Barcelona, Spain) and were of analytical grade. The hexane used to prepare the standard solution was GC grade and also from Scharlab S.L. The solid adsorbents used were standardized aluminum oxide 90 and anhydrous sodium sulfate (analytical reagent VOL. 40, NO. 20, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. PAH concentrations (µg/g) found in lichens collected at sampling points 1 to 6. grade), both from Merck (Darmstadt, Germany). The aluminum oxide was activated at 550 °C and stored in the dark in a glass container with a glass stopper. It was deactivated with the appropriate amount of distilled water to prepare 3% (w/w) deactivated sorbent. 2.2. Description of the Study Area and Sampling Sites. As mentioned above, the 8608 m long Somport tunnel connects France and Spain in the Central Pyrenees. The area is mountainous with mixed black pine, oak, birch, and beech forests. Lichens of various species are quite abundant at both sides of the tunnel. The species chosen for this study was the epiphytic Parmelia sulcata, as it is abundant in remote areas with a moderately humid climate and has medium sensitivity to pollution. Lichens of this species were collected from black pines at points approximately 1 m from the ground, at the six sites shown in Figure 1 (1, Villanu ´ a; 2, Barranco de Ip; 3, Canfranc Estacioń; 4, Espe´lungue´re; 5, Route Urdos-tunnel; 6, Peyrene´re). The sampling site at Espe´lungue´re was placed at about 1000 m from the highway while Peyrene´re was at about 100 m of distance. These were the more distant sampling sites from the main road, as can be seen in Figure 1. A minimum of four black pines were sampled at each of these points and then a pooled sample was prepared. Between 1.0 and 1.5 g (dry mass) of lichen thalli was taken at each sampling point. None of the sampling points were close to the road but all of them were at the same lateral distance from the higway to avoid any concentration profile. In the laboratory, the lichens were separated from the bark and other materials like dust, dried at 35 °C for 3 or 4 days and ground in an agate mortar to homogenize the samples. All samples were stored in aluminum foil at 0 °C until analysis. Air samplers were placed at Torreta de Fusileros near Canfranc, at 1180 m above sea level, by the road to the tunnel on the Spanish side, approximately 1.5 km from the tunnel, and near the auberge de Peilhou on the French side, approximately 3 km from the tunnel at 780 m above sea level. These places were the first available for sampling with electric 6386

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facilities in the area. The air monitors were installed 1.5 m above the ground, with the filter cartridge at a height of about 2 m. In both cases there was a similar distance of about 50 m from the monitor to the higway. The third air sampler, which yielded samples with distinct PAH profiles, was placed inside the tunnel. 2.3. Air and Lichen Sampling and Sample Preparation. Two different air samplers were used. In the tunnel a commercially available high-volume air sampler supplied by MCV was used, which can operate with air flows of 20-80 m3/h and collects particles on 200 mm diameter glass fiber filters with 0.45 µm pores. Filters with smaller pores could not be used since they were quickly blocked by the high amount of particulates. The samplers used at the other two sites were built in-house, each consisting of the following: an ASF Thomas, TF5, 90 L/min pump from Air Control; two 12 mm diameter, 32 mm long Micragold MG 102-1232 moisture traps from Micrafilter (UK); and two 47 mm diameter, in-line polypropylene filter holders supplied by Osmonics, each housing a preweighed glass fiber filter with 0.1 µm pores (see Figure 2 for a schematic diagram). In the period from April to October 2004, 100-500 m3 of air was sampled and five different samples were collected at each site outside the tunnel. Each sample corresponded to every 15-day period of continuous sampling, day and night, as longer periods saturated the air filter. Particulates were trapped on the preweighed glass fiber filters. Samples were taken inside the tunnel in two different diurnal periods, at 30 m3/h every day (from 7:30 to 13:30) and every night (from 22:00 to 4:00) throughout the whole of April 2004 in working days. No weekend samples were taken. After the sampling, the filters were dried, weighed, then stored in glass containers at 0 °C in the dark until analysis. 2.4. Lichen Extraction. Portions (0.2 g) of the dried lichen samples were extracted by dynamic sonication-assisted solvent extraction (DSASE), as described by Domen ˜ o et al. (20), using hexane at a flow-rate of 0.2 mL/min for 5 min at room temperature. The total extract volume collected for

FIGURE 4. PAH concentrations (µg/g) found in filters from air samplers outside the tunnel. each sample was 1 mL, which was concentrated to 100 µL under a nitrogen stream. Sixteen PAHs in the concentrated extract were subsequently identified and quantified by GCMS operating in selected ion monitoring (SIM) mode, as described below. Detection limits and quality control parameters obtained in these experimental conditions can be taken from Domen ˜ o et al. (20). 2.5. Filter Extraction. Each filter was accurately weighed then extracted in four batches of 20 mL dichloromethane, in an ultrasonic bath, for 15 min. This extraction procedure was repeated four times and the combined extract was evaporated to 1 mL by a gentle stream of nitrogen. The concentrated extract was cleaned by applying it to a glass column of 10 mm internal diameter containing 3 g of 3% water deactivated alumina with 2 cm of anhydrous sodium sulfate on top, and eluting the PAHs using 20 mL of hexane/ dichloromethane (75/25). The eluates were reduced to about 1 mL under a gentle stream of nitrogen. Sixteen PAHs in the concentrated extract were identified and quantified by GCMS operating in SIM mode, as described below. 2.6. GC-MS Analysis. The analytes were identified and quantified using an HP 6890 gas chromatograph coupled to

an HP 5973 mass spectrometer (both from Hewlett-Packard). Analytes were separated on a Factorfour VF5-ms 60 m × 250 m × 0.25 µm (i.d.) column (Varian), using helium as a carrier gas at 1 mL/min. The GC system was equipped with a split/splitless injector operating in the splitless mode with 1.0 min of splitless time. The oven temperature was held at 50 °C for 3 min, increased by 20 °C/min to 150 °C and then by 10 °C/min to 240 °C, which was then held for 10 min. The MS was operated in SIM mode with EM and temperature set at 1900 eV and 270 °C, respectively.

3. Results and Discussion 3.1. Lichens. Figure 3 shows the results obtained in the lichen analyses. The total concentration of PAHs found ranged from 1.2 to 1.65 µg/g in the samples from the Spanish side (points 1, 2, and 3) and from 0.91 to 1.92 µg/g in the French samples (points 4, 5, and 6). Thus, very similar levels were found at the two sides of the tunnel. In the Spanish samples, the most abundant PAH found was naphthalene, which is usually associated with emissions from light vehicles (21). The concentrations of the other PAHs were very similar, although slightly higher values were found VOL. 40, NO. 20, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 5. PAH concentrations (µg/g) found in filters from air samplers inside the tunnel. for phenanthrene, dibenzofurane, and fluoranthene. Values for the heaviest PAHs, which are generally removed from the air by direct (e.g., wet) deposition processes, varied considerably. In contrast, in the French samples the most abundant PAHs, except for naphthalene, were the heaviest molecules, from pyrene to benzo(g,h,i)perylene. These results were consistent with expectations, since the French side is much wetter than the Spanish side and, thus, wet deposition is likely to be considerably higher there. Furthermore, proximity to the road strongly influences the concentrations as well as the identity of the compounds, as indicated by the high levels of some PAH found at point 5 between Urdos and the tunnel, the closest sampling point to the road. This lichen sampling point and number 6 are along the passage road, representing a most likely other vehicle composition than through the tunnel, as well as before and after. Phenanthrene, pyrene, and benzo(b)fluoranthene are components of fossil fuels and varying proportions of these compounds in the atmosphere are associated with combustion processes (22). Benzo(a)pyrene is usually emitted from automobiles, both with and without catalytic converters (23), while benzo(a)anthracene and chrysene generally originate from diesel and natural gas combustion (24). Phenanthrene is mainly from motorized traffic, especially diesel trucks. Lower concentrations of anthracene than phen6388

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anthrene were found, possibly because it is less thermodynamically stable (25). However, the Phen/Antr ratio was not as high as would be expected according to previous studies (26), possibly due to the high solubility of phenanthrene (27). In general, the values found in the lichens were similar to those found in other biomonitors (27, 28). The BaA/Chr ratio indicates the distance from contamination sources (29) and in this case the highest value (> 1.0) suggests that the main sources were close to the sampling point, which means close to the highway The ratios are generally close to 0.4 if the sources are distant (more than 50 km). These results agree with the traffic data supplied by the Tunnel managers, which were 1675 light vehicles during 2003 and 345 trucks and heavy traffic in the same period. However, a high rate of the light vehicles use diesel instead of gasoline and the rate of liquid gas is negligible. 3.2. Particulate Samples Outside the Tunnel. Figure 4 shows the PAH profiles and levels found in the particulates at both sides of the tunnel. Concentrations ranged from 6.79 to 13.54 µg/g at the Spanish side and from 12.63 to 23.3 µg/g at the French side. As for the lichens, the highest value was found for naphthalene. However, concentrations of dibenzo(a,h)anthracene were also high, which indicates that traffic was a major source

FIGURE 6. Average values of PAHs in particulates sampled in Fusileros multiplied by 15, in Peilhou multiplied by 10, lichens multiplied by 30 and inside the tunnel. All values expressed in µg/g. of the PAHs, according to various authors (12, 30, 31). The most homogeneous values were for the PAHs with the highest molecular weightssbenzo(b)fluoranthene, benzo(k)fluoranthene, benzo(g,h,i)pyrene, and chryseneswhich are associated with particles and with motorized traffic. Calculations of the total concentrations of PAHs in particles per unit volume of air, based on the amounts found and the known volumes of air sampled, indicate that the concentrations of PAHs in the French and Spanish air samples ranged from 0.073 to 0.135 ng/m3 and from 0.0532 to 0.096 ng/m3, respectively. As mentioned above, the French area is more heavily polluted than the Spanish side, which could be attributed to differences in their altitude and topography. The French valley is quite narrow and the pollutants cannot be easily transported for long distances, while the Spanish valley is more open and windy, facilitating atmospheric diffusion and transport of pollutants. Furthermore the French air sampler was situated at an altitude of 780 m, while the Spanish air sampler was placed in Torreta Fusileros at an altitude of 1180 m, and these data justify that the heaviest compounds were more concentrated in the French area. 3.3. Particulate Samples Inside the Tunnel. Some differences were found between the day and night samples collected in the tunnel, as can be seen in Figure 5. The total PAH concentrations in these samples varied from 24.3 to 164.1 µg/g and from 18.3 to 265.2 µg/g, respectively (or, 0.781.60 ng/m3 air sampled and 0.20-1.71 ng/m3 air sampled, respectively). These values are consistent with the results of previous studies carried out in tunnels (32). Clear differences in the PAH profiles can also be seen. The concentrations of naphthalene, phenanthrene, fluoranthene, and pyrene, which are related to traffic emissions, especially from diesel engines, were highest in the day samples, while the concentration of dibenzo(a,h)anthracene, which has been used as a remote indicator of traffic emissions (33, 34), was highest in the night samples. The profile of samples collected inside the tunnel correlated well with that of samples collected at Peilhou.

3.4. Comparison of Results from the Lichen and Particle Analyses. The concentrations and profiles of the PAHs found in the sampled particles from the air monitors and inside the tunnel as well as in lichens were compared to assess the potential utility of lichens as biomonitors and to identify probable sources of the PAHs. The PAH concentrations in the particles were found to be nearly 2 orders of magnitude higher than the concentrations in the lichens. In addition, large PAHs with more than four rings accounted for >90% of the total PAH content (excluding naphthalene, since it dominated the profiles and would have masked differences) in samples from inside the tunnel, and exceeded 60% in most of the other samples, both lichen and particulate. Figure 6 shows the comparison of the average values found in Fusileros, Peilhou, and inside the tunnel, and also the lichens sampled in Villanu ´ a. To facilitate the comparison, values from Fusileros were multiplied by 15, those from Peilhou were multiplied by 10, and values of lichens were multiplied by 30. As can be seen, all profiles are similar to that obtained at night inside the tunnel and validate the lichens as biomonitors of air pollution. These findings also suggest that the PAHs have a pyrogenic origin and confirm that traffic has a strong influence on PAH contamination in the area (13, 35). High proportions of heavy PAHs are often found in particles (36, 37), but they are surprising in lichens. It is possible that substantial proportions of the lighter PAHs were desorbed or degraded during atmospheric transport and, thus, were not concentrated in the lichens. As mentioned above, the ratios between some specific PAHs are good indicators of the sources of the contamination (29, 38-40). According to the literature, Phe/Ant ratios 1, and BaA/BaA+Chr ratios >0.35 suggest a pyrogenic origin (41). On the other hand, Ph/An ratios >10 and Flu/Pyr ratios >1 suggest a mixture of pyrogenic and petrogenic origins, while Ph/An ratios 0.1 and >0.35, respectively) corroborate the hypothesis that the PAHs found had a largely pyrogenic origin. Furthermore, the Flu/Flu+Pyr ratios found in lichen samples and particles collected outside the tunnel (> 0.5), indicate that combustion of coal and/or wood may have contributed some of the PAHs. The data obtained suggest that the main source of the PAHs found in the lichens and particles was road traffic, but other sources seem to have made minor contributions. For instance, other petrogenic sources appeared to contribute to the PAHs in the particles collected inside the tunnel, while 6390

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other combustion sources, such as household heating systems, seem to have contributed to the PAHs in the lichen samples and particles collected outside the tunnel. The results of the study also indicate that lichens, and more specifically the species Parmelia sulcata, are potentially useful indicators of atmospheric pollution by PAHs. Lichens absorb pollutants throughout their lifetimes, and their PAH profiles indicate both the origin and proximity of the contamination source(s). In addition, the PAH levels and profiles from the air samples collected inside the tunnel at day clearly show that traffic, especially light vehicular traffic, is a major source of the PAHs. Day samples showed the highest concentration of pyrene whereas dibenzo(a,h)anthracene was more concentrated in night samples. Comparison of the air samples taken close to the same road on the two sides of the Pyrenees also shows that the climate influences pollution, indicating that wet deposition increases the concentration of relatively heavy PAHs in both the lichens and the particles. Finally, the lichens and air samples provide useful and complementary information since lichens provide indications of the air pollution over prolonged periods while air samples give indications of pollution profiles during the sampling period. Thus, combining biomonitoring and sampling atmospheric particles can provide valuable complementary information on pollution levels.

Acknowledgments This study was financed by the project PAP (Pyrenees Air Pollution) from the Pyrenees working Community (Comunidad de Trabajo de los Pirineos). We acknowledge the assistance of Sophie Veschambre, Mariela Moldovan, and David Amoroux in supplying the French samples and Jesu´s Santamarıá for sampling the particulates inside the tunnel.

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Received for review January 23, 2006. Revised manuscript received August 4, 2006. Accepted August 4, 2006. ES0601484

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Comparison of PAHs Extracted from Lichens and Atmospheric

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