Journal of Environmental Quality
TECHNICAL REPORTS Organic Compounds in the Environment
Distribution and Source Apportionment of Polycyclic Aromatic Hydrocarbons in Soils and Leaves from High-Altitude Mountains in Southwestern China Bingfing Shi,* Qilin Wu, Huixiang Ouyang, Xixiang Liu, Bo Ma, Weiyuan Zuo, and Shengyu Chen
P
olycyclic aromatic hydrocarbons (PAHs) are a class
Abstract
of widely distributed persistent organic pollutants that can pose serious threats to human health and ecosystems because of their mutagenic, carcinogenic, and teratogenic properties (Falandysz, 1998; Jakobsson and Asplund, 2000; Agarwal et al., 2009). Polycyclic aromatic hydrocarbons may be generated from organic matter diagenesis and anthropogenic processes (Simoneit, 1977; Laflamme and Hites, 1978; Wakeham et al., 1980a,b). However, high concentrations of PAHs in the environment are mainly related to human activities (Edwards, 1983). Common sources of PAHs include emissions from industrial processes, domestic heating systems, and automobiles. Because of their semivolatility, most anthropogenic PAHs are transported long distances in the atmosphere, and these chemicals have been detected in the soil and water of many alpine ecosystems and remote areas around the world (Escartin and Porte, 1999; Srogi, 2007; Nam et al., 2008). According to the “Global Distillation” hypothesis (Wania and Mackay, 1996), winds carry the volatile PAHs from warm regions to cold regions, such as polar habitats and high-altitude mountainous areas, where they condense and become trapped in snow, soils, and vegetation. Concentrations of PAHs in the surface soil at mountainous sites is the net result of cumulative atmospheric deposition and losses due to volatilization, biodegradation, and mixing/burial at depth. Cold environments such as those characteristic of highaltitude mountains tend to have slow loss processes (Wilcke et al., 2002). Owing to the lipophilic and hydrophobic nature of these organic pollutants, they are readily concentrated in biota and can undergo biomagnification up the food chain (Fernandez et al., 2005). Animals and people may suffer adverse effects from PAHs if these chemicals are consumed in high quantities through dietary sources (Kelly and Gobas, 2001). Additionally, PAHs in high-altitude mountainous areas may lead to reductions in biodiversity and impair the functioning of mountain ecosystems (Pan et al., 2013).
Several studies have investigated the distribution patterns and geographic sources of polycyclic aromatic hydrocarbons (PAHs) in mountainous areas. Little is known about how different sources contribute to PAH concentrations at different elevations along mountain slopes. To estimate the distribution and sources of PAHs at different altitudes in mountainous areas of southwestern China, samples of soils and leaves from Keteleeria trees were collected from 1000 to 1500 m asl in the Dawangling forest and analyzed for PAHs. Total PAH concentrations ranged from 93.9 to 802.3 ng g-1 (average, 252.3 ng g-1) in soils and from 4.1 to 100.9 ng g-1 (average, 23.1 ng g-1) in leaves. Our results suggest that soil PAH levels in the study area could be classified as “weakly contaminated.” The PAH levels in leaves from the Dawangling forest were lower than those found in Himalayan spruce needles from the central Himalayas in China and from an agricultural station in southern England. Total PAHs in the Dawangling forest soils increased with elevation, primarily due to the low-molecularweight PAHs, which accumulated in samples from higher altitudes. In contrast, high-molecular-weight PAHs were inversely related to or unrelated to elevation. The PAH profiles were similar in soils and leaves from all mountainous regions. Diagnostic ratios showed that the PAHs in soils at different altitudes were from different pollution emission sources; therefore, PAHs in the entire study area were probably derived from mixed sources. Cluster analyses confirmed that liquefied petroleum gas, coal/ wood combustion, and petroleum combustion were likely the predominant PAH sources in this region.
Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.
Dep. of Chemistry and Life Sciences Baise Univ., 21 2nd Zhongshan Road, Baise Guangxi 533000, China. Assigned to Associate Editor Joseph Pignatello. Abbreviations: Ane, acenaphthene; Ant, anthracene; Any, acenaphthylene; Baa, benzo(a)anthracene; Bap, benzo(a)pyrene; Bbf, benzo(b)fluoranthene; Bgp, benzo(ghi) perylene; Bkf, benzo(k)fluoranthene; Chr, chrysene; Daa, dibenzo(a,h) anthracene; Fla, fluoranthene; Flu, fluorene; HMW, high-molecular-weight; IIp, indeno(1,2,3-cd)pyrene; LMW, low-molecular-weight; Nap, naphthalene; PAH, polycyclic aromatic hydrocarbon; Phe, phenanthrene; Pyr, pyrene; TOC, total organic carbon.
J. Environ. Qual. 43:1942–1952 (2014) doi:10.2134/jeq2014.04.0177 Received 18 Apr. 2014. *Corresponding author ([email protected]).
1942
Over the past few decades, there has been a growing interest identifying and quantifying PAH levels in mountainous regions. Several studies have evaluated PAHs in soil, vegetation, water, and air samples from mountainous areas in Europe, America, and Asia. For example, studies on PAHs have been conducted in the Rocky Mountains (Blais et al., 1998), Alps (Weiss et al., 2000), Laja River basin (Barra et al., 2005), Andes (Estellano et al., 2008), Pyrenees (Vandrooge et al., 2004), Qingzang Plateau (Sun et al., 2007), and Mount Qomolangma (Wang et al., 2007). These studies and others have not only investigated the geographic sources of PAHs in mountainous areas (Estellano et al., 2008) along with PAH distribution patterns (Grimalt et al., 2004), especially along elevation gradients (Wang et al., 2007; Estellano et al., 2008), but previous research has also shown that the presence of PAHs in alpine ecosystems can be attributed to a combination of long-range atmospheric transport and regionalscale atmospheric transport (Hageman et al., 2010; Lavin et al., 2012). However, little is known about how different sources contribute to the PAH concentrations at different elevations along mountain slopes or about how climatic factors may interact with PAH concentration trends in high-altitude areas (Lavin et al., 2012). In addition, the question of whether or not high mountains can act as barriers to the long-range atmospheric transport of PAHs has not been investigated directly (Vighi, 2006; Lavin and Hageman, 2013). Rapid industrial expansion and increases in automobile emissions have elevated PAH concentrations in China’s environment. Although a few studies have reported on PAH concentrations in environmental samples from high-altitude areas of China (Wang et al., 2007), the fate of PAH contaminants in the alpine ecosystems of southwestern China has not been adequately explored; hence, information on this specific area is extremely limited. The objective of this paper was to carry out a preliminary study of the levels of PAHs in soil and leaves from the Dawangling Mountains in southwestern China. Samples were collected at 1000 to 1500 m asl along the forested slopes of the Dawangling Mountains. Leaves from the Keteleeria tree, which is a widely distributed type of Keteleeria sp. plants in the study area, were selected for analyses. We used leaves instead of manufactured passive samplers for PAH analyses to avoid costs associated with sampler deployments. The altitudinal distribution patterns of PAHs and the possible sources for these pollutants in the alpine ecosystem were also investigated.
average annual temperature in the study area is 21.5°C, the relative humidity is 75%, and the mean annual rainfall is 1200 mm. The prevailing winds move from east to west. Baise is one of several new industrial centers and tourist cities in China. This city has the largest aluminum production and processing complex in China and has a large petrochemical industry. The city has a high population density and heavy vehicular traffic. Leaves from Keteleeria trees and soil samples were collected at altitudes of 1000 to 1500 m asl in the Dawangling Mountains between September and December 2013 (Fig. 1). Each sample was a mixture of five soil samples collected at the four corners and the center in an area of about 10 × 10 m2 at five elevations in each mountain. Soil samples were collected 0 to 5 cm below the surface layer. The samples were prepared by shaking the soil from grass roots, and then the soil samples were evenly mixed and dried for 5 d at room temperature in a clean, shady room. The samples were ground in a mortar, passed through a 0.5-mm sieve, and preserved at -4°C until analyzed. The influence of some soil properties (e.g., total organic carbon [TOC] content and particle size distribution) on the results was alleviated by sieving the soil particles to 0.1 is indicative of a combustion source, whereas a ratio of 0.5 are suggestive of coal, grass, and wood combustion, whereas values between 0.4 and 0.5 are suggestive of petroleum (i.e., liquid fossil fuels such as vehicle fuels and crude oil) combustion; values 18; Table 4), which indicates that the PAHs probably entered the study area via atmospheric deposition over long distances. The ratios of Phe/Ant and Fla/Pyr varied from 18.9 to 86.3 and from 0.08 to 0.11, respectively; these data are suggestive of a petrogenic origin. However, the ratio of Baa/Chr varied between 0.24 and 1.03 in forest soils, which suggests a pyrogenic origin. This apparent conflict may be the result of co-contributions from used motor oil and pyrogenic pollutants from nearby power plants (Fang et al., 2003). The Phe/Ant, Fla/Pyr, and Baa/Chr ratios were not sensitive enough to be used to distinguish petrogenic PAHs from pyrogenic PAHs in the soils; these pollutants likely came from multiple sources. Moreover, estimates of PAH sources did not show differences that could be related to altitude. The ratios of Ant/(Ant + Phe), Fla/(Fla + Pyr), Baa/(Baa + Chr), and IIp/(IIp + Bgp) yielded some interesting data regarding the different sources of PAHs to the mountainous study area. The ratios of Ant/(Ant + Phe) varied between 0.012 and 0.050 in forest soils, and the ratios of Fla/(Fla + Pyr) were >0.90 (Table 4). The ratios of Baa/(Baa + Chr) varied from 0.12 to 0.89 in all of the forest samples. The IIp/(IIp + Bgp) ratios changed from 0.37 to 0.71. The above ratio values suggest that traffic emissions, coal combustion, and evaporative and uncombusted petroleum products might have contributed to the occurrence of PAHs in forest soils. Baise has the largest number of aluminum production and processing plants in China and has a large petrochemical industry.
Table 4. Some diagnostic ratios of soil and leaf samples from Dawangling forest, southwest China. Pyrolytic origin Petrogenic origin Reference
Phe/Ant†
Fla/Pyr
Baa/Chr
Ant/(Ant + Phe)
Fla/(Fla + Pyr)
Baa/(Baa + Chr)
IIp/(IIp + Bgp)
15 Soclo (1986), Gschwend and Hites (1981)
>1 0.1 0.5 0.35 0.18
TECHNICAL REPORTS Organic Compounds in the Environment
Distribution and Source Apportionment of Polycyclic Aromatic Hydrocarbons in Soils and Leaves from High-Altitude Mountains in Southwestern China Bingfing Shi,* Qilin Wu, Huixiang Ouyang, Xixiang Liu, Bo Ma, Weiyuan Zuo, and Shengyu Chen
P
olycyclic aromatic hydrocarbons (PAHs) are a class
Abstract
of widely distributed persistent organic pollutants that can pose serious threats to human health and ecosystems because of their mutagenic, carcinogenic, and teratogenic properties (Falandysz, 1998; Jakobsson and Asplund, 2000; Agarwal et al., 2009). Polycyclic aromatic hydrocarbons may be generated from organic matter diagenesis and anthropogenic processes (Simoneit, 1977; Laflamme and Hites, 1978; Wakeham et al., 1980a,b). However, high concentrations of PAHs in the environment are mainly related to human activities (Edwards, 1983). Common sources of PAHs include emissions from industrial processes, domestic heating systems, and automobiles. Because of their semivolatility, most anthropogenic PAHs are transported long distances in the atmosphere, and these chemicals have been detected in the soil and water of many alpine ecosystems and remote areas around the world (Escartin and Porte, 1999; Srogi, 2007; Nam et al., 2008). According to the “Global Distillation” hypothesis (Wania and Mackay, 1996), winds carry the volatile PAHs from warm regions to cold regions, such as polar habitats and high-altitude mountainous areas, where they condense and become trapped in snow, soils, and vegetation. Concentrations of PAHs in the surface soil at mountainous sites is the net result of cumulative atmospheric deposition and losses due to volatilization, biodegradation, and mixing/burial at depth. Cold environments such as those characteristic of highaltitude mountains tend to have slow loss processes (Wilcke et al., 2002). Owing to the lipophilic and hydrophobic nature of these organic pollutants, they are readily concentrated in biota and can undergo biomagnification up the food chain (Fernandez et al., 2005). Animals and people may suffer adverse effects from PAHs if these chemicals are consumed in high quantities through dietary sources (Kelly and Gobas, 2001). Additionally, PAHs in high-altitude mountainous areas may lead to reductions in biodiversity and impair the functioning of mountain ecosystems (Pan et al., 2013).
Several studies have investigated the distribution patterns and geographic sources of polycyclic aromatic hydrocarbons (PAHs) in mountainous areas. Little is known about how different sources contribute to PAH concentrations at different elevations along mountain slopes. To estimate the distribution and sources of PAHs at different altitudes in mountainous areas of southwestern China, samples of soils and leaves from Keteleeria trees were collected from 1000 to 1500 m asl in the Dawangling forest and analyzed for PAHs. Total PAH concentrations ranged from 93.9 to 802.3 ng g-1 (average, 252.3 ng g-1) in soils and from 4.1 to 100.9 ng g-1 (average, 23.1 ng g-1) in leaves. Our results suggest that soil PAH levels in the study area could be classified as “weakly contaminated.” The PAH levels in leaves from the Dawangling forest were lower than those found in Himalayan spruce needles from the central Himalayas in China and from an agricultural station in southern England. Total PAHs in the Dawangling forest soils increased with elevation, primarily due to the low-molecularweight PAHs, which accumulated in samples from higher altitudes. In contrast, high-molecular-weight PAHs were inversely related to or unrelated to elevation. The PAH profiles were similar in soils and leaves from all mountainous regions. Diagnostic ratios showed that the PAHs in soils at different altitudes were from different pollution emission sources; therefore, PAHs in the entire study area were probably derived from mixed sources. Cluster analyses confirmed that liquefied petroleum gas, coal/ wood combustion, and petroleum combustion were likely the predominant PAH sources in this region.
Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.
Dep. of Chemistry and Life Sciences Baise Univ., 21 2nd Zhongshan Road, Baise Guangxi 533000, China. Assigned to Associate Editor Joseph Pignatello. Abbreviations: Ane, acenaphthene; Ant, anthracene; Any, acenaphthylene; Baa, benzo(a)anthracene; Bap, benzo(a)pyrene; Bbf, benzo(b)fluoranthene; Bgp, benzo(ghi) perylene; Bkf, benzo(k)fluoranthene; Chr, chrysene; Daa, dibenzo(a,h) anthracene; Fla, fluoranthene; Flu, fluorene; HMW, high-molecular-weight; IIp, indeno(1,2,3-cd)pyrene; LMW, low-molecular-weight; Nap, naphthalene; PAH, polycyclic aromatic hydrocarbon; Phe, phenanthrene; Pyr, pyrene; TOC, total organic carbon.
J. Environ. Qual. 43:1942–1952 (2014) doi:10.2134/jeq2014.04.0177 Received 18 Apr. 2014. *Corresponding author ([email protected]).
1942
Over the past few decades, there has been a growing interest identifying and quantifying PAH levels in mountainous regions. Several studies have evaluated PAHs in soil, vegetation, water, and air samples from mountainous areas in Europe, America, and Asia. For example, studies on PAHs have been conducted in the Rocky Mountains (Blais et al., 1998), Alps (Weiss et al., 2000), Laja River basin (Barra et al., 2005), Andes (Estellano et al., 2008), Pyrenees (Vandrooge et al., 2004), Qingzang Plateau (Sun et al., 2007), and Mount Qomolangma (Wang et al., 2007). These studies and others have not only investigated the geographic sources of PAHs in mountainous areas (Estellano et al., 2008) along with PAH distribution patterns (Grimalt et al., 2004), especially along elevation gradients (Wang et al., 2007; Estellano et al., 2008), but previous research has also shown that the presence of PAHs in alpine ecosystems can be attributed to a combination of long-range atmospheric transport and regionalscale atmospheric transport (Hageman et al., 2010; Lavin et al., 2012). However, little is known about how different sources contribute to the PAH concentrations at different elevations along mountain slopes or about how climatic factors may interact with PAH concentration trends in high-altitude areas (Lavin et al., 2012). In addition, the question of whether or not high mountains can act as barriers to the long-range atmospheric transport of PAHs has not been investigated directly (Vighi, 2006; Lavin and Hageman, 2013). Rapid industrial expansion and increases in automobile emissions have elevated PAH concentrations in China’s environment. Although a few studies have reported on PAH concentrations in environmental samples from high-altitude areas of China (Wang et al., 2007), the fate of PAH contaminants in the alpine ecosystems of southwestern China has not been adequately explored; hence, information on this specific area is extremely limited. The objective of this paper was to carry out a preliminary study of the levels of PAHs in soil and leaves from the Dawangling Mountains in southwestern China. Samples were collected at 1000 to 1500 m asl along the forested slopes of the Dawangling Mountains. Leaves from the Keteleeria tree, which is a widely distributed type of Keteleeria sp. plants in the study area, were selected for analyses. We used leaves instead of manufactured passive samplers for PAH analyses to avoid costs associated with sampler deployments. The altitudinal distribution patterns of PAHs and the possible sources for these pollutants in the alpine ecosystem were also investigated.
average annual temperature in the study area is 21.5°C, the relative humidity is 75%, and the mean annual rainfall is 1200 mm. The prevailing winds move from east to west. Baise is one of several new industrial centers and tourist cities in China. This city has the largest aluminum production and processing complex in China and has a large petrochemical industry. The city has a high population density and heavy vehicular traffic. Leaves from Keteleeria trees and soil samples were collected at altitudes of 1000 to 1500 m asl in the Dawangling Mountains between September and December 2013 (Fig. 1). Each sample was a mixture of five soil samples collected at the four corners and the center in an area of about 10 × 10 m2 at five elevations in each mountain. Soil samples were collected 0 to 5 cm below the surface layer. The samples were prepared by shaking the soil from grass roots, and then the soil samples were evenly mixed and dried for 5 d at room temperature in a clean, shady room. The samples were ground in a mortar, passed through a 0.5-mm sieve, and preserved at -4°C until analyzed. The influence of some soil properties (e.g., total organic carbon [TOC] content and particle size distribution) on the results was alleviated by sieving the soil particles to 0.1 is indicative of a combustion source, whereas a ratio of 0.5 are suggestive of coal, grass, and wood combustion, whereas values between 0.4 and 0.5 are suggestive of petroleum (i.e., liquid fossil fuels such as vehicle fuels and crude oil) combustion; values 18; Table 4), which indicates that the PAHs probably entered the study area via atmospheric deposition over long distances. The ratios of Phe/Ant and Fla/Pyr varied from 18.9 to 86.3 and from 0.08 to 0.11, respectively; these data are suggestive of a petrogenic origin. However, the ratio of Baa/Chr varied between 0.24 and 1.03 in forest soils, which suggests a pyrogenic origin. This apparent conflict may be the result of co-contributions from used motor oil and pyrogenic pollutants from nearby power plants (Fang et al., 2003). The Phe/Ant, Fla/Pyr, and Baa/Chr ratios were not sensitive enough to be used to distinguish petrogenic PAHs from pyrogenic PAHs in the soils; these pollutants likely came from multiple sources. Moreover, estimates of PAH sources did not show differences that could be related to altitude. The ratios of Ant/(Ant + Phe), Fla/(Fla + Pyr), Baa/(Baa + Chr), and IIp/(IIp + Bgp) yielded some interesting data regarding the different sources of PAHs to the mountainous study area. The ratios of Ant/(Ant + Phe) varied between 0.012 and 0.050 in forest soils, and the ratios of Fla/(Fla + Pyr) were >0.90 (Table 4). The ratios of Baa/(Baa + Chr) varied from 0.12 to 0.89 in all of the forest samples. The IIp/(IIp + Bgp) ratios changed from 0.37 to 0.71. The above ratio values suggest that traffic emissions, coal combustion, and evaporative and uncombusted petroleum products might have contributed to the occurrence of PAHs in forest soils. Baise has the largest number of aluminum production and processing plants in China and has a large petrochemical industry.
Table 4. Some diagnostic ratios of soil and leaf samples from Dawangling forest, southwest China. Pyrolytic origin Petrogenic origin Reference
Phe/Ant†
Fla/Pyr
Baa/Chr
Ant/(Ant + Phe)
Fla/(Fla + Pyr)
Baa/(Baa + Chr)
IIp/(IIp + Bgp)
15 Soclo (1986), Gschwend and Hites (1981)
>1 0.1 0.5 0.35 0.18
