Polycyclic aromatic hydrocarbons (PAHs) in urban surface dust of Guangzhou, China: Status, sources and human health risk assessment

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Abstract

Ninety-six urban surface dust samples collected from Guangzhou, a typical urban center in South China, were analyzed for 16 PAHs (2–6 rings). ∑ PAHs concentrations in the urban surface dust ranged from 0.84 to 12.3 μg/g with a mean of 4.80 μg/g. High molecular weight compounds (4–6 rings) contributed to 62 to 94% of ∑ PAHs mass in the surface dust samples. Four hotspots with highest ∑ PAHs were identified via kriging prediction mapping, representing the highly-urbanized regions: central downtown, highway and industrial area. Two major origins of PAHs inputs to urban surface dust were identified as vehicle emissions (51.9%) and coal combustion (26.8%). The 95% UCL of Incremental Lifetime Cancer Risk (ILCR) due to human exposure to urban surface dust PAHs in central South China was 3.03 × 10−6 for children and 2.92 × 10−6 for adults.

Highlights

► The status and composition of PAHs in urban surface dust were studied. ► ∑ PAHs distribution correlated closely with the different human activities. ► Vehicle emission and coal combustion were the primary sources of PAHs. ► Human health risk of exposure to surface dust PAH via three pathways was assessed.

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are one of the most ubiquitous classes of anthropogenic organic pollutants found in urban environment such as atmosphere, precipitation, urban surface dust, sediment and soil (Larsen and Baker, 2003). They are released into the urban environment mainly through anthropogenic activities such as vehicle emissions, coal and fossil fuel combustion for power generation, petroleum refining, straw and firewood burning, industrial processing, chemical manufacturing, oil spills and coal tars (Peng et al., 2011). Several PAHs are known carcinogens such as benzo[a]pyrene (BaP) and benz[a]anthracene (BaA) and some are the precursors to carcinogenic daughter compounds such as benzo[b]fluoranthene (BbF) (Larsen and Baker, 2003, Dickhut et al., 2000). The toxicity of PAHs including probable mutagenic and carcinogenic effects may exert potential health risk to urban residents (Colombo et al., 2006, Szabová et al., 2008).

PAHs in the urban surface dust are mainly derived from deposition of PAHs containing particulates in the atmosphere and absorption of emitted PAHs via direct exposure to vehicle exhaust emissions (Martuzevicius et al., 2011, Mostafa et al., 2009). Urban surface dust represents a hazardous carrier of organic compounds which bears a dynamic relationship with atmospheric aerosol by resuspension into and redeposition from the atmosphere and should be considered as an air pollutant of concern (Han et al., 2009). In addition, some surface dust has become a potentially significant pollutant source of PAHs to surface water, marine sediment, and consequently the food chain (Mostafa et al., 2009) because of the effects of run-off water (Mai et al., 2003). Several projects have studied the concentration and distribution of PAHs in surface dust (Liu et al., 2007, Dong and Lee, 2009, Fang et al., 2004). However, the health risk of surface dust PAH exposure is less understood, especially urban surface dust in urbanized densely populated areas.

Guangzhou, as the economic and culture center of the Pearl River Delta region, has an area of 7434 km2 and a population reaching 10 million (Li et al., 2006). It is geographically connected with many developed metropolitan cities in South China, e.g. Shenzhen, Hong Kong and Macao. Featured by a typical subtropical monsoon climate in South China, it is cool and dry in winter, while wet and hot in summer. However, data concerning PAH concentrations in the urban surface dust and their potential health risk is limited. The major objectives of the present study were to (1) determine the levels and distribution of PAH compounds; (2) identify potential PAHs sources to those found in urban surface dust; and (3) examine the human health risks for PAH exposure to urban surface dust via inhalation, ingestion and dermal contact.

Section snippets

Site description

The central urban area of Guangzhou (113.3°E and 23.2°N) are comprised of four districts: Tianhe, Liwan, Yuexiu and Haizhu, while the suburban area under investigation in this study was Panyu district. The population density varied, from 11,931 people km−2 for Tianhe, 30,574 people km−2 for Yuexiu, 14,885 people km−2 for Haizhu to 12,411 people km−2 for Liwan and 1926 people km−2 for Panyu (Guangdong Statistical Bureau, 2009).

Sampling

There were 96 urban surface dust samples collected in total in August 2010

Characterization of PAHs

Concentrations of ∑ PAHs (sum of the 2–6 ring PAHs) in urban surface dust of Guangzhou city varied from 0.84 to 12.30 μg/g with an average of 4.80 μg/g, as shown in Table 2. This result indicated that PAHs tend to accumulate in dust particles, which could be used as an indicator of urban environmental pollution. The highest ∑ PAHs concentration was found in the pavement surface dust from the bustling commercial street where the high concentrations of PAHs may have resulted from the accumulation of

Conclusion

In spite of the typical subtropical monsoon climate in summer, PAHs represented widespread and highly-accumulated organic pollutants in the urban surface dust of Guangzhou city. ∑ PAHs ranged from 0.84 to 12.3 μg/g with an average of 4.80 μg/g in urban surface dust collected from central Guangzhou areas. About 62%–94% of PAH mass was contributed by high molecular weight PAHs, suggesting a combustion origin. The contamination levels varied in different functional groups, with high PAH contamination

Acknowledgments

This research was financially supported by the Research Grants Council of the University Grants Committee of Hong Kong (HKBU 260209). We thank the graduate students from Sun Yat-sen University for assistance in field work.

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