Spatial and seasonal variations, sources, air-soil exchange, and carcinogenic risk assessment for PAHs and PCBs in air and soil of Kutahya, Turkey, the province of thermal power plants

Highlights

• Air and soil PAH and PCB levels were investigated around coal-fired power plants

• It was shown that power plants are major sources for PAHs and weak sources for PCBs

• PAHs mainly deposited to soil in winter while in summer they mostly volatilized

• For PCBs, volatilization was higher compared to deposition in both seasons

• Generally, estimated carcinogenic risks were below the acceptable risk level of 10^− 6

Abstract

Atmospheric and concurrent soil samples were collected during winter and summer of 2014 at 41 sites in Kutahya, Turkey to investigate spatial and seasonal variations, sources, air-soil exchange, and associated carcinogenic risks of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The highest atmospheric and soil concentrations were observed near power plants and residential areas, and the wintertime concentrations were generally higher than ones measured in summer. Spatial distribution of measured ambient concentrations and results of the factor analysis showed that the major contributing PAH sources in Kutahya region were the coal combustion for power generation and residential heating (48.9%), and diesel and gasoline exhaust emissions (47.3%) while the major PCB sources were the coal (thermal power plants and residential heating) and wood combustion (residential heating) (45.4%), and evaporative emissions from previously used technical PCB mixtures (34.7%). Results of fugacity fraction calculations indicated that the soil and atmosphere were not in equilibrium for most of the PAHs (88.0% in winter, 87.4% in summer) and PCBs (76.8% in winter, 83.8% in summer). For PAHs, deposition to the soil was the dominant mechanism in winter while in summer volatilization was equally important. For PCBs, volatilization dominated in summer while deposition was higher in winter. Cancer risks associated with inhalation and accidental soil ingestion of soil were also estimated. Generally, the estimated carcinogenic risks were below the acceptable risk level of 10^− 6. The percentage of the population exceeding the acceptable risk level ranged from < 1% to 16%, except, 32% of the inhalation risk levels due to PAH exposure in winter at urban/industrial sites were > 10^− 6.

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants having two or more fused aromatic rings. PAHs are prevalent in environmental compartments like atmosphere, surface waters, sediment and soil (Motelay-Massei et al., 2003, Kaya et al., 2012), which are carcinogenic and mutagenic even at low levels (Ravindra et al., 2008, Wang et al., 2009). PAHs have natural (forest fires and volcanic activities) and anthropogenic sources (traffic, fossil fuel combustion, and industrial processes) (Aydin et al., 2014, Wang et al., 2015). Anthropogenic PAHs have either pyrogenic or petrogenic origins. Petrogenic sources are crude oil and petroleum products while pyrogenic PAHs emitted from incomplete combustion of fuels like coal and wood in industries and power plants (Okedeyi et al., 2013).

Polychlorinated biphenyls (PCBs) are anthropogenic persistent organic pollutants (POPs) that are widespread, toxic, and persistent in the environment, and could be transported to large distances (Biterna and Voutsa, 2005). PCBs were extensively used in various industrial applications like capacitors, transformers, and paints over the period of 1930–1975 (Dyke et al., 2003, Badawy et al., 2010, Gueguen et al., 2011). However, their production was discontinued and their use was banned in many countries several decades ago. PCBs are emitted into the environment from PCB containing wastes, open burning, waste incineration, evaporation from PCB containing products and contaminated surfaces, and accidental spills to soil (Vallack et al., 1998, UNEP (United Nations Environmental Programme), 1999, Breivik et al., 2002). PCBs could also form during the combustion of organic matter if chlorine is present (Weber et al., 2001). It was reported that PCB emissions from the combustion of different fuels (coal, wood, crude oil, gasoline/diesel) for industrial activities and power generation contribute to their atmospheric levels (Dyke et al., 2003, Biterna and Voutsa, 2005).

Coal is an important fuel for power generation in Turkey. Coal-fired thermal power plants are potentially the main air pollution source in Kutahya, Turkey, a province having two coal-fired power plants operating at their full capacities. PAHs already exist in coal but can also be formed during the combustion processes. Coal combustion also leads to the formation of PCBs (Lee et al., 2005). Therefore, it is important to explore the levels and profiles of PAHs and PCBs in the vicinity of coal-fired power plants (Sahu et al., 2009).

The public perception about poor air quality in Kutahya and associated health effects is that the thermal power plants are the source of these problems. Since the air quality measurement studies are very limited even on conventional pollutants, and there has been no study investigating POP levels, an extensive sampling study covering the whole province was planned to investigate the PAH and PCB levels in the region. The specific objectives of this study were (1) to explore the spatial distributions and seasonal variations of PAH and PCB levels in air and soil, (2) to identify their possible sources, (3) to investigate their air-soil exchange, and (4) to determine the exposure to PAHs and PCBs and associated carcinogenic risks in Kutahya region, Turkey.