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Diurnal variations of air-soil exchange of semi-volatile organic compounds (PAHs, PCBs, OCPs and PBDEs) in a central European receptor area Celine Degrendele, Ond#ej Audy, Jakub Hofman, Jiri Ku#erík, Petr Kukucka, Marie D Mulder, Petra P#ibylová, Roman Prokeš, Milan Sá#ka, Gabriele E. Schaumann, and Gerhard Lammel Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b05671 • Publication Date (Web): 23 Mar 2016 Downloaded from http://pubs.acs.org on March 23, 2016
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Diurnal variations of air-soil exchange of semi-volatile organic compounds (PAHs, PCBs, OCPs
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and PBDEs) in a central European receptor area
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Céline Degrendele1, Ondřej Audy2, Jakub Hofman2, Jiři Kučerik3, Petr Kukučka2, Marie D. Mulder2,
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Petra Přibylová2, Roman Prokeš2, Milan Sáňka2, Gabriele E. Schaumann3 and Gerhard Lammel1,2*
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1
Max Planck Institute for Chemistry, Multiphase Chemistry Department, Hahn-Meitner-Weg 1, 55128
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Mainz, Germany 2
Masaryk University, Research Centre for Toxic Compounds in the Environment, Kamenice 5, 625
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00 Brno, Czech Republic 3
Institute for Environmental Sciences, University of Koblenz-Landau, Fortstr. 7, 76829 Landau, Germany
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Corresponding author: Prof. Gerhard Lammel, Masaryk University, Research Centre for Toxic
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Compounds in the Environment, Kamenice 5, 625 00 Brno, Czech Republic Tel: +420 54949 4106,
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Fax: +420 54949 2840. Email:
[email protected] ACS Paragon Plus Environment
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Abstract
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Concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs),
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organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs) in air and soil, their
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fugacities and the experimental soil-air partitioning coefficient (KSA) were determined at two
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background sites in the Gt. Hungarian Plain in August 2013. The concentrations of the semi-volatile
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organic compounds (SOCs) in the soil were not correlated with the organic carbon content, but with
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two indirect parameters of mineralization and aromaticity, suggesting that soil organic matter quality
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is an important parameter affecting the sorption of SOCs onto soils. Predictions based on the
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assumption that absorption is the dominant process were in good agreement with the measurements for
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PAHs, OCPs and the low chlorinated PCBs. In general, soils were found to be a source of PAHs, high
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chlorinated PCBs, the majority of OCPs and PBDEs and a sink for the low chlorinated PCBs and γ-
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hexachlorocyclohexane. Diurnal variations in the direction of the soil-air exchange were found for two
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compounds (i.e. pentachlorobenzene and p,p’-dichlorodiphenyldichloroethane), with volatilization
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during the day and deposition in the night. The concentrations of most SOCs in the near-ground
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atmosphere were dominated by re-volatilization from the soil.
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Introduction
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Semi-volatile organic compounds (SOCs) including polycyclic aromatic hydrocarbons (PAHs) and
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persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs), organochlorine
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pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs) have been characterized by their
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environmental and human health effects.1 Due to their semi-volatility in combination with slow
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degradability in air, top soil, surface waters and on vegetation surfaces, these compounds may undergo
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a series of volatilizations and subsequent depositions (“multihopping”), which enhances their long-
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range transport potential (“grasshopper effect”).2–5 Regulatory actions taken internationally over the
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last two decades in order to reduce or eliminate major primary sources of POPs associated with
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production and use has resulted in a slow decline of their atmospheric concentrations in Europe.6–8
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However, secondary sources such as air-surface exchange may dominate the current and future
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presence of SOCs in the atmosphere.8–12
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Soils represent an important reservoir of PAHs and POPs in the world.10,13,14 In background soils, far
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from primary sources, the occurrence of those chemicals is influenced by long-range atmospheric
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transport (LRAT), dry and wet deposition (affecting both gases and particles), volatilization,
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degradation and leaching. Soil-air exchange of SOCs has been characterized as a key process driving
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the environmental fate of those pollutants on regional and global scales.7,15,16 Many studies assessed
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the direction of soil-air exchange by quantifying the soil and the air fugacities using predictions or
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laboratory/field measurements. For example, soil fugacity has been estimated from predictions of the
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soil-air partitioning coefficient (KSA), which often assumes that absorption into the soil bulk
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constituents, such as the soil organic matter (SOM), is the main mechanism occurring and that
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adsorption processes can be neglected.17–21 However, some studies have pointed out that adsorption to
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carbonaceous sorbents such as black carbon (BC) or minerals may also play a crucial role,21–24
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although this may be limited for background soils25 and non-polar compounds.26 Moreover, soil
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fugacities determined from laboratory experiments27 may not be relevant to real environmental
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conditions, while those derived from field measurements28,29 were limited by the lack of a robust and
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reproducible method ensuring that both phases were in equilibrium.30 Vertical gradients of
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atmospheric concentrations have also been used to assess the direction of the gas exchange between
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the soil and the air31 as well as micrometeorological methods.32 Recently, Cabrerizo et al. (2009)30
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developed a soil fugacity sampler which ensures optimal field data of the POP and PAH fugacities in
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soil and therefore provides accurate soil-air fugacity gradients.
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SOM quantity and soil temperature have been identified as key parameters influencing the exchange
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of SOCs between the air and the soil.6,13,15,33 However, recent studies suggested that the quality of the
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SOM, related to its aromaticity10,21,34, the clay minerals35 and the soil moisture,36,37 may also influence
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chemical partitioning that enhances the soil sorption capacity for SOCs.
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The aim of this study was to characterize the air-soil exchange of PAHs, PCBs, OCPs and PBDEs
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using the soil fugacity sampler previously described30 at two background sites in Central Europe.
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Moreover, the influence of diurnal variations, soil properties and soil moisture on KSA was assessed
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and measured KSA values were compared with various predictions.
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Methodology
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Sampling
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Air and soil samples were collected in August 2013 at two background sites in the Great Hungarian
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Plain: Kecskemetpuszta (KP) and Bugacpuszta (BP). This area represents the main atmospheric
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transport route for anthropogenic emissions from the densely populated and highly industrialized
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central and western Europe. The Plain can be considered as the closest receptor area for these
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emissions. KP (46°58'N, 19°33'E) is a background station of the European Monitoring and Evaluation
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Programme (EMEP) network38 located about 70 km south-east of Budapest. KP is located in a forest
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clearing characterized by an uncultivated grassland. BP (46°42’N, 19°36E) is located about 40 km
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south-east of KP on an uncultivated grassland used for grazing. Both soils were classified as haplic
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arenosol.
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At each site, three plots which were within 200 m from each other were selected for soil and air
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sampling. Composite soil samples were collected once at each plot from the uppermost 5 cm of soil
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prior to air sampling. A composite soil sample consisted of nine individual samples distanced 1 m
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from each other. At both sites the uppermost 5 cm of soil were horizon A with uniform soil properties
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i.e., brownish black colour, fine sand texture, loose, single grain structure and dense fine roots. The
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lower transition A/C horizon did not change very much with depth or between sampling sites (depth
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from 5 to 9 cm) and this horizon was not sampled.
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Ambient air samples were collected at each plot at a height of 91 or 111 cm from 05/08/13 to 17/08/13
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using a low volume air sampler (flow rate of 2.3 m3.h-1, Leckel MVS, PM10 inlet) which collected
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gaseous and particulate phases. Gases were collected on two polyurethane foam (PUF) plugs
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(Gumotex Břeclav, density 0.030 g.cm-3, 55 cm diameter, 5 cm depth) which were pre-cleaned via
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Soxhlet extraction with acetone and dichloromethane for eight hours each. Particles were collected on
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quartz fiber filters (QFFs, Whatman QMA, 47 mm). Day, night and 24 h samples were collected, with
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volumes ranging from 6 to 53 m3. Moreover, at each plot, two soil fugacity samplers (Baghirra PM10-
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35), which have been previously described,30 were simultaneously used. Briefly, these low-volume air
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sampler’s inlets consist of a stainless steel plate with a surface of 1 m2, located 3 cm above the soil
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surface. The air was sampled with a flow of 10 L min-1, from a chamber located on the centre of the
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stainless steel plate to a QFF and a PUF plug in series (same materials as described above). Due to the
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low flow rates used and to the large surface of the sampler, the sampled gas phase is in contact with
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the soil for sufficient time to equilibrate,30 which is generally not the case with the conventional air
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sampling. In general, the sampling periods were similar to the ones for ambient air (i.e. 8-24 h)
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resulting in a sample volume of 1.2-13.8 m3. Furthermore, five of the six plots were artificially
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watered once by gentle application of 10 mm of purified water onto the sampled area plus the
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surrounding strip of 0.5 m in order to assess the influence of soil moisture on soil-air exchange. The
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climatic conditions during the sampling were characterized by high temperatures (i.e. average ambient
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temperature of 297 K), with a day-night temperature difference of about 14 K. Except for one
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precipitation event (4.7 mm) which occurred on August, 14th from 5 to 7 am, the soils were dry unless
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artificially watered. Due to limited sorption capacities of the PUF at elevated temperatures, partial
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breakthrough of naphthalene, acenaphthylene, acenaphthene, fluorene, pentachlorobenzene and
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hexachlorobenzene in at least some of the PUF samples collected by the low volume air sampler
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(Leckel) is likely.39
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Meteorological parameters such as air and soil temperatures, relative humidity, wind direction and
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velocity were continuously monitored. Details about the air samples and meteorological measurements
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are available in Tables S1 and S2 of the Supplementary Information (SI).
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Sample preparation and analysis
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All air samples were extracted with dichloromethane using an automatic warm Soxhlet extractor
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(Büchi B-811, Switzerland). Surrogate recovery standards (D8-naphthalene, D10-phenanthrene, D12-
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perylene, PCB30, PCB185 and isotopically 13C labelled BDE28, BDE47, BDE100, BDE99, BDE154,
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BDE153, BDE183, Wellington Laboratories, Canada, LGC, UK) were spiked on each PUF prior to
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extraction. The concentrated extracts were divided, with 10% used for PAH analysis and the
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remaining for the analysis of halogenated compounds.
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Samples dedicated to PAH analysis were cleaned-up on an activated silica column and reduced under
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a gentle stream of nitrogen. The 16 USEPA-prioritized PAHs (naphthalene (NAP), acenaphthylene
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(ACY), acenaphthene (ACE), fluorene (FLN), phenanthrene (PHE), anthracene (ANT), fluoranthene
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(FLT), pyrene (PYR), benzo(a)anthracene (BAA), chrysene (CHR), benzo(b)fluoranthene (BBF),
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benzo(k)fluoranthene
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dibenz(a,h)anthracene (DHA) and benzo(g,h,i)perylene (BPE)) were analyzed by gas chromatography
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(GC) coupled to a mass spectrometer (MS) operated in the positive electron ionization mode. Samples
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dedicated to PCB, OCP and PBDE analysis were cleaned-up on a H2SO4 modified silica column,
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eluted with 30 mL of dichloromethane/n-hexane mixture (1:1) and reduced under a gentle stream of
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nitrogen. Seven PCBs (PCB28, PCB52, PCB101, PCB118, PCB138, PCB153 and PCB180), 12 OCPs
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(pentachlorobenzene (PeCB), hexachlorobenzene (HCB), α-hexachlorocyclohexane (HCH), β-HCH,
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δ-HCH,
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dichlorodiphenyldichloroethane (DDD), p,p’-DDD, o,p’-dichlorodiphenyltrichloroethane (DDT) and
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p,p’-DDT) and nine PBDEs (BDE28, BDE47, BDE66, BDE100, BDE99, BDE85, BDE154, BDE153
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and BDE183) were analyzed by GC-MS/MS (for PBDEs) and GC-MS (for PCBs and OCPs) in the
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positive electron ionization mode. The methods are detailed in the SI (Table S3).
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The soil collected during the sampling (50-100 g for each plot) were sieved and divided into five
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fractions used for different analysis. The first fraction was used to quantify SOCs present in the soils
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and was subject to the same analyses as described above for the air samples. The second fraction was
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used to quantify the main constituents and properties of the soils (e.g., total organic carbon (TOC),
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humic and fulvic acids) and the remaining fractions were used for specific analysis (e.g. BC,
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thermogravimetric analysis). All the methods are detailed in the SI and an example of soil properties is
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shown in Figure S1.
γ-HCH,
(BKF),
benzo(a)pyrene
(BAP),
o,p’-dichlorodiphenyldichloroethylene
indeno(123-cd)pyrene
(DDE),
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Results and discussion
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(IPY),
o,p’-
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SOCs concentrations in soils
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The soil concentrations of all SOCs investigated (Figure 1 and Table S4) were generally similar
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amongst BP soils while large variabilities were observed within KP soils (i.e. within
