ISSN 1064-2293, Eurasian Soil Science, 2017, Vol. 50, No. 3, pp. 296–304. © Pleiades Publishing, Ltd., 2017. Original Russian Text © A.P. Zhidkin, A.N. Gennadiev, T.S. Koshovskii, 2017, published in Pochvovedenie, 2017, No. 3, pp. 311–320.

SOIL CHEMISTRY

Input and Behavior of Polycyclic Aromatic Hydrocarbons in Arable, Fallow, and Forest Soils of the Taiga Zone () A. P. Zhidkin*, A. N. Gennadiev, and T. S. Koshovskii Moscow State University, Moscow, 119991 *e-mail: [email protected] Received August 5, 2016

Abstract⎯Contents of 11 most prevalent polycyclic aromatic hydrocarbons (PAHs) in snow and soils of ara- ble, fallow, and forest areas significantly remote from impact technogenic sources of polyarenes have been examined in the Torzhok district of Tver oblast. From the analysis of snow samples, the volumes and compo- sition of PAHs coming from the atmosphere onto the areas of different land use have been determined. Light hydrocarbons prevail in PAHs. They make up 65–70% of total PAHs; their share in soils reaches almost 95%. An increase in the content of PAHs is revealed in fallow soils compared to arable and afforested areas. A direct relationship is revealed between the lateral distribution of total PAHs and the content of organic carbon. The distribution of total PAHs is surface-accumulative in forest soils, mainly uniform in arable soils, and deep- accumulative in fallow soils. PAH groups characterized by similar radial distributions and ratios between their reserves in snow and soils are distinguished: (1) fluorene and phenanthrene, (2) biphenyl and naphthalene, (3) benzo(a)anthracene, chrysene, perylene, and benzo[a]pyrene, and (4) anthracene and benzo[ghi]pyrene.

DOI: 10.1134/S1064229317030139

INTRODUCTION and fluoranthene, as well as, according to some The increased interest in polycyclic aromatic hydro- authors, 4-ring chrysene and pyrene and 5-ring carbons (PAHs) is related to the carcinogenic and benzo[b]fluoranthene, and benzo[k]fluoranthene. mutagenic activity of some of them, which poses a The dominance of phenanthrene over other PAHs human health risk. A large body of data has been accu- was noted in soils of some background and slightly mulated on the properties of PAHs, their content, and contaminated areas, including in the study of soils in composition in environmental components, as reported the Central Caucasus (near the Mount Elbrus), as well in some reviews [5, 8–10, 12, 13, 15, 23, 24, 31, 34]. as arable and virgin steppe soils of the Khomutovskaya Most research deals with the study of technogenic steppe in southern Donetsk oblast. It should be PAHs in soils of contaminated areas near cities and emphasized that phenanthrene is detected in appre- industrial objects. Polyarenes in soils of agricultural ciable amounts in parent rocks of different genesis, lands and background territories remote from impact especially in magmatic and metamorphic hard rocks, technogenic sources are less understood. where is makes up 15–27% of total PAHs [5]. The presence of PAHs in background soils is related, The behavior of PAHs in soil cover is insufficiently first, to different natural sources of their input: cosmo- understood at present [5, 10, 34]. It is generally genic, petrogenic, biogenic, and natural pyrogenic (vol- believed that the migration of PAHs in soils is low canism and forest fires) and, second, to the global dis- because of the strong sorption of these compounds by persion of technogenic emissions in the atmosphere. soil material and their low solubility [25, 32]. Low- Information on the annual input of PAHs onto the molecular-weight PAHs can migrate with true solu- soil surface from the air is sparse and varies among the tions [22], while most PAHs, especially heavy ones, authors [34]. Their input varies from 4 to 40 t/ha per move only together with sorbing particles. PAHs are year on urbanized areas and near large industrial cen- mainly associated with the colloidal soil fraction, their ters. In forest soils of Germany and in lakes of Fin- further fate is determined by processes in which they land, the rate of PAH emission is several times lower: are involved [35, 38]. Therefore, an appreciable radial about 0.4–15 t/ha per year [26, 33]. The composition transport of PAHs is observed in podzolic and solo- of PAHs coming from the atmosphere onto the earth netzic soils [3, 7, 11]. Features of lateral PAH transport surface significantly varies among literature sources. are almost not covered in literature. However, it may be noted that the highest contribu- The content of PAHs is significantly affected by tions are made by 3–4-ring phenanthrene, fluorene, land use pattern. It is shown that tillage decreases the

296 INPUT AND BEHAVIOR OF POLYCYCLIC AROMATIC HYDROCARBONS IN ARABLE 297 content of PAHs in the topsoil because of agroturba- The following plots differing in land use were tion and improved aeration [16, 17]. However, some selected for the study: (a) plowland, (b) 10-year-old authors note an increase in the content of PAHs in the fallow, (c) 20-year-old fallow, and (d) forest area with upper horizons of arable soils due to their input with a tree stand more than 100 years old (Fig. 1). The plots fertilizers and irrigation water [17, 34, 37]. On aban- are located at less than 5 km from one another, which doned fallow lands, the maximum PAH accumulation ensures the similarity of initial environmental condi- in the uppermost 5- to 10-cm-thick layer is restored tions and soils within their areas. [17, 20]. Saison et al. [29] experimentally found that a To determine the amounts and composition of lower content of PAHs remains in arable soils than PAHs incoming from the atmosphere, snow samples under background grass vegetation. were collected on the selected plots in March of 2015 Fertilizers and the increased humus content can and 2016. On the areas with differently aged fallows, favor the sorption fixation of PAHs in soils [14]. How- snow was sampled on watersheds in different parts of ever, some authors showed that agricultural activity the catchment basin, as well as on slopes and on the results in an increase in the solubility and, hence, bottom of a hollow. On the plowland and under forest, removal of PAHs from the soil profile [18, 28, 29]. snow was collected on watersheds in triplicates. A total The behavior of PAHs in forest soils is less studied. of 32 snow samples were collected and analyzed. At In soils under forest vegetation, a significant exceeding each sampling site, the volume of snow sample was of PAH content in organic horizons over that in mineral determined and the reserve of snow was calculated. In horizons is noted. The transformation rate of PAHs in some snow samples, PAH analysis was performed in soils under forest is largely determined by properties of four replicates. forest litter and humus horizons of soils [34]. Testing of soil cover on the selected plots was per- formed in catenas on slopes of different exposures. Thus, available literature data far from exhaustively Seven catenas were studied using 26 sampling points characterize the behavior of PAHs in background and (Fig. 1). All of the studied slopes are morphologically slightly contaminated soils; they are sometimes con- similar: they have a maximum steepness of about 4 tradictory and not completely convictive, which calls degrees, a convex longitudinal profile, a convex or lin- for further investigations on this topic. ear crossing profile, and a length of 200 to 350 m. Such The aim of this work was to reveal features of PAH slopes are typical for the area under study. The step of input from the atmosphere and the behavior of PAHs soil sampling along the catenas was about 50 m on the in soils of arable, fallow, and afforested lands signifi- average in the range from 30 to 70 m depending on the cantly remote from the impact technogenic sources of length and complexity of the slope profile. On plow- polyarenes. lands and fallows, two soil samples were taken in each point from depths of 0–30 and 30–50 cm. Under for- est, soil samples were taken from depths of 0–5, 0–30, OBJECTS AND METHODS OF STUDY and 30–50 cm. A total of about 100 soil samples were The objects of study are located in the Torzhok dis- collected and analyzed. trict of Tver oblast, at 13–18 km to the west of the city The soil cover of the area under study is developed of Torzhok. The area is located far from any large on binary deposits: the surface layer of stony sandy and industrial enterprises; only motor transport and stove loamy sandy deposits of glaciofluvial origin is under- heating in rural settlements can be local technogenic lain by heavy morainic loams at depths of 30 to 60 cm. sources of PAHs in this area. The traffic on the nearest The nonuniform thickness of the upper loamy sandy roads is not heavy. Most houses in the nearest settle- layer results in the differentiation of soil cover. On the ments to the objects of study are abandoned or used plot under forest, podzolized lithobarrier soddy pod- for summer residence, without stove heating. Some burs and lithobarrier soddy podzols with an increased share of PAHs in soils can be related to the atmo- thickness of the loamy sandy layer are identified. On spheric input of polyarenes from remote regions of plowlands, the soils are lithobarrier Al–Fe–humus their intensive technogenic production. agrozems with an increased thickness of the loamy The area under study belongs to the zone of mixed sandy layer. On fallow areas, agrosoddy-podzolic soils forests with the dominance of secondary forests. The and texturally differentiated agrozems are developed, relief consists of large ridge-hilly elevations divided by which are displaced by dark-humus gley soils and tex- lows, to which the valleys of the main rivers (, turally differentiated gray-humus stratozems on the Osuga, and T’ma) are confined. Ridges are composed bottoms of hollows. by glacial deposits with inclusions of large limestone Samples of soils and snow-melt water were ana- outliers. Precipitation, about 600 mm, is uniformly lyzed by analytical engineer N.I. Khlynina in the Lab- distributed throughout the year. Moraine, outwash oratory of Carbonaceous Substances of the Biosphere, sands, and binary deposits are characteristic parent the Department of Landscape Geochemistry and Soil rocks. The active agricultural development of the area Geography, Geographical Faculty, Moscow State has been continued for more than 300 years [2]. University. PAHs were studied by spectrofluorimetry

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(a) 1 6 (b) 2а 7 TTEL3-5EL3-5 TTEL3-4EL3-4 2b 8 ТТТ-17Т-17 TTEL3-3EL3-3 3 9 TTEL3-2EL3-2 ТТ-16ТТ-16 4 10 TTEL3-1EL3-1 ТТ-15ТТ-15 5 11 ТТ-12ТТ-12 ТТ-14ТТ-14 ТТ-11ТТ-11 ТТТ-13Т-13 TEP3-5TEP3-5 ТТ-23ТТ-23 TEP3-4TEP3-4 ТТ-25ТТ-25 ТТТ-22Т-22 TEP3-3TEP3-3 ТТТ-24Т-24 ТТ-26ТТ-26 TEP3-2TEP3-2 ТТТ-42Т-42 ТТТ-41Т-41 TEPV-5TEPV-5 ТТ-27ТТ-27 TTEP3-1EP3-1 ТТТ-44Т-44 TTEPV-4EPV-4 TTEPV-2EPV-2 TTEPV-3EPV-3 ТТ-46ТТ-46 ТТТ-43Т-43 ТТ-48ТТ-48 ТТТ-36Т-36 ТТТ-45Т-45 ТТ-35ТТ-35 ТТ-38ТТ-38 ТТ-34ТТ-34 ТТ-47ТТ-47 ТТТ-37Т-37 ТТ-33ТТ-33 0 150150 300300 600600 m ТТ-49ТТ-49 ТТТ-32Т-32 ТТТ-5Т-5 (c) 12 14 ТТ-31ТТ-31 13 15 ForestForest TorzhokTorzhok N PPlowlandlowland

TTRTTR 20-year-old20-year-old ffallowallow

10-year-old10-year-old ffallowallow 0 150 300 600 m 0033366 1212 kmkm

Fig. 1. Schematic map of studied plots and sampling sites. Panels A and B: (1) soil sampling points; (2) snow sampling points (a, in 2015; b, in 2016); (3) catchment basin boundary; (4) horizontals spaced at 5 m; (5) motor roads; (6) catenas; (7) forest areas; (8) meadow; (9) 20-year-old fallow; (10) 10-year-old fallow; (11) plowland. Panel C: (12) studied plots; (13) afforested areas; (14) water bodies; (15) railroad. at low temperatures (Shpolskii spectroscopy) [1]. The absorbance of test solution was measured against a analysis of PAHs was performed on a Fluorat-Pan- blank solution on a spectrophotometer. orama spectrofluorimeter (Lumex, Russia) equipped To estimate the lateral displacement of soil solid- with an LM-3 monochromator and a Cryo-1 acces- phase material by the magnetic tracer method, the sory. Individual polyarenes were identified and quan- content of spherical magnetic particles (SMPs) in soils tified from characteristic lines in the fluorescence was determined. The determination of SMP content spectra of bitumoid solutions at –196°C using an included the separation of the magnetic fraction from international certified standard (SRM 2260a, NIST). water suspension by passing in separation funnels In each sample, 11 most prevalent individual PAHs through a constant magnetic field and the calculation containing two aromatic rings (biphenyl and naphtha- of the SMP share in the ferromagnetic fraction of soil lene homologues), three rings (fluorene, phenan- under a Carl Zeiss Axio Scope A40 microscope in threne, and anthracene), four rings (chrysene, pyrene, slides applied on a transparent plastic support (lexan). and benzo(a)anthracene), five rings (perylene and The procedure is described in detail earlier [4, 6]. benzo[a]pyrene), and six rings (benzo[ghi]perylene) were determined. The extraction of PAHs was per- RESULTS AND DISCUSSION formed with n-hexane at room temperature. Content and composition of PAHs coming from the The content of organic carbon in soils was deter- atmosphere. The total content of the studied PAHs mined by the Tyurin method with spectrographic (total PAHs) in snow samples was 7 to 79 ng/g in dif- detection, including the dilution of solutions. The ferent sampling points (Table 1). Total PAHs in snow

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Table 1. Content and composition of PAHs in snow on the studied plots Land use Parameter forest 20-year-old fallow 10-year-old fallow plowland Number of samples 3 7 8 3 Total PAHs, ng/g snow 27* (7–52)** 49 (11–79) 32 (9–46) 25 (20–31) Shares of individual compounds in total PAHs, % Fluorene 4.6 1.1 2.3 2.6 Biphenyl 24.3 8.4 19.0 6.2 Naphthalene homologues 39.4 40.3 30.6 31.8 Phenanthrene 15.1 24.4 14.5 35.0 Chrysene 3.0 4.4 4.0 2.4 Pyrene 5.2 6.4 5.4 7.8 Anthracene 0.0 1.9 1.3 0.1 Benzo(a)anthracene 1.5 1.8 2.6 3.5 Benzo[a]pyrene 0.9 0.5 0.7 0.9 Benzo[ghi]perylene 6.1 9.3 17.0 7.3 Perylene 0.0 1.5 2.7 2.4 * Here and below, mean values for the plot. ** Here and below, variation range. were 27 and 25 ng/g, on the average, on adjacent plots other heavy PAHs agree with data on the absence of under forest and plowland and 32 and 49 ng/g on adja- other local technogenic sources of PAHs on this area. cent fallow plots (Table 1). The obtained results indicate Content and composition of PAHs in soils. The con- a significant quantitative similarity of PAH input from tent of total PAHs in soil samples varies from 1 to the atmosphere on different plots under study; however, 767 ng/g. Among the studied compounds, light 2–3- a significant variation is observed within the plots. ring PAHs prevail in most samples: phenanthrene From the PAH reserves revealed in snow, the mean (55% on the average for all samples), naphthalene rate of PAH input from the atmosphere to the given area homologues (about 29%), and biphenyl (about 9%). during the year was calculated (under the supposition The total share of light PAHs in the studied samples is that the rates of PAH input in different seasons were almost 95%. The composition of PAHs in soils agrees similar). The rate was found to be about 0.06 t/ha per with the revealed dominance of light hydrocarbons in year, which can be considered as very low. From the PAHs coming from the atmosphere. The prevalence of available literature data, the rate of PAH input from the light PAHs in soils of slightly contaminated areas is atmosphere to relatively background areas in Western also confirmed by literature data [5]. The share of Europe varies from 0.4 to 15 t/ha per year [34]. 4-ring compounds in total PAHs is only about 4%; the share of 5–6-ring PAHs is lower than that of light The composition of PAHs coming from the atmo- PAHs by one–two orders of magnitude: only about sphere is relatively homogeneous on all of the studied 1% (Table 2). plots regardless of land use pattern. The dominant compounds are naphthalene homologues (39% of The total PAH concentrations in the studied soils are total PAHs on the average), phenanthrene (19%), low and correspond to the content of these compounds biphenyl (15%), and benzo[ghi]perylene (14%). They in soils of other background areas [3, 8, 10, 35]. The make up 80–85% of total PAHs (Table 1). revealed contents of total PAHs significantly vary on the studied plots: from 43 to 767 ng/g on the 20-year-old Naphthalene homologues, phenanthrene, and fallow, from 11 to 195 ng/g on the 10-year-old fallow, biphenyl are light 2–3-ring PAHs. The dominance of from 25 to 49 ng/g under forest, and from 18 to 43 ng/g these hydrocarbons, especially phenanthrene, in the on the plowland (Table 2). PAHs coming from the atmosphere agrees with litera- ture data [21, 30, 33, 36]. This variability of total PAHs is mainly determined by the variations in the content of phenanthrene, The high proportion of heavy 6-ring whose share exceeds 85% on some plots. The highest benzo[ghi]perylene coming from the atmosphere can variation in the content of phenanthrene is noted in be related to a local technogenic source of PAHs: points spaced at only tens or hundreds of meters from according to literature data [19, 27], this polyarene is one another on fallow plots (from 0 to 721 ng/g in sep- a marker of vehicle emissions. Trace amounts of arate sampling points). The variation in the content of

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Table 2. Content and composition of PAHs in soils of the studied plots Land use Parameter forest 20-year-old fallow 10-year-old fallow plowland 0–5 cm 0–30 cm 30–50 cm 0–30 cm 30–50 cm 0–30 cm 30–50 cm 0–30 cm 30–50 cm Number of samples 5 5 5 17 9 13 7 9 9 Total PAHs, ng/g 57* 35 16 193 260 43 180 31 33 (38–87)** (25–49) (9–23) (43–767) (49–459) (11–195) (29–377) (18–43) (15–89) Total PAHs without 45 19 12 29 32 19 30 18 16 phenanthrene, ng/g (31–58) (14–27) (6–18) (12–53) (13–73) (8–39) (9–60) (6–33) (7–39) Shares of individual compounds in total PAHs, % Fluorene0.01.95.30.50.42.12.40.83.1 Biphenyl 24.3 5.2 21.6 4.4 3.3 5.1 4.7 1.2 9.0 Naphthalene 34.2 46.3 42.2 9.1 7.9 33.5 9.3 46.6 30.7 homologues Phenanthrene 21.7 44.0 27.0 85.0 87.8 55.5 83.2 43.4 52.1 Chrysene 3.0 1.1 1.9 0.2 0.3 0.6 0.1 1.2 0.6 Pyrene 9.6 0.8 1.9 0.4 0.1 1.1 0.2 4.0 4.0 Anthracene0.50.10.00.00.00.20.00.00.1 Benzo(a)anthracene 2.0 0.5 0.2 0.1 0.1 0.6 0.0 1.8 0.2 Benzo[a]pyrene1.10.00.00.00.00.00.00.10.0 Benzo[ghi]perylene 3.5 0.0 0.0 0.1 0.0 1.3 0.0 0.8 0.3 Perylene 0.2 0.0 0.0 0.2 0.1 0.0 0.0 0.0 0.0 phenanthrene can be related to the initial heterogene- accumulative distribution with the decrease in the PAH ity of its concentrations in morainic and glaciofluvial concentration with depth, deep-accumulative distribu- deposits on this area. tion with the PAH concentration increasing with depth, A trend of increasing total PAHs is revealed in the and uniform distribution with the PAH concentration soil series: plowland–10-year-old fallow–20-year-old varying only slightly along the soil profile. fallow. The total PAH content in this series progres- It is found that a surface-accumulative distribution sively increases: 31–43–193 ng/g in the 0- to 30-cm is typical for total PAHs in all forest soils; arable soils layer and 33–180–260 ng/g in the 30- to 50-cm layer. are mainly characterized by uniform distribution, and This trend is observed for all 11 studied PAHs, as well fallow soils have a deep-accumulative distribution. as for 10 PAHs excluding phenanthrene (Table 2). The maximum PAH content in the 30- to 50-cm layer is more manifested in the 10-year-old fallow than in The obtained trend is probably due to the decrease the 20-year-old fallow. in the degradation rate of PAHs in fallow soils com- pared to better aerated and more turbated arable soils. A tendency toward changes in the PAH composition An increase in the content of PAHs in fallow soils along the soil profile is revealed. The concentration of compared to arable soils was also noted by other light polyarenes usually increases and that of heavy authors [17, 20]. compounds decreases with depth [5]. A deep-accumu- lative distribution is revealed for phenanthrene and flu- In forest soils, the content of total PAHs averaged orene in 70 and 80% of the studied soil profiles, respec- over the plot area is low: its value in the 0- to 30-cm tively. A surface-accumulative distribution in soils is layer is almost similar to that on plowland (35 ng/g), typical for naphthalene, benzo[a]pyrene, perylene, and and the value in the 30- to 50-cm layer is significantly pyrene. It is manifested in soils on all plots regardless of lower than on all of the other studied plots (16 ng/g), land use. The sharpest surface-accumulative distribu- which can be due to the partial deposition of pol- tion of radial distribution is noted for benzo(a)anthra- yarenes in tree crowns and their retention in the litter, cene, anthracene, and benzo[ghi]perylene. The where PAHs are more subjected to decomposition increased content of light PAHs in deep soil horizons because of photodestruction. can be due to their vertical migration, as well as more The radial distribution of PAHs was analyzed in soils intensive decomposition in the upper soil horizons. of different land use patterns. The following types of Heavy PAHs, in turn, are prevalent in the upper hori- their radial distribution were distinguished: surface- zons because of their predominantly atmospheric

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Forest 10-year-old fallow 4.5 60 4.5 50 4.0 4.0 50 3.5 3.5 40 3.0 40 3.0 30 2.5 2.5 30 2.0 2.0 20 1.5 20 1.5 1.0 1.0 10 10 0.5 0.5 0 0 0 50 100150 200 0 200 400 20-year-old fallow Plowland 4.5 900 4.5 45 4.0 800 4.0 40 Total PAHs, ng/g PAHs, Total 3.5 700 3.5 35 Carbon,%; SMP, μg/g Carbon,%; SMP, 3.0 600 3.0 30 2.5 500 2.5 25 2.0 400 2.0 20 1.5 300 1.5 15 1.0 200 1.0 10 0.5 100 0.5 5 0 0 0 100 200 300 0 50 100150 200 Distance from the watershed, m 123

Fig. 2. Lateral distributions of (1) organic carbon, (2) SMPs, and (3) total PAHs on slopes of western exposure under different land use patterns. input and accumulation on the sorption barrier and in The increased content of humus probably favors the humus-accumulative horizon. the sorption of PAHs; hence, even a small decrease or increase in the content of organic carbon affects the The lateral distribution of PAHs was also estimated. radial distribution of polyarenes in the studied low- The distribution features on slopes of different expo- humus soils. The absence of intracatena correlations sures were simultaneously estimated for SMPs (tracers between PAHs and humus on one side and SMPs on of solid-phase transfer), including fine soil particles, the other side can indicate that the diversity of soils which can be potential carriers of sorbed polyarenes. In and parent rocks within catenas under these condi- addition, correlation between the contents of PAHs and tions is a more significant factor for the lateral distri- organic carbon in soils was studied in catenas. bution of polyarenes than the migration of soil solid- Joint analysis of the lateral distributions of PAHs phase material. and SMPs revealed no clear relations between these Comparative estimation of PAH content in snow and parameters within a catena. However, correlations soils. In this section, the reserves of PAHs in snow and between the lateral distribution of total PAHs and the soil samples collected at the same sites are compared. content of organic carbon are unambiguously estab- Differences in the composition of PAHs coming from lished in the upper 30-cm-thick soil layers (Fig. 2). The the atmosphere (in snow samples) and in soils of the coefficient of correlation is 0.91 for the afforested slope, studied plots are revealed. 0.87 for the plowed slope, and 0.77 for the 10-year-old fallow. A lower correlation is observed for the old fallow The dominance of light naphthalene homologues, on the slope, where the content of organic carbon grad- phenanthrene, and biphenyl is a common feature of ually decreases down the catena, and total PAHs grad- PAHs coming from the atmosphere and present in ually decreases to the mid-catena and then abruptly soils. The share of each of the above light PAHs in increases in two points. Nonetheless, the revealed cor- snow and soils is appreciably varied. In snow, the share relation between the lateral distributions of organic car- of phenanthrene is higher (23% in snow cover against bon and total PAHs is well manifested (Fig. 2). 80% in soils) and the shares of naphthalene homo-

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Table 3. Reserves and shares of individual PAHs in soils and snow PAHs in the 0- to 30-cm soil layer PAHs in snow cover Ratio of PAHs in snow to PAHs PAH share of total share of total μg/m2 μg/m2 in the 0- to 30-cm PAHs, % PAHs, % soil layer Fluorene 428 0.9 29 1.7 0.07 Biphenyl 2076 4.3 230 13.3 0.11 Naphthalene homologues 6313 13.2 637 37.0 0.10 Phenanthrene 38363 80.3 389 22.6 0.01 Chrysene 159 0.3 66 3.8 0.42 Pyrene 220 0.5 113 6.6 0.51 Anthracene 5 0.0 27 1.6 5.49 Benzo(a)anthracene 57 0.1 34 1.9 0.59 Benzo[a]pyrene 15 0.0 10 0.6 0.67 Benzo[ghi]perylene 72 0.2 159 9.3 2.20 Perylene 54 0.1 27 1.5 0.49 Total 47761 100.0 1720 100.0 0.04 logues and biphenyl are lower (37% against 13% and From the results of study, four associations of 13% against 4%, respectively) (Table 3). PAHs are distinguished depending on the ratios The composition of PAHs in snow samples is char- between their reserves in snow and soils and their acterized by a significantly higher share of medium radial distributions (Fig. 3). and heavy polyarenes than in soil samples. The share The first and second groups include PAHs whose of heavy PAHs is 17% in snow and only 2% in soils (0- reserves in soils exceed their reserves in snow in 10– to 30-cm layer). The largest differences are observed 100 times. These groups include only light PAHs: for benzo[ghi]perylene, whose mean share is 9% in phenanthrene, fluorene, biphenyl, and naphthalene. PAHs from snow samples and only 0.2% in PAHs from Fluorene and phenanthrene can be included in the the 0- to 30-cm soil layer.

The proportions of individual PAHs in snow and 10 soils vary significantly and form the following series: Anthracene phenanthrene (their reserve in snow makes up 1% of the reserve in the soil) – fluorene (7%) – naphtha- lene homologues (10%) – biphenyl (11%) – chrysene Benzo[ghi]perylene (42%) – perylene (49%) – pyrene (51%) – benzo(a)anthracene (59%) – benzo[a]pyrene (67%). 1 Benzo[a]pyrene For two polyarenes, the reserve in snow exceeds that Chrysene Perylene, Pyrene in the soil: benzo[ghi]perylene (in 2.2 times) and Benzo(a)anthracene anthracene (in 5.5 times).

This series, except anthracene, is closely related to Biphenyl the molecular structures of PAHs. Light 2–3-ring 0.1 PAHs are in the beginning of the series; their reserves Naphthalene in snow vary from 1 to 11% of their reserves in the soil. Fluorene Medium and heavy 4–5-ring PAHs are in the middle of the series; their reserves in snow vary from 42 to in snow and the 0- to 30-cm soil layer in snow and30-cm the 0- to Ratio between the mean PAH reserves the mean PAH between Ratio 67% of their reserves in the soil. The reserve of heavy Phenan- 6-ring benzo[ghi]perylene in snow is more than dou- 0.01 threne ble its reserve in the soil. 0.1 1 10 100 Ratio between the mean PAH contents The series of PAHs corresponding to their concen- in the 0- to 30-cm and the 30- to 50-cm soil layers trations in snow and soils can be related to their prop- erties. According to literature data, light PAHs are mainly inherited by soils from rocks; there are also Fig. 3. Diagram of ratios between the PAH reserves in some indications that they can result from biogeo- snow and soils and the radial distributions of individual chemical processes [5]. polyarenes.

EURASIAN SOIL SCIENCE Vol. 50 No. 3 2017 INPUT AND BEHAVIOR OF POLYCYCLIC AROMATIC HYDROCARBONS IN ARABLE 303 first group: polyarenes with deep-accumulative distri- and a deep-accumulating distribution is typical for fal- bution. The second group includes biphenyl and low soils. However, the radial distributions of individ- naphthalene mainly characterized by the surface- ual polyarenes differ significantly and are not always accumulative type of radial distribution. determined only by land use. For the third PAH group―benzo(a)anthracene, Groups of polyarenes characterized by similar chrysene, perylene, pyrene, and benzo[a]pyrene―soil radial distributions in soils and ratios between reserves exceed their reserves in snow in 1.5–2 times. reserves in snow and soils are distinguished: (1) fluo- PAHs from this group have a surface-accumulative dis- rene and phenanthrene; (2) biphenyl and naphtha- tribution in 60–85% of the studied soils. lene; (3) benzo(a)anthracene, chrysene, perylene, The fourth group includes anthracene and and benzo[a]pyrene; and (4) anthracene and benzo[ghi]perylene. Their reserves in snow cover exceed benzo[ghi]pyrene. those in soils. Anthracene and benzo[ghi]perylene have surface-accumulative distributions in more than 85% of ACKNOWLEDGMENTS soils. The work was supported in part by the Russian Sci- ence Foundation (project no. 14-27-00083). 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