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 (Tver Oblast) A. P. Zhidkin*, A. N. Gennadiev, and T. S. Koshovskii Moscow State University, Moscow, 119991 Russia *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.