Transformation of Petroleum Products in the

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cycloparaffins. Accumulation of F e, Mn, V. , and other metals contained in oil. Evaporation fro m soil fro m. 20 to 40% of light fractions—alkanes, cycloparaffins, P.
ISSN 00978078, Water Resources, 2014, Vol. 41, No. 7, pp. 854–864. © Pleiades Publishing, Ltd., 2014. Original Russian Text © A.P. Khaustov, M.M. Redina, 2013, published in Geoekologiya, 2013, No. 6, pp. 502–515.

ENVIRONMENTAL POLLUTION

Transformation of Petroleum Products in the Geological Environment Accompanying Changes in Their Bitumen Status A. P. Khaustov and M. M. Redina Ecological Faculty, Peoples’ Friendship University of Russia, Podol’skoe sh. 8/5, Moscow, 117198 Russia Email: [email protected] Received June 22, 2012; in final form, March 25, 2013

Abstract—The main problems in geoenvironmental estimation of petroleum product transformations are analyzed with their bitumen status taken into account. A fourzone model is proposed to describe the distri bution of oil products, taking into account their transformations in geological environments. A nonequilib rium system of water–rock–petroleum product (as pollutants) interaction is substantiated with the identifi cation of two genetic branches (abiogenic and biogenic), which form the final results of pollution. Formation mechanisms of vertical and horizontal zonalities at environmental petroleum pollution of geological environ ment are described. Polycyclic aromatic hydrocarbons are considered as priority components of pollution. Keywords: geological environment, petroleum products, pollution, transformation of chemical composition, descending flow, migrant indication, polycyclic aromatic hydrocarbons DOI: 10.1134/S0097807814070082

INTRODUCTION When oil enters geological environment from land surface it starts experiencing active degradation. This process takes place generally 2–3 weeks before its biodestruction begins and depends on many factors, including ambient temperature, spill volume, petro leum product (PP) composition, rock and soil mois ture content, their physicochemical properties (exter nal factors), and the properties of PP [11, 14]. The interaction produces complex organic–mineral aggre gates, which, eventually, can be even more toxic than the original substances. Until now, no reliable forecast models have been created to describe at least the main processes or stages of hydrocarbon (HC) transforma tions in geological media. Nevertheless, studies of this problem are very few in both Russian and foreign liter ature. The need to solve this critical problem is due to the very rapidly increasing extent of rock pollution by PP. Thus, according to official EMERCOM data, the area of polluted soils in 2010 was 44.7 thousand ha, while that in 2011 was 71.5 thousand ha, implying an increase by 60%. We note also that oil cracking and the subsequent combustion of commercial PP increases their “technogenic level,” resulting in the formation of not only stable organic pollutants (SOP), but also readily oxidizable forms with many intermediate com pounds with natural organic–mineral complexes.

THEORETICAL ANALYSIS Rocks (as well as soils and waters) participate in the processes of oxidation and biogenic destruction of PP. However, the main feature is the sorption processes, whose rate increases with increasing hydrophoby and decreasing solubility. The sorption on rocks proceeds in the following order: olefins → naphthenes → paraf fins, while the rate of biodegradation decreases in the direction alkanes (paraffins) → aromatic HC → naph thenes. Those differently directed schemes show that the system of threecomponent fluid water–gas–PP is not equilibrium in its physical nature. When interacting with rocks, it becomes even more inequilibrium, hence even more complex mechanisms of such inter actions. From this viewpoint, the wellknown V.I. Ver nadsky’s scheme “water, rock, various gases, living (organic) matter” can be supplemented by a techno genic component of PP (Fig. 1). On the other hand, according to S.L. Shvartsev [15, p. 24], for water–rock system, it is assumed that “chemical elements are active only when in solution, and the mechanisms of interaction, whatever the type of dissolution… pass through the complete dissolution and precipitation of secondary minerals.” In the case of mineral solutions, this scheme was observed and proved experimentally. However, in the case of HC, which are very diverse and show phase transitions (with solubility limits of compounds taken into account), it was found that they can exist as individual substances in intermediate forms. Therefore, the transport and transformation of PP can be represented

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as two interacting branches that form the final spec trum of HC of natural–technogenic compounds. The first branch is the oxidation by atmospheric oxygen of the oil itself as a product of reduction medium from alkanes to naphthenes. The second branch is the phase transition (oil–gas) with simulta neous interaction between the phases and soils, water, and rocks and the formation of new substances (trans formation products). Aerobic oxidation of HC by bacteria follows a com plex multistage scheme under the effect of enzymes oxygenases, which catalyze the addition of oxygen to HC molecule. The result is the appearance of sub stances, such as spirits, aldehydes, carbonic acids, etc. up to carbon dioxide and water. Chemical analyses made under a PP lens 5 years after its formation shoed water to contain aliphatic (7 pieces), alicyclic (2 pieces), and aromatic (7 pieces) acids, which have formed at the bioloigical decay of HC. Those acids can further form more stable organic–mineral compounds of technogenic genesis, or they can be washed out from rocks by water, form ing hydrophobic minerals (compounds). Experiments with polycyclic aromatic hydrocarbons (PAH) showed that, in the case of bacterial oxidation under labora tory conditions, 70% of carbon from HC is trans formed into CO2, 10% stays in bacterial biomass, and about 20% passes into soil humus. It is worth mention ing that bacteria get the oxygen they need from water contained in soils and rocks, while the film that forms from kirs and hinders the penetration of oxygen, has a very weak hampering effect on biological oxidation processes. The problem of transformation of hydrocarbon pollutants is associated not only with their physical composition; PPs migrate in free, liquid, dissolved, and gaseous state. This causes problems with fixation and identification of fluxes of individual compounds, the construction of adequate models of PP migration, and their functioning, which hampers the assessment of remediation works. The geoenvironmental estimation of pollution of geological medium components is mostly based on the total concentrations of PP with no allowance made for the processes of natural PP fractionation and transfor mation into new compounds. PP balance equations assume their vertical migra tion with moisture fluxes in the system “topsoil– underlying soils–capillary zone–saturated zone” [9]: ΔW 0 = W 0 – R 0 – E 0 – W w C 0 /ρ 0 , where W0 is PP input through direct infiltration as a free matter into the aeration zone; R0 is the rate of decay due to chemical and biological processes; E0 is the rate of PP evaporation; Ww is the rate of water infil tration in the absence of PP lens; C0 is PP solubility in water (assumed to vary from 0 to 100 mg/dm3), ρ0 is PP density. WATER RESOURCES

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OP Water

Rock

Gases

Organic matter Transformation products of initial OP

Fig. 1. Scheme of nonequilibrium geochemical system involving oil products.

The equation does not take into account the phase transitions of substances that are due to the following leading processes: in the atmosphere—evaporation and chemical oxidation; in soils—biooxidation and biodecay; in rocks—sorption and diffusion; in the capillary zone—the formation of entrapped HC forms; in the saturation zone—spreading over the lens and migration within it in dissolved forms. Of great importance are the age of oil pollution, the anisotropy of the motion, and the type of pollutants. Moreover, not all PP components can be oxidized, even in a favorable environment. For example, many PAH have not been shown to be biodegradable. At the same time, the concentration in soils of phosphorus and nitrogen, as well as some microcomponents at temperatures from 20 to 40°C, as well as soil moisture content, which are favorable for bacterial development, abruptly increase the decay rate of even most diffi cultly decomposable fractions, such as mazuts and lubricants. The substances that are proved to decompose actively are as follows: among singlering structures, this are benzene, toluene, xylene, trimethylbenzene, tetramethylbenzene, alkylbenzene; among double ring structures, this are naphthalene, methylnaphtha lene, dimethylnaphthalene; among threering struc tures, this are phenanthrene, anthracene, pyrene, benz(a)anthracene, benzperylene. During the first two or three months, abiogenic transformations can reduce the amount of oil by 20–30%. The largest errors in the construction of models of vertical migration are due to the neglect of the role of soils layer. PP “decay constants” are governed by vari ous processes, though the prevailing role belongs to biodegradation: for aromatic HCs, λ is of the order of n × 10–2 to n × 10–3 day–1. This is several orders of mag

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KHAUSTOV, REDINA Initial oil composition

Highly sensitive biodegradation by 80– 100%—n and isoalkanes. Decomposable by saprophytic microbacteria, pseudomonades, some yeasts, and fungi. Isoalkanes: the susceptibility to decomposition decreases with increasing chain branching

Moderately sensitive (biodegradation by 45– 60%)—cycloalkanes (2, 3 rings), di and triarenes. Decomposable by a very few few microorganisms: bacteria—representatives of genera Nocardia, Pseudo monas, Xanthomonas, etc.; some fungi

Stable (biodegradation by 30–45%)—n and isoalkanes. Surfactants: weakly degradable; experience shows degradation by cyanobacteria Phormidium tenuissimum and unicellular cyanobacteria Synehocystis minuseula and Synehococcus elongates

Sensitive (biodegradation by 60– 80%)—cycloalkanes (5, 6 rings), monoarenes, Saromatics. Cycloalkanes can be decomposed by the same microorganisms as alkanes, though are more resistant to decomposition. Lowmolecular arenes: when in high concentration, can be a hazard for microorganisms. Decomposable by a few microorganisms, mostly from genera Nocardia and Pseudomonas

Highly stable (biodegradation by 0–30%)—tetraarenes, naphtenoarenes. Surfactants: weakly degradable. Resins, asphaltenes: weakly destructible (years); in the case of Kerch Strait accident: biodestruction by microorganisms of genera Achomobacter, Acinetobacter, Pseudomonas Shewanella, Kocuria

Fig. 2. Classification of oil HC biodegradation susceptibility, according to [7].

nitudes greater than dissolution (λ from 3 × 10–10 to 3 × 10–9 day–1) and evaporation (from 5.4 × 10–6 for petrols to 2.4 × 10–8 m/day for diesel fuel). Considered with respect to natural losses, the decrease in the lens shape will average 2–3 cm/year. In principle, this is an integral characteristic of spontaneous PP degradation in the saturation zone. With the application of remedi ation technologies, for example, forced aeration or evacuation, in situ PP degradation can be increased more than tenfold (Fig. 2). One more problem is the lack of reliable extraction procedures (it can be 85% for aliphatic HCs and only 20% for aromatic HCs) and their identification by the features of natural and anthropogenic genesis [12, 13]. A hampering factor, which sometimes cause seri ous errors, is the presence in aqueous solutions and in the top part of the aeration zone of the socalled pseudoPP. These can be bitumoids leached from peat or humus soils and belonging to PAC group. Their presence is believed to suggest the technogenic nature of pollution; they actively dissolve in hexane and other organic solvents. Those substances contribute to total PP, increasing their overall concentrations. With their carcinogenic and mutagenic effect, PAH are poorly soluble in water, but well accumulate on mineral rock matrix. The longterm tolerance of hydrophobic PAH to oxidation and their limited abil

ity to biodegradation allows them to accumulate in large amounts in individual media. The estimates of PAH lifetime in different environmental components are contradictory, which is primarily due to their spe cific structure. PAH are very stable in the atmosphere, where their transformation into other forms takes place during interaction with ozone with the formation of polynu clear quinones, while reactions with NO2 lead to the formation of nitrobenz(a)pyrenes—very strong mutagenic ecotoxicants. This scheme of complex for mation can be extended to the air phase in soils and rocks in the threecomponent system of immiscible fluids. This conclusion is supported by the permanent presence of diverse forms of nitrogen compounds in both soils and waters migrating downward. In addition to nitrobenz(a)pyrene, much likely is the formation of nitrobenzene and similar aromatic pollutants. This creates the problem of the choice of reliable indicators of the technogenic character of individual compounds. The indication properties of compounds should be considered, primarily, from the viewpoint of their lifetime in a given medium. Thus, shortlived compounds (sugars, nitrogen compounds) are too ephemeral to be regarded as stable, as they are actively consumed by many microorganisms. On the other hand, there are more longliving components of WATER RESOURCES

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organics, which can serve as indicators of seasonal and manyyear activity of both natural and technogenic genesis. They are identified in media based on lipoid and bitumen statuses. Among bitumens, these are pri marily PAH, pollutants that are most widespread and similar to petroleum pollutants in terms of structure, though their content of oil varies from 1 to 4% [10].

The fractionation in the system HC–water–rock consists in that the rocks mostly accumulate high molecular compounds (resins, asphaltenes, etc.), while the substance that reach aquifers are benzene, toluene, xylene, etc., which have relatively high solu bility (in the Englishlanguage literature, they are denoted as BTEX group).

The diversity of PP properties is due, on the one hand, to their wide occurrence, and, on the other hand, their extremely high biogeochemical potential. Additionally, there exists a regularity in the differenti ation of HC during PP migration in the form of verti cal (layerbylayer) and horizontal (lateral) geochem ical zonality even in homogeneous geological media.

Of particular importance is the role of soil cover as a powerful buffer on the infiltration path of HC, as well as the presence of loamy beds in the aeration zone. PAH sorption calculations, based on carbon and water distribution coefficients, as well as the concentrations of organic carbon in rocks (Kd), are given in [6]. This coefficient describes the distribution of matter between the liquid and solid phases at vertical migra tion of pollutant; under the accepted conditions, it varied from 8.3 to 96.8 mL/g. The concentration of PP in water was take to vary from 18 to 1.2 mg/L; the amount of matter adsorbed on rocks varied from 12 to 210 mg/kg.

The structure of the top part of the section is pro posed to be described as four zones with division into subzones and with identification of PP occurrence forms, indicators of individual compounds (PAH), and processes of their natural fractionation (table). This approach is most promising for use in the practice of geoenvironmental monitoring. Until now, out of the hundreds of PAH of different structure, which have been found to occur in the nature, only one (benz(a)pyrene) is actively controlled in Russia; 6 such compounds are controlled in EU, and 16 in the United States. In the opinion of Yu.I. Pikovskii, the most informative among dynamic characteristics are heavy saturated and unsaturated HCs in soil and sub soil air. Among static characteristics, high informativ ity is typical of PAH in the composition of epigenetic bituminous matter of soils and rocks [10]. However, even they, by the diversity of their structure are classi fied into highly mobile (pyrene, benzfluoranthene, anthracene), mobile (benz(a)pyrene, perylene, chry sene, etc.), and lowmobility (mostly, highmolecular compounds). In the simulation of migration, all PP are conven tionally divided onto mobile and stable components. Here, the conventionality implies the nonequilibrium, which is due, on the one hand, to the character of the medium, in which PP migrate, and, on the other hand, their composition and properties. For example, the medium can include two or even three layers, and contain in its section soils (sands)–(sand clays)– loams (clays). PPs can be represented by liquids with different densities and composition, viscosity, temper ature, and the content of water, gas, and, solid parti cles. They have different solubility limits in water, the possibility of interaction with organic acids in soils, the rates of migration and diffusion in the vertical and horizontal directions. The interaction and superposi tion of those conditions create different conditions for the natural fractionation of HC, as a phenomenon of formation of their nonequilibrium states in geological medium. As the consequence, HC migration is accompanied by the formation of a technogenic geochemical zonality, which was mentioned above, as well as a manifestation of gas zonality above PP lens. WATER RESOURCES

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The difference between the material and mechani cal composition of geological media causes layerby layer fractionation of HC, or the “chromatographic effect.” The key characteristic here is the retention time of the mobile phase (HC) by the stationary phase (soils and rocks). However, since this process incorpo rates sorption, desorption, and elution, every time a new equilibrium state forms in the nonequilibrium system PP–water–rocks. In this case, we can clearly see the wellknown chromatographic principle of two limiting cases: a matter in the given system either does not interact with the stationary phase at all or it is fast bound without any displacements. In the limiting sit uations, no separation of matter will take place, and all observed chromatographic separations will lie between those two limiting cases. This key principle allows us to identify a group of HCs, which theoretically can be used in constructing migration models for individual objects. The chromatographic effect can be illustrated by data of chemical analyses of PP in alluvial deposits. Within four years after an accident, isoprenelike HC C19H40 and C20H42 were actively deposited [5]. Light HCs intensely infiltrated down to the depth of 2–3 m where they were also deposited. Thus, the initial com position of oil was transformed through a decrease in the concentration of methane fraction with the forma tion of a technogenic floating PP lens. The deposition of HCs, the more so, light HCs, can be considered as such only conventionally. It is very likely that, dissolved in subsoil water, they create the conditions for the formation of reducing environ ment, which can be clearly seen from the abrupt decrease in oxygen and the development of anaerobic bacteria. This is suggested by the formation of a meth ane cap, which results from the vital activity of this bacterial species. According to [16–18], 77% of BTEX, dissolved in the oil body, were removed through anaerobic decay and only 17%, through aero

Conditions: temperature regime, light intensity, humidity, mechanical composition of substrate, the presence or absence of soil cover; HC transport with surface runoff; oil physicochemical properties (primarily, viscosity and gas factor, HC solubility); pollution zone size and PP layer thickness. Autoremediation due to reactions of hydration, dehy dration, oxidation, reduction, etherification, methyl epsy, condensation. Removal of light HC fraction. Microbiological assimilation of light HC fractions; hydrophobization of dense fractions. The presence of biooxidizing bacteria—more than 20 genera; fungi—more than 10 genera. The presence of microorganisms in clear ecosystems 0.05–5% of the total number. Selective response of soil–vegetation cover

Soils as a powerful natural filter, depositing and trans forming HC pollution. The presence of PAH because of aerogenic pollution (lowmolecular compounds) and transformation of soil organics (highmolecular compounds). Vertical migration following the scheme: light PAH migrate into underlying horizons; dense PAH accumu late in the top organogenic horizons. Retention of indi vidual PAH—depending on soil mechanical composi tion: phenanthrene → naphthalene → anthracene → chrysene. The attainment of maximal concentration at biogeochemical barriers. Immobilization of HC at groundwater flow, manifesta tion of hydrophoby, changes of physicochemical envi ronments. The same factors and processes as on the surface + mechanical sorption, peat in soils, the degree of humifi cation, soil acidity (pH); deterioration of aeration of soil layers (primarily, horizon A), change in the redox condi tions, changes in morphological, physicochemical, and microbiological properties; biodegradation (10–90%) up to complete degradation with impossibility for vegeta tion development.

Soils

Conditions and physicochemical factors that govern the processes of PP transformations

Land surface

Vertical zones

Transformation of oil products in geoenvironments

Evaporation—a few days, all over the area and, partially, from soil horizons. The evaporation is 80% for benzenes, 22% for kerosene, 2.15% of oil, and 0.3% for residual fuel oil. For all PPs, the losses due to abiotic destruction are 36% in 15 days. The rates of evaporation are highest for alkanes, cycloalkanes, and benzenes. Evapora tion areas are of up to 15 km2. Formation of asphaltic⎯resinous substances— months or years; all over the pollution area. When soils and rocks are soaked, slimes form. Fresh pollution—up to 2 years; mature pollu tion—up to 4 years; old pollution—more than 4 years. Oil and PP biodestruction can reach 50%

Evaporation from soil from 20 to 40% of light fractions—alkanes, cycloparaffins, PAH. At pH 7.4, light PPs degrade by 64–90%, at pH 4.5, they degrade by as little as 18–20% [10]. PAH balance in the precipitation⎯soil system of background landscapes, μg/m2 [3]: —podzolic soil (middle taiga): input with precip itation is 9.94, output is 6.26; increase is 4.21; reserves are 1134; —gley⎯podzolic soils (northern taiga): 11.97; 4.49; 7.7; 218.5, respectively. Migration of stable organic compounds: transition from soils into plants (35–70%); from soils into water (12–18%); into atmospheric air (18%). The oil capacity of forest and (or) coarsehumus podzolic horizons is 0.7–1.1 kg/m2, and that of highland peat bogs is up to 112 km/m2 [2]. Oil concentration in the litter and horizon A can reach 20% of soil mass. Oil penetration into soils with notwashing regime can penetrate below 2 m. Data on peat soils taken from materials of Usa accident response showed the following differen tiation of PP qualitative composition:

Biodegradation products of PP components— spirits, aldehides, carbonic acids (aliphatic— carbonic, propionic, butyric acid, etc.; alicy clic—cyclohexane and dimethylhexane; aro matic—benzoic, methylbenzoic, hydroxyben zoic, salicylic, trimethylbenzoic, etc.). Response to the effect of microorganisms [7]. —n and isoalkanes: highly sensitive, degrades at 80–100% of the original concentration; —cycloalkanes (5, 6 rings), sensitive monoare nes, 60–80%; —cycloalkanes (2, 3 rings), di and triarenes: moderately sensitive—45–60%; —tetraarenes, naphthenoarenes: stable, 30– 45%; —pentaarenes, asphaltenes, resins: highly toler ant, 0–30%. Dominating in the composition of pollution are alkanes → aromatic HCs → cycloparaffins. Accumulation of Fe, Mn, V, and other metals contained in oil

Duration, extent of PP transformation stages

Due to evaporation: volatile lowmolecular HC (methane, ethane, propane, PAH, sulfur and nitrogencontaining compounds). Filmtype, emulsified, and dissolved in surface runoff forms of HC. Asphaltic−resinous substances (oxikerites, huminokerites–bitumen insoluble or weakly sol uble substances—kirs). Biodegradation decreases following the scheme: nalkanes → branched alkanes → aromatic HCs → naphthenes. Titer of microorganisms on PPrich media increases to 107 cell/g. Dominating in the pollution are (over time): methane–naphthene fraction → naphthene– aromatic → asphaltic⎯resinous

Chemicals and their groups resulting from physicochemical processes

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Rocks of aeration zone to groundwater table: • Unsaturated zone “air– water” with dissolved PP; • Capillary zone “air–PP”; • Zone of mobile PP

Vertical zones

Table. (Contd.)

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The same factors with predominance of mechanical sorption controlled by permeability. Infiltration coefficient from 102 (gravel) to 10–3 m/day (clayey sand)

The vital activity of HCoxidizing microorgan isms requires 10 parts of C and 1 part of N. In unpolluted soils, C/N ratio reaches 17, while in PPpolluted media, it reaches 400–420. A decrease is recorded in mobile P and exchange K and Mg. Optimal soil moisture content for biodegrada tion is 15–35% and optimal temperature is 20– 28°C; at t = 6–15°C, the activity drops 2.5–4 times; at t = 45°C. Microorganism activity is suppressed. Soils as a source of secondary pollution and manifestation of carcinogenic synergism with respect to microorganisms and vegetation

Conditions and physicochemical factors that govern the processes of PP transformations

Duration, extent of PP transformation stages

Depth of 30–60 cm and, in some cases, up to 120 cm (peat—cryptopodzol soils underlain by loams, carbonate)

Benzene–kerosene fraction

Processes proceed similar to differentiation in soils with the formation of nearly all forms of HC—from light PP to heavy residual oils; in some cavities, they can occur in pure (commer cial) form

Sorption on soils (L/m3): • gravel⎯coarsegrained sand—8; • coarse⎯medium sand—15; • medium⎯fine sand—25; • clayey sand—40

Association of compounds with organic acids of Duration of up to 10 years soils and the formation of aliphatic, acyclic, and aromatic acids as a result of HC biodegradation

More than 3–8 cm

More than 5–10 cm

Light paraffins, polyaromatic compounds

Heavy paraffin and oily compounds

Bitumen oxidation products: inactive—resin– 5–7 cm asphaltene substances; active—aromatic com pounds (one, two, threering structures). The accumulation of heavy PAHs dominates

Chemicals and their groups resulting from physicochemical processes

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relatively anoxic zone immediately above the oil body

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about 40 m; the area is the same as that the contains maximal concentrations of CO2 (more than 10%), CH4 (more than 10%), and main PP body in soils HCs (more than 1 ppm); H2S generation is possible

lower O2 concentrations (10–20%), HC con about 125 m; the area is the same as that of the centrations below 1 ppm; higher concentra transitional zone in subsoil water; tions of CO2 (0–10%) and CH4 (0–10%); H2S generation is possible;

transitional zone;

nearby territory, having not been subject to pollution;

In the case described in Baedecker and others [17]: input of 400 m3 of oil into soils; continu ous observations since 1976, data of 1997 are given:

Extension of the scale of pollution, depending on the ratio of zone sizes and the character of the air⎯water⎯PP mixture. According to laboratory data, 500⎯600 pore volumes are to pass through polluted soil for HC concentration in water to start decreasing. The existence time of pollutant flows varies from several months to several decades, depending on aeration zone thickness and composition and PP properties

HC concentration on barriers: lenses with a thickness from a few cm to a few m, persisting from a few days to a few tens of years

Longtime stationary state (immobilization): heavy still bottoms, oils, and other highden sity liquids. Diffusion coefficients for HCs—from 10–3 cm2/s (sandstones, aleurolites); up to 10–9 cm2/s (argillites, dense limestones)

Duration, extent of PP transformation stages

O2 concentrations are close to atmospheric ones;

Sorption following the scheme: olefins → aro matic HCs → cycloparaffins → paraffins until equilibrium is attained according to the scheme of chromatographic effect. Appear ance of diffusion effect. According to data in [6], PAH form associons in the section, which include pyrene, perylene, 3,4benzpyrene, 1,12benz perylene, 11,12benzfluoranthene, phenan threne, anthracene, chrysene. Associations change depending on soil com position and the magnitude of the load. They penetrate the entire aeration zone down to the capillary fringe with total concentrations from 63 to 1.3 μg/kg. Dominating components: • in gas phase—CH4; • dissolved in water—C2H6 and naphthene compounds; • in liquid form—PP of a wide fraction; • sorbed on rocks—heavy sulphuric oils, asphaltic–resinous substances, paraffins [4]

Chemicals and their groups resulting from physicochemical processes

relatively unpolluted zone;

• Capillary zone Soils with low permeability PP–water HC penetration through aeration zone: mobile low density PP, liquid commercial PP (mobile) and HC (mostly naphthenes and aromatic HC, HC gases) dis solved in aggressive wastewaters. Immobilization: dense components of HC (mazuts, oils, and other highdensity liquids) Barriers within aeration zone: accumulation of all forms of HC compounds, as well as metals in the form of organic–mineral compounds Highpermeability rocks—sources of secondary pollu tion for subsoil water. HC dissolution and washing out into infiltration recharge domain. Dissolved HC are more mobile than individual liquid phase of PP. Pore space colmatage due to the sorption of heavy frac tions (asphalt–paraffin). Changes in the structure of vertical flows, up to the for mation of fastflow zones. Penetration through aeration zone: highmobility and lowmobility lowdensity PP, dissolved in wastewater wateremulsified particles of liquid commercial PP (highmobility) and HC dissolved in water (mostly cycloparaffins) and aromatic HC, HCgases; partially, heavy still bottoms, oils, and other highdensity liquids Formation of gas geochemical zonality above the level of polluted subsoil waters:

Vertical zones

Table. (Contd.)

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by liability to HC biodestruction: nalkanes > 175–200 m; iso and anteisoalkanes > isoprenoid alkanes > cycloalkanes > arenes > asphaltenes > resins; BTEX–HC, which are an intermediate stage About 250 m of arene degradation; formation of complex compounds of Fe and Mn with phenol acids

(4) transitional zone from anoxic to oxygen with low HC concentrations due to aerobic biodestruction;

(5) O2 saturation zone with higher concentrations of benzene, toluene, ethylbenzene, and xylene (BTEX group)

(3) anoxic zone with high concentrations of HC, Mn+2, eduction of carbonic acids, aldehydes, and About 100–120 m; Fe+2, and CH4; ketons to alcohols and further to HCs; reduc tion of oxy and oxo compounds to volatile HCs. Formation of halogen and nitro deriva tives (less). Reduction of metals and sulfates: H2S generation is possible;

equilibrium zone between oxidation and About 75–100 m; reduction environments; Eh is close to 0. Increasing activity of microorganisms; decomposition of organic remains. Biode struction products: intermediate—oxy and oxo compounds (acohols, aldehydes, ketons), carbonic acids; final—CO2 and water;

(2) zone of lower O2 concentration and saturation with dissolved PP, as well as with transformation products of organic and inorganic genesis;

Zone sizes are determined by PP composition and migration conditions in the aquifer. In the case described in Baedecker and others [17]: input of 400 m3 of oil into soils; continu ous observations since 1976, data of 1997 are given according to [16]

The size can be more than 100 km2. By data of API (USA), statistical size of leakages were determined (a sample of 600 cases): 35%—40 m2, 37%—40–70 m2, 14%—70–100 m2. Pollution duration is determined by a combi nation of the above situations for overlying lay ers; it varies up to 30–40 and even 70 years.

Duration, extent of PP transformation stages

technogenically unaffected zone of oxidation environment;

Isolation of mobile lowdensity HCs from lowmobility light and heavy PPs;

Original watersoluble oil components. Solubility in water, following the scheme: aro matic compounds → cycloparaffins → poly cyclic → alkenes → paraffins. HC transformation products: active transform ers (alkenes, cycloalkenes, metal, Hal, Scontaining compounds, oxides, spirits, sim ple ethers, acids—the most hazardous ecotox icants (2–3 hazard class), stablemobile trans formers. Complex aliphatic and aromatic esters— dominating migration form: Ocontaining structures of bitumens, rocks, and modern deposits (3rd–4th hazard classes)

Chemicals and their groups resulting from physicochemical processes

(1) PP unpolluted waters saturated with O2;

In the zone of capillary fringe development—abrupt Subsoil water (saturation zone) dilution of PP in the horizontal and vertical directions, resulting in HC input in the aquifer. Formation of a floating PP lens, extending to the zone of capillary fringe and the top part of aquifer soils. Propagation of PP pollution in the space: emulsified and dissolved PP. Formation of substances “water in oil” and “oil in water” with fragmentary manifestation of reduc tion medium. A decrease in the concentrations of O2, SO4 and an increase in NH4, Fe, and Mn ions and gases H2S and CO2. As compared with soils, low titer of microorganisms (Corg down to 30 mg/dm3, Norg of 0.1–0.3 mg/dm3). Sorption on a mineral matrix of hydrophobic (lipophilic) organic substances dissolved in water—typical of SOP and PAH. Formation of geochemical HC zonality in the aquifer:

Vertical zones

Table. (Contd.)

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Oil, nonaqueous liquid phase CH4 Methanogenesis



SO4 Sulfate reduction Fe(III)s Iron reduction

–

NO3 Mn4+

O2 Aerobic degradation

Fig. 3. Horizontal geochemical zonality and HC biodegra dation processes (according to US Geological Survey).

bic degradation; 6% stayed in subsoil water. Thus, we cannot speak about deposition of even heavy HCs. According to [16–18], after an accident with crude oil spill, the period of formation of a zone of reduction geochemical environment spans for about five years. Those processes reach their peak within 5–6 years, depending on the rate of dissolved HC motion in sub soil water. Under different conditions, the extent of anaerobic degradation varies very widely, because, in particular, of water exchange in the aquifers. The ratio of anaerobic to aerobic degradation can be 60 : 40. In this case, the reduction of Mn is 5%, that of Fe is 19%, and 36% is accounted by methanogenesis. The pollution of soil stratum over the petroleum body leads to the formation of specific gas regime (Fig. 3). Volatile petroleum components have evapo rated, experienced biological decay inside, and extended in the aeration zone. The distribution of gases (HC, O2, CO2, and CH4) in the aeration zone was determined during 1997 and used to identify three geochemical zones: —a relatively clear zone: O2 concentrations are nearly atmospheric; —a transitional zone: lower O2 concentrations (10–20%), HC concentrations below 1 ppm; higher CO2 concentrations (0–10%) and CH4 (0–10%); —relatively anoxic zone immediately over the oil body; it contains maximal concentrations of CO2 (more than 10%), CH4 (more than 10%), and HC (more than 1 ppm). There also exists an opinion [2, 3] that HC differ entiation takes place only in loams and podzol soils, while there is no such differentiation in gley, bog, and sand soils. Additionally, dominating in the organic matter is the accumulation of HC structures with odd number of C atoms (C25–C35). Peat soils accumulate alkanes with both even and odd number of C atoms, while in mineral horizons, the mass fraction of alkanes with odd number of C atoms is much less; it equalizes with the even type in soilforming rocks. With such logics of reasoning, alkanes with an even number of C atoms can become reliable markers for the assess

ment of pollutant motion with vertical moisture flows, as they reach capillary fringe and form lenses of tech nogenic HC on groundwater table. In the construction of migration models, PP are assumed not to meet with water, and their existence form is regarded as a threecomponent system of immiscible fluids: water, air, and PP. Such models assume an equilibrium distribution of mass exchange between medium components, which is incorrect in principle. The upper boundary of biodegradation is determined by the rate of free oxygen transport, but it is always present on groundwater table, as well as in dissolved form in the aquifer proper. Therefore, bioox idation will be ubiquitous, and the rate of selfpurifica tion will be increased by rock sorption and capillary effects. However, under certain conditions (changes in the gradients of moisture content and temperature), the situation may become favorable for the deposition of PP (especially, heavy HCs) both in the aeration zone an in the upper part of the saturation zone. Numerous experiments with different petroleum pollutants showed the lack of equilibrium in the three component system mentioned above. In this case, it is clear that geochemical transformations in the process of infiltration through the soil layer and further through the aeration zone is to be taken into account in detail. Compared with the saturation zone, this is even more inequilibrium system for nearly all volatile dissolved substances (both organic and inorganic). Moisture content and temperature play a primary role here as both an immobilizer and a solvent for the entire spectrum of substances in different aggregate states. If the structure of the aeration zone is heteroge neous, PP migration processes become much more complex. The most readily soluble products (benzene and toluene among monoaromatic compounds and linden and naphthalene among PAC) most likely migrate along fastflow zones, which occupy different positions and volumes in the aeration zone. The rates of descending water flow through such zones are much greater than those in nearby zones (n × 10–3–n × 10–4 m/s). Such natural conductors will also serve as sources of secondary, pollution since sorption mecha nisms work when PPpolluted water moves through coarsegrained and cavernous rocks. The processes of natural rewashing of polluted rocks will take place even after the top layer of polluted soils is removed, and such processes can persist for decades. Calculations [6], carried out for a 6m stratum of sandyloam soils polluted by benzene in the amount of 300 mg/kg, showed that once the pollution source and the infiltration flow are stopped, the characteristics will persist for 200 years and the concentrations of this pollutant in the moisture reaching groundwater table will increase from the current value of 37 to 90 mg/L in the future. Similar results were obtained for toluene. Among the forms of mobile PP, the doubtless lead ing role belongs to gas component. It forms because of concentration of diffusing gaseous HC in free cavity or WATER RESOURCES

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pore space of soils in the aeration zone. Most often, these are mobile (derivatives from liquid PP), which are not always recorded on land surface; however, they occur ubiquitously in the pores of overlying soils above liquid PPs. Thus, according to data of A.Ya. Gaev with coau thors [4], the gaseous phase of PP (mostly methane) under Orsk Oil Refinery is 2.25–3 times greater in area than that of watersoluble, the total pollution area being 500 ha. Methane dominates in the gaseous phase; ethane and naphthene compounds, in water soluble phase; and PP of wide fraction, in the liquid phase. Present in the adsorbed state, are mostly heavy sulphurous, asphalticresinous, and paraffin com pounds. The solubility of HCcompounds in water increases with decreasing number of C atoms in the chain, i.e., in the order of paraffins, naphtenes, aro matic hydrocarbons. The highest solubility is typical of benzene, toluene, xylene, ethylbenzene. When in aqueous medium, benzene, under favorable condi tions, can transform into phenol, catechol, and hydro quinone. The transformants show other types of bio logical activity as compared with benzene. The trans formation of other aromatic compounds, including PAC, in water follows the same principle. From the viewpoint of water use for drinking water supply, of greatest hazard is benz(a)pyrene, whose concentration in water can be as high as 0.3– 2.0 ng/dm3. By its carcinogenic effect it is comparable with dibenz(a,h)anthracene; however, no toxicologi cal standards have been developed for it, as well as for other PAC, though water medium accelerates chemi cal transformations of substances, including both HC and organic–mineral complexes, salts, compounds with ether bonds and amides. By materials about an accident [5], four years later, the oil that had reached groundwater table consists of a mixture of HC C7–C24 with the predominance of HC C7–C18, i.e., soluble alkanes. A powerful pollution source for aeration zone rocks, as well as subsurface and surface waters are oil sludge storages and drilling muds, as well as liquid water–oil mixtures from shale pits. The concentration of bitumen substances here can be different in both mechanical and physicochemical composition. The HC fraction can vary from a few units to 70–80%, rep resented (in addition to HCs) by heterocompounds, containing atoms of oxygen, nitrogen, sulfur, and halogens. Identified among persistent organic pollut ants (POP), are PAC, chlorinated saturated HCs, and phthalates [1, 8]. Chlorine derivatives of alkanes are very strong tox icants. As well as PAC, they are components of oil (their concentrations can be as high as 20–25 g/kg), while their concentrations in crudeoil emulsion is even greater. The presence of those HCcompounds in oil is due to hydrolytic processes of ion exchange dur ing the formation of deposits. Solid wastes, containing WATER RESOURCES

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PP, show the presence of homologues C14H29Cl– C27H55Cl. Galenoalkanes, as well as PAC, are actively adsorbed on the mineral matrix; therefore, they are rarely seen in experiments with aqueous extracts. The multiple impact of moisture onto polluted soils causes an increase in their concentrations in aqueous solu tions, suggesting the priority role of water in the for mation and redistribution of oil pollution from the land surface downstream along the section. Chlorine derivatives of alkanes show low solubility in water and low chemical activity. As well as in the case of PAH, their extraction from rock and water samples requires special techniques because of their high depositing capacity [1]. Esters of phthalic acid are abundant in the wastes of oil production, storage, and processing. Compounds from C16H22O4 to C32H54O4 were identi fied. Unlike chlorine derivatives of alkanes, those compounds show high water solubility, hence their active migration with descending groundwater flows down to the zone of saturation. The formation of phthalates under oxidation conditions is attributed to aromatic structures. It was shown that Chashkinskaya oil can contain 20% and more of phthalate structures, while aqueous extracts from polluted soils can contain from 20 to 86% of those structures [8]. The environmental hazard of phthalates is due to their active impact on the reproductive function and hormone system. They readily penetrate into the organism with solutions where they are assimilated in fat deposits. The phthalate structure shows high bio chemical tolerance and it can be detected in nearly all media. Geophthalates are believed to be among the most stable occurrence form of benzene ring in organic matter. CONCLUSIONS The group of compounds PAH + alkanes + phtha lates dominates in the interaction in the oil–water– rocks system. In the case of water–oil interaction, benzene, toluene, and naphthalene are first to pass into solution, while phthalates stay in the system and can serve as a reliable marker in studying HC migra tion in neighboring media. Their concentrations in water can be as high as 10 MAC and even more. PP transformation can be conventionally divided into abiotic phase (from fresh to mature pollution) and biotic degradation on land surface, in aeration zone, and saturation zone. Each zone forms a system of geochemical indicators of its own, which, based on the bitumen status, allow the extent of manifestation of layerbylayer vertical zonality. Horizontal geochemical zonality forms in satura tion zone and comprises five zones, including the zone of reduction conditions, identified by high concentra tions of HC, Mn, Fe, and CH4. In their turn, those zones for a gas cap above the saturation zone, which can be identified by different concentrations and rela tionships between O2, CO2, and CH4.

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Soils are a powerful buffer on the infiltration paths of all types of PP, especially PAH. Because of protec tion properties of soil substrate, selective accumula tion of PP is recorded in subsoil waters. The equilibrium–nonequilibrium state of geochemical systems is not an exotic manifestation or a special case. This is a fundamental property of all dissipative systems with nonequilibrium dynamics that produce new substances. Along with the transforma tion of PP as pollutants, degradation of geological medium components is taking place. The processes that lead to the destruction of oil and PP as an integral formation are, from this viewpoint, the cause of selforganization and evolution of the sys tem as a whole. They are incommensurable in time and space with processes taking place in the geological environment, and their superposition leads to the for mation of new qualities in the newly forming natural– technogenic system. One form of selforganization of the system can be considered through the manifestation of vertical and horizontal geochemical zonality, differentiation and transformation of HCcompounds, and a mobile sys tem oil–water–gaseous phase, which forms above a polluted body of waterbearing rocks in the aeration zone. It also inherits the genetic features of both verti cal and horizontal geochemical zonality of pollutants in saturation zone. The acquired qualities of the new system from the environmental–geological point of view, may not be indifferent to elements of biota and break the estab lished links in ecosystems. This takes place because of changes in irreversible fluxes of matter, energy, and information, leading to equilibrium in open evolving systems. In ecology, those principles were formulated long ago as postulates and laws. Many of them have been formalized and developed into prognostic models. REFERENCES 1. Bachurin, B.A. and Odintsova, T.A., Mining and pro cessing wastes as a source of emission of organic pollut ants, in Gornyi informatsionnoanaliticheskii byulleten’ (Mining Information–Analytical Bulletine), Moscow: MGGU, 2009, issue 7, pp. 374–380. 2. Gabov, D.N., Beznosikov, V.A., Kondratenok, B.M., et al., Saturated hydrocarbons in the background and contaminated soils of the Cisurals, Eurasian Soil Sci., 2010, no. 10, pp. 1102–1108. 3. Gabov, D.N., Beznosikov, V.A., Kondratenok, B.M., et al., Polycyclic aromatic hydrocarbons in the soils of technogenic landscapes, Geochem. Int., 2010, no. 6, pp. 569–579. 4. Gaev, A.Ya., Fetisov, V.V., Yakshina, T.I., et al., On the method of studying hydrocarbon pollution, Vestn. Vo ronezh. Gos. Univ., Ser.: Geol., no. 11, pp. 261–263. 5. Galinurov, I.R., Safarov, A.M., Ostrovskaya, Yu.V., et al., Assessing remote consequences of oil pollution of

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flood–floodplain complexes of small rivers, Electronic Sci. J. “Neftegazovoe delo,” 2011, no. 2, pp. 152–166. Galitskaya, I.V. and Pozdnyakova, I.A., On the problem of pollution of groundwater and aeration zone rocks by oil products and PAH in Moscow territory, Geoekologiya, 2011, no. 4, pp. 337–343. Kodina, L.A., Geochemical diagnostics of oil–gas pol lution, in Vosstanovlenie neftezagryaznennykh pochven nykh ekosistem (Reclamation of OilPolluted Soil Eco systems), Moscow: Nauka, 1988, pp. 112–122. Odintsova, T.A., Development of technology for iden tifying and monitoring oil pollution, Extended Abstract of Cand. Sci. (Tech.) Dissertation, Perm: Mining Insti tute, Ural Branch RAS, 2010. Osnovy izucheniya zagryazneniya geologicheskoi sredy legkimi nefteproduktami (Principles of Studying Geo logical Medium Pollution by Light Oil Products), Og nyanik, N.S., Paramonova, N.K., Briks, A.L., et al., Eds., K.: A.P.N., 2006. Pikovskii, Yu.I., Prirodnye i tekhnogennye potoki uglevodorodov v okruzhayushchei srede (Natural and Technogenic Flows of Hydrocarbons in the Environ ment), Moscow: MGU, 1993. Khaustov, A.P. and Redina, M.M., Okhrana okruzha yushchei sredy pri dobyche nefti (Environmental Protec tion at Oil Production), Moscow: Delo, 2006. Khaustov, A.P. and Redina, M.M., Geochemical model of oil product transformations and indications at their vertical migration in landscapes, in Geokhimiya landshaftov i geografiya pochv (k 100letiyu M.A. Gla zovskoi). Dokl. Vseros. nauch. konf., Moskva, 4–6 apre lya 2012 g. (Landscape Geochemistry and Soil Geogra phy (To the 100th Anniversary of M.A. Glazovskaya). Reports AllRuss. Sci. Conf., Moscow, April 4–6, 2012), Moscow: Geograf. Fak., MGU, 2012, pp. 342–344. Khaustov, A.P., Redina, M.M., and Kalabin, G.A., Problems in the formation of fresh groundwater quality under hydrocarbon pollution, in “Pit’evye podzemnye vody. Izuchenie, ispol’zovanie i informatsionnye tekh nologii.” Mater. mezhdunar. nauch.prakt. konf. 18⎯22 aprelya 2011 g. (Drinking Groundwater: Study ing, Use, and Information Technologies, Mater. Intern. Sci.Pract. Conf., April 18–22, 2011), Part 3, Moscow obl., pos. Zelenyi: VSEGINGEO, 2011, pp. 17–33. Khaustov, A.P., Redina, M.M., and Lushchenkova, E.O., Problems of assessing the transformations of hydrocar bon pollutions after emergency spills, Zashch. Okruzh. Sredy Neftegazov. Kompl., 2011, no. 6, pp. 8–13. Shvartsev, S.L., Fundamental mechanisms of interac tion in the water–rock system and its inner geological evolution, Litosfera, 2008, no. 6, pp. 3–24. Delin, G.N., Essaid, H.I., Cozzarelli, I.M., et al., Ground Water Contamination by Crude Oil. http://mn. water.usgs.gov/projects/bemidji/results/factsheet.pdf. Cited May 20, 2012. Baedecker, M.J., Cozzarelli, I.M., Eganhouse, R.P., et al., Crude oil in a shallow sand and gravel aquifer, III—Biogeochemical reactions and mass balance modeling in anoxic groundwater, Appl. Geochem., 1993, vol. 8, pp. 569–586. Bennett, P.C., Siegel, D.I., Baedecker, M.J., et al., Crude oil in a shallow aquifer, I—Aquifer characteriza tion and hydrogeochemical controls on inorganic sol utes, Appl. Geochem., 1993, vol. 8, pp. 529–549.

Translated by G. Krichevets WATER RESOURCES

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