ASSESSMENT OF THE RAILWAY INFLUENCE ON THE HEAVY METAL ACCUMULATION IN SOIL

Dep. «Chemistry and Engineering Ecology», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipro, Ukraine, 49010, tel. +38 (097) 091 74 51, e-mail samarskaya.av@gmail.com, ORCID 0000-0002-0828-9457 2 Dep. «Chemistry and Engineering Ecology», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipro, Ukraine, 49010, tel. +38 (067) 774 04 64, e-mail j.v.zelenko@gmail.com, ORCID 0000-0001-5551-0305


Introduction
Rail transport operation has a negative influence on the environmental quality.This influence can be seen in the environmental contamination with both organic (oil products, polycyclic aromatic hydrocarbons, polychlorinated biphenyls), and inorganic substances (heavy metals, SO2, CO, CO2, NO2, etc.).
Studies devoted to railway transport as a factor of environmental pollution confirm the hypothesis that this mode of transport can bring to soil such persistent and dangerous pollutants as heavy metals (hereinafter -HM) [1, 4-7, 10-14, 17-20].
The obtained data demonstrate the significant content of iron, which is natural for railway transport, lead, cadmium, copper and zinc, which may indicate specificity of the cargoes transported, loaded and unloaded at this station.
Another study, conducted by Kajetan Dzierżanowski and Stanisław W. Gawronski also confirms the assumption that railway transport plays a significant part in the HM accumulation in soil and plants.The study was conducted in situ at the Warsaw-Otwock railway connection using the X-ray fluorescent spectrometer [11].The authors compare the obtained results with the permissible levels of HM concentration in the surface layer for transport lands, mg/kg approved in Poland [11].The presented data show the high content of such metals as barium, chromium, copper, nickel, mercury and iron typical of railways.It should be noted that it is difficult to assess the degree of the railway operation influence on the HM accumulation without comparing the obtained data with those at the referent sites or background concentration.It can only be concluded that the approved standards for Ba, Cr, Cu and Ni have been exceeded.
However, the data on the HM accumulation in plants in the area adjacent to the Warsaw-Otwock railway junction is of greater interest.For example, Viola arvensis accumulates approximately 230 mg/kg Zn, Vicia cracca -≈ 30 mg/kg Mo, Cerastium dubium -≈ 160 mg/kg Cu, 400 mg/kg Mn, 8 mg/kg Pb, 34000 mg/kg Fe [11].This, in turn, confirms the railway transport influence on the HM introduction and accumulation both in the soil of adjacent territories and in plants that grow there.
According to the results of chemical analysis of the soil samples from the Białystok Fabryczny, Siemianówka and Waliły railway stations in 2015 [20], the pollution levels appear to be much lower than in previous studies.However, the soil biotesting shows significant toxicity of the soil of the Białystok Fabryczny and Siemianówka stations [20].The information is given in Table 2 It is important the fact that at present in Ukraine there are no legally approved permissible levels of HM concentration for transport and communication lands, industry and urban territories.
As for the HM sources at railway transport, they are, in the first place, cargo transportation, its dispersing, scattering and spilling on the track and adjacent territories [1, 5-7, 10-14, 19].For example, the total amount of losses during the transportation of mineral fertilizers in bulk in covered cars is up to 8%, in gondola cars up to 28%.When transported in multi-purpose cars annually up to 7% of ore and 3% of cement are lost [7].
According to the State Statistics Service of Ukraine [3], the railway transport ranks first in terms of cargo transportation volumes.The Tables 3 and 4 show the cargo turnover, volumes of cargo transportation in 2017, and transportation of various types of cargo by rail in 2017, respectively.
T ab le 3 Moreover, the HM accumulation in soil during the railway operation is influenced by a wide range of factors: intensity and speed of train movement; age of the railway and degree of its operation; initial braking speed, braking length; the nature and volumes of transported cargoes; weather conditions; relief; granulometric and chemical content of soil; vegetative cover.

Cargo
Therefore, the HM content in the railway infrastructure soil can differ considerably and vary widely.Accordingly, the study of the railway transport influence on the HM emission into the soil is an important direction of scientific research.

Purpose
The main purpose of the article is analyzing the current state of the railway infrastructure soil contamination with HM; assessing and determining the rail transport share in the problem of the HM accumulation in soil.
In order to achieve the purpose, the following stages are realized: literary review of the problem; analytical assessment of soil contamination levels of railway stations with heavy metals; calculations of total contamination and potential environmental risks of soil contamination with HM; development of recommendations for further monitoring the toxicological state of soil.
The research subject is the total content of HM.Determining the total forms are enough for the space between tracks, since the moving ones play a minor role in this case, there is no migration in the «soil-plant» and «soil-plant-man» chains.
The sampling scheme is shown in Figure 1.Sampling was carried out every 15 m between (1) and outside both rails (2).The weight of each sample is 250-300 g, the depth of sampling is 0-20 cm.The total area of the investigated sites is 600 m 2 .The principle of the sampling choice is determined by the fact that the stations are surrounded by buildings and the HM distribution at different distances cannot be assessed.
The reference sites are at a distance 250 m from each station.The sampling was carried out using the «envelope» method.
Figure 2 shows the places of the soil sampling.It was carried out at the end of August 2017 in dry, hot weather.
The HM concentration in station soil was determined by the atomic-adsorption method.Total forms of HM were extracted with nitric acid (1:1).The HM content in the studied soil samples was calculated using the formula (1): where Хis the mass fraction of the i-th metal, determined in the air-dry soil sample, mg/kg; С1is the concentration of the i-th metal in the studied acid extract of soil, found according to the calibration graph, mg/dm 3 ; С0is the concentration of the i-th metal in the control sample found according to the calibration graph, mg/dm 3 ; Vis the volume of the investigated solution, cm 3 ; mis the weight of the air-dry soil sample, g.In order to assess the level of the HM accumulation in soil, we calculated a total contamination index Zс, which reflects the complex influence of the whole group of elements and is determined as the additive sum of the excess of elements concentration coefficient above the background level using formula 2 [2]: where nis the number of elements under consideration, Ксis the coefficient of concentration (accumulation), the ratio of actual concentration to background content [2].
Although this methodolgy is used in many works related to the assessment of HM accumulation in soil, the disadvantage of the Zс indicator is that it does not reflect the toxicity of each metal, therefore, it is advisable to use such an indicator as RIpotential environmental risk of soil contamination, which is determined by the formula 3 [9,15,16]: where Eiis a risk factor for the і -th HM, where Тіis the factor reflecting the toxicity of the і-th HM and the degree of environmental sensitivity to this metal, the values of Ті for Hg, Cd, As, Ni, Cu, Pb, Cr, Zn and Mn are 40, 30, 10, 5, 5, 5, 2, 1 and 1, respectively; fiis the ratio of the actual concentration of HM, (Сі) to its background content (Sі) [9,15,16].Classifications of Zc and RI are presented in the Tables 5 and 6.

Findings
The research results are presented in Table 7.We determined the concentration of total forms of Mn, Cu, Zn, Ni, Pb, Cd, and Fe in the soil of «KP», «ZK», «T» stations and at the three refer- ence sites where the anthropogenic influence is quite insignificant.The given data across the board exceed the reference indexes and the background concentration, which shows the direct railway transport influence on the HM accumulation in soil.
The obtained results indicate that the soil state of the «KP» station corresponds to a low ecological risk and a low degree of contamination, since it is a passenger station only and pollution occurs mostly due to the friction of wheels and rails, that of the pantograph and contact wire, as well as the herbicide use.
The soil contamination of the «ZK» station is characterized by a significant potential environmental risk and a very high degree of pollution.This station is a freight-passenger one and the pollution level is mainly due to the loading and unloading processes.
The soil of the «T» station is characterized by an average potential environmental risk and a moderate degree of pollution.Although this station is used for the freight trains reformation, but due to transporting large volumes of bulk ore cargoes HM fall into the station soil.Moreover, the station is not electrified.

Originality and practical value
For the first time the potential ecological risk of soil contamination was determined on the basis of the physical-chemical analysis of the HM content in the soil of the «KP», «ZK» and «T» stations.The obtained data prove the necessity and urgency of constant monitoring the HM content in the railway infrastructure soil.
The results of the study can be used as a justification of the reasonability of introducing the environmental monitoring programs for the railway lands, the environmental protection measures for the soil treatment from HM, protection of the territories adjacent to railway from the propagation and accumulation of the mentioned pollutants as well as correcting the railway exclusion zone

Conclusions
Taking into consideration the fact that the railway transport operation can lead to the significant level of the soil contamination with HM, which exceeds the regulatory one, it is necessary to develop recommendations for non-purpose (agricultural) use of land sites within the damping zone of railways.
According to the presented data, differentiating the railway mainline zones with high pollution indicators was carried out and the recommendations on the measures for decontamination and detoxification of the railway infrastructure soil were developed.
We recommend to calculate the Zc and RI indices for assessing the levels of soil contamination, as well as to determine the HM concentration at the reference sites, since the use of background concentration for comparison generates many questions and concerns, although it is used by many researchers.And as a final stage of assessment we suggest carrying out biotesting, which demonstrates the toxic influence (or its absence) of the investigated soil on plants, crustaceans, bacteria and other living organisms.
T ab le 7

Fig. 1 .Fig. 2 .
Fig. 1.The scheme of sampling at railway stations 1the area of sampling between rails, 2the area of sampling outside both rails

HM concentration in surface layer of the Warsaw-Otwock railway ground and permissible levels of HM concentration
Table 1 presents the results of Kajetan Dzierżanowski and Stanisław W. Gawronski`s investigation and the permissible levels of HM concentration in Poland, approved in 2002.
T ab le 1

Results of chemical analysis of the soil samples from the Białystok Fabryczny, Siemianówka and Waliły railway stations
.