Effects of Metals from Oil to Polluted Soil

Oil pollution of extraction areas is an undesirable phenomenon, but very present, es-pecially in old farms. In the context in which the depollution of these areas, in Roma-nia, is carried out from public funds, this fact is more and more difficult to achieve. That is why the effect of pollutants on the environment is being analyzed more and more, it often remains that the depollution is done naturally. This material analyzes the effect of metals present in crude oil (Cu, Pb, Zn, Ag, Ni, Mn, As, Cd, V, Cr, S), on the soil affected by a historical accidental pollution in the Moinesti area, Romania. This article presents the results of analyzes performed by metal detection techniques, namely optical emission spectrophotometry with inductive coupled plasma and atomic absorption spectrophotometry. The metals determined in the polluted soil were statis-tically analyzed regarding the dispersion, standard deviation and coefficient of varia-tion compared to the control sample and compared with the results from two areas in Romania. The risk of exploitation of polluted areas was also analyzed, namely the method of pollution indices and the method of combining the effects of pollutants


Introduction
Crude oil is defined as a solution consisting of hydrocarbons, metals, non-metals, water [1].
If we were to fully analyze the crude oil extracted from all areas of the earth, we would probably determine more than half of the elements of the periodic table, with concentrations ranging from high percentages of carbon and hydrogen and low percentages of nitrogen and sulfur. Transitional metals would also be determined.
Metal constituents are in different percentages in different areas of exploitation around the world, but may differ in the same deposit (Table 1).
Metals can provide information on crude oil migration and its age [4]. T.F.Yen was able to show that the metals in crude oil can be grouped into petroporphyrins and neporphyrins. Thus, five classes were determined, namely [5]: -metalloporphyrin chelates (V, Ni), -complex metal complexes, small tetradentate ligands (V, Ni, Fe, Cu, Cr, Co), -carboxylic acid salts of the functional polar groups of resins (Mo, Zn, Ge), colloidal minerals (silica and NaCl), -organometallic compounds (Hg, Sb, As).
Porphyrins are the first compounds isolated from crude oil that have demonstrated the organic nature of crude oil.
Porphyrin is a macrocyclic system consisting of four pyrrole rings linked by four methine groups, being a class of nitrogen-derived macrocycles. Porphyrins can accept two hydrogen ions to form a diacid with +2 charge or they can give up two protons to become a -2 anion with charge. This characteristic of porphyrins leads to the formation of organometallic complexes with a structure similar to hemoglobin in the blood and that of chlorophyll in green plants. Porphyrins in crude oil demonstrate its formation at low temperatures from organic matter (at high temperatures, porphyries decompose) [6]. Non-porphyrins in crude oil include other ring systems such as strongly substituted porphyrins. Porphyrins with UV properties other than those mentioned above and porphyrin decomposition products is detected in oil samples [7].
Asphaltenes have bound in their composition metals such as vanadium, nickel and iron which vary in amounts from 5 ppm to several thousand. Asphalt metals are partially bound in porphyrins, which are an integral part of them [8].

Geology of structures
The analyzed area is placed in Moinesti city, parts of bacau Conty, Romania. Area is parts of the External Unit of the Eastern Carpathian Flysch, being constituted by three folds oriented north-south, with faulted flanks.
The deposits that make up the analyzed structure belong to the Eocene, Oligocene and Miocene [10].
The Eocene appears in the facies of the Bisericani (Church) Layers, being made up of black and green shale marls, micaceous, slightly sandy.
The Oligocene develops under the characteristic facies known in the External Unit of the flysch, being composed of the following horizons: The Miocene consists of blackish compact clays and marls, with intercalations of compact sandstones and salt.
The oil area deposits consists mainly of siliceous sandstones with a higher clay content, so that the flow properties are slightly diminished by the horizons of the SupraKliwa and Kliwa sandstones which have an insignificant volume of clay.
The extraction of crude oil took place between 1960-2000, after which it was abandoned.
No soil decontamination was performed because the concentration in petroleum substances was below the intervention threshold, ie below 1000 mg / kg dry matter (the land being a less sensitive area).
The oil extraction and treatment facilities were removed and the land was cultivated with flowers (marigolds).
Soil samples were collected using geological probes at a depth of 100 mm from 12 places located in an oil extraction and treatment area.
The treatment of the soil samples taken in order to perform the analyzes was performed according to the standard SR ISO 11464/1998 -Soil quality.
Pretreatment of samples for physico-chemical analyzes. Thus, the samples were oven dried and crushed with an electric soil mill.

Atomic absorption spectrophotometry
The determinations were performed using a Shi-madzu AA-6300 double beam spectrophotometer (Shimadzu Corporation, Japan).
It is equipped with: ASC-6100F autosampler, flame atomizer and graphite furnace, deuterium lamp for background correction and cavity cathode lamps for the studied elements.
The method SR ISO 8288: 2001 was used to determine copper and zinc. SR EN 14083: 2003 and SR EN ISO 15586: 2004 methods were used to determine cadmium and lead, with modifications to suit the type of matrix analyzed.
Each determination was performed in three repetitions. For the calibration, 5 concentrations of the reference solutions were used, the correlation coefficients of the calibration rights being in the range 0.9780-0.9997.
To evaluate the degree of recovery of heavy metals from the analyzed soils, a series of samples were created with solutions of known concentrations of these metals, the recorded recovery degrees being: 91.14% for Cd, over 93.52% for Pb, 94.92% for Cu and 95.02% for Zn.

Inductively coupled plasma optical emission spectrophotometry
Initial determinations of macro and microelements were made by inductively coupled plasma optical emission spectrometry using a Perkin Elmer Op-tima 5300 DV spectrometer.

Analysis of experimental data
Atomic absorption spectrophotometer control, data acquisition and analysis. Primary spectral data was performed using WizAArd (Shimadzu Corporation, Japan).
The quantitative data matrix was processed in Microsoft Excel (Microsoft) for statistical calculations (arithmetic mean calculation, standard deviation, Pearson correlation coefficient).
The Pearson coefficient was used to characterize the correlations between the measured contaminant concentrations.

Analysis of the environment polluted with metals
The exploitation of crude oil is a set of operations that can lead to soil and groundwater pollution.
The interest of researchers to study the risk of environmental pollutants is well known, the research works being focused on determining the hydrocarbon content in soil and plants and less on those dedicated to qualitative and quantitative analysis of soil and plant metal content [11,12].
The studies focused on the development of a model for assessing the risk of pollutants determined from oil, for certain study areas.
A model for assessing the risk in exploitation of the land affected by pollution, on the Bayesian model was developed by Aguilera [13] and developed by Diana Mariana Cocârță [14].
An analysis of a land, which must be returned to use after the completion of onshore operations includes in addition to determining the content of petroleum products and determining 14 elements of the periodic table, namely Cu, Pb, Zn, Ag, Ni, Mn, As, Cd, V , Cr and S [15] (figure 2 and table 2). An analysis of the effects of metals found in soils in areas where there have been oil mines, was performed by A. R. Karbassi [16,17,18]: After a pollution, the analyzes must indicate if there are traces of petroleum product (THP), radioactive elements and especially metals.
For the analysis of the environmental impact of metal pollution from the exploitation of oil fields, a variant of risk composition based on Baysian networks is proposed [19], starting from the relation: Where ( ) are data taken from the acyclic graph of the variables . Muller designed a pollution index also called Igeo [25] and defined by the equation: Where: Cn is the metal concentration measured in the sample collected, Bn -metal concentration as reference, 1,5 -a calculation factor,.
Another model for determining pollution classes was described by Enrich-ment [26] in relation to: is the concentration of manganese in the soil sample taken, Tables 3 and 4 show the pollution classes for the two mathematical models presented above. Intervention threshold sensitive area Igeo=4-5 Intervention threshold less sensitive area Igeo≥5 Extreme pollution Another method of determining ecological risk measurement levels is re-presented by the relationships between the ecological risk description and the risk index [28,29].
is the metal concentration in the analyzed sample, -the metal concentration in the control sample, -toxicity factor,(toxicity factor is As = 10, Cu = Pb = Ni = 5, Zn = Mn = 1, Cr = 2), it is the ecological risk factor, represents the risk index of the presence of metals in the soil. The pollution classes used in the method of determining the levels of ecological risk measurement are expressed in Table 5.

Discussion
Oil exploration can also create accidental pollution with heavy metals.
Even if the concentration of total hydrocarbons in the soil is within the limits that do not require intervention for depollution, rather high concentrations of metals have been determined.
The analyzes found that the metals were adsorbed by the soil (through plants) and in the control sample area collected from more than 1 km away from the crude oil exploitation area.
Crude oil extraction areas are usually located at fairly large distances from human settlements, but the presence of metals in the soil can lead to their leaching in transitional waters (groundwater).
Also, in the analyzed plants, metal concentrations were discovered, which makes it necessary to determine the metallic elements in the case of the analysis of an oil exploitation area, under ecological reconstruction.
The plants, as seen especially in the control sample, take the metals from the air, being transferred to the soil.
For the treatment of the soil, in the analyzed area marigolds and lettuce were used as crops.
It is recommended not to use these vegetable products.

Conclusions
It is observed that the pollution with metals, coming from crude oil, is present in the extraction area, being over 10 times bigger than a residential area. All samples collected have determined values of the amount of metals within the control limits. Depollution intervention is not recommended, but it is recommended to maintain agricultural crops that naturally treat the removal of metals. Lead pollution is present especially in the area of the biphasic separator, where the elimination of gases in the atmosphere, due to the opening of the safety valve and the nontightening of the valves created the possibility to remove metals in the exhaust gases It's an alert threshold. Zinc pollution is present in areas where gas leaks have occurred, the area being at moderate risk in operation. As can be seen, metal pollution is only monitored in three cases, with the amounts of metals in the soil showing close values in the test sample. Also, the analysis of the risk in operation by the two methods is very useful, the results being similar comparative.