Soil science
E. Asrari; H. Talebi
Abstract
Introduction In the last few decades, due to process of shifting from traditional activities and based on manual activities to industrial ones, the need for using oil and coal and its derivatives has increased. Using these materials has caused some problems for environment as hydro carbon contamination. ...
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Introduction In the last few decades, due to process of shifting from traditional activities and based on manual activities to industrial ones, the need for using oil and coal and its derivatives has increased. Using these materials has caused some problems for environment as hydro carbon contamination. Soil is a major contributor to the various kinds of pollution, especially hydro carbon pollution. Due to the importance of soil in the life cycles and its vitally direct and indirect influence on all the organisms and human being, elimination of this pollutant is necessary. For this reason, some different methods have been developed. In this research, capability of soil washing by sodium dodecyl sulfate ionic detergent has been measured. In order to fulfill the existing necessity and solve this problem, a wide-ranging effort has been started from the past until now, which can be referred to the issue of washing contaminated soil as one of the issues raised. At the beginning of this technology, washing with pure water was considered and after a while, it was invalidated due to inefficiency in the tested cases. With advances in this emerging technology, the discussion of stronger solvents was explored, in which detergents became more attractive due to their lower potential toxicity and environmental degradability. Actually, the effect of major parameters on removing the hydrocarbons has been investigated and in this research has been afforded to purify polluted soil with creosote by considering actual conditions in industry.Materials and Methods The first sample has been taken from original soil of Razi industrial estate. It has coarse sandy loam texture with 31% clay, 11% silt and 57% of sand, pH equal 7, organic matter amount 2.3 % weight and density equal 1/8 gram per m3. Therefore, pure soil was extracted from 6 layers of soil to the depth of 0.5 m from Razi industrial area in Isfahan. Then, it was mixed by a concrete mixer specific to the block making. Afterwards, creosote was added evenly during stirring so the soil was contaminated deliberately. After storing in the laboratory for 3 weeks and homogeneity, the initial sample was chosen and its contamination was measured. This measurement was based on the amount of added oil to the certain volume of soil (about 30000 milligram in each kilogram). For avoiding error and having assurance from the amount of initial contamination, the sample was transferred to the laboratory and 25 gr of it was taken. Its hydrocarbon texture was extracted by solvent and its polar compositions were removed by passing on the silica gel absorbent. Then, a hydrocarbon was measured. The real pollutant amount of sample was 26776 milligram in each kilogram of soil. Secondary samples were chosen from basic sample, these chosen samples were washed under the different planned conditions. After finishing several complementary washing stages in different conditions, the soil samples remaining from washing were dried under different conditions. Then the amount of remained contamination in each sample was measured and recorded separately. At the next stage, the recorded results were analyzed. Stay time, temperature, pollutant concentration and washer concentration has been chosen as variable parameters. Results and Discussion According to the results, washing by pure water and temperature of 30°C would not be successful but by increasing temperature, the removing efficiency increased. Increasing temperature to 90°C increased the efficiency up to 18.5%. In addition, adding detergent to the environment increased the success of this method in reducing sample pollution. Increasing efficiency up to 4 g/L of detergent increased the efficiency up to 40% directly, but there was no significant change for increasing more than this amount. At this stage, the results showed that in the presence of detergent, increasing temperature caused to increase efficiency directly. The only difference was that increasing temperature (without detergent) increased efficiency directly, but in presence of detergent, increasing efficiency was significance up to 50% and after that it increased very slightly. The last studied parameter was time. These changes included increasing efficiency due to increasing time from 10 min to 20 min. Removing pollutant efficiency has been reduced by increasing time. Under all optimum conditions, in temperature of 90°C for 20 minutes and 4 g/L surfactant, Hydrocarbon removing efficiency was 61%. The economically optimum temperature is 50oC with regard to economical cases and the slight difference resulting from increase of temperature from 50 to 90°C.Conclusion Generally, the results revealed the suitability of ionic sodium dodecyl sulfate for cleaning soil under conditions of contamination. But 39 % of pollutant in polluted soil after washing by considering optimal conditions has been reminded. It must be mentioned that due to inefficiency of this amount of contamination reduction from contaminated soils for the discharge of these soils into the environment, this method can be introduced as a pollution reduction or a method for pretreatment of complementary methods.
zeinab bigdeli; ahmad golchin; saeid shafiei
Abstract
Introduction: Dynamics of organic carbon and nitrogen are controlled by several factors, including physical, chemical and biological properties of soil. Heavy metals contaminate soils and change soil properties and affect organic carbon and nitrogen dynamics. Since toxicities of heavy metals are different ...
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Introduction: Dynamics of organic carbon and nitrogen are controlled by several factors, including physical, chemical and biological properties of soil. Heavy metals contaminate soils and change soil properties and affect organic carbon and nitrogen dynamics. Since toxicities of heavy metals are different and organic carbon and nitrogen dynamics are affected by available concentrations of these metals, the aims of this experiment were to assess the effects of different levels of soil cadmium on mineralization of organic carbon and nitrogen.
Materials and Methods: To assess the effects of different levels of soil cadmium on mineralization of organic carbon and nitrogen, a factorial pot experiment was conducted using litter bag method. The factors examined were different levels of soil cadmium (0, 10, 20, 40, and 80 mg kg -1soil) and incubation periods (1, 2, 3 and 4 months) that were applied in three replications. Soil samples were artificially contaminated with cadmium to desirable levels using cadmium sulfate and the samples were placed in plastic pots and the pots incubated at constant moisture and temperature for one month. Then litter bags containing 15 g wheat residues were buried in pots and incubated for different periods of time. At the end of incubation periods, the remaining amounts of plant residues were measured and analyzed for organic carbon and nitrogen concentrations using Walkley and Black and Kjeldahl methods respectively. The decomposition rate constants of organic carbon and nitrogen were calculated using Mt = M0 e –kt equation. Organic carbon and nitrogen losses were calculated by subtracting the remaining amounts of organic carbon and nitrogen in one incubation time interval from those of former one.
Results and Discussion: The results showed that the effects of soil cadmium levels and incubation periods were significant on organic carbon and nitrogen mineralization. The losses of organic carbon and nitrogen from wheat residues decreased as the levels of soil cadmium increased. The highest and the lowest organic carbon and nitrogen losses were measured in control and treatments with 80 mg Cd kg -1 soil respectively. Increase in soil cadmium levels decreased the losses of organic carbon and nitrogen from wheat residue. The losses of organic carbon for a period of four months were 37.54, 37.21, 36.11, 35.12 and 33.69 (%) in treatments with soil cadmium levels of 0, 10, 20, 40 and 80 mg kg -1 respectively. The loss of organic carbon in the first month of incubation was (30.78%) and in the other three months of incubation was (9.74%) with a sum of (40.52%) for a period of 4 months. Similarly, the loss of organic nitrogen in the first month of incubation was 23.69% and in the other three months of incubation was 8.56% with a sum of 32.25 (%) for a period of 4 months. The highest losses of organic nitrogen from wheat straw residue were measured in treatment of control cadmium (31.64 percent) and lowest losses of organic nitrogen (23.86percent) related to treatment with 80 mg of cadmium / kg of soil. The losses of organic nitrogen, after 4 months were 31.64, 30.69, 28.68, 26.25, and 23.86 (%) when treatment of cadmium contamination of soil was 0, 10, 20, 40 and 80, respectively. The decomposition rate constants for organic carbon were 0.0076, 0.0075, 0.0073, 0.0070 and 0.0066 day -1 when soil cadmium levels were 0, 10, 20, 40, and 80 mg kg -1 respectively. The rate constants for organic nitrogen at the mentioned soil cadmium levels were also 0.0061, 0.0059, 0.0054, 0.0048 and 0.0044 day -1 respectively.
Conclusions: The results of this research indicate that contamination of soils by heavy metals increases the residence time of organic carbon and nitrogen in soils and slows down the cycling of these elements. The mineralization rate of organic nitrogen was affected by soil cadmium levels more than that of organic carbon. The amounts of organic carbon and nitrogen losses are higher in the first month of incubation than those of other months and decomposition of wheat residue had a fast and a slow stage. The results of this study indicate that due to the adverse effects of heavy metals on soil organisms, mineralization rate of plant residue carbon is slower in polluted soils compared with non polluted soils.
Mohsen Hamidpour; Leila Akbari; Hossein Shirani; Ali akbar Mohammadi
Abstract
Introduction: Soil contamination by heavy metals is a major concern throughout the world, due to persistence of metals in the environment and their toxicity and threat to all living organisms. Several strategies have been used to immobilize heavy metal ions in soils. Immobilization can be achieved by ...
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Introduction: Soil contamination by heavy metals is a major concern throughout the world, due to persistence of metals in the environment and their toxicity and threat to all living organisms. Several strategies have been used to immobilize heavy metal ions in soils. Immobilization can be achieved by adding natural and synthetic amendments such as zeolites and organic materials. Because of large specific surface area, high cation exchange capacity (CEC), low cost and wide spread availability, zeolites are probably the most promising materials interacting with many heavy metal ions in contaminated soils and water. Organic amendments such as vermicompost contains a high proportion of humified organic matter (OM), may decrease the bioavailability of heavy metals in soil by adsorption and by forming stable complexes with surface functional groups, thus permitting the re-establishment of vegetation on contaminated sites. Recent studies showed that the co-application of zeolite and humic acids could be effective in reducing the available fraction of Pb in a garden polluted soil. Fractionation of heavy metals cations in amended polluted-soils is needed to predict elemental mobility in soil and phyto-availability to plants. Therefore, the objective of this study was to investigate the effects of co-application of zeolite and vermicompost on Zn redistribution in a contaminated soil.
Material and Methods: A contaminated soil was collected from the top 20 cm in the vicinity of zinc mine in Zanjan province, western north of Iran. The soil sample was air-dried, passed through 2-mm sieve and stored at room temperature. The soil sample was thoroughly mixed to ensure uniformity. Sub-samples were then digested using the hot-block digestion procedure for total Zn concentration. The experiment was conducted under greenhouse condition. The polluted soil was put in polyethylene pots and mixed well vermicompost and zeolite at the rate of 0, 50 and 100 g kg-1 soil. The treatments were evaluated in a 3 × 3 factorial design and were arranged in a randomized block design with three replications. After incubation for 45 days, five seeds of corn were sown in each pot. After germination the seedlings were thinned to 3 per pot. Plants were grown for 2 months under control conditions. After the corn had been harvested, soil samples were air-dried, and analyzed for pH, cation exchange capacity (CEC), and electrical conductivity (EC). Chemical fractionations of Zn in soils collected after the pot trial were investigated using the procedure of Salbu et al. (1998). This procedure subdivides the heavy-metal distribution into an water-extractable+exchangeable fraction, a form bound to carbonates, a form bound to Fe and Mn oxides, a form bound to organics, and a residual form. An analysis of variance was used to test significance (P≤0.05) of treatment effects and Duncan multiple range test (P≤0.05) was used to compare the means (SAS, 2002).
Results and Discussion: Soil pH gradually decreased with application of both vermicompost and zeolite amendments. This may be due to degradation of organic matter and releasing of organic and inorganic acids such as carbonic, citric and malic acids as well as H+ produced from mineralization of nitrogen in the organic matter. Electrical conductivity (EC) of soils increased with increasing amounts of vermicompost and zeolite applications. The highest EC was observed in pots containing 10% w/w zeolite and 10% w/w vermicompost. Addition of zeolite significantly increased soil CEC. The overall distribution of Zn in different fractions was in the sequence residual (38.6%)> Fe and Mn oxides bound (31.0 %) > carbonated (21.6%)> organic (4.3%)≈exchangeable +water soluble (4.4 %). The application of vermicompost significantly decreased concentration of Zn in water+exchangeable fraction as compared to the control soil. Although singly zeolite amendment had not significant effect on water+exchangeable Zn concentration, this form decreased significantly with co-application of vermicompost and zeolite. This may be due to redistribution of Zn from this form to less available forms (e.g. organic and residual fractions). The addition of vermicompost had not significant effect on the carbonated fraction of Zn, whereas co-application of zeolite and vermicompost significantly decreased concentration of Zn bound in carbonates. Singly zeolite and co-application of amendments decreased the concentration of Zn in Fe and Mn oxides bound. Although singly compost and zeolite amendments increased concentration of Zn bound to organics, this form decreased furthest with co-application of them. Zeolite and vermicompost alone had not significant effect on mobility factor (MF) of Zn over the un-amended soil. Co-application of vermicompost and zeolite to polluted soil resulted in a significant decrease in MF values of Zn compared to control.
Conclusion: Co-application of vermicompost and zeolite to polluted soil resulted in redistribution of Zn from available forms (exchangeable +water soluble) to less available form (e.g. organic), thus may be useful for the immobilization of Zn from polluted sites.
