Somayeh Sadr; Zahra Movahedi Rad
Abstract
Introduction: The study of the spatial distribution of heavy metals is very important in land management and planning. The geostatistics theory is used to estimate spatial variables in unmeasured points. By using the CoKriging estimator and using information about the correlation between variables, ...
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Introduction: The study of the spatial distribution of heavy metals is very important in land management and planning. The geostatistics theory is used to estimate spatial variables in unmeasured points. By using the CoKriging estimator and using information about the correlation between variables, a more accurate estimation of a variable (main variable) can be obtained using auxiliary information (secondary variables). Due to the importance of Isfahan Province because of the large population living in this province and the extent of agricultural and industrial activities, there is a need for sufficient information on the distribution of selenium in this area. The present study investigated the distribution of selenium and provided maps of its distribution in the surface soils of this province. Material and methods: The study region has an area of about 6800 km2 and covers a large part of the agricultural lands and the major industrial centers of Isfahan. Samples were taken from depths of 0 to 20 cm from the soil surface and 255 samples from the whole area in 4 × 4 km networks by using a stratified random sampling design. All soil samples were analyzed for pH, electrical conductivity (EC), sand, clay, silt content, and organic matter percentage. Total selenium concentrations were measured by XRF in only 72 samples. Statistical and geostatistical calculations were performed by SPSS and WinGslib, respectively, and maps were drawn by ILWIS and Surfer software. Results and discussion: The mean concentration of selenium in the study area was 0.63 mg/kg with a min and max amount of 0.5 and 1.5 mg/kg, respectively. There was a positive and significant correlation between the selenium concentration and soil’s EC. Therefore, EC was used to reduce the selenium estimation error by the CoKriging method. While toxicity level of selenium starts at 5 (mg/kg) for humans and animals, in this study, deficiency threshold for total soil selenium was 0.6 mg/kg and, therefore, the study area can be identified as selenium-deficient because more than 50% of the area had a concentration of less than 0.6 mg/kg and about 12% of the area has a high concentration of selenium in unpolluted soils. No toxicity of this element to humans and livestock was observed. Large parts of Isfahan Province have an arid climate with alkaline pH soils. Given the low levels of selenium in both agricultural and non-agricultural lands, it seems that the native material of this area, which is often the alluvial constituent of the Zayandehrood River, is poor in selenium. On the other hand, the deficiency of this element in agricultural lands indicates that farmers in these areas do not use selenium-containing fertilizers. The highest concentration of selenium was located in the city of Mobarake. There is a huge steel industry in this area. The dominant wind direction of the region is introduced as a threat factor in the transfer of selenium-containing atmospheric emissions from the industrial areas of Mobarka to more populated areas of the province Conclusion: Industries are more concentrated in the city of Isfahan and its surrounding areas and thus selenium concentration is higher in these areas than the neighboring areas. The steel industry in Mobarakeh is an agent for the introduction of selenium into the atmosphere and finally the soil. Winds probably play a role in transmitting selenium to the northeastern part of the region. However, no toxicity of this element was observed in all the studied areas but even selenium deficiency was observed. Therefore, using selenium-rich fertilizers in the region is recommended.
Seyed Javad Hosseinifard; Hossein Shirani; ُSomaye Sadr; Hakimeh Hashemipour
Abstract
Introduction: Increasing concentrations of heavy metals in the environment have raised serious environmental concerns. Cadmium is one of the most toxic heavy elements in organisms and it has no biological role. So far, little research has been done on the status of heavy metals in pistachio orchards ...
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Introduction: Increasing concentrations of heavy metals in the environment have raised serious environmental concerns. Cadmium is one of the most toxic heavy elements in organisms and it has no biological role. So far, little research has been done on the status of heavy metals in pistachio orchards and factors affecting them. Therefore, the purpose of this study was to determine the relationship between cadmium extracted with DTPA in soil and other soil physical and chemical properties in agricultural soils of Rafsanjan using stepwise regression and artificial neural network modeling. Material and methods: In this study, 140 soil samples from two depths of 0 to 40 and 40 to 80 cm were collected from pistachio orchards in six regions of Rafsanjan suburb. Soil characteristics including available Cd and Zn concentration measured using DTPA, P concentration by Olsen method, percent of sand, clay and silt by hydrometer method, and pH and electrical conductivity of soil saturated extract by pH meter and EC meter, respectively, were measured. In order to investigate the relationship between available Cd and physical and chemical properties of the soil, stepwise regression and artificial neural network (multi-layer feed forward) were used. Results and dissussion: The results showed a significant and positive correlation between phosphorus and clay content and soil cadmium, a negative and significant correlation between Cd-DTPA and pH and clay percentage, and a positive correlation between available Cd and available Zn, total Zn, and total Cd. The results also showed that both modeling methods are accurate in estimating soil cadmium concentration, although the neural network model was more accurate. The R2 and root of mean square error for the neural network model were 84.3% and 0.01% for the test data, and 27.2% and 1.43% for the stepwise regression model, respectively. Also, cadmium concentration showed the highest sensitivity to zinc concentration and other parameters such as clay, pH, phosphorus, EC, and sand were in the next order of importance, respectively. These results confirm that due to the consumption of zinc containing fertilizers and the increased consumption of phosphate fertilizers which have high impurity in the amount of cadmium, an increase in soil cadmium concentration is observed in the pistachio orchards. Conclusion: Zinc and phosphorus fertilizers used in pistachio orchards have a significant impurity of cadmium that can cause soil contamination by cadmium due to its long-term use and absorption of this toxic element in pistachio plant and fruit. Therefore, while complying with national and international standards in the production and import of fertilizers, the use of these fertilizers should be optimized by analyzing and interpreting the results of soil and leaf analysis to reduce the risk of pistachio fruit contamination to cadmium.
