Spatial variability of soil total and DTPA-extractable cadmium caused by long-term application of phosphate fertilizers, crop rotation, and soil characteristics

Increasing cadmium (Cd) accumulation in agricultural soils is undesirable due to its hazardous influences on human health. Thus, having more information on spatial variability of Cd and factors effective to increase its content on the cultivated soils is very important. Phosphate fertilizers are main contamination source of cadmium (Cd) in cultivated soils. Also, crop rotation is a critical management practice which can alter soil Cd content. This study was conducted to evaluate the effects of long-term consumption of the phosphate fertilizers, crop rotations, and soil characteristics on spatial variability of two soil Cd species (i.e., total and diethylene triamine pentaacetic acid (DTPA) extractable) in agricultural soils. The study was conducted in wheat farms of Khuzestan Province, Iran. Long-term (27-year period (1980 to 2006)) data including the rate and the type of phosphate fertilizers application, the respective area, and the rotation type of different regions were used. Afterwards, soil Cd content (total or DTPA extractable) and its spatial variability in study area (400,000 ha) were determined by sampling from soils of 255 fields. The results showed that the consumption rate of di-ammonium phosphate fertilizer have been varied enormously in the period study. The application rate of phosphorus fertilizers was very high in some subregions with have extensive agricultural activities (more than 95 kg/ha). The average and maximum contents of total Cd in the study region were obtained as 1.47 and 2.19 mg/kg and DTPA-extractable Cd as 0.084 and 0.35 mg/kg, respectively. The spatial variability of Cd indicated that total and DTPA-extractable Cd contents were over 0.8 and 0.1 mg/kg in 95 and 25 % of samples, respectively. The spherical model enjoys the best fitting and lowest error rate to appraise the Cd content. Comparing the phosphate fertilizer consumption rate with spatial variability of the soil cadmium (both total and DTPA extractable) revealed the high correlation between the consumption rate of P fertilizers and soil Cd content. Rotation type was likely the main effective factor on variations of the soil DTPA-extractable Cd contents in some parts (eastern part of study region) and could explain some Cd variation. Total Cd concentrations had significant correlation with the total neutralizing value (p?<?0.01), available P (p?<?0.01), cation exchange capacity (p?<?0.05), and organic carbon (p?<?0.05) variables. The DTPA-extractable Cd had significant correlation with OC (p?<?0.01), pH, and clay content (p?<?0.05). Therefore, consumption rate of the phosphate fertilizers and crop rotation are important factors on solubility and hence spatial variability of Cd content in agricultural soils.     

Cadmium removal from Cd-contaminated soils using some natural and synthetic chelates for enhancing phytoextraction

The influence of a natural (citric acid) and two synthetic chelates (HEDTA, EGTA) on Cd phytoextraction with radish was studied. The experiment was conducted with Cd treatments including 0 (control), 5, 20, 60 and 100?mg?Cd?kg^?1 soil. When plants were fully developed, the designated HEDTA, EGTA and citric acid were applied to establish experimental treatments. Ten days after chelate applications, soil and plant samples were taken. Results indicated that synthetic chelates can considerably increase Cd concentration in soil solution compared with citric acid. Among the applied chelates, HEDTA provided more significant influences on soil solution. Cadmium concentration in both shoots and roots of radish was increased due to enhancing influence of chelate applications on Cd concentration in soil solution. Cadmium concentration in radish shoots was more than that of roots. This can be attributed to higher bioavailability and solubility of Cd in soil solution. In all treatments which received HEDTA, the cadmium concentration in both shoots and roots of radish was increased more than that of other applied chelates. Although HEDTA is more efficient in phytoextracting Cd than other chelates, due to durability of synthetic chelates toxic effects on soils, we recommend using larger amounts of light acids.     

An integrated multi criteria approach for landfill siting in a conflicting environmental, economical and socio-cultural area

Landfill site selection is a complicated multi criteria land use planning that should convince all related stakeholders with different insights. This paper addresses an integrating approach for landfill siting based on conflicting opinions among environmental, economical and socio-cultural expertise. In order to gain optimized siting decision, the issue was investigated in different viewpoints. At first step based on opinion sampling and questionnaire results of 35 experts familiar with local situations, the national environmental legislations and international practices, 13 constraints and 15 factors were built in hierarchical structure. Factors divided into three environmental, economical and socio-cultural groups. In the next step, the GIS-database was developed based on the designated criteria. In the third stage, the criteria standardization and criteria weighting were accomplished. The relative importance weights of criteria and subcriteria were estimated, respectively, using analytical hierarchy process and rank ordering methods based on different experts opinions. Thereafter, by using simple additive weighting method, the suitability maps for landfill siting in Marvdasht, Iran, was evaluated in environmental, economical and socio-cultural visions. The importance of each group of criteria in its own vision was assigned to be higher than two other groups. In the fourth stage, the final suitability map was obtained after crossing three resulted maps in different visions and reported in five suitability classes for landfill construction. This map indicated that almost 1224 ha of the study area can be considered as best suitable class for landfill siting considering all visions. In the last stage, a comprehensive field visit was performed to verify the selected site obtained from the proposed model. This field inspection has confirmed the proposed integrating approach for the landfill siting.     

Effect of fertilizer application on soil heavy metal concentration

A large amount of chemicals is annually applied at the agricultural soils as fertilizers and pesticides. Such applications may result in the increase of heavy metals particularly Cd, Pb, and As. The objective of this study was to investigate the variability of chemical applications on Cd, Pb, and As concentrations of wheat-cultivated soils. Consequently, a study area was designed and was divided into four subareas (A, B, C, and D). The soil sampling was carried out in 40 points of cultivated durum wheat during the 2006–2007 periods. The samples were taken to the laboratory to measure their heavy metal concentration, soil texture, pH, electrical conductivity, cationic exchange capacity, organic matter, and carbonate contents. The result indicated that Cd, Pb, and As concentrations were increased in the cultivated soils due to fertilizer application. Although the statistical analysis indicates that these heavy metals increased significantly (P value < 0.05), the lead and arsenic concentrations were increased dramatically compared to Cd concentration. This can be related to overapplication of fertilizers as well as the pesticides that are used to replant plant pests, herbs, and rats.     

Portland cement solidified construction waste using MSW leachate and phosphate admixtures

Journal of Material Cycles and Waste Management - Many dumping sites all over the world release leachate into the environment. The primary goal of this study was to convert raw municipal...