sequential extraction

The behavior of heavy metals in the soil as one of the environmental challenges has attracted the attention of many researchers. The present study was conducted to evaluate the phosphorus solubilizing bacteria on remobilization of cadmium (Cd) and lead (Pb) in two calcareous soils.

Phosphorus, cadmium and lead in the forms of KH2PO4, Cd(NO3)2 and Pb(NO3)2 simultaneously were introduced to the soils to promote the formation of phosphate minerals of added metals in two selected soils. Ater two months the soils were inoculated with two Pseudomonas species and incubated for 3 months. Sequential extraction scheme were applied to determine the chemical forms of Cd and Pb 5, 25, 60 and 90 days after incubation.

The results showed that application of phosphorus solubilizing bacteria changed chemical forms of Cd and Pb. Inoculation with Pseudomonas decreased the soluble and exchangeable cadmium while increased organic matter-bound Cd concentration. Inoculation by Pseudomonas increased carbonate-bound Pb and decreased Fe-Mn oxide and organic matter bound Pb. In the other hand, phosphate solubilizing bacteria (Pseudomonas) decreased mobility and bio-availability of cadmium and immobilization of lead.

In fact, the behavior of heavy metals in the presence of phosphorus solubilizing bacteria was different and depends on the type of metal and soil properties. In present study, bacteria cause immobilization of cadmium and remobilization of lead.

One of the promising tools for evaluating heavy metals bioavailability in the environment is the knowledge of their partitioning among the various soil constituents. The present study was conducted in order to investigate the changes of chemical forms of cadmium (Cd) and lead (Pb) under the influence of phosphorus solubilizing bacteria in the soil.

Phosphorus (KH2PO4), Cd(NO3)2 and Pb(NO3)2 simultaneously were introduced into the soil to promote the contamination and formation of phosphate minerals of added metals in two selected soils. After two months the soils were inoculated with two Enterobacter species and incubated for 3 months. A single (DTPA) and sequential extraction scheme were applied to determine the chemical forms of Cd and Pb 5, 25, 60 and 90 days after incubation.

The results revealed that DTPA extractable Cd and Pb were decreased in the presence of the phosphorus solubilizing bacteria. Soluble+ exchangeable Cd fraction was decreased whereas, the fractions associated with organic matter and oxides were increased in inoculated soils during the incubation time. In the other hand Soluble+ exchangeable and carbonate fractions of Pb were increased and organic matter and oxides associated Pb fractions were decreased in the presence of phosphorus solubilizing bacteria. Carbonate and oxides associated are the abundant Cd and Pb fractions in studied soil.

Although the Cd and Pb chemical fractions were affected in the presence of phosphorus solubilizing bacteria, but two metals contradictory were differ in behavior in the studied soils. Indeed, the destination of added metals in the soil in the presence of microbes may be different.

The aim of this study was to determine the concentration of heavy metals in the sediments and the bivalve molluscs, Solen dactylus, in the estuaries covered by mangrove trees of west (Khamir estuary) and east (Shahrno estuary-Jask) of Hormozgan province and also to assess the pollution, bioaccumulation and toxicity of heavy metals (Fe, Ni, Cu and Pb), in these areas. Sediments were studied to determine the grain size, organic carbon, organic matter, total and partial concentration and bioavailability of metals. The results showed that the environmental factors such as organic matter and grain size of sediments affect the distribution of heavy metals. According to the results, there was no significant difference between the sediments of two stations in the accumulation of metals (P>0.05). contamination and enrichment factors for Ni and Pb showed a moderate degree of contamination and enrichment. The geochemical speciation of the studied metals indicated more bioavailability for Cu and Pb. The Risk Assessment Code and the screening quick reference table (SQRT) indicate the high risk in Cu for Shahrno estuary and in Pb for Khamir estuary, and both metals are above the threshold effect level (TEL) for the clam in the area. The results of S. dactylus's bioaccumulation factor showed that Cu accumulated more than other metals in both regions. In general, the present study showed that the sediments of the studied areas are contaminating in terms of Cu and Pb.

Oxidation of sulfide mineralized zones during the weathering processes is intensified by biological and chemical reactions and the resulting acid mine drainage (AMD) causes the release and mobility of toxic and heavy metals from the parent rock and their concentration in soil or water. In this study, soil samples taken from around the village of Doustbaglu (northwest of Meshginshahr), which is considered a typical mineralization and alteration area, were studied and chemical species, toxicity and origin of heavy elements such as As, Cd, Cu, Cr, Pb, Sb, Ni and Zn were determined.

In this study, total concentration and bioavailability of heavy elements (i.e. As, Cd, Cu, Cr, Pb, Sb, Ni and Zn) in five surface soil samples were evaluated by Tessier sequential extraction method in five phases (exchangeable, bound to carbonate, bound to iron and manganese oxides, bound to organic matter and residual phase) and using of the Visual Minteq thermodynamic software.

The results of the sequential extraction method show that the highest concentration of the total concentration of all 8 heavy elements studied were retained in the residual fraction (stabilized in the mineral structure). This indicates the geogenic origin of these elements and can be considered the result of erosion and weathering of rocks in the region. Compared to other elements, Sb has a higher concentration in potentially available fractions (e.g. exchangeable, carbonate-bound, bound to Fe-and Mn-oxides, and/or organic matter) and can be readily available to plants and toxic. The software output delineates that the predominant species in the examined samples were lead (Pb) as Pb (SO4)22-, Pb2+ and PbSO4(aq); copper as CuSO4 (aq) and Cu2+; nickel as NiSO4 (aq), Ni2+ and NiSO4; antimony as Sb(OH)3, Sb(OH)2+ and Sb(OH)61-; zinc as Zn(SO4)22-, ZnSO4(aq) and Zn2+; Arsenic as H3AsO3 and H2AsO4-; Cadmium as Cd(SO4)22-; and Cd2+ The predominant species of chromium were CrSO4+, CrOHSO4(aq) and HCrO4-. In general, the free water-soluble species of these elements are more mobile than other species; instead, the concentration of these species is very low in comparison, and most of these elements are more present in the form of complexes with low mobility.

 Based on sequential extraction results; all 8 studied elements show high ecological risk potential and significant pollution in the sediment of waterways and surface soil horizons of the Doustbaglu area. Analysis of the findings of Visual Minteq software indicates that the most active types of elements and related concentrations, among all possible types, include: Cd2+(1.49%), CrOHSO4(aq)(25.20%), Cu2+(10/38%), Pb2+(1/37%), ZnSO4(aq) (18.83%), respectively. Since more mobile species have low concentrations and on the other hand, according to the results of sequential extraction, most of the studied elements are present in the remaining phase, so the bioavailability and toxicity of these elements are estimated to be negligible. In general, it can be concluded that only a small percentage of elements are present in bioavailable fractions, and this can alleviate concerns about the possibility of element release by changing environmental conditions and thus accessibility to plants.

Joghatay plain is located in Sabezvar Ophiolitic Zone and next to the chromite mine. In this research, the soil pollution by heavy metals have been investigated with respect to geochemical, statistical and environmental indicators in Joghatay plain.Material and

Samples were collected seasonally from soil in Joghatay plain within May 2014, and the concentration of heavy metals were measured using ICP-MS method. To the geochemical phases of metals in soil were determined using BCR sequential extraction method.

The result of the analysis of heavy metals in soil samples has shown high concentrations of some elements such as Chromium, Nickel and Cobalt in the southern part of the region. Assessment and correlation of heavy metals in Joghatay region soils by multivariate statistical methods (Pearson correlation, cluster analysis and principal component analysis) show a strong positive correlation between Cobalt, Nickel, Chromium, Iron, Manganese and Magnesium due to the same source  (ophiolitic unit area).

The pollution index (geoaccumulation index, enrichment factor, contamination factor and modified contamination degree) indicates that soil has strongly polluted with regard to Chromium and Nickel and moderately polluted to Cobalt. Sequential extraction method has indicated that more than 50% of Nickel and Chromium concentration in intercahnageable phase. On the other hand ophiolitic rocks and Chromit mining leads releasing of these elements in the area. Though, as far as it gets away from ophiolitic rocks these elements concentration will be decreased. Also element speciation in different phases reveals that the rest elements have concentrated in residual phases and have a lithogenic source.

The serpentinite soils in ophiolitic zone of Robat Sefid in 60km south of Mashhad (Khorasan-e-Razavi) were examined to evaluate the pollution potential of heavy elements in the area soils. Main parameters of soil texture, EC, pH, organic matter (OM%) and calcium carbonate equivalent (CCE%) were determined in geochemical lab of geology department in the Ferdowsi University of Mashhad. Total concentration of Cr, Ni, Co, Mn and Zn in soil samples were measured by using AAS analysis method. Selective sequential extraction (SSE) was conducted to determine those heavy metals concentration in 5 different soil phases based on Tessier method. Correlation coefficient of geochemical parameters, and also geo-accumulation index (Igeo) and enrichment factor (EF) were computed to assess the pollution level in the soil samples. Those calculated indices represented different levels of heavy metals enrichment and soil pollution in studied area. According to potential ecological risk index (RI), the risk was high. Also, pollution load index (PLI) value was more than 1, which indicates polluted soils. The correlation was significant between Cr, Ni and Co to sand (%), which indicate sand-size heavy metals bearing minerals such as chromites are abundant in the soils. Concerning the mobility factor (Mf) and risk assessment code (RAC), Co, Ni and Mn categorized in low to moderate levels. The Mn and Ni element with high activity and bio-accessibility could be considered as pollutant elements in the area.

Behavior of metals in soils, such as mobility and bioavailability based on the total concentration of heavy metals, is not predictable. Absorption and toxicity of metals are dependent on their chemical fraction. Therefore, investigation of mobility and bioavailability of heavy metals are very important in the environmental studies.
Using BCR modified sequential extraction procedure, different forms Cu in the soil of rice fields irriggated by Amol industrial wastewater were determined in this study. Samples were analyzed by the Atomic Absorption Sens AA model.
The results showed that the residual form and the acid soluble, exchangeable, carbonate form were at their maximuum and minimum amounts (77.17 and 2.7), respectively. Moreover, mobility factor and recovery percent were obtained to be 2.39 and 96.6, respectively.
Mobility and bioavailability of copper in soil of rice farms in this area are low. Therefore, the possibility of pollution by this metal is low.