The Combination of Lime and Plant Species Effects on Trace Metals (Copper and Cadmium) in Soil Exchangeable Fractions and Runoff in the Red Soil Region of China

The water-soluble heavy metal ions in contaminated soil may enter aquatic ecosystem through runoff, thus causing negative impact on the water environment. In this study, a two-year in situ experiment was carried out to explore an effective way to reduce the runoff erosion and water-soluble copper (Cu) and cadmium (Cd) in a contaminated soil (Cu: 1,148 mg kg−1, Cd: 1.31 mg kg−1) near a large Cu smelter. We evaluated the ability to influence soil properties by four Cu-tolerance plant species (Pennisetum sp., Elsholtzia splendens, Vetiveria zizanioides, Setaria pumila) grown in a contaminated acidic soil amended with lime. The results show that the addition of lime can significantly reduce the exchangeable fraction (EXC) of Cu and Cd in soil (81.1–85.6% and 46.3–55.9%, respectively). Plant species cannot change the fraction distributions of Cu and Cd in the lime-amended soils, but they can reduce the runoff generation by 8.39–77.0%. Although water-soluble Cu concentrations in the runoff were not significantly differed and water-soluble Cd cannot be detected among the four plant species, the combined remediation can significantly reduce 35.9–63.4% of Cu erosion to aquatic ecosystem, following the order: Pennisetum sp. > Elsholtzia splendens > Vetiveria zizanioides > Setaria pumila. The implication of this study would provide valuable insights for contaminated soil management and risk reduction in the Cu and Cd contaminated regions.

Zinc and copper fractions in Oxisols of different textures fertilized with pig slurry

HIGHLIGHTS Higher concentrations of exchangeable Zn were found in areas with pig slurry application. No higher concentrations of Cu were found in the exchangeable fraction in areas using pig slurry. In all study areas, it was observed that more than 70% of Cu is in recalcitrant forms.

Combined Effects of Inoculating Serendipita Indica on Soybean Growth and Soil Health Under Cd Stress

Cadmium (Cd) pollution in the soil is a global environmental problem. Plants-microbial technology has been regarded as a potential technique for the remediation of Cd polluted soils. Here, we aimed to explore the combined effects of inoculating (Serendipita indica) S. indica on soybean growth and soil health under Cd stress. Therefore, a pot experiment was conducted to investigate the S. indica on soybean growth and the soil enzyme activities, pH and chemical forms of Cd in the soil under Cd 0, 10, 20, 30 mg/kg soil teatments. Results reflected that compared to non-inoculated ones, the application of S. indica can still enhance the dry weight (66.57%), shoot height (90.35%) and promote the net photosynthesis rate (72.18%), transpiration ratio (80.73%), and stomatal conductance (119.05%) photosynthesis of soybean under Cd 30 mg/kg soil. Furthermore, The pH, phosphatase (116.39%) and catalase (4.17%) activities in the S. indica treatments were increased under Cd 10 mg/kg soil. Meanwhile, inoculated S. indica treatments significantly shifted Cd from exchangeable fraction to other more stable fractions, primarily decreased Cd concentrations (23.66%) under Cd 20 mg/kg soil. The Cd pollution assessment in soil indicated that S. indica could effectively reduce Cd pollution in the Cd 10 mg/kg soil treatments. This work suggests that S. indica may be a potential method for not only promoting plant growth, but also relieving the phytotoxicity of Cd and remediating Cd contaminated soil.

Chemical Speciation and Potential Mobility of some Metals of Selected Farmland in Kogi State, North Central Nigeria

The contamination of agricultural soils with heavy metals is of concern because if the soil is contaminated, the metals can be transferred to food crops. The availability of these metals to food crops depends on the forms in which they are present in the soils. In this study, sequential extraction technique was applied to assess the exchangeable, carbonate-bound, Fe-Mn oxide bound, organic bound and residual fractions in the topsoil of farmlands in Kogi State, North Central Nigeria. Proportions in non-residual soil phases were 82.6 % Cd, 48.6 % Co, 72.5 % Cu, 73.2 % Ni, 41.9 % Pb, and 84.3 % Zn. Lead (Pb) and cobalt (Co) showed the highest phase of 58.1% and 51.4 %, respectively in the residual phase. The low concentration of lead in the non-residual fraction (41.9 %) and the highly mobileexchangeable phase and pH sensitive carbonate phase is an indication that there is no increase in anthropogenic input of Pb into the environment. Cadmium, zinc and nickel are most abundant in exchangeable fraction and this can be of concern especially cadmium. Keywords: Heavy metals, Metal speciation, Farmlands, Food crops, Metal uptake

The Variation of Heavy Metals Bioavailability in Sediments of Liujiang River Basin, SW China Associated to Their Speciations and Environmental Fluctuations, a Field Study in Typical Karstic River

The bioavailability of heavy metals (HMs) in sediments is closely related to the security of the aquatic environment, but their impacts are poorly researched, particularly in karstic rivers. Therefore, Liujiang River Basin was taken as an example in this study. Seven HMs were analyzed to determine the bioavailability and speciations of HMs in sediments. Moreover, the impacts of environmental factors on HMs were identified. The obtained results suggested that HMs in the sediments are all within their permissible exposure limit (PEL), but Cd and Zn are significantly higher than the soil baseline. Most HMs were found to be in a residual fraction, while their exchangeable fraction was found to be in an extremely low ratio. HMs in bioavailable parts are significantly higher than in the exchangeable and carbonate-bound phases but lower than in the non-residual phase, which demonstrated that HM bioavailability is not confined to the exchangeable and carbonate-bound phases. The correlation coefficients commonly decreased with decreasing speciation ratios, which suggested that the overall bioavailability of metals should be determined by speciation ratios instead of speciations themselves. Noteworthily, most HMs in the residual form were found to be significantly correlated with their overall bioavailability, which highlighted the potential bioavailability of residual form. The non-correlations between pH, electrical conductivity (EC), total dissolved solids (TDS), and HM bioavailability suggested that HMs in the carbonate-bound phase are stable and unsusceptible to environmental variations, while the significant correlations between redox potential (Eh), turbidity, organic matter (OM), main grain size (Mz), and HM bioavailability suggested that HMs in the reducible and oxidizable forms are susceptible to environmental fluctuations. Therefore, the variation of HM bioavailability in karstic rivers is largely regulated by their reducible and oxidizable forms instead of their carbonate-bound form.

Chemical Speciation and Mobility Factors of Heavy Metals in Soil Around an Integrated Steel Complex Communities

Some heavy metals, consisting of Fe, Cd, Co, Cu, Mn, Ni, Pb and Zn were determined using USEPA Method 3050B for total metal concentration. Six composite samples were located from Aladja (ALJ), Ovwian (OVW), Ejevwu (EJW), Ekete Inland (EKI}, Orhuwhorun (ORH), and Otor-Udu (OTU) towns. In addition, chemical speciation was carried out on these samples using method employed by Tessier et al. as modified by Kersten and Forstner to assess their speciation pattern and the fraction of abundance as determinant of environmental pollution. From the results obtained, concentrations of Fe, Cd and Mn were more predominant in the residual fraction (F5) in the form of Fe3+, Cd2+ Mn2+ respectively for both wet and dry seasons. Co was more in the exchangeable fraction (F1) as Co2+ for both seasons. Concentration of Cu in the form of Cu2+ is higher in Fe-Mn oxide fraction (F3) for wet season and dry season’s organic fraction (F4). Pb and Zn were abundant in Fe-Mn oxide fraction (F3) for both seasons as divalent ions. Mobility factor calculated for the metals shows pattern in the order: Pb > Co > Zn > Mn > Fe > Cd > Cu > Ni for wet season and Co > Zn > Mn > Cu > Pb > Ni > Cd > Fe for dry season; which is as a result of changes in some physiochemical parameters such as acidity, pH, among others. From this result, there is the need to ensure that future health catastrophe is averted from the accumulation and release of Pb2+, Zn2+, Co2+ and Mn2+ especially into the environment.

Bioavailability and geochemical forms of Pb and Zn in Kosovo contaminated soils

<p>Mitrovica area (northern Kosovo) presents contamination by PTE in agricultural soils caused by smelter emissions and their transfer and accumulation in cultivated plants. Soil A and B, sampled from two sites in Mitrovica municipality, showed a total content of Pb and Zn of 2153 and 3087 mg kg<sup>-1</sup>, and 3214 and 4619 mg kg<sup>-1</sup>. A pot experiment was performed to understand the phytoremediation potential of two non-food crops (Sorghum bicolor L. Moench and Brassica napus Westar), chosen for their economic importance and heavy metal accumulation capacities. Bioconcentration factor, translocation factor and tolerance Indexes clearly indicated a better performance of canola in tolerating Pb and Zn, especially in soil B, even if contained higher amounts of both metals. To evaluate different chemical and physical forms of Pb and Zn in the two soils, a modified BCR extraction scheme was employed to determine amounts bound to different soil components: exchangeable fraction (acid-soluble, carbonate and exchangeable bound), reducing fraction (metal bound to Fe- or Mn-oxides), oxidizable fraction (organic and sulphide bound), and residual fraction (strongest binding with crystalline structure). A comparison of the sum of Pb and Zn concentrations obtained from BCR relative to total digestion values (pseudo-total concentrations) showed recoveries close to 100%. Very small amounts of Pb were released during step 1 (exchangeable fraction) (6,86% - soil A and 2,12% - soil B). The highest concentration of Pb, 62,62% in soil A and 56,68% in soil B, decreased in the reducing fraction (step 2), probably occurring mainly as forms bound to Fe/Mn oxides. Step 3 (oxidizable-organic matter “OM” and sulphides) released amounts of 23,15% and 20,32% of total Pb in soil A and B. Residual fraction presented very different amounts of Pb (7,87% in soil A and 20,88% in soil B). Unlike Pb, no important differences were found in the distribution of Zn among the various fraction of the two soils, with the greater amounts contained in the exchangeable fraction of both soils, 31.11% in soil A and 21.92% in soil B. Very small amounts of Zn were released during step 2 (19,3% in soil A and 22,27% in soil B) whereas step 3 released the highest amounts of Zn in both soils (36,56% in A and 40,17% in B). Residual fraction presents similar amounts of total Zn, 13,03% in A e 15,64% in B, showing an opposite trend with respect to Pb. So, a major portion of total Pb was associated to the reducing fraction, while Zn was found mostly in oxidable one, indipendent on the origin of samples. Pb strongly interacts with Fe-/Mn oxides, and, in soil B, a greater amount is immobilized in the residual fraction. These results suggest lower mobility and bioavailability of Pb in soil B with respect to soil A, partially explaining the pot experiment.</p>

Speciation Variation and Bio-Activation of Soil Heavy Metals (Cd and Cr) in Rice-Rape Rotation Lands in Karst Regions

Heavy metals in soil are in a high background state in Karst areas, and agricultural activities will affect the bioactivity of heavy metals. The heavy metal (Cd and Cr) bioactivity and their activation effects in rice-rape rotation lands in Karst areas were studied based on field experiments and laboratory analysis, and the influencing factors of heavy metal activity were analyzed based on the physical and chemical properties of soil. The results suggest that the residual fraction was the largest and the exchangeable fraction was the smallest for both Cr and Cd in rice-rape rotation lands in Karst areas. During the rice-rape rotation process, Cd and Cr tended to be released from the residual fraction and transformed into the other four fractions. The fractions with high bioactivity, including the exchangeable fraction and carbonate fraction, increased to different degrees. Rice-rape rotation could activate the activity of soil Cd and Cr in Karst areas. It is also revealed that the activity of soil Cd and Cr in Karst areas was closely associated with soil pH and electric potential (Eh). In the 0–20 cm soil layer, Cr showed a significant negative correlation with pH (r = −0.69, p < 0.05), while both Cr and Cd showed significant negative correlations with Eh, and the correlation coefficients were −0.85 (p < 0.01) and −0.83 (p < 0.01), respectively. In the 20–40 cm soil layer, Cr showed significant negative correlations with Eh, and the correlation coefficient was −0.95 (p < 0.01). No significant correlation between the activity of soil Cd and Cr and soil mechanical composition was observed. This study revealed that special attention should be paid to changes in pH and Eh in consideration of heavy metal activity in the rice-rape rotation process.

Bioavailability of soil Cu, Fe, Mn and Zn from soil fractions

Cationic micronutrients bioavailability depends on the chemical characteristics of soil fractions. Fourteen soils received individual doses of five micronutrients (Cu, Fe, Mn, Zn, B) arranged in seven treatments set according a Baconian Matrix. The soils incubated with treatments during 15 days had corn cultivated in greenhouse for 30 days, in three consecutive growth cycles. The cationic micronutrients were determined in the corn shoots after each growth cycle. Soil samples collected before the first and after each growth cycle had the available concentrations of Cu, Fe, Mn and Zn determined by single extractions (Mehlich-1 and DTPA-pH 7.3) and by sequential extraction. Correlation analysis was performed for the Cu, Fe, Mn and Zn concentrations determined in the corn shoots, the available concentrations of Cu, Fe, Mn and Zn in the soils (Mehlich-1 and DTPA) and the concentrations of Cu, Fe, Mn and Zn in the soil fractions (sequential extraction). The distribution of available metals forms in fractions reflected their affinity with soil components. Soil available Cu correlated with Cu bound to organic matter. The exchangeable fraction was the main source of soil available Mn and Zn. The Fe availability related mainly to the Mn oxides, Fe oxides, and exchangeable fractions. The plants absorbed Cu mainly from the Mn-oxides and organic matter fractions. Manganese absorbed by plants originated from the exchangeable and Mn-oxides fractions. The Zn absorbed by plants originated mainly from the exchangeable fraction. Correlations of single metal extractions (Mehlich-1 and DTPA) with Cu, Mn and Zn contents in plants were positive.

Characterization of landfill deposited sediment from dredging process during different maturation stages

A long-term monitoring of deposited sediment in the environment is considered in order to examine the mechanism of incorporation of Cu and Cd into mineral fractions and to investigate their bioavailability during landfill maturation. Using the sequential extraction technique (BCR-Community Bureau of Reference), the dominant presence of Cu and Cd in the oxidation and residual fraction was determined, which suggests a low risk of bioavailability of these metals in the environment. The maturation of the deposited sediment indicates that the Cu and Cd content decreases over time in the exchangeable fraction and increases in the oxidation fraction. X-ray techniques XRF and EDS indicated a prevalence of silicates in the tested samples, which indicates the possibility of presence silicate compounds that can bind metals and thus convert them into less mobile forms in the sediment. By imaging the samples with a scanning electron microscope SEM, the formation of heterogeneous structures over time was determined, which confirms the formation of new minerals and the potential possibility of incorporating copper and cadmium in them. In order to determine the mineral forms and dominant compounds in the examined sediment samples, X-ray diffraction analysis was applied, and the transformation pathways were explained.