[Effect of EDDS Application on Soil Cu/Cd Availability and Uptake/transport by Castor].

To investigate the effect of chelating agents on plant uptake of heavy metals, castor (Ricinus communis L.) was used as the test plant. Soil culture and pot experiments were conducted to study the effects of different concentrations of ethylenediamine disuccinic acid (EDDS) on the forms of Cu and Cd in soil and their absorption and transport by castor. The results showed that the application of EDDS significantly increased the content of available Cu and Cd. After 15 days of cultivation, the available Cu and Cd concentrations in the soil increased by 43.01%-103.55% and 51.78%-69.43%, respectively. EDDS promoted the conversion of reducible Cu to weak acid extractable and increased the mobility of Cu. Meanwhile, the application of EDDS promoted the absorption, transport, and enrichment of Cu in castor. Under the application of 2.5 mmol·kg-1 EDDS and 5.0 mmol·kg-1 EDDS, the Cu concentrations in the shoots were 4.88 times and 16.65 times higher than that of the control (P< 0.05), and the Cu concentrations in the roots were 2.89 times and 3.60 times higher than that of the control (P< 0.05), respectively. The Cu transport coefficient significantly increased by 72.73% and 381.82% when treated with EDDS 2.5 and EDDS 5.0. Simultaneously, the phytoextraction of Cu in shoots, roots, and their sum were 14.08, 2.16, and 4.70 times higher than that of the control (P<0.05), respectively, when treated with EDDS 5.0. Furthermore, EDDS significantly increased the Cd concentrations in castor. When treated with EDDS 2.5 the shoots and roots increased by 15.15% and 57.42%, respectively, and the phytoextraction of total Cd significantly increased by 13.44%. Generally, the EDDS treatment could increase the available Cu and Cd in soil, promote the uptake of Cu and Cd, and improve the phytoremediation efficiency of castor. Among them, the addition of 5.0 mmol·kg-1 EDDS had the best effect for Cu, whereas the addition of 2.5 mmol kg-1 EDDS had a higher increase in the phytoextraction of Cd.

[Remediation Effect of Two Iron-modified Biochars on Slightly Alkaline Arsenic and Cadmium Contaminated Soil].

As a good passivation agent for heavy metals, modified biochar has been widely used in environmental remediation. In order to explore the effects of different modification methods on arsenic (As) and cadmium (Cd) passivation in soil by biochar, this study used co-precipitation and impregnation pyrolysis to prepare iron-modified biochar. Through adsorption experiments and soil culture experiments, the properties of biochar, adsorption capacity, and the As and Cd passivation ability in soil were analyzed. The results showed that both modification methods could increase the iron (Fe) content and zero charge point of biochar, and the Fe minerals supported by Fe-modified biochar (FeBC-1) prepared by co-precipitation were mainly Fe3O4, FeO(OH), and γ-Fe2O3. The Fe-modified biochar (FeBC-2) prepared by impregnation pyrolysis mainly consisted of α-Fe2O3 and γ-Fe2O3. FeBC-1 showed strong adsorption and removal ability for As and Cd, with a removal rate of 21.40%-34.14%, which could significantly promote the conversion of non-obligate adsorbed As to residual As in soil, whereas FeBC-2 only had a good adsorption effect on As. The adsorption capacity of BC, FeBC-1, and FeBC-2 for Cd were proportional to their CEC. The adsorption and removal effect of BC on Cd was better than that of FeBC-1 and FeBC-2, which could significantly promote the conversion of soil acid-soluble Cd to stable residue Cd.

[Spatial Distribution and Risk Assessment of Heavy Metals in Surface Sediments from the Middle and Upper Reaches of the Yangtze River].

The hydrological regime of rivers significantly changes after dam impoundment, which in turn affects the particle composition and heavy metal fractions of the river sediments. From June to July 2019, the sediments from 26 sampling sections were collected along the main stream of the Yangtze River from Panzhihua City in the upper reaches of the Yangtze River to Hukou City in the middle reaches of the Yangtze River. The concentrations and fractions of As, Cd, Co, Cr, Cu, Ni, Pb, and Zn were measured using the BCR three-step extraction procedure. The pollution status and potential ecological risk of heavy metals in sediments were evaluated using the geo-accumulation index, the sediment quality guideline, and the risk assessment coding method (RAC). The results showed that the average particle size of sediments in the upper reaches of the Yangtze River (Jinsha River cascade reservoir section and the Three Gorges reservoir section) decreased from upstream to downstream, the total concentrations of As and Zn increased, and the variation trend in the middle reaches was not obvious. The content of clay particles was significantly positively correlated with the acid-soluble fraction concentrations of Cd and Ni. Cd was mainly in the residual fraction (59.26%) and acid-soluble fraction (24.67%). Large parts of Cr and Ni were residual fractions accounting for 92.41% and 83.41%, respectively. As, Co, Cu, Pb, and Zn were mainly in the residual fraction and the reducible fraction. The order of decrease for the pollution degree (Igeo) of As, Cd, Co, Cr, Ni, and Zn was the Jinsha River, the middle reaches of the Yangtze River, and the Three Gorges Reservoir. The decrease order of bioavailability (RAC) of Cd, Co, Cr, Cu, Ni, and Zn was the Three Gorges Reservoir, the Jinsha River, and the middle reaches of the Yangtze River. The bioavailability of As and Pb decreased in the order of the middle reaches of the Yangtze River, the Three Gorges, and the Jinsha River. According to the classification of the RAC, Cd in the Three Gorges Reservoir area exhibited a high risk with the RAC accounting for 48.44%. Cu, Ni, and Zn showed a low or medium risk.

[Effect of Citric Acid and Phosphorus Coexistence on Cadmium Adsorption by Soil].

In brown-red soil, the effect of phosphorus and citric acid co-existence on the adsorption of cadmium was studied using indoor experiments and isothermal equilibrium adsorption analysis. After treatment with different doses of phosphorus and citric acid, the fractions of cadmium were altered by varying dry and wet conditions. The results showed that:① Soil treated with 10 mg·L-1 of CdCl2 solution showed no notable effect on cadmium adsorption when a low concentration of phosphorus was added (40 mg·L-1); however, higher a concentration of added phosphorus (80 mg·L-1) significantly increased cadmium adsorption (an increase of 78 g·kg-1 and 7.89% compared to the control treatment); ② Using a 40 mg·L-1 phosphorus solution, the addition of citric acid proportionally reduced cadmium adsorption. This inhibition effect was more notable for the soil treated with low-dose phosphorus (40 mg·L-1) than the high-dose treatment with 1 mmol·L-1 and 5 mmol·L-1 citric acid (cadmium adsorption decreased by 30.89% and 40.97%, respectively). The effect of citric acid was not significant, however, at higher concentrations of phosphorus. When the concentration of citric acid reached 5 mmol·L-1, cadmium adsorption was only 1% lower than without citric acid treatment; ③ Periodic dry-wet alternation significantly promoted the transformation of cadmium from a weak acid extractable and reducible state to an oxidizable and residual state in the soil. That is, the availability of cadmium in soil subjected to the combined action of phosphorus and citric acid decreased with an increase in wet and dry alternations.

[Effect of Water Regimes on Pb and Cd Immobilization by Biochar in Contaminated Paddy Soil].

An incubation experiment was conducted to explore the influence of 30% water holding capacity (WHC), flooding, and alternate dry-wet conditions on changes in heavy metal fractions with 1% rice straw biochar in Pb and Cd co-contaminated paddy soils, to provide a scientific basis for a water regime of biochar remediation on heavy metal contaminated paddy soil. Results showed that flooding and alternating wet-dry conditions could significantly increase soil pH, the contents of dissolved organic carbon (DOC), and amorphous iron oxide (Feo) after adding biochar. Compared with a 30% WHC treatment, when the soil is flooded and alternating wet-dry conditions, the content of the TCLP extractable Pb decreased by 31.87% and 20.33%, respectively, and the content of the TCLP extraction Cd decreased by 25.29% and 16.07%, respectively. Under flooding, the acid soluble Pb and Cd content decreased by 24.78% and 20.14%, respectively, and the acid soluble Cd content decreased over time. The decreasing order of available Pb and Cd content was flooding > alternating dry-wet > 30% WHC. Correlation analysis results showed that soil pH and Feo have significant negative correlation with available heavy metals, which means flooding with biochar could effectively immobilize Pb and Cd by increasing soil pH and Feo content. Flooding and biochar have a synergistic interaction on promoting the transformation of Pb and Cd to more stable fractions in acidic co-contaminated heavy metal polluted paddy soil.

[Effects of Exogenous Spermidine on Seed Germination and As Uptake and Accumulation of Rice Under As5+ Stress].

As pollution in farmland has a toxic effect on the growth of crops, which reduces their yield and quality. The effects of exogenous spermidine (Spd) on rice seed germination and seedling growth under As5+ stress were studied. The results showed that exogenous Spd could promote the germination of rice seeds under As5+ stress, improve the germination potential and germination rate of seeds, and promote the growth of seedling roots. The addition of Spd could increase the activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) of rice seedlings and roots under As5+ stress, and reduce the content of malondialdehyde (MDA) in rice buds and roots. When As5+ concentration was 25 µmol·L-1, adding 500 µmol·L-1 and 1000 µmol·L-1 Spd, MDA content in rice roots was decreased by 12.3% and 31.3% and CAT activity of rice shoots was increased by 105.1% and 101.4%, and CAT activity of rice roots was increased by 29.9% and 57.1%, respectively. The addition of Spd also affected the uptake and accumulation of As in rice. When the concentration of As5+ was 25 µmol·L-1, adding 500 µmol·L-1 and 1000 µmol·L-1 Spd, the concentration of As in rice shoots decreased by 69.4% and 75.1%, and As concentration in rice roots decreased by 7.6% and 24.4%, respectively. Spd could therefore effectively alleviate the toxic effect of As5+ on rice.

[Phosphorus Forms and Distribution Characteristics in the Sediment and Soil of the Water-Level-fluctuating Zone in the Main Stream of the Three Gorges Reservoir].

Hydrological regimes changed after the Three Gorges Reservoir (TGR) became fully operational, with the water level fluctuating between 145 m and 175 m. This has altered phosphorus (P) distribution within sediments and soils of the water-level-fluctuating zone (WLFZ). Eleven field investigations within the main stream were carried out in June 2016. The aim of the study was to determine lateral (sediment and WLFZ soil) and longitudinal variations (from the end of the backwater area to the Three Gorges Dam) of phosphorus species. P fractions were analyzed using a Standards, Measurements, and Testing (SMT) protocol. Results showed that both TP and NaOH-P content in sediment exhibited a clear increasing trend from the end of the backwater area to the Three Gorges Dam, while HCl-P declined. Average of totals P, OP (organic P), HCl-extracted P (HCl-P, calcium-bond P), and NaOH-extracted P (NaOH-P, metal oxide-bound P) in sediment were (859.6±106.8), (224.6±113.9), (435.3±77.7), and (101.5±31.6) mg·kg-1, respectively. The concentration average of P species in sediment was higher than in WLFZ soil. In both sediment and soil, HCl-P was the main form of P, accounting for 51.3% and 58.2% of TP, while the ratio of NaOH-P to TP was 11.7% and 8.1%, respectively. P fractions with a higher coefficient of variation had greater spatial heterogeneity.

[Effects of Flooding and Drying on the Transformation of Soil Inorganic Phosphorus in the Water-Level-Fluctuating Zone of the Three Gorges Reservoir, China].

The implementation of the Three Gorges Project formed a water-level-fluctuating zone, and flooding and drying affects the soil properties and water quality of the Water-Level-Fluctuating Zone. The laboratory simulation or field sampling were conducted; however, the results cannot reflect the real conditions in practice. The effects of flooding and drying on the physical and chemical properties of soil and the transformation characteristics of inorganic phosphorus were studied in order to provide a theoretical reference for soil phosphorus loss and water eutrophication in water-level-fluctuating zone of the Three Gorges Reservoir. To investigate the conversion of soil phosphorus, plastic pots with soil were suspended at different depths (0, 2, 5, and 15 m) and submerged for 30, 60, and 180 d, and exposed for 180 d. The effects of submerged depth and time on the soil physical and chemical properties and inorganic phosphorus forms were studied. The results showed that soil pH, organic matter, total phosphorus, and available phosphorus decreased and then increased subsequently during the flooding period. After exposure for 180 d, soil pH, organic matter, and total phosphorus content decreased, while available phosphorus content increased. After flooding, the ratio of various forms of inorganic phosphorus to total phosphorus was Fe-P > Al-P > Ca8-P > Ca2-P. The content of Ca2-P and Ca8-P decreased at 0 m and 2 m and decreased at 5 m and 15 m and then increased with increased flooding time. After exposure for 180 days, the content of inorganic phosphorus increased significantly, and the content of inorganic phosphorus decreased as flooding depth increased. Al-P content increased with the flooding time, but there was no obvious change with flooding depth. The content of Fe-P did not change with the time and the depth of flooding.

[Fractions Transformation of Heavy Metals in Compound Contaminated Soil Treated with Biochar, Montmorillonite and Mixed Addition].

A compound contaminated soil sampled from Lingxiang City,Hunan Province,was used to investigate the effects of biochar (BC) and montmorillonite (MM) addition on heavy metals fractions.The addition amounts of BC and MM were 1%,2%,5%,respectively,and the mixture treatment was 1% BC+1% MM.BCR (European Community Bureau of Reference) sequential extraction method was used to assess the fractions of heavy metals in soil after incubation.The results indicated that adding BC alone significantly reduced the available contents of Pb,Cu and Cd.Among montmorillonite treatments,MM5% treatment decreased the weak acid extractable content of Cu,Pb,Zn,Cd by 27.6%,19.2%,25.6%,19.2%,respectively.BC+MM treatment worked well,decreased the weak acid extractable content of Cu,Pb,Zn,Cd by 15.8%,15.9%,13.1%,12.0%,and increased the residual content by 39.0%,110.1%,9.6%,62.5%,significantly reducing the mobility of the four elements.For the stabilization effect,MM treatment worked better than BC treatment,and a combination of two amendments worked the best.

[Remediation of Cd/Ni Contaminated Soil by Biochar and Oxalic Acid Activated Phosphate Rock].

Taking soil contaminated with a combination of Cd and Ni as the research objective, biochar, and oxalic acid activated phosphate rock (APR) were applied both together and separately for the remediation of this contaminated soil. The effects of different ratios of amendments on the remediation of Cd and Ni heavy metals in the soil and on inorganic nitrogen and microbial biomass nitrogen (MBN) in the soil were compared. The results show that an increasing amount of biochar and APR, increases the soil pH gradually and acid-extractable Cd and Ni are gradually transformed into reducible, oxidable and residual Cd and Ni, resulting in a reduction in Cd and Ni bioavailability. After 40 days incubation, the acid extractable Ni decreased by 37.04% with a 14.8% increase in residual Ni, and acid extractable Cd decreased 40.28% with a 35.20% increase in residual Cd with the amendment of C50P3 (Applying 50 g·kg-1 biochar and 3 g·kg-1 APR) when compared to C0P0 treatment (Applying nothing). Furthermore, the MBN content for C50P0 (Applying 50 g·kg-1 biochar only) and C0P3 (Applying 3 g·kg-1 APR only) increased by 1.5 and 1 times, respectively, while the content of ammonium nitrogen decreased by 12.5% and 6.4%, respectively and the content of nitrate nitrogen decreased by 11.6% and 10.2%, respectively. This comparison shows that the combined effect of the application of biochar and APR is superior to each respective separate treatment. A mixture of 50 g·kg-1 of biochar and 3g·kg-1 of APR (C50P3) demonstrates the best effect on the remediation of the Cd and Ni in soil. Furthermore, the application of amendments promoted the transformation of inorganic nitrogen into organic nitrogen.

[Effects of Phosphate Rock and Decomposed Rice Straw Application on Lead Immobilization in a Contaminated Soil].

The soils treated with phosphate rock (PR) and oxalic acid activated phosphate rock (APR) mixed with decomposed rice straw were incubated in different moisture conditions for 60 days to study the effect on the basic property of the soil and on the speciation variation of Pb. The results showed that all these three types of immobilizing materials increased the pH, the Olsen-P, the exchangeable Ca and the soil cation exchange capacity, and APR showed more obvious effect; the pH and the exchangeable Ca of soil in the flooding treatment were higher than those in normal water treatment (70%), but the Olsen-P of soil in normal water treatment was a little bit more. These materials reduced exchangeable Ph fraction, and converted it into unavailable fraction. But the APR was better than raw PR in immobilizing lead, and the exchangeable Pb fraction was reduced by 40.3% and 24.2%, compared with the control, respectively, and the immobilization effect was positively correlated with the dosage. Decomposed rice straw could transform the exchangeable Ph fraction in soil into organic-bound fraction, while the flooding treatment changed it into the Fe-Mn oxide-bound and residue fractions.

[Effects of low molecular weight organic acids on speciation of exogenous Cu in an acid soil].

In order to ascertain the effect of LMWOA (citric acid, tartaric acid, oxalic acid) on Cu-contaminated soils and to investigate the change of Cu species, a red soil derived from quartz sandstone deposit was added by Cu (copper) in the form of CuSO4 x 5H2O so as to simulate soil Cu pollution, keeping the additional Cu concentrations were 0, 100, 200, 400 mg x kg(-1) respectively. After 9 months, different LMWOA was also added into the simulated soil, keeping the additional LMWOAs in soil were 0, 5, 10, 20 mmol x kg(-1) respectively. After 2 weeks incubation, the modified sequential extraction method on BCR (European Communities Bureau of Reference) was used to evaluate the effects of these LMWOAs on the changes of copper forms in soil. The result showed that the percentage of weak acid dissolved Cu, the most effective form in the soil increased with three organic acids increase in quantity in the simulated polluted soil. And there was a good activation effect on Cu in the soil when organic acid added. Activation effects on Cu increased with concentration of citric acid increasing, but it showed a rise trend before they are basically remained unchanged in the case of tartaric acid and oxalic acid added in the soil. On the contrary, the state of the reduction of copper which was regarded as a complement for effective state decreased with the increased concentration of organic acid in the soil, especially with citric acid. When 20 mmol x kg(-1) oxalic acid and citric acid were added into the soil, the activation effect was the best; whereas for tartaric, the concentration was 10 mmol x kg(-1). In general, the effect on the changes of Cu forms in the soil is citric acid > tartaric acid > oxalic acid.

[Effect of phosphate and organic acid addition on passivation of simulated Pb contaminated soil and the stability of the product].

Organic acids can improve the phosphorus availability, influence the immobilization of heavy metals in soil, and has very complicated function in phosphorus activation and heavy metal passivation. This research took simulated Pb contaminated soil as material, phosphate and citric acid as remediation matter, adopted BCR continuous extraction, 0.01 mol · L(-1) CaCl2 and toxicity characteristic leaching procedure (TCLP) to evaluate the remediation effect. Besides, malic acid and NaNO3 were taken as desorption reagents to discuss the stability of the phosphorus-citric acid-Pb system. The results showed that: in the absence of citric acid, the amount of acid extracted Pb decreased along with the increase of P concentration; when the P concentration was 100 and 400 mg · kg(-1), acid extractable Pb increased with the increasing of citric acid concentration. However, residual Pb changed in the opposite direction from acid extractable Pb. The phenomenon showed that P improved the bioavailability of Pb, while citric acid had the opposite effect. With a certain organic acid concentration, extractable Pb contents extracted by 0.01 mol · L(-1) CaCl2 and TCLP both decreased with the increasing P concentration, therefore, P had immobilization effect on Pb in contaminated soil. But at a fixed P concentration, extractable Pb contents by 0.01 mol · L(-1) CaCl2 and TCLP changed in the opposite trend with the increasing citric acid concentration. The desorption rate of Pb in soil increased with the increasing malic acid concentration, the decreasing pH and the increasing ionic strength. The desorption extent of Pb in soil with P only was lower than that with both P and citric acid. But the stability of Pb passivated by the former was higher.

[Distribution of Bt protein in transgenic cotton soils].

A pot experiment with red soil, yellow brown soil, and yellow cinnamon soil was conducted to detect the Bt protein content in rhizosphere and non-rhizosphere soils at different growth stages of transgenic Bt cotton and common cotton by using enzyme linked immunosorbent assay (ELISA). With the planting of transgenic Bt cotton, the Bt protein content in rhizosphere soil was significantly higher than that in non-rhizosphere soil; while in common cotton soils, there was no significant difference in the Bt protein content between rhizosphere soil and non-rhizosphere soil. At bud stage of transgenic Bt cotton, the Bt protein content in rhizosphere soil was in the order of yellow cinnamon soil > yellow brown soil > red soil, being 144% 121%, and 238% of that in common cotton rhizosphere soil; at florescence stage of transgenic Bt cotton, the Bt protein content in rhizosphere soil was in the order of yellow brown soil > yellow cinnamon soil > red soil, being 156% , 116% , and 197% of that in common cotton rhizosphere soil, respectively. Regardless of planting Bt cotton or common cotton, the Bt protein content in rhizosphere and non-rhizosphere soils had an initial increase with the growth of cotton, peaked at florescence stage, and then decreased. Throughout the whole cotton growth period, the Bt protein content in transgenic Bt cotton rhizosphere soil was higher than that in Bt cotton non-rhizosphere soil, and also, higher than that in common cotton rhizosphere soil, indicating that transgenic Bt cotton could release its Bt protein to rhizosphere soil.

Mercury in soils of three agricultural experimental stations with long-term fertilization in China.

Mercury (Hg) in the agricultural ecosystem is a global concern because of its high potential toxicity. The objectives of this study were to determine the concentration and distribution of Hg in soils from three long-term experimental stations, i.e., Taoyuan (TY) and Qiyang (QY) in Hunan Province and Fengqiu (FQ) in Henan Province of China, and thus to assess the possible food and health risk of long-term applications of fertilizers. Soil samples at each site were collected from different fertilization plots and also from soil profiles with depths 0-100 cm. There were significant differences in soil Hg concentrations in 0-20 cm (A) or 20-40 cm (B) horizon among the three experimental stations. QY station showed significantly higher Hg concentrations than TY and FQ stations. However, there were no significant differences in soil Hg concentrations between A and B horizons at each station. It was concluded that the soil Hg concentrations at the three sites were mainly controlled by the parent materials. Moreover, chemical fertilizer, especially phosphorous fertilizers, could influence the soil Hg concentrations to some extent at the station with lower soil Hg concentrations, for example, at TY station. There were minimal amounts of Hg resulting from applications of the other chemical fertilizers and organic manure, and thus the fertilization had very low risk to the food security of the agro-ecosystems in the terms of Hg inputs and contamination.