[Enrichment Characteristics of Heavy Metals and Health Risk in Different Vegetables].

The health risk caused by heavy metal accumulation in vegetables is of great concern. In this study, a database of heavy metal content in a vegetable-soil system in China was constructed through literature review and field sample collection. A systematic analysis of seven heavy metal contents in edible parts of vegetables and their bioaccumulation capacity among different vegetables was also performed. Additionally, the non-carcinogenic health risks of four types vegetables were assessed by using Monte Carlo simulation (MCS). The mean values of Cd, As, Pb, Cr, Hg, Cu, and Zn in the edible parts of the vegetables were 0.093, 0.024, 0.137, 0.118, 0.007, 0.622, and 3.272 mg·kg-1, and the exceedance rates of the five toxic elements were:Pb (18.5%)>Cd (12.9%)>Hg (11.5%)>Cr (4.03%)>As (0.21%). Leafy vegetables showed high Cd enrichment, and root vegetables showed high Pb enrichment, with mean bioconcentration factors of 0.264 and 0.262, respectively. Generally, legumes vegetables and solanaceous vegetables showed lower bioaccumulation for heavy metals. The health risk results indicated that the non-carcinogenic risk for single elements of vegetable intake was within the acceptable range, with the health risk for children being higher than that for adults. The mean non-carcinogenic risk for single elements were:Pb>Hg>Cd>As>Cr. The multi-element combined non-carcinogenic risks of four types vegetables were:leafy vegetables>root vegetables>legume vegetables>solanaceous vegetables. Planting lower-heavy metal bioaccumulation vegetables in heavy metal-contaminated farmland is an effective method to minimize the health risk.

The risks of sulfur addition on cadmium accumulation in paddy rice under different water-management conditions.

Recently, the application of sulfur (S) has been recommended to control the accumulation of cadmium (Cd) in rice in contaminated paddy soil. However, the effects of exogenous S on Cd transfer in paddy rice systems under different water-management practices have not been systematically investigated. Pot experiments were performed to monitor the composition of soil pore water and the Cd accumulation in iron plaque and rice tissue were compared under different S (0 and 200 mg/kg Na2SO4) and water (continuous and discontinuous flooding) treatments. Sulfur application significantly increased Cd concentrations in soil pore water under discontinuous flooding conditions, but slightly reduced them under continuous flooding. Moreover, the oxidation/reduction potential (Eh) was the most critical factor that affected the Cd levels. When the Eh exceeded -42.5 mV, S became the second critical factor, and excessive S application promoted Cd dissolution. In addition, S addition elevated the Cd levels in iron plaque and reduced the Cd transfer from the iron plaque to rice roots. In rice, S addition inhibited Cd transfer from the rice roots to the straw; thus, more Cd was stored in the rice roots. Nevertheless, additional S application increased the Cd content in the rice grains by 72% under discontinuous flooding, although this effect was mitigated by continued flooding. Under simulated practical water management conditions, S addition increased the risk of Cd contamination in rice, suggesting that S application should be reconsidered as a paddy fertilization strategy.

Cadmium accumulation in wheat and maize grains from China: Interaction of soil properties, novel enrichment models and soil thresholds.

The cadmium (Cd) activity in soil has been widely studied. However, the interactive effects of soil properties (e.g. soil pH, CEC, and SOM) on Cd transfer from soil to grain are generally overlooked. In total 325 datasets including soil pH, CEC, SOM, and soil Cd content were used in this study. The descriptive statistics indicated that Cd content in wheat and maize soils ranged from 0.05 to 10.31 mg/kg and 0.02-13.68 mg/kg, with mean values of 0.87 and 1.14 mg/kg, respectively. Cd contents in wheat and maize grains were 0.01-1.36 mg/kg and 0.001-1.08 mg/kg with average values of 0.15 and 0.10 mg/kg, respectively. The results of SEM demonstrated that the interactive effects of soil properties contributed more to Cd transfer from soil to wheat grain than the soil Cd content. Subsequently, CITs-MLR indicated that the critical factors, including soil pH and total soil Cd content, could mask the contribution of other soil properties on Cd accumulation in grain; soil CEC may prevent Cd from leaching and therefore improve grain Cd level of wheat especially at acidic soil condition. The result of derived Cd thresholds revealed that current Cd thresholds are not completely suitable to wheat and maize grain at different soil conditions. This study provides a new model for further investigation on relationships between soil properties, soil Cd content and grain Cd level.

Arsenic transfer and accumulation in the soil-rice system with sulfur application and different water managements.

Rice (Oryza sativa L.) can readily accumulate arsenic (As), owing to its high capacity to take up As and special flooding cultivation, which poses a potential risk to human health. Although sulfur (S) can influence As accumulation in rice, its behavior in the rice-soil system is not clear under practical water management conditions. In this study, the transfer and soil solution dynamics of As in the whole soil-rice system was investigated under continuous flooding or intermittent drainage, either with S addition or not. The results showed that intermittent drainage effectively reduced As concentration in soil solution regardless of S conditions, and it only reduced As content in rice without S addition. Exogenous S decreased As concentration in soil solution and rice, except in the roots of mature rice, under continuous flooding. Sulfur addition significantly decreased the total As and As(III) contents in rice grains, by 62% and 79% under continuous flooding and by 50% and 76% under intermittent drainage, respectively. Moreover, the addition of S resulted in impaired iron plaque and inhibited binding of As. Sulfur also reduced As translocation from rice roots to shoots. Therefore, S could alleviate the crisis of excessive accumulation of As in rice grains caused by flooded environment through various adjustments to the soil-rice system.

Dietary supplementation with selenium-enriched earthworm powder improves antioxidative ability and immunity of laying hens.

Selenium (Se) has been recognized as an essential dietary nutrient for decades, and organic Se sources rather than inorganic ones are increasingly advocated as Se supplements. Earthworms have been studied as a feed additive and animal protein source for many yr. The aim of this study was to evaluate the effect of Se-enriched earthworm powder (SEP) on the antioxidative ability and immunity of laying hens. A total of 120 27-wk-old laying hens were randomly divided into 4 groups (30 hens per group). Laying hens were fed diets supplemented with SEP having 0, 0.5, or 1 mg/kg of Se or with earthworm powder alone. After 5 wk of supplementation, serum from the hens was tested for nutritional components (protein, globulin, albumin, triglycerides, total cholesterol, and glucose), antioxidative properties (glutathione peroxidase, superoxide dismutase, catalase, and nitric oxide), and immune responses (lysozymes, immunoglobulin G, IL-2, and interferon gamma). We found that SEP with 1.0 mg/kg of Se upregulated the hens' total protein, albumin, glutathione peroxidase, superoxide dismutase, IgG, and IL-2 and downregulated triglycerides, total cholesterol, glucose, and nitric oxide. These results indicate that SEP improves antioxidative levels and immune function of laying hens, indicating potential benefit from use of SEP as a feed additive in the poultry industry.

[Accumulation and Translocation of Cd in Brassica rapa Under the Influence of Selenium].

Cadmium (Cd) is a highly toxic heavy metal. Brassica rapa (pak choi) is a vastly common vegetable, which readily accumulates Cd. Given the current conditions of Cd contamination in domestic soil, it is important to reduce Cd accumulation in the edible part of pak choi. Research has shown that selenium (Se) can regulate Cd uptake by plants. Cd accumulation (three cultivars) and Cd uptake kinetics in pak choi were investigated under hydroponic conditions. Results showed that the three levels of selenite significantly reduced Cd content in the Hangzhouyoudonger shoot by 50%, while the levels in Suzhouqinggen and Shanghaiqing shoots were not significantly decreased with elevated levels of selenite. Selenite reduces the Cd translocation factors, and higher levels had more obvious effects; 50 µmol·L-1 of selenite significantly decreased the factors by 50% in Hangzhouyoudonger and Suzhouqinggen shoots. Selenite also increased iron (Fe) and manganese (Mn) contents in pak choi, especially in the Hangzhouyoudonger shoot, where 50 µmol·L-1 increased the Fe content by approximately 50%. In the uptake kinetics of Cd, both selenite and selenate significantly increased Cd uptake rates and Vmax by over 100%. Therefore, Se could reduce Cd accumulation in pak choi. This also depended on the tested cultivar. Therefore, reduction effects of Se on the Cd content mainly stemmed from the alteration of Cd translocation in pak choi instead of the uptake competition between Cd and Se.

[Heavy Metal Contents in Animal Manure in China and the Related Soil Accumulation Risks].

The environmental risks posed by heavy metals (HMs) in animal manure are increasing because of the use of trace metals as additives in feedstuffs. Manure samples were collected, and published literature was reviewed in this study to systematically analyze the HMs content in animal manure and compare the results to different sources of animal manures. Results show that the distribution of HMs content in animal manure was skewed. The ranges were between not detected (ND)-147 mg·kg-1 for Cd, ND-1919 mg·kg-1 for Pb, 0.003-2278 mg·kg-1 for Cr, ND-978 mg·kg-1 for As, ND-103 mg·kg-1 for Hg, ND-1747 mg·kg-1 for Cu, ND-11547 mg·kg-1 for Zn, and 1.22-1140 mg·kg-1 for Ni. The means (medians) of those elements were 2.31(0.72) mg·kg-1, 13.5(8.96) mg·kg-1, 36.3(12.0) mg·kg-1, 14.0(3.52) mg·kg-1, 0.97(0.07) mg·kg-1, 282(115) mg·kg-1, 656(366) mg·kg-1, and 21.8 (13.1) mg·kg-1 for Cd, Pb, Cr, As, Hg, Cu, Zn, and Ni, respectively. Means were significantly higher (1-13 times) than the medians. According to maximum limits of Cd, Pb, Cr, As, and Hg for organic fertilizers NY 525-2012, about 12.3% (for Cd), 2.58% (for Pb), 2.76% (for Cr), 20.6% (for As), and 3.69% (for Hg) of the data were above the limits. According to the composting regulations of Germany, about 53.9% (for Cu), 45.7% (for Zn), and 0.59% (for Ni) exceeded the maximum limits. The heavy metal contents in animal manure of different regions differs significantly. As and Cd contents in animal manure in the Shandong Province tend to be higher with their average values at 1.7 times and 10.1 times of the mean contents for national scale, respectively; the heavy metal contents in eastern China tend to be higher. Cd and As contents in animal manure tend to be higher in Northeast and Eastern China, while Cu and Zn contents were higher in Eastern and South China. After comparing HMs content in different sources of manures, we found that Cd, As, Hg, Cu, Zn, and Ni mean contents in pig manure were 1.0-3.0 times, 1.8-6.8 times, 1.1-15.8 times, 4.9-17.5 times, 2.7-12.0 times, and 1.7-2.1 times that of cattle manure, sheep manure, and poultry manure. The Pb content in poultry manure was the highest, with the mean being 2.8, 2.5, and 2.2 times higher than pig manure, cattle manure, and sheep manure, respectively. When recycling animal manure into the crop field, the accumulation rates for Cd were under 0.02 mg·(kg·a)-1 in over 90% of the circumstances and the accumulation rates for Pb were all below 0.15 mg·(kg·a)-1. When applying poultry manure, Cr in soil is easily accumulated with the maximum accumulation rate of 0.28 mg·(kg·a)-1.

[Toxicity of Chromium to Root Growth of Barley as Affected by Chromium Speciation and Soil Properties].

Tri-and hexavalent chromium have different chemical properties, and their levels of toxicity to plants are different. However, there is no limit set by the soil environmental quality risk control standard for Cr(Ⅲ) or Cr(Ⅵ). Therefore, studying the ecological toxicity of Cr has important implications for protecting the environment. Based on the dynamics of the Cr(Ⅲ) and Cr(Ⅵ) levels in soil solution collected from eight soils, the toxicity thresholds of the two Cr forms to barley roots were investigated through model calculation and correlation analysis under different soil properties. The results showed that both Cr forms and the soil properties had significant effects on the root length of barley. The effective concentrations of Cr(Ⅲ) added to the soils that led to 10% inhibition (EC10), 50% inhibition (EC50), and no-observed-effect concentrations (NOEC) were significantly higher than those of Cr(Ⅵ). The EC50 of Cr(Ⅲ) ranged from 298.8 to 2014.1 mg·kg-1 (6.7-fold variation); the EC50 of Cr(Ⅵ) ranged from 8.0 to 126.6 mg·kg-1 (15.8-fold variation). Under the same soil conditions, the EC50 of Cr(Ⅲ) was 2.8 to 101.7 times higher than that of Cr(Ⅵ), suggesting the higher phytotoxicity of Cr(Ⅵ) than Cr(Ⅲ). Correlation analysis showed that the pH and soil organic matter were the main factors that influenced the Cr toxicity thresholds, as indicated by the root length of barley. The concentration of chromium in the soil solution was below the detection limit of the TAS-990 when Cr(Ⅲ) was applied at 1280 mg·kg-1 (or less) to soils, whereas for Cr(Ⅵ), the level was 40 mg·kg-1 (or less). Cr(Ⅲ) adsorption to the soil was significantly stronger than that of Cr(Ⅵ). The toxicity of Cr(Ⅵ) was significantly higher than that of Cr(Ⅲ), which was also influenced by soil properties.

Accumulation of potentially toxic elements in agricultural soil and scenario analysis of cadmium inputs by fertilization: A case study in Quzhou county.

Fertilizer application has greatly increased crop yield, however impurities in mineral or organic fertilizers, such as heavy metals, are being added to agricultural soils, which would pose a high risk for soil and crop production. 115 soil samples were collected from Quzhou, a typical agricultural county in the North China Plain, to investigate the total content of cadmium (Cd), arsenic (As), lead (Pb), nickel (Ni), copper (Cu), zinc (Zn) and chromium (Cr) in soils. The contamination levels and source apportionment of studied elements were explored by the pollution indices, multivariate statistical approaches and geostatistical analysis. The ranges of Cd, As, Pb, Ni, Cu, Zn and Cr were between 0.08 and 0.35, 5.34-15.9, 7.34-38.9, 12.9-61.3, 7.80-27.0, 31.4-154, and 17.0-50.5 mg/kg and with the mean values 0.16, 9.20, 16.0, 24.7, 17.6, 61.1, and 29.5 mg/kg, respectively. The studied area was slightly polluted mainly by Cd, and higher pollution was found in soils under vegetable crops. The application of mineral phosphate fertilizer and livestock manure were the main source of Cd and Zn, and other elements (As, Pb, Ni and Cu) might originate from soil parent materials. Scenario analyses were performed using the R programming language, based on the cadmium contents in mineral phosphate fertilizers and livestock manures. The results showed that the long-term application of phosphate fertilizers would lead to some Cd enrichment in soil without risk of substantial pollution. Compared to pure mineral fertilizers, the long-term application of blended fertilizers (30% livestock manures and 70% phosphate fertilizers) or livestock manures would incur a higher Cd pollution risk within a short period, with a maximum probability of Cd risk of 55.21%. Mitigation measurements and scientific agronomic practices should be developed to minimize the risk of potential toxic elements in agricultural soil.

[Absorption and Transportation of Selenium Nanoparticles in Wheat and Rice].

Hydroponics experiments were carried out to study the effects of different sizes of selenium nanoparticles (SeNPs) and different pH on the absorption and transportation of Se by wheat (Triticum aestivum L.) and rice (Oryza sativa L.). The results showed that SeNPs with different sizes (50, 100, and 150 nm) had various characteristics with respect to absorption and translocation in wheat and rice. There was no significant difference in the uptake of SeNPs with different sizes by wheat roots after 24 h and 72 h; however, the highest Se content in wheat shoots was (1.89±0.47) µg·g-1 dry weight (DW) and (5.18±1.51) µg·g-1 DW under the 50 nm SeNPs treatment after 24 h and 72 h, respectively. Moreover, the transfer factor for Se in wheat under the 50 nm SeNPs treatment was 2.38 times higher than that of the 100 nm and 150 nm treatments. The Se content of rice roots treated for 24 h with the 50 nm SeNPs increased by 11.18% and 41.81% compared to those treated with the 100 nm and 150 nm SeNPs, respectively. There were, however, no significant differences in Se content between all of the SeNPs treatments after 72 h. The Se content of rice shoots and the Se transfer factor both reached the maximum when 50 nm SeNPs were applied. In addition, Se absorption by plants was also affected by pH. Specifically, the amount of Se absorbed by wheat roots treated with SeNPs was the greatest at a pH of 6 after 24 h, which was 89.47% higher than wheat treated with selenite. Furthermore, the highest Se transfer factor occurred at a pH of 4 in wheat. The uptake of SeNPs in rice was markedly lower than that of selenite at low pH values (pH=3.5 and 5.5) and SeNPs was more readily transported at a pH of 3.5. These results demonstrate that SeNPs could be taken up by wheat and rice and that it could be transferred more easily as small particle size (50 nm) than the larger ones (100 nm and 150 nm) at low pH values (pH 3.5).

Selenium Uptake and Biotransformation in Brassica rapa Supplied with Selenite and Selenate: A Hydroponic Work with HPLC Speciation and RNA-Sequencing.

Vegetables are an ideal source of human Se intake; it is important to understand selenium (Se) speciation in plants due to the distinct biological functions of selenocompounds. In this hydroponic study, the accumulation and assimilation of selenite and selenate in pak choi (Brassica rapa), a vastly consumed vegetable, were investigated at 1-168 h with HPLC speciation and RNA-sequencing. The results showed that the Se content in shoots and Se translocation factors with selenate addition were at least 10.81 and 11.62 times, respectively, higher than those with selenite addition. Selenite and selenate up-regulated the expression of SULT1;1 and PHT1;2 in roots by over 240% and 400%, respectively. Selenite addition always led to higher proportions of seleno-amino acids, while SeO42- was dominant under selenate addition (>49% of all Se species in shoots). However, in roots, SeO42- proportions declined substantially by 51% with a significant increase of selenomethionine proportions (63%) from 1 to 168 h. Moreover, with enhanced transcript of methionine gamma-lyase (60% of up-regulation compared to the control) plus high levels of methylselenium in shoots (approximately 70% of all Se species), almost 40% of Se was lost during the exposure under the selenite treatment. This work provides evidence that pak choi can rapidly transform selenite to methylselenium, and it is promising to use the plant for Se biofortification.

Difference between selenite and selenate in selenium transformation and the regulation of cadmium accumulation in Brassica chinensis.

Se can regulate Cd accumulation and translocation in plants; however, such effects can be controversial because of the differences in plant species and Se species. In this study, pak choi was cultured under hydroponic conditions, and the effects of selenite and selenate on Cd accumulation were investigated in the edible parts of this vegetable. The results showed gradual improvements in the effects of the two Se species on the Cd content in pak choi shoots at the four assessed growing stages. Selenite did not lead to significant changes in Cd accumulation in the shoots until day 40, when it significantly reduced the accumulation by 34%. Selenate was always found to increase the Cd content in the shoots, and the differences on days 19 and 40 were 16% and 45%, respectively, compared with those of the Cd (only) treatment. Accordingly, selenate invariably enhanced Cd translocation from the roots to the shoots, whereas selenite insignificantly reduced the translocation only on day 40. Generally, selenomethionine (SeMet) accounted for much larger proportions in selenite-treated plants, while SeO42- was the dominant Se species in selenate-treated plants. However, under both Se treatments, the SeMet proportion increased substantially from day 19 to day 40 when that of SeO42- exhibited a drastic decrease; therefore, the relative proportion of seleno-amino acids to SeO42- may be the key factor for the regulation of Cd accumulation in pak choi via treatment with selenite and selenate at the different growing stages.

[Lead Uptake and Accumulation in Rice (Oryza sativa L.) with Water Management and Selenite Fertilization].

Lead (Pb) accumulation in rice grains has been identified as a potential threat to human health. Our study investigated the effects of varied rates of selenite fertilization (0, 0.5 and 1.0 mg·kg-1) on the dynamics of Pb in soil solutions, and its uptake and translocation by rice under different water management scenarios (aerobic and flooded) in pot experiments. Plants were harvested at seedling stage and at maturity to determine the Pb contents, and soil solutions were extracted during the growing season to monitor the Pb dynamics. Results showed that flooding the soil significantly increased Pb concentrations in DCB extracts and rice roots both at seedling stage and maturity. Root Pb contents in flooded treatments were 4.2-8.5 and 1.4-1.5 times higher than those under aerobic conditions at rice seedling stage and maturity. Flooding also decreased the percentage of Pb in rice shoots. The Pb content in soil solutions, rice seedlings, rice roots and stems at maturity were significantly decreased by selenite additions. Relative to the control treatment, selenite additions decreased the rice root Pb contents by 5.4%-24.3% and 2.7%-61.7% under flooding and aerobic conditions at seedling stage, respectively; while decreased Pb in rice root by 56.1%-64.1% and 53.8%-63.2% respectively, at maturity. No significant differences existed in grain Pb levels among the treatments. Results demonstrated that water management regimes and selenite additions affected Pb uptake by rice roots significantly, but had no significant influence on Pb accumulation in rice grains.

[Application of ICP-mS and AFS to detecting heavy metals in phosphorus fertilizers].

In order to investigate heavy metals in phosphorus fertilizers in China, 159 samples of phosphorus fertilizers including imported fertilizers and domestic fertilizers were collected from fertilizer markets, and the contents of heavy metals were determined by ICP-MS and AFS after microwave digestion. The results showed that the phosphorous fertilizers contained certain amount of heavy metals, and there was great variability in the contents of heavy metals. The mean contents of Cd, Cu, Zn, Cr, Pb, Ni, As and Hg were 0. 77, 35.6, 102.7, 24. 1, 16.6, 15.4, 19.4 and 0. 08 mg kg-1 fertilizer, respectively; based on the calculation of P2O5, the mean contents of above heavy metals were 4. 48, 258. 4, 767. 4, 190. 0, 151.3, 134. 5, 155. 8 and 8. 79 mg kg-1 P2 O5, respectively. The contents of heavy metals Cd, Cr, Pb, As and Hg in the tested samples accord with the ecological index of arsenic, cadmium, lead, chromium and mercury for fertilizers (GB/T 23349-2009), with the exception of Cd in one imported sample of diammonium phosphate and As in one sample of mono-ammonium phosphate. Analyzing the contents of heavy metals in imported fertilizers, the Cd contents in imported fertilizers was ranged from 0. 02 to 27. 2 mg kg-1 fertilizer, the mean and median Cd contents in imported fertilizers were 3. 20 and 0. 41 mg kg-1 fertilizer, respectively. And the Cu, Cr and Hg contents in the imported fertilizers were higher than that of domestic fertilizers, the mean contents of Cu, Cr and Hg in imported fertilizers were 39. 4, 26. 6 and 0. 47 mg kg-1 fertilizer, respectively.

Application of rhizosphere interaction of hyperaccumulator Noccaea caerulescens to remediate cadmium-contaminated agricultural soil.

There is an urgent requirement for selecting appropriate technologies to solve food safety problems due to soil contamination. In this study, the hyperaccumulator Noccaea caerulescens and a high Cd accumulator pakchoi cultivar (Brassica rapa L. spp. Chinenesis cv.) were grown in a moderately Cd-contaminated soil with three planting systems (monocrop, inter-crop, and crop-rotation) and three growing durations (25, 50, and 75 days) to study the role of rhizosphere interaction of both species on the uptake of Cd. The Cd accumulations in the shoot of pakchoi were significantly reduced in the inter-crop treatment, also the decreased percentage increased with rhizosphere interaction between the two species. In the inter-crop systems of 75 days, the Cd concentration and amount in the shoot of pakchoi represented 54% and 83% reduction, respectively, while the total depletion of Cd decreased by approximate 19%. Although the Cd concentration and amount in the shoot of pakchoi were significantly reduced by 52% and 44%, respectively, in the crop-rotation treatment, the decreased percentage were markedly lower than in the inter-crop treatment. Therefore, the rhizosphere interaction of hyperaccumulator with non-hyperaccumulator may reduce the risk of vegetable contamination during making full use of or remediating the contaminated soil.

[Uptake and translocation of selenate or selenite by wheat and rice seedlings].

Solution culture experiments were carried out to study the uptake and translocation of selenate (Na2SeO4) or selenite (Na2SeO3) by wheat and rice seedlings. When supplied with Na2SeO4 in nutrient solution, the concentrations of selenium (Se) in normal shoots and roots of rice were 30.3 mg x kg(-1) and 39.0 mg x kg(-1) respectively, and the absorbed Se was quickly translocated to shoots accounting for 80% of the total uptake. Se concentrations in wheat shoots and roots were 1.76 mg x kg(-1) and 6.99 mg x kg(-1) respectively, accounting for 62% in shoots. However, when supplied with Na2SeO3, Se concentrations in shoots and roots of rice were 4.40 mg x kg(-1) and 230 mg x kg(-1) respectively, 1.24 mg x kg(-1) and 88.3 mg x kg(-1) in shoots and roots of wheat respectively, and only 8.2% was transferred to shoots. The influence of phosphorus (P) starvation on Se uptake was different for rice and wheat seedlings. Comparing to normal plants, the Se concentrations in the shoots and roots of rice under P starvation condition were decreased, however increased for wheat. In Na2SeO3 uptake kinetics, K(m) of wheat seedlings was 8.7 folds of that of rice, and the affinity of wheat root to selenite was much weaker than that of rice. The Se uptake rate of wheat (V(max)) was 14% lower than that of rice. The uptake and translocation mechanisms of selenate and selenite by rice and wheat seedlings were revealed. And the results demonstrate that the absorbed selenate is quickly translocated to shoot and selenite is mainly accumulated in root. These results provide basic information for biofortification of crops with Se.

Selenium speciation in soil and rice: influence of water management and Se fertilization.

Rice (Oryza sativa) is the staple food for half of the world's population, but the selenium (Se) concentrations in rice grain are low in many rice-growing regions. This study investigated the effects of water management on the Se speciation dynamics in the soil solution and Se uptake and speciation in rice in a pot experiment. A control containing no Se or 0.5 mg kg(-1) of soil of selenite or selenate was added to the soil, and plants were grown under aerobic or flooded conditions. Flooding soil increased soluble Se concentration when no Se or selenite was added to the soil, but decreased it markedly when selenate was added. Selenate was the main species in the +selenate treatment, whereas selenite and selenomethionine selenium oxide were detected in the flooded soil solutions of the control and +selenite treatments. Grain Se concentration was 49% higher in the flooded than in the aerobic treatments without Se addition. In contrast, when selenate or selenite was added, the aerobically grown rice contained 25- and 2-fold, respectively, more Se in grain than the anaerobically grown rice. Analysis of Se in rice grain using enzymatic hydrolysis followed by HPLC-ICP-MS and in situ X-ray absorption near-edge structure (XANES) showed selenomethionine to be the predominant Se species. The study showed that selenate addition to aerobic soil was the most effective way to increase Se concentration in rice grain.

[Effect of the soil bulk density on the root morphology and cadmium uptake by Thlaspi caerulescens grown on Cd-contaminated soil].

A pot experiment was conducted using a soil contaminated with 2.12 mg x kg(-1) Cd to study the effect of the variety of the soil bulk density on the Zn/Cd uptake by the hyperaccumulator Thlaspi caerulescens and the removal of Cd and Zn from the soil. The contaminated soil received 0, 0.1%, 2% of soil conditioner and the plants were harvested after 100 days. The results showed that soil amendment with the soil conditioner (EB. a) significantly decreased the soil bulk density. Compared to the control, the bulk density value decreased from 1.27 g x cm(-3) to 1.09 g x cm(-3) at the level of 2% soil conditioner. The increased biomass of shoot and root was observed at the treatment of EB. a amendment. The total root length, root hair length and root/shoot ratio were all significantly enhanced (p < 0.05) by the addition of EB. a. The significant positive relationships between the total root length and the removed Cd/Zn from soil were determined (p < 0.05). Compared with the control,the total root length was increased by 2.6 folds at the addition of 2% soil conditioner; the Cd concentration and removal of Cd from soil were significantly elevated by 20% and 30% respectively. The phytoextraction efficiency of Cd was improved from 15% to 19%. However, the Zn concentration and removal of Zn were not significantly elevated by the addition of soil conditioner. The present results demonstrate that the decreased soil bulk density may improve the root system of T. caerulescens and enhance the phytoextraction efficiency of Cd.

Phytotoxicity and bioavailability of cobalt to plants in a range of soils.

Risk assessments of existing substances, including metals, in the environment are being carried in the European Union, which require estimation of the predicted no-effect concentration (PNEC) derived from biological toxicity assays. Few toxicity data exist for Co and higher plants, and the influence of soil properties on Co toxicity also needs to be evaluated systematically. We investigated phytotoxicity and bioavailability of Co to barley (Hordeum vulgare L.), oilseed rape (OSR; Brassica napus L.) and tomato (Lycopersicon esculentum L.) shoot growth in ten soils varying widely in soil properties using a standardised shoot biomass assay. The effective concentration of added Co causing 50% inhibition (EC(50)) ranged from 40 to 1708 mg kg(-1), from 7 to 966 mg kg(-1) and from 7 to 733 mg kg(-1) for the barley, OSR and tomato test, respectively, representing 43-, 138-, and 105-fold variation among soils. The EC(50) based on the Co concentration in soil solution varied less among soils (4-15 fold) than that based on the total added Co, suggesting that solubility of Co is a key factor influencing its toxicity to plants. Regressions of soil Co toxicity threshold values with various soil properties, showed that exchangeable calcium (Ca) concentration was the most consistent single predictor. For risk assessment, we suggest that Co toxicity threshold values for plants be normalised using the soil exchangeable Ca.

Accumulation of cadmium in the edible parts of six vegetable species grown in Cd-contaminated soils.

Species difference in Cd accumulation is important for selection of agronomic technologies aimed at producing low-Cd vegetables. Six vegetable species (Chinese leek, pakchoi, carrot, radish, tomato and cucumber) were grown in pot and field experiments to study the accumulation of Cd under different conditions. In the field trial (Cd 2.55 mg kg(-1)), Cd concentrations in the edible parts ranged from 0.01 to 0.1 mg kg(-1) and were below the permissible limits (0.2 mg kg(-1) for pakchoi and leek; 0.1 mg kg(-1) for carrot and radish; 0.05 mg kg(-1) for cucumber and tomato), but exceeded the limit in pakchoi, Chinese leek, carrot and tomato at a Cd addition level of 2.0 mg kg(-1). Plant Cd concentrations increased linearly with the increasing concentration of Cd added to the soil, with the slope of the regression lines varying by 28-fold among the six species. The bioconcentration factor (BCF) varied substantially, and was much higher in the pot experiment than in the field trial. It is concluded that the vegetable species differed markedly in the Cd accumulation and species performed consistently under different growth conditions.