Effects of steel slag amendments on accumulation of cadmium and arsenic by rice (Oryza sativa) in a historically contaminated paddy field

Environmental Science and Pollution Research - Paddy soil contamination by cadmium (Cd) and arsenic (As) is a great concern. Field experiments were conducted to study the effects of steel slag (SS,...     

Dual-continuum analysis of a cadmium tracer field experiment

Cadmium penetration into a sandy-loam soil during the field ponded infiltration at Kralovska luka site in Southern Slovakia was observed in a controlled experiment. Adsorption of cadmium was examined using the radioactive tracer techniques in laboratory batch tests. Quite deep (115m)Cd penetration during the field experiment (65 cm beneath the soil surface) gives evidence of the particle-facilitated transport of cadmium through preferential pathways. More than 40% of the applied cadmium moved deeper than 10 cm. The field experiment was analyzed using both conventional single-continuum approach (based on Richards' equation for water flow and advection-dispersion equation for Cd transport) and dual-continuum approach. The latter approach allowed us to simulate more adequately the observed movement of cadmium.     

Remediation mechanisms of mercapto-grafted palygorskite for cadmium pollutant in paddy soil

The immobilization agent was the key factor that determined the success of remediation of heavy metal polluted soil. In this study, mercapto-grafted palygorskite (MP) as a novel and efficient immobilization agent was utilized for the remediation of Cd-polluted paddy soil in pot trials, and the remediation mechanisms were investigated in the aspect of soil chemistry and plant physiology with different rice cultivars as model plants. Mercapto-grafted palygorskite at applied doses of 0.1–0.3% could reduce Cd contents of brown rice and straws of different cultivars significantly. Both reduced DTPA-extractable Cd contents in rhizosphere and non-rhizosphere soil and decreasing Cd contents in iron plaques on rice root surfaces confirmed that MP was an efficient immobilization agent for Cd pollutant in paddy soil. In the aspect of soil chemistry, the pH values of rhizosphere and non-rhizosphere soils had no statistical changes in the MP treatment groups, but their zeta potentials decreased obviously, indicating that MP could enhance the fixation or sorption of Cd on soil compositions. In the aspect of antioxidant system, MP could increase POD activity of rice roots significantly to alleviate the stress of Cd to roots, and resulted in the decrease of T-AOC, SOD, and CAT activities of rice roots of the selected cultivars. MP had no inhabitation or enhancement effects on TSH of rice roots but enhance the contents of MTs and NPT to binding Cd to complete detoxification process. MP as a novel and efficient immobilization agent could complete the remediation effects through soil chemistry and plant physiological mechanisms.

     

Feasibility of phosphate fertilizer to immobilize cadmium in a field

To reduce effectively cadmium (Cd) phytoextractability by phosphate fertilizer in Cd contaminated soil, fused and superphosphate (FSP) was applied at the rate of 0, 33.5 (recommendation level), 167.5, and 335 kg P ha⁻¹ for radish (Raphanus sativa L.). Unlike from what we expected, soil Cd extractability and Cd concentration in radish increased with increasing FSP application in the field. To determine the effect of FSP on Cd immobilization, FSP was mixed with the selected soil at the rate of 0, 200, 400, 800, and 1600 mg P kg⁻¹ and then incubated for 8 weeks. As observed in the field study, NH₄OAc extractable Cd concentration increased slightly with FSP addition up to 400 mg P kg⁻¹ and thereafter dramatically decreased upon increasing its application rate. Soil pH and negative charge were decreased at low level of FSP application up to 400 mg P kg⁻¹, but thereafter continually increased with increasing application level. This could be indirect evidence that net soil negative charge was increased by the specific adsorption of phosphate at the high rate of FSP application over 400 mg P kg⁻¹. The labile Cd fraction (water soluble and exchangeable + acidic fraction) increased with increasing FSP application by 400 mg P kg⁻¹ and thereafter gradually decreased with corresponding increase in unlabile fraction (oxidizable and residual fraction). Based on these results, FSP might be applied with a very high rate over 800 mg P kg⁻¹ to decrease Cd extractability in the selected field. However, this level is equivalent to 1440 kg P ha⁻¹, which is about 43 times higher than the recommendation levels for radish production and resulted in a significant increase in water soluble P concentration creating a new environmental problem. Therefore, the feasibility of FSP to reduce Cd extractability in the field is very low.     

Preliminary study of phosphorus runoff and drainage from a paddy field in the Taihu Basin

An investigation into phosphorus runoff and drainage from a paddy field was carried out at Changshu Agricultural Ecological Station of CAS during the year 2000. According to the preliminary study, some results indicated: (1) Total phosphorus (TP) content of regular irrigation water was 19 times higher than TP content of P0 (zero rate of P fertilization) stand water. This indicates that paddy fields are a potential source of phosphorus pollution by runoff and drainage into the Taihu Lake Basin (TLB); (2) During the first 10 days after phosphate fertilizer application, the TP concentration of stand water in the paddy field was very high, therefore this was the high risk period for Taihu Lake phosphorus contamination; (3) Four mathematical models of P losses from a paddy field in the TLB are developed. These are based on data for the year 2000, but they will be improved as more data is acquired in future years.     

Characteristics of nitrate horizontal transport in a paddy field of the Tai Lake region,China

The characteristics of nitrate horizontal transport in a major paddy soil, Wu Shan soil in the Tai Lake region, were studied. The concentration of nitrate during horizontal movement decreased with the increasing in distance from the tracer source, the change following a logarithmic function. The concentration of the nitrate was strongly correlated with the soil moisture content, as an exponential function. The horizontal transport velocity of nitrate was significantly correlated with the distance of the tracer source as power function. Therefore, the velocity of nitrate horizontal transport was controlled by the concentration gradient of nitrate, and soil water potential gradient from beginning to the 20 cm mark in the horizontal column. However, the velocity of nitrate horizontal was stable beyond 20 cm, where it was controlled by soil matric potential.     

Shifts in herbicide tolerance in paddy field periphyton following herbicide application

Herbicide susceptibility was examined in various algal strains isolated from herbicide-treated and untreated paddy fields. Diatom strains showed obvious tolerance to the herbicides simetryn and pretilachlor irrespective of herbicide exposure, while the susceptibility of green algae mostly reflected their history of herbicide exposure. Cross-resistance was also induced in some algae. Rapid development of herbicide tolerance indicated that the tolerance seemed to be conferred by tolerant strains already present in the communities. Thus, changes in genetic composition within a population seem to be the main mechanism by which paddy periphyton gain herbicide tolerance.     

Modeling transport and fate of nitrogen from urea applied to a near-trench paddy field

A simple but comprehensive model is developed to quantify N losses from urea applied to a near-trench paddy field, considering all the N-transformations such as urea hydrolysis, volatilization, nitrification, denitrification, and all the important transportations like runoff, lateral seepage, vertical leaching and crop uptake. Seasonal average data of field observations for three crop seasons were used for model calibration and validation, which showed that ammonia volatilization accounted for 26.5-29.4% of the applied N and N uptake by crop occupied 38.2-44.8%, while N losses via surface runoff, vertical leaching and lateral seepage varied from 5.6-7.7%, 4.0-4.9% to 5.0-5.3% of the applied N, respectively. These observed results were well predicted by our model, indicating that the model performed effectively at quantifying N losses via individual processes in a wide range of urea application rates and benefit for developing water and fertilizer management strategies for near-trench paddy fields.     

投入产出分析在固体废物管理中的应用

通过构建固体废物投入产出表,分析包括资源提供、产品生产、废弃物循环利用及废物处置部门在内的国民经济各部门之间的经济技术关系。并对理想条件及其他条件下固体废物资源化对于资源节约、废物减量及经济发展的影响进行了定量分析。     

Dissipation of epoxiconazole in the paddy field under subtropical conditions of Taiwan

The environmental fate and distribution of fungicide epoxiconazole were studied by a rice paddy field model ecosystem. One week before the head-sprouting stage, rice plant was treated separately once with OPUS (tradename of epoxiconazole) 12% SC 2.1 kg ha(-1) and 1.4 kg ha(-1), respectively. Soil, water and rice plant were sampled seven days intervals nine times after application. The bioconcentration factor of epoxiconazole on mosquito fish in the ecosystem was also determined, based on the amounts of epoxiconazole content both in fish and water. This was initiated one day after the fungicide treatment, and continued for four days. In addition, the residue of epoxiconazole in rice grains was analyzed after harvest. After harvest, both planted water spinach (Ipomoea aquatica Forsk) and edible amaranth (Amaranthus mangostanüs L.) were analyzed. The results showed that epoxiconazole degraded in the local environment under the experimental conditions described. The degradation equations were in accordance with the first order kinetics. The DT50 of soil, field water and rice plant were 20-69 days, 11-20 days and 14-39 days, respectively. The bioconcentration factors of epoxiconazole on mosquito fish were 12.9 and 10.6 from 2.1 kg ha(-1) and 1.4 kg ha(-1) treatment, respectively. Residues of epoxiconazole in both rice and harvest vegetables were non-detectable. This indicates that epoxiconazole applied to rice at the recommended rates and application frequencies will not accumulate on rice grain and successive cropping vegetables.     

抗侵蚀型生态沟渠构建及其稻田应用效果

根据沟渠水力学和工程力学特征,通过引进三维植物网护坡技术,构建了一种抗侵蚀型稻田生态沟渠,横断面0.9 m2,沟壁和沟底水生植物覆盖度分别为62.8%和35.3%,沟壁抗坡面侵蚀强度较土质沟渠可提高2倍以上,在优化污染物拦截去除功能的同时,大大延长了其使用寿命。稻田应用实验表明,径流排水停留时间超过48 h后,SS、TN和TP去除率分别达59.5%、57.8%和45.3%,配置比例按照1 hm2水稻田配300 m该型生态沟渠实施,则超过80%以上的稻田径流排水能够得到有效处理。该型生态沟渠工程造价约245元/m,接近传统混凝土排水渠单价,经近2年的运行观测,沟渠系统结构稳定,净化植物长势良好。     

丙溴磷在稻田环境中的残留动态研究

确立了气相色谱法测定丙溴磷残留量的检测方法.采用该方法,丙溴磷在土壤、植株、糙米、稻壳和田水中的平均添加回收率为87.2％～103.6％,变异系数为3.20％～11.50％,最低检测质量浓度:田水为0.005 mg/kg;土壤、植株、糙米和稻壳为0.050 mg/kg.残留动态研究表明,丙溴磷在田水、植株和土壤中的半衰...     

Remediation of cadmium contamination in paddy soils by washing with chemicals: selection of washing chemicals

The efficiencies of neutral salts, strong acids, and chelates were tested for extracting cadmium (Cd) from three paddy soils. The higher the selectivity of the cations of the added neutral salts toward soil adsorption sites, the lower the pH in the extracts and the more soil Cd could be extracted. In addition, soil carbon and nitrogen contents and mineral composition were closely associated with the amount of Cd extracted. Calcium chloride and iron(III) chloride were selected as wash chemicals to restore Cd-contaminated paddy soils in situ. Washing with calcium chloride led to the formation of Cd chloride complexes, enhancing Cd extraction from the soils. The washing also substantially decreased soil levels of exchangeable and acid-soluble Cd, which are the major forms of bioavailable Cd for rice (Oryza sativa L.). The optimum conditions for in situ soil washing were also determined for calcium chloride.     

Mass balance and long-term fate of PCDD/Fs in a lagoon sediment and paddy soil, Niigata, Japan

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in a sediment core and in samples of surface sediment and paddy soil collected from the Toyano lagoon and Kameda basin in Niigata, Japan, were analyzed to elucidate the temporal trends of their concentrations in the lagoon sediment and the relationship between the sediment and the paddy soil. The mass balance of these pollutants was also estimated to determine their long-term fate in surface waters. An analysis by chemical mass balance identified the agrochemicals pentachlorophenol and 2,4,6-trichlorophenyl 4-nitrophenyl ether as the major sources of PCDD/Fs. On the basis of the findings regarding the mass balance in the Kameda basin over the last 40 years, we estimate that more than half the input of PCDD/Fs to the Kameda basin has disappeared. We suggest that the PCDD/Fs that flowed out from the paddy fields have been transferred to the lower basin.     

Application of micrometeorological approaches to measure methane exchange in a dry paddy field in the western coast of Korea

The exchange processes of CH₄ were investigated in a paddy field in the Hari area of Kang Hwa Island over an 8 day period in late April 2002. The quantification of CH₄ fluxes was made under dry field condition of early spring by concurrently measuring its concentrations (at the two heights of 1 and 5 m) and the relevant micrometeorological parameters. To help elucidate the factors determining the mobilization characteristics of CH₄, the results of our measurement data were examined using a number of approaches. The results of the trajectory analysis indicated that its concentration changed very sensitively with the influence of different source types, as seen from the air mass movement patterns. The concentrations and fluxes of methane, when examined over this short-term scale, showed moderately strong patterns across 24 h period in which higher values tend to occur during morning or evening. The overall results of our field measurements suggest that CH₄ exchange processes in the paddy area proceeded in a fairly complicated manner. The study area behaved as a net source of CH₄ to the atmosphere with a net daily emission rate of 3.6 mg m⁻² despite the fact that downward deposition was observed more frequently than upward emission.     

淹水条件下蚕沙复配材料对酸性水稻土中镉铅钝化的影响

通过室内淹水土培实验,研究蚕沙配施蚕沙炭、膨润土、腐殖质钾和泥炭对酸性水稻土中镉（Cd）、铅（Pb）的钝化效果,从土壤pH、有机质、有效态Fe、Mn含量变化初步探析蚕沙复配材料对镉、铅的钝化机制。结果表明,蚕沙复配材料均不同程度地提高了土壤pH和有机质含量,有效态Cd、Pb的含量随着淹水时间的延长都有不同程度的降低。培养28 d后,与对照相比,添加了蚕沙+蚕沙炭（CB）、蚕沙+腐殖质钾（CF）、蚕沙+蚕沙炭+腐殖质钾（CBF）、蚕沙+泥炭（CN）处理的土壤有效态Cd分别降低了16.07%、15.51%、11.08%、7.76%,有效态Pb则降低了32.54%、27.12%、37.72%、42.31%。其中蚕沙+蚕沙炭（CB）对镉的钝化效果最好,蚕沙+泥炭（CN）处理对铅的钝化效果最好,综合来看,CB和CN处理同时对镉铅有很好的钝化效果,可以作为镉铅复合污染土壤的修复材料。相关分析结果显示,土壤的pH、有机质与有效态Cd、Pb含量均呈显著负相关关系,表明蚕沙复配材料对土壤中镉、铅的钝化作用可以通过提高土壤的pH、有机质含量来实现。     

Kinetic and dynamic aspects of soil-plant-snail transfer of cadmium in the field

The proper use of bioaccumulation in the assessment of environmental quality involves accounting for chemical fluxes in organisms. Cadmium (Cd) accumulation kinetics in a soil-plant-snail food chain were therefore investigated in the field under different soil contamination (from 0 to 40 mg kg(-1)), soil pH (6 and 7) and season. Allowing for an accurate and sensitive assessment of Cd transfer to snails, toxicokinetics appears an interesting tool in the improvement of risk assessment procedures and a way to quantify metal bioavailability for a defined target. On the basis of uptake fluxes, snails proved to be sensitive enough to distinguish moderate soil contaminations. The soil pH did not appear, in the range studied, as a modulating parameter of the Cd transfer from soil to snail whereas the season, by influencing the snail mass, may modify the internal concentrations. The present data specifying a time integrated assessment of environmental factors on metal bioavailability and transfer to terrestrial snails should ensure their rational use in environmental biomonitoring.     

菜籽饼施加对镉-铜污染土壤中重金属形态转化及其植物有效性的影响

选择菜籽饼作为有机物料,模拟水田条件,研究菜籽饼施用后重金属污染土壤中镉-铜的赋存形态的变化及其有效性的影响。结果表明,菜籽饼施加后,土壤pH波动在0.5内,变化较小。但在一定程度促进土壤中镉、铜由弱酸提取态向可还原态转化,残渣态占比变化均较小。经培养一定时间,植物有效态DTPA-Cd由1.26±0.03下降至0.69±0.03,下降幅度约为45.2%,DTPA-Cu由82.9±0.09下降至48.7±0.09,最大下降幅度约为41.3%,下降较为明显。同时,土壤溶液中可溶性碳（DOC）和可溶性氮（DON）的含量显著增加,分别增加约4.14倍和6.48倍,因此,菜籽饼应用于重金属污染水稻土改良,可以间接降低水稻中重金属的含量。     

Phosphorus interception in floodwater of paddy field during the rice-growing season in TaiHu Lake Basin

A field experiment located in TaiHu Lake Basin in China was conducted, by application of superphosphate or a mixture of superphosphate with manure, to elucidate the interception of P export during a typical rice growing season through 'zero-drainage water management' combined with sound irrigation, rainfall forecasting and field drying. P concentrations in floodwater rapidly declined before the first event of field drying, and subsequently tended to return to the background levels. Before the first field drying TPP was the predominant P form in floodwater on fields with no P input, DRP on plots that received superphosphate only, and DOP on plots treated with the mixture of superphosphate and manure. Thereafter TPP became the major form. No P export was found from the paddy fields, but a retention of 0.65kgha(-1), mainly due to soil P sorption. The results recommend the zero-drainage water management for full-scale areas for minimizing P export.