Effects of arsenic concentrations and forms on arsenic uptake by the hyperaccumulator ladder brake

Ladder brake (Pteris vittata L.) is a newly discovered arsenic hyperaccumulator. No information is available about arsenic effects on ladder brake. This study determined the effects of different arsenic concentrations (50 to 1000 mg kg(-1)) or forms (organic vs. inorganic and arsenite vs. arsenate) applied to soils on growth and arsenic uptake by ladder brake. Young plants were grown in a greenhouse for 12 or 18 wk. Ladder brake was highly tolerant of arsenic and survived in soil containing up to 500 mg As kg(-1). The fact that addition of arsenate up to 100 mg As kg(-1) increased fern biomass by 64 to 107%, coupled with higher arsenic concentration in younger fronds at low soil arsenic concentrations and older fronds at high soil arsenic concentrations, implies that arsenic may be beneficial for fern growth. Addition of 50 mg As kg(-1) was best for fern growth and arsenic accumulation, resulting in the highest fern biomass (3.9 g plant(-1)), bioconcentration factor (up to 63), and translocation factor (up to 25). With an exception of FeAsO4 and AlAsO4, which had the lowest effects due to their low solubility, little difference was observed among other arsenic forms mainly because of arsenic conversion in soil. Aboveground biomass was mostly responsible for accumulation of arsenic by plant (75-99%). Up to 26% of the added arsenic was removed by ladder brake, showing the high efficiency of ladder brake in arsenic removal. The results suggest that ladder brake may be a good candidate to remediate arsenic-contaminated soils.     

Mycorrhizae increase arsenic uptake by the hyperaccumulator Chinese brake fern (Pteris vittata L.)

Chinese brake fern (Pteris vittata L.) is a hyperaccumulator of arsenic (As) that grows naturally on soils in the southern United States. It is reasonable to expect that mycorrhizal symbiosis may be involved in As uptake by this fern. This is because arbuscular mycorrhizal (AM) fungi have a well-documented role in increasing plant phosphorus (P) uptake, P and As have similar chemical properties, and ferns are known to be colonized by AM fungi. We conducted a factorial greenhouse experiment with three levels of As (0, 50, and 100 mg kg(-1)) and P (0, 25, and 50 mg kg(-1)) and with and without Chinese brake fern colonized by a community of AM fungi from an As-contaminated site. We found that the AM fungi not only tolerated As amendment, but their presence increased frond dry mass at the highest As application rate. Furthermore, the AM fungi increased As uptake across a range of P levels, while P uptake was generally increased only when there was no As amendment. These data indicate that AM fungi have an important role in arsenic accumulation by Chinese brake fern. Therefore, to effectively phytoremediate As-contaminated soils, the mycorrhizal status of ferns needs to be taken into account.     

Hycrest crested wheatgrass accelerates the degradation of pentachlorophenol in soil

We investigated the effects of vegetation on the fate of pentachlorophenol (PCP) in soil using a novel high-flow sealed test system. Pentachlorophenol has been widely used as a wood preservative, and this highly toxic biocide contaminates soil and ground water at many sites. Although plants are known to accelerate the rates of degradation of certain soil contaminants, this approach has not been thoroughly investigated for PCP. The fate of [14C]PCP, added to soil at a concentration of 100 mg/kg, was compared in three unplanted and three planted systems. The plant used was Hycrest, a perennial, drought-tolerant cultivar of crested wheatgrass [Agropyron desertorum (Fischer ex Link) Schultes]. The flow-through test system allowed us to maintain a budget for 14C-label as well as monitor mineralization (breakdown to 14CO2) and volatilization of the test compound in a 155-d trial. In the unplanted systems, an average of 88% of the total radiolabel remained in the soil and leachate and only 6% was mineralized. In the planted system, 33% of the radiolabel remained in the soil plus leachate, 22% was mineralized, and 36% was associated with plant tissue (21% with the root fraction and 15% with shoots). Mineralization rates were 23.1 mg PCP mineralized kg-1 soil in 20 wk in the planted system, and for the unplanted system 6.6 mg PCP kg-1 soil for the same time period. Similar amounts of volatile organic material were generated in the two systems (1.5%). Results indicated that establishing crested wheatgrass on PCP-contaminated surface soils may accelerate the removal of the contaminant.     

Approximating phosphorus release from soils to surface runoff and subsurface drainage

Phosphorus application in excess of crop needs has increased the concentration of P in surface soil and runoff and led many states to develop P-based nutrient management strategies. However, insufficient data are available relating P in surface soil, surface runoff, and subsurface drainage to develop sound guidelines. Thus, we investigated P release from the surface (0-5 cm depth) of a Denbigh silt loam from Devon, U.K. (30-160 mg kg-1 Olsen P) and Alvin, Berks, Calvin, and Watson soils from Pennsylvania (10-763 mg kg-1 Mehlich-3 P) in relation to the concentration of P in surface runoff and subsurface drainage. A change point, where the slopes of two linear relationships between water- or CaCl2-extractable soil P and soil test phosphorus (STP) (Olsen or Mehlich-3) meet, was evident for the Denbigh at 33 to 36 mg kg-1 Olsen P, and the Alvin and Berks soils at 185 to 190 mg Mehlich-3 P kg-1. Similar change points were also observed when STP was related to the P concentration of surface runoff (185 mg kg-1) and subsurface drainage (193 mg kg-1). The use of water and CaCl2 extraction of surface soil is suggested to estimate surface runoff P (r2 of 0.92 for UK and 0.86 for PA soils) and subsurface drainage P (r2 of 0.82 for UK and 0.88 for PA soils), and to determine a change point in STP, which may be used in support of agricultural and environmental P management.     

Chemical extraction methods to assess bioavailable arsenic in soil and solid media

Soil ingestion by children is an important pathway in assessing public health risks associated with exposure to arsenic-contaminated soils. Soil chemical methods are available to extract various pools of soil arsenic, but their ability to measure bioavailable arsenic from soil ingestion is unknown. Arsenic extracted by five commonly used soil extractants was compared with bioavailable arsenic measured in vivo by immature swine (Sus scrofa) dosing trials. Fifteen contaminated soils that contained 233 to 17 500 mg kg(-1) arsenic were studied. Soil extractants were selected to dissolve surficially adsorbed and/or readily soluble arsenic (water, 1 M sodium acetate, 0.1 M Na2HPO4/0.1 M NaH2PO4) and arsenic in Fe and Mn oxide minerals (hydroxylamine hydrochloride, ammonium oxalate). The mean percent of total arsenic extracted was: ammonium oxalate (53.6%) > or = hydroxylamine hydrochloride (51.7%) > phosphate (10.5%), acetate (7.16%) > water (0.15%). The strongest relationship between arsenic determined by soil chemical extraction and in vivo bioavailable arsenic was found for hydroxylamine hydrochloride extractant (r = 0.88, significant at the 0.01 probability level). Comparison of the amount of arsenic extracted by soil methods with bioavailable arsenic showed the following trend: ammonium oxalate, hydroxylamine hydrochloride > in vivo > phosphate, acetate > water. The amount of arsenic dissolved in the stomach (potentially bioavailable) is between surficially adsorbed (extracted by phosphate or acetate) and surficially adsorbed + nonsurficial forms in Fe and Mn oxides (extracted by hydroxylamine hydrochloride or ammonium oxalate). Soil extraction methods that dissolve some of the amorphous Fe, such as hydroxylamine hydrochloride, can be designed to provide closer estimates of bioavailable arsenic.     

Plant availability of zinc and copper in soil after contamination with brass foundry filter dust: effect of four years of aging

We investigated the effect of 4 yr of aging of a noncalcareous soil contaminated with filter dust from a brass foundry (80% w/w ZnO, 15% w/w Cu0.6Zn0.4) on the chemical extractability of Zn and Cu and their uptake by barley (Hordeum vulgare L.), pea (Pisum sativum L.), and sunflower (Helianthus annus L.). Pot experiments were conducted with the freshly contaminated soil (2250 mg kg-1 Zn; 503 mg kg-1 Cu), with the contaminated soil aged for 4 yr in the field (1811 mg kg-1 Zn; 385 mg kg-1 Cu), and with the uncontaminated control soil (136 mg kg-1 Zn; 32 mg kg-1 Cu). In comparison with the uncontaminated soil, the growth of barley and pea was clearly reduced in both contaminated soils, while toxicity symptoms did not systematically vary from the freshly contaminated to the 4 yr aged soil. The sunflower did not grow in the contaminated soils. The slow oxidative dissolution of the brass platelets led to an increase in the solubility and the plant uptake of Cu from the freshly contaminated to the 4 yr aged soil. In an earlier study, we found that the fine-grained ZnO dissolved in the field soil within 9 mo and that about half of the released Zn was incorporated into a layered double hydroxide phase and about half was adsorbed to the soil matrix. These changes in Zn speciation did not lead to a reduction of the Zn contents in the shoots and roots of barley and pea grown in the aged soil as compared with the freshly contaminated soil.     

Soil-to-root transfer and translocation of polycyclic aromatic hydrocarbons by vegetables grown on industrial contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) are possible contaminants in some former industrial sites, representing a potential risk to human health if these sites are converted to residential areas. This work was conducted to determine whether PAHs present in contaminated soils are transferred to edible parts of selected vegetables. Soils were sampled from a former gasworks and a private garden, exhibiting a range of PAH concentrations (4 to 53 to 172 to 1263 and 2526 mg PAHs kg-1 of dry soil), and pot experiments were conducted in a greenhouse with lettuce (Lactuca sativa L. var. Reine de Mai), potato (Solanum tuberosum L. var. Belle de Fontenay), and carrot (Daucus carota L. var. Nantaise). At harvest, above- and below ground biomass were determined and the PAH concentrations in soil were measured. In parallel, plates were placed in the greenhouse to estimate the average PAH-dust deposition. Results showed that the presence of PAHs in soils had no detrimental effect on plant growth. Polycyclic aromatic hydrocarbons were detected in all plants grown in contaminated soils. However, their concentration was low compared with the initial soil concentration, and the bioconcentration factors were low (i.e., ranging from 13.4 x 10(-4) in potato and carrot pulp to 2 x 10(-2) in potato and carrot leaves). Except in peeled potatoes, the PAH concentration in vegetables increased with the PAH concentration in soils. The PAH distribution profiles in plant tissues and in soils suggested that root uptake was the main pathway for high molecular weight PAHs. On the opposite, lower molecular weight PAHs were probably taken up from the atmosphere through the leaves as well as by roots.     

土壤-植物系统中磷和砷相互作用关系的研究进展

砷元素导致的环境污染问题日益突出，施磷已成为植物修复砷污染土壤过程中必要强化措施之一。土壤-植物系统中磷和砷的相互作用关系是非常复杂的，研究表明：磷和砷在土壤中往往是共生的，但又存在竞争吸附关系；磷和砷在不同植物中的相互作用关系主要有拮抗效应和协同效应；有必要通过分子生物学手段对磷和砷表达基理进行深入研究，获得对砷具有超积累能力的植株。     

Influence of plant growth on degradation of linear alkylbenzene sulfonate in sludge-amended soil

Widespread application of sewage sludge to agricultural soils in Denmark has led to concern about the possible accumulation and effects of linear alkylbenzene sulfonate (LAS) in the soil ecosystem. Therefore, we have studied the uptake and degradation of LAS in greenhouse pot experiments. Sewage sludge was incorporated into a sandy soil to give a range from very low to very high applications (0.4 to 90 Mg dry wt. ha(-1)). In addition, LAS was added as water solutions. The soil was transferred to pots and sown with barley (Hordeum vulgare L. cv. Apex), rape (Brassica napus L. cv. Hyola 401), or carrot (Daucus carota L.). Also, plant-free controls were established. For all additions there was no plant uptake above the detection limit at 0.5 mg LAS kg(-1) d.w, but plant growth stimulated the degradation. With a growth period of 30 d, LAS concentrations in soil from pots with rape had dropped from 27 to 1.4 mg kg(-1) dry wt., but in plant-free pots the concentration decreased only to 2.4 mg kg(-1) dry wt. When LAS was added as a spike, the final concentration in soil from planted pots was 0.7 mg kg(-1) dry wt., but in pots without plants the final concentration was much higher (2.5 mg kg(-1) dry wt.). During degradation, the relative fraction of homologues C10, C11, and C12 decreased, while C13 increased.     

Arsenic distribution in Florida urban soils: comparison between Gainesville and Miami

Arsenic contamination is of concern due to its effect as a carcinogen. Understanding the distribution of arsenic in urban soils is important for establishing baseline concentrations from which anthropogenic effects can be measured. The soil cleanup target level (SCTL) for arsenic in Florida (0.8 and 3.7 mg kg(-1) in residential and commercial areas, respectively) is lower than in most states and is near the arsenic background concentrations in Florida soils. The objective of this study was to characterize the distribution of arsenic in the soils of two Florida cities, Gainesville and Miami. More than 200 soil samples were collected from three land-use classes in each city (residential, commercial, and public land), digested with USEPA Method 3051a, and analyzed with graphite furnace atomic absorption spectrophotometry. Arsenic concentrations varied greatly in Gainesville, ranging from 0.21 to approximately 660 mg kg(-1) with a geometric mean (GM) of 0.40 mg kg(-1) (after discarding outliers), which was significantly lower than the GM of 2.81 mg kg(-1) in Miami, although Miami samples ranged only from 0.32 to approximately 110 mg kg(-1). Arsenic concentrations in 29 and 4% of the Gainesville soil samples and 95 and 33% of the Miami samples exceeded the Florida residential and commercial SCTL, respectively. This study is the first to provide information on arsenic distribution in urban soils of Florida, and the data are useful for assessing arsenic contamination and determining the need for remediation.     

Soil mixing to decrease surface stratification of phosphorus in manured soils

Continual applications of fertilizer and manure to permanent grassland or no-till soils can lead to an accumulation of P at the surface, which in turn increases the potential for P loss in overland flow. To investigate the feasibility of redistributing surface stratified P within the soil profile by plowing, Mehlich-3 P rich surface soils (128-961 mg kg(-) in 0-5 cm) were incubated with lower-P subsoil (16-119 mg kg(-1) in 5-20 cm) for 18 manured soils from Oklahoma and Pennsylvania that had received long-term manure applications (60-150 kg P ha(-1) yr(-1) as dairy, poultry, or swine manure for up to 20 yr). After incubating a mixture of 5 g surface soil (0- to 5-cm depth) and 15 g subsoil (5- to 20-cm depth) for 28 d, Mehlich-3 P decreased 66 to 90% as a function of the weighted mean Mehlich-3 P of surface and subsoil (i.e.. 1:3 ratio) (r2 = 0.87). At Klingerstown, Northumberland County, south central Pennsylvania, a P-stratified Berks soil (Typic Dystrochrept) (495 mg kg(-1) Mehlich-3 P in 0- to 5-cm depth) was chisel plowed to about 25 cm and orchardgrass (Dactylis glomerata L.) planted. Once grass was established and erosion minimized (about 20 wk after plowing and planting), total P concentration in overland flow during a 30-min rainfall (6.5 cm h(-1)) was 1.79 mg L(-1) compared with 3.4 mg L(-1) before plowing, with dissolved P reduced from 2.9 to 0.3 mg L(-1). Plowing P-stratified soils has the potential to decrease P loss in overland flow, as long as plowing-induced erosion is minimized.     

Uptake and distribution of iodine in rice plants

Rice (Oryza sativa L.) plants were cultivated in an experimental field and separated at harvest into different components, including polished rice, rice bran, hull, straw, and root. The contents of iodine in these components and the soil were determined by inductively coupled plasma-mass spectrometry and radiochemical neutron activation analysis, respectively. Iodine content varied by more than three orders of magnitude among the plant components. Mean concentration of iodine in the entire plants was 20 mg kg(-1) dry weight, and the concentration of iodine in the surface soil (0-20 cm depth) was 48 mg kg(-1). The highest concentration of iodine (53 mg kg(-1) dry weight) was measured in root and the lowest concentration (0.034 mg kg(-1) dry weight) in polished rice. While the edible component (polished rice) accounted for 32% of the total dry weight, it contained only 0.055% of iodine found in the entire rice plants. Atmospheric gaseous iodine (5.9 ng m(-3)) was estimated to contribute <0.2% of the total iodine content in the biomass of rice plants; therefore nearly all of the iodine in the rice plants was a result of the uptake of iodine from the soil. The content of iodine in the aboveground part of rice plants was 16 mg kg(-1) dry weight and the percentage of iodine transferred per cropping from the soil into the aboveground biomass corresponded to 0.27% (20 mg m(-2)) of the upper soil layer content.     

Fungal inoculum properties: extracellular enzyme expression and pentachlorophenol removal in highly contaminated field soils

This study was conducted to improve the pentachlorophenol (PCP) bioremediation ability of white-rot fungi in highly contaminated field soils by manipulating bioaugmentation variables. These were the dry weight percentage of fungal inoculum addition (31-175 g kg(-1)), PCP concentration (100-2137 mg kg(-1) PCP), fungal inoculum formulation, and time (1-7 wk). Five fungal isolates were used: the New Zealand isolates Trametes versicolor (L.: Fr.) HR131 and Trametes sp. HR577; the North American isolates Phanerochaete chrysosporium Burds. (two isolates) and Phanerochaete sordida (Karst.) Erikss. & Ryv. Pentachlorophenol removal, manganese peroxidase, and laccase activity, and the formation of chloroanisoles in the contaminated field soils were measured. The majority of PCP removed by the Trametes isolates was in the first week after bioaugmentation. The maximum PCP removal by the fungi varied from 50 to 65% from a 1065 mg kg(-1) PCP contaminated field soil. Pentachlorophenol was preferentially converted to pentachloroanisole (PCA) by the Phanerochaete isolates (>60%), while 2 to 9% of the PCP removed by two Trametes isolates was converted to PCA. A pH increase was measured following bioaugmentation that was dependent on PCP concentration, fungal inoculum addition, and formulation. This, together with rapid initial PCP removal, possibly changed the bioavailability of the remaining PCP to the fungi and significantly decreased the sequestering of PCP in the contaminated field soils. The research supports the conclusion that New Zealand Trametes spp. can rapidly remove PCP in contaminated field soils. Bioavailability and extractability of PCP in the contaminated field soil may significantly increase after bioaugmentation.     

Substrate organic matter to improve nitrate removal in surface-flow constructed wetlands

A wetland mesocosm experiment was conducted in eastern North Carolina to determine if organic matter (OM) addition to soils used for in-stream constructed wetlands would increase NO3--N treatment. Not all soils are suitable for wetland substrate, so OM addition can provide a carbon and nutrient source to the wetland early in its development to enhance denitrification and biomass growth. Four batch studies, with initial NO3--N concentrations ranging from 30 to 120 mg L-1, were conducted in 2002 in 21 surface-flow wetland mesocosms. The results indicated that increasing the OM content of a Cape Fear loam soil from 50 g kg-1 (5% dry wt.) to 110 g kg-1 (11% dry wt.) enhanced NO3--N wetland treatment efficiency in spring and summer batch studies, but increases to 160 g kg-1 (16% dry wt.) OM did not. Wetlands constructed with dredged material from the USACE Eagle Island Confined Disposal Facility in Wilmington, NC, with initial OM of 120 g kg-1 (12% dry wt.), showed no improvement in NO3--N treatment efficiency when increased to 180 g kg-1 (18% dry wt.), but did show increased NO3--N treatment efficiency in all batch studies when increased to 220 g kg-1 (22% dry wt.). Increased OM addition and biosolids to the Cape Fear loam and dredged material blends significantly increased biomass growth in the second growing season when compared to no OM addition. Results of this research indicate that increased OM in the substrate will reduce the area required for in-stream constructed wetlands to treat drainage water in humid regions. It also serves as a demonstration of how dredged material can be used successfully in constructed wetlands, as an alternative to costly storage by the USACE.     

Application of two organic wastes in a soil polluted by lead: effects on the soil enzymatic activities

The effects of adding a crushed cotton gin compost (CCGC) and a poultry manure (PM) on the enzymatic activities of a Typic Xerofluvent soil polluted with Pb were studied in the laboratory. Three hundred grams of sieved soil (<2 mm) were mixed with PM at a rate of 10% or CCGC at a rate of 17.2%, applying to the soil the same amount of organic matter with each organic amendment. Urease, protease-BBA, beta-glucosidase, alkaline phosphatase, and arylsulfatase activities were measured at four different incubation times (1, 7, 15, and 45 d) in soils containing seven concentrations (100, 250, 500, 1000, 2500, 5000, and 8000 mg kg-1) of Pb, and in the same soils amended with CCGC and PM. In all treatments and incubation times, the inhibition percentage of soil enzyme activities by Pb was lower in soils amended with the PM and CCGC than in nonamended soils, and it differed with the organic amendment. In this respect, the in the 8000 mg Pb kg-1 treatment at the end of the incubation period, the protease-BBA activity inhibition percentage was lower (14.7 and 33.9% lower, respectively) in CCGC- than in PM-amended soils. Since the adsorption capacity of Pb was higher in CCGC- than the PM-amended soils, the addition of organic wastes with higher humic acid concentration is more beneficial for remediation of soils polluted with Pb.     

Comparison of plant families in a greenhouse phytoremediation study on an aged polycyclic aromatic hydrocarbon-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous, recalcitrant, and potentially carcinogenic pollutants. Plants and their associated rhizosphere microbes can promote PAH dissipation, offering an economic and ecologically attractive remediation technique. This study focused on the effects of different types of vegetation on PAH removal and on the interaction between the plants and their associated microorganisms. Aged PAH-polluted soil with a total PAH level of 753 mg kg(-1) soil dry weight was planted with 18 plant species representing eight families. The levels of 17 soil PAHs were monitored over 14 mo. The size of soil microbial populations of PAH degraders was also monitored. Planting significantly enhanced the dissipation rates of all PAHs within the first 7 mo, but this effect was not significant after 14 mo. Although the extent of removal of lower-molecular-weight PAHs was similar for planted and unplanted control soils after 14 mo, the total mass of five- and six-ring PAHs removed was significantly greater in planted soils at the 7- and 14-mo sampling points. Poaceae (grasses) were the most effective of the families tested, and perennial ryegrass was the most effective species; after 14 mo, soils planted with perennial ryegrass contained 30% of the initial total PAH concentration (compared with 51% of the initial concentrations in unplanted control soil). Although the presence of some plant species led to higher populations of PAH degraders, there was no correlation across plant species between PAH dissipation and the size of the PAH-degrading population. Research is needed to understand differences among plant families for stimulating PAH dissipation.     

Impact of manure phosphorus fractions on phosphorus loss from manured soils after incubation

The risk of P loss from manured soils is more related to P fractions than total P concentration in manure. This study examined the impact of manure P fractions on P losses from liquid swine manure- (LSM), solid cattle manure- (SCM), and monoammonium phosphate- (MAP) treated soils. Manure or fertilizer was applied at 50 mg P kg soil, mixed, and incubated at 20°C for 6 wk to simulate the interaction between applied P and soil when P is applied well in advance of a high risk period for runoff. Phosphorus fractions in manure were determined using the modified Hedley fractionation scheme. We used simulated rainfall (75 mm h?1 for 1 h) to quantify P losses in runoff from two soils (sand and clay loam). The proportion of total labile P (total P in water+NaHCO fractions) in manure was significantly greater in LSM (70%) than SCM (44%). Mean dissolved reactive P (DRP) load in runoff over 60 min was greatest from MAP-treated soil (18.1 mg tray?1), followed by LSM- (14.0 mg tray?1) and SCM- (11.0 mg tray?1) treated soils, all of which were greater than mean DRP load from the check (5.2 mg tray?1). Total labile P (water+NaHCO) in manure was a more accurate predictor of runoff DRP loads than water extractable P, alone, for these two soils. Therefore, NaHCO extraction of manure P may be a useful tool for managing the risk of manure P runoff losses when manure is applied outside a high risk period for runoff loss.     

土壤As动态影响下枸杞质量评价及环境风险预测

选择柴达木盆地诺木洪农场3种类型农田进行20 cm表层土壤砷（As）含量检测。第1种为新开垦原生地,第2种为20年耕种地,第3种为50年耕种地,检测As含量分别为16.29、14.90、14.04 mg·kg^-1。3种土壤As含量均达到无公害食品标准（25 mg· kg^-1）和绿色食品标准（20 mg·kg^-1）。多年耕种并没有造成农田表层土壤As积累。农田灌溉用河水中未检出As。生产中使用的22种农药、肥料均检测到As,其中15种杀虫剂、杀真菌剂、除草剂、植物激素等,每年输入土壤As 4513.59 mg·hm^-2;7种肥料每年输入土壤As 258015.24 mg·hm^-2。施肥是土壤中As输入的重要来源,最主要的输入源是磷酸二铵,占到50％;其次为复合肥、鸡粪和有机肥。每年随作物输出As总量为4380 mg·hm^-2。模拟田间灌溉,进行土壤柱淋漓试验,农田20 cm表层土壤每年随灌溉淋漓输出As为245230.65 mg·hm^-2,这与随着肥料、农药输入量几乎相等。表层土壤As处在一个输入、输出相对稳定的动态平衡状态。从土壤中输出的As,随灌溉水输入到水系统中,继而造成水系统As的积累,最终将影响到地区农业的可持续发展。     

Availability of arsenic, copper, lead, thallium, and zinc to various vegetables grown in slag-contaminated soils

To anticipate a possible hazard resulting from the plant uptake of metals from slag-contaminated soils, it is useful to study whether vegetables exist that are able to mobilize a given metal in the slag to a larger proportion than in an uncontaminated control soil. For this purpose, we studied the soil to plant transfer of arsenic, copper, lead, thallium, and zinc by the vegetables bean (Phaseolus vulgaris L. 'dwarf bean Modus'), kohlrabi (Brassica oleracea var. gongylodes L.), mangold (Beta vulgaris var. macrorhiza ), lettuce (Lactuca sativa L. 'American gathering brown'), carrot (Daucus carota L. 'Rotin', 'Sperlings's'), and celery [Apium graveiolus var. dulce (Mill.) Pers.] from a control soil (Ap horizon of a Entisol) and from a contaminated soil (1:1 soil-slag mixtures). Two types of slags were used: an iron-rich residue from pyrite (FeS2) roasting and a residue from coal firing. The metal concentrations in the slags, soils, and plants were used to calculate for each metal and soil-slag mixture the plant-soil fractional concentration ratio (CRfractional,slag), that is, the concentration ratio of the metal that results only from the slag in the soil. With the exception of TI, the resulting values obtained for this quantity for As, Cu, Pb, and Zn and for all vegetables were significantly smaller than the corresponding plant-soil concentration ratios (CRcontrol soil) for the uncontaminated soil. The results demonstrate quantitatively that the ability of a plant to accumulate a given metal as observed for a control soil might not exist for a soil-slag mixture, and vice versa.     

Effects of a waste paper product on soil phosphorus, carbon, and bulk density

Applications of manures to agricultural fields have increased soil test values for P to high levels in parts of the USA and thus increased the likelihood that P will be transported to surface water and degrade its quality. Waste paper applications to soils with high STP (soil test P) may decrease the risk of P transport to surface water by decreasing DRP (dissolved reactive P) by the formation of insoluble Al-P complexes and providing organic matter to improve infiltration. A field experiment was conducted near Booneville, AR (USA) to assess the effects of different rates of a waste paper product addition on STP, soil bulk density, and total soil C with a soil with approximately 45 mg Bray1-P kg-1 soil (dry weight). A Leadvale silt loam soil (fine-silty, siliceous, thermic Typic Fragiudult) was amended with 0, 22, 44, or 88 Mg waste paper product ha-1 to supply approximately 90, 170, or 350 kg Al ha-1, respectively. One year after additions, there was a strong negative correlation between waste paper product application rates and soil bulk density, and a strong positive correlation between rates and total soil C content. Soil bulk density and total C 2 yr after additions, and soil DRP and Bray1-P were not affected by waste paper additions. These results support the hypothesis that decreases in DRP in runoff from soils receiving waste paper additions were probably due to changes in soil organic matter and bulk density, rather than changes in the chemical forms of soil P.