Effect of lead, mercury and cadmium on a sulphate-reducing bacterium

A sulphate-reducing bacterial strain isolated from the south-west coast of India resembling Desulfosarcina in its physiology was tested for its behaviour towards HgCl(2), CdSO(4) and Pb(NO(3))(2). The order of toxicity to growth of these metal salts in a lactate-based medium at 50 microg ml(-1) concentrations was Cd>Pb>Hg and to respiration Pb>Cd>Hg. Inhibitory concentrations (viz. 100 microg ml(-1) of HgCl(2) and 200 microg ml(-1) of Pb(NO(3)(2)) had a stimulatory effect when the substrate was changed to acetate. With sodium acetate at 0.1% concentration, Hg and Pb had maximum stimulatory effect for growth and sulphide production. Experiments conducted directly with sediment slurries amended with lactate showed that all three metals (at levels below their inhibitory concentrations, i.e. 50 microg ml(-1) of metal salt for Cd and Hg and 100 microg ml(-1) for Pb) inhibited sulphate-reducing activity (SRA) with Pb decreasing the peak production by 68%. The order of toxicity in both lactate and acetate-amended slurry was Pb>Cd>Hg and Pb>Hg>Cd, respectively. With acetate, SRA in the presence of Cd and Hg was stimulated 110% and 27%, respectively. Pb inhibited SRA by 11%. There is a general reduction in the inhibition of sulphide production in slurries as compared with pure culture of the isolate.     

Moss bags as sentinels for human safety in mercury-polluted groundwaters

An equation to estimate Hg concentrations of <4 μg/L in groundwaters of a polluted area in NE Italy was set out by using transplants of the aquatic moss Rhynchostegium riparioides as trace element bioaccumulators. The equation is derived from a previous mathematical model which was implemented under laboratory conditions. The work aimed at (1) checking the compliance of the uptake kinetics with the model, (2) improving/adapting the model for groundwater monitoring, (3) comparing the performances of two populations of moss collected from different sites, and (4) assessing the environmental impact of Hg contamination on a small river. The main factors affecting Hg uptake in the field were—as expected—water concentration and time of exposure, even though the uptake kinetics in the field were slightly different from those which were previously observed in the lab, since the redox environmental conditions influence the solubility of cationic Fe, which is a negative competitor of Hg²⁺. The equation was improved by including the variable ‘dissolved oxygen concentration’. A numerical parameter depending on the moss collection site was also provided, since the differences in uptake efficiency were observed between the two populations tested. Predicted Hg concentrations well fitted the values measured in situ (approximately ±50 %), while a notable underestimation was observed when the equation was used to predict Hg concentration in a neighbouring river (?96 %), probably due to the organic pollution which hampers metal uptake by mosses.     

The linear accumulation of atmospheric mercury by vegetable and grass leaves: Potential biomonitors for atmospheric mercury pollution

One question in the use of plants as biomonitors for atmospheric mercury (Hg) is to confirm the linear relationships of Hg concentrations between air and leaves. To explore the origin of Hg in the vegetable and grass leaves, open top chambers (OTCs) experiment was conducted to study the relationships of Hg concentrations between air and leaves of lettuce (Lactuca sativa L.), radish (Raphanus sativus L.), alfalfa (Medicago sativa L.) and ryegrass (Lolium perenne L.). The influence of Hg in soil on Hg accumulation in leaves was studied simultaneously by soil Hg-enriched experiment. Hg concentrations in grass and vegetable leaves and roots were measured in both experiments. Results from OTCs experiment showed that Hg concentrations in leaves of the four species were significantly positively correlated with those in air during the growth time (p?<?0.05), while results from soil Hg-enriched experiment indicated that soil-borne Hg had significant influence on Hg accumulation in the roots of each plant (p?<?0.05), and some influence on vegetable leaves (p?<?0.05), but no significant influence on Hg accumulation in grass leaves (p?>?0.05). Thus, Hg in grass leaves is mainly originated from the atmosphere, and grass leaves are more suitable as potential biomonitors for atmospheric Hg pollution. The effect detection limits (EDLs) for the leaves of alfalfa and ryegrass were 15.1 and 22.2 ng g^–1, respectively, and the biological detection limit (BDL) for alfalfa and ryegrass was 3.4 ng m^–3.     

Entrained-flow adsorption of mercury using activated carbon

Bench-scale experiments were conducted in a flow reactor to simulate entrained-flow capture of elemental mercury (Hg0) by activated carbon. Adsorption of Hg0 by several commercial activated carbons was examined at different C:Hg ratios (by weight) (350:1-29,000:1), particle sizes (4-44 microns), Hg0 concentrations (44, 86, and 124 ppb), and temperatures (23-250 degrees C). Increasing the C:Hg ratio from 2100:1 to 11,000:1 resulted in an increase in removal from 11 to 30% for particle sizes of 4-8 microns and a residence time of 6.5 sec. Mercury capture increased with a decrease in particle size. At 100 degrees C and an Hg0 concentration of 86 ppb, a 20% Hg0 reduction was obtained with 4- to 8-micron particles, compared with only a 7% reduction for 24- to 44-micron particles. Mercury uptake decreased with an increase in temperature over a range of 21-150 degrees C. Only a small amount of the Hg0 uptake capacity is being utilized (less than 1%) at such short residence times. Increasing the residence time over a range of 3.8-13 sec did not increase adsorption for a lignite-based carbon; however, increasing the time from 3.6 to 12 sec resulted in higher Hg0 removal for a bituminous-based carbon.     

Difference in ozone uptake in grassland species between open-top chambers and ambient air

Exposure-response data from open-top chamber (OTC) experiments are often directly applied to ambient air (AA) conditions. Because microclimatic conditions are modified and pollutant uptake by plants may differ (i.e. 'chamber effect'), there is concern about the influence of OTCs on these relationships. In addition, AA concentrations are often measured at a height which differs from canopy height and correction for the concentration gradient (i.e. 'gradient effect') is necessary. To quantify the relative contribution of plant characteristics and microclimatic factors to these effects, ozone uptake by horizontal leaves at the top of the canopy was calculated for plants grown in OTCs or AA by using a resistance analogy model. Data from an OTC experiment in 1996/97 for six species typical of productive grasslands were used. Ozone concentration inside OTCs was set equal to the concentration measured at a height of 3 m above ground (C(z(ref))) or at canopy height (C(0)). The gradient effect resulted in a 16-27% lower average C(0) than C(z(ref)), depending on species. The main determinant of the chamber effect was a systematic difference in leaf-to-air vapour pressure deficit between OTCs and AA which affected stomatal resistance and ozone uptake. In case of monocultures both effects were species-specific. In species mixtures the gradient effect differed between mixing ratios, whereas the chamber effect was species-specific. Because of the inter-specific difference in the chamber effect on ozone uptake, it is concluded that ozone effects on species mixtures differ systematically between OTCs and AA. The data underline that extrapolation of ozone flux-response relationships from OTC experiments must be based on canopy-level ozone concentrations, and that these relationships should be applied only to single species under microclimatic conditions similar to those prevailing in the experiment.     

Mercury accumulation in grass and forb species as a function of atmospheric carbon dioxide concentrations and mercury exposures in air and soil

The goal of this study was to investigate the potential for atmospheric Hg degrees uptake by grassland species as a function of different air and soil Hg exposures, and to specifically test how increasing atmospheric CO(2) concentrations may influence foliar Hg concentrations. Four common tallgrass prairie species were germinated and grown for 7 months in environmentally controlled chambers using two different atmospheric elemental mercury (Hg major; 3.7+/-2.0 and 10.2+/-3.5 ng m(-3)), soil Hg (<0.01 and 0.15+/-0.08 micro g g(-1)), and atmospheric carbon dioxide (CO(2)) (390+/-18, 598+/-22 micro mol mol(-1)) exposures. Species used included two C4 grasses and two C3 forbs. Elevated CO(2) concentrations led to lower foliar Hg concentrations in plants exposed to low (i.e., ambient) air Hg degrees concentrations, but no CO(2) effect was apparent at higher air Hg degrees exposure. The observed CO(2) effect suggests that leaf Hg uptake might be controlled by leaf physiological processes such as stomatal conductance which is typically reduced under elevated CO(2). Foliar tissue exposed to elevated air Hg degrees concentrations had higher concentrations than those exposed to low air Hg degrees , but only when also exposed to elevated CO(2). The relationships for foliar Hg concentrations at different atmospheric CO(2) and Hg degrees exposures indicate that these species may have a limited capacity for Hg storage; at ambient CO(2) concentrations all Hg absorption sites in leaves may have been saturated while at elevated CO(2) when stomatal conductance was reduced saturation may have been reached only at higher concentrations of atmospheric Hg degrees . Foliar Hg concentrations were not correlated to soil Hg exposures, except for one of the four species (Rudbeckia hirta). Higher soil Hg concentrations resulted in high root Hg concentrations and considerably increased the percentage of total plant Hg allocated to roots. The large shifts in Hg allocation patterns-notably under soil conditions only slightly above natural background levels-indicate a potentially strong role of plants in belowground Hg transformation and cycling processes.     

Absence of Hg transpiration by shoot after Hg uptake by roots of six terrestrial plant species

In this paper we investigated if, and to what extent, six different plant species accumulate, translocate and emit mercury (Hg) into the air. The Hg uptake by roots, distribution of Hg to the shoot and release of Hg via shoots of garden pea, spring wheat, sugar beet, oil-seed rape, white clover and willow were investigated in a transpiration chamber. The airborne Hg was trapped in a Hopcalite trap or a gold trap. Traps and plant materials were analysed for content of Hg by CVAAS. The results show that all plant species were able to take up Hg to a large extent from a nutrient solution containing 200 microg L(-1) Hg. However, the Hg translocation to the shoot was low (0.17-2.5%) and the Hg that reached the leaves was trapped and no release of the absorbed Hg to the air was detected.     

Dissipation of 2,4-D in soils of the Humid Pampa region, Argentina: a microcosm study

Phenoxy herbicides like 2,4-dichlorophenoxyacetic acid (2,4-D) are widely used in agricultural practices. Although its half life in soil is 7-14d, the herbicide itself and its first metabolite 2,4-dichlorophenol (2,4-DCP) could remain in the soil for longer periods, as a consequence of its intensive use. Microcosms assays were conducted to study the influence of indigenous microflora and plants (alfalfa) on the dissipation of 2,4-D from soils of the Humid Pampa region, Argentina, with previous history of phenoxy herbicides application. Results showed that 2,4-D was rapidly degraded, and the permanence of 2,4-DCP in soil depended on the presence of plants and soil microorganisms. Regarding soil microbial community, the presence of 2,4-D degrading bacteria was detected even in basal conditions in this soil, possibly due to the adaptation of the microflora to the herbicide. There was an increment of two orders of magnitude in herbicide degraders after 15d from 2,4-D addition, both in planted and unplanted microcosms. Total heterotrophic bacteria numbers were about 1x10(8) CFUg(-1) dry soil and no significant differences were found between different treatments. Overall, the information provided by this work indicates that the soil under study has an important intrinsic degradation capacity, given by a microbial community adapted to the presence of phenoxy herbicides.     

Effects of alfalfa and organic fertilizer on benzo[a]pyrene dissipation in an aged contaminated soil

BACKGROUND: A climate-controlled pot experiment was conducted to investigate the effects of planting alfalfa and applying organic fertilizer on the dissipation of benzo[a]pyrene from an aged contaminated agricultural soil. RESULTS: Short-term planting of alfalfa inhibited the dissipation of benzo[a]pyrene from the soil by 8.9%, and organic fertilizer enhanced benzo[a]pyrene removal from the soil by 11.6% compared with the unplanted and unfertilized treatments, respectively. No significant interaction was observed between alfalfa and organic fertilizer on benzo[a]pyrene dissipation. Sterilization completely inhibited the removal of benzo[a]pyrene from the soil indicating that its degradation by indigenous microorganisms may have been the main mechanism of dissipation. Furthermore, significant positive relationships were observed between benzo[a]pyrene removal and the contents of soil ammonium nitrogen, nitrate nitrogen, and total mineral nitrogen at the end of the experiment, suggesting that competition between plants and microorganisms for nitrogen may have inhibited benzo[a]pyrene dissipation in the rhizosphere of alfalfa and the addition of organic fertilizer may facilitate microbial degradation of benzo[a]pyrene in the soil.     

柠檬酸对褐土中DTPA提取态铜、镉含量及对紫花苜蓿吸收铜、镉的影响

为了阐述有机酸对土壤中重金属生物有效性的影响,通过盆栽实验,研究了Cu、Cd复合污染下柠檬酸对褐土中二乙基三胺五乙酸(DTPA)提取态铜和镉含量的影响,并探讨了柠檬酸对植物吸收铜、镉的影响。结果表明,土壤中DT-PA-Cu含量随柠檬酸添加量的增加而减小,添加高浓度铜(Cu 1 000)处理中,DTPA-Cu含量减小更明显。在添加低铜浓度(Cu600)处理下,柠檬酸添加量为2和12 mmol/kg时,土壤DTPA-Cu含量随土壤镉含量的增加而增加,而柠檬酸含量为5mmol/kg时,DTPA-Cu含量在低镉处理(Cd 1)时含量最低。紫花苜蓿中铜含量随柠檬酸添加量的增加明显降低。土壤中DTPA-Cd含量随柠檬酸添加量的增加而减小,且随铜添加量的增加而降低。紫花苜蓿中的镉含量随柠檬酸添加量的增加先增加后减小;在相同柠檬酸添加量处理时,紫花苜蓿中镉的含量随镉含量的增加而增加;在低镉处理下,铜的加入对较低柠檬酸浓度时紫花苜蓿镉含量影响不明显,但柠檬酸浓度为12 mmol/kg时,紫花苜蓿中镉含量随铜添加量的增加而明显增加。     

A reactive transport model for mercury fate in soil—application to different anthropogenic pollution sources

Soil systems are a common receptor of anthropogenic mercury (Hg) contamination. Soils play an important role in the containment or dispersion of pollution to surface water, groundwater or the atmosphere. A one-dimensional model for simulating Hg fate and transport for variably saturated and transient flow conditions is presented. The model is developed using the HP1 code, which couples HYDRUS-1D for the water flow and solute transport to PHREEQC for geochemical reactions. The main processes included are Hg aqueous speciation and complexation, sorption to soil organic matter, dissolution of cinnabar and liquid Hg, and Hg reduction and volatilization. Processes such as atmospheric wet and dry deposition, vegetation litter fall and uptake are neglected because they are less relevant in the case of high Hg concentrations resulting from anthropogenic activities. A test case is presented, assuming a hypothetical sandy soil profile and a simulation time frame of 50 years of daily atmospheric inputs. Mercury fate and transport are simulated for three different sources of Hg (cinnabar, residual liquid mercury or aqueous mercuric chloride), as well as for combinations of these sources. Results are presented and discussed with focus on Hg volatilization to the atmosphere, Hg leaching at the bottom of the soil profile and the remaining Hg in or below the initially contaminated soil layer. In the test case, Hg volatilization was negligible because the reduction of Hg²⁺ to Hg⁰ was inhibited by the low concentration of dissolved Hg. Hg leaching was mainly caused by complexation of Hg²⁺ with thiol groups of dissolved organic matter, because in the geochemical model used, this reaction only had a higher equilibrium constant than the sorption reactions. Immobilization of Hg in the initially polluted horizon was enhanced by Hg²⁺ sorption onto humic and fulvic acids (which are more abundant than thiols). Potential benefits of the model for risk management and remediation of contaminated sites are discussed.     

TiO2光催化降解水中土霉素的动力学研究

环境中抗生素的出现及其引起的危害正受到越来越多的关注。以高压汞灯为光源,选用较为广泛的抗生素土霉素（OTC）为处理对象。考察了初始质量浓度、反应过程中光照、催化剂投加量、溶液起始pH、溶液中DOM和NO^-₃对光催化降解的影响,研究了其光降解动力学。结果表明,TiO₂光催化氧化法能够有效去除水中半微量的OTC,OTC的光降解过程符合一级反应动力学模型;UV/TiO₂联用工艺对TOC也有很好的去除效果,反应90 min,TOC去除率可达74%;OTC的初始浓度从30 mg/L增大到90 mg/L,反应速率从0.0619 min^-1降低到0.0130 min^-1;随着光催化剂投加量的增大,光降解速率常数先增大后减小;增加溶液的pH值,速率常数逐渐减小;溶液中的DOM和NO^-₃也可以影响光降解效率。     

Characteristics of oxytetracycline sorption and potential bioavailability in soils with various physical-chemical properties

Veterinary antibiotics are widely used for disease treatment, prevention and animal growth promoting. Frequent detection of veterinary antibiotics in environments, caused by land application of untreated or even treated antibiotics-containing animal wastes, has posed the growing concern of their adverse effect on natural ecosystems. Oxytetracycline (OTC) is one of the most widely-used veterinary antibiotics in livestock industry. OTC present as a cation, zwitterions, or net negatively charged ion in soils complicates predicting its sorption characteristics and potential bioavailability and toxicity. This study was to identify soil properties influencing OTC sorption and its subsequent bioavailability in five soils with various physical-chemical properties. A solution used to determine bioavailable analytes in soils and sediments, 1 M MgCl₂ (pH 8.5), was chosen to desorb the potentially bioavailable fraction of OTC sorbed onto soils. Our results demonstrated that soils with higher illite content and permanent cation exchange capacity have higher OTC sorption capacity, but increase the availability of sorbed OTC indicated by higher release of sorbed OTC from soils into aqueous phase in 1 M MgCl₂ (pH 8.5). Reversely, soil organic matter (SOM), clay, kaolinite, variable cation exchange capacity, DCB-Fe and -Al have lower OTC sorption capacity, but decrease the release of sorbed OTC from soils into 1 M MgCl₂. These findings indicate that SOM and clay greatly influence OTC adsorption and potential availability. This study contributes significantly to our understanding of the potential bioavailability of sorbed OTC and the effects of soil properties on OTC sorption behaviors in soils.     

Modification of trace metal accumulation in the green mussel Perna viridis by exposure to Ag, Cu, and Zn

To examine the Cd, Hg, Ag, and Zn accumulation in the green mussel Perna viridis affected by previous exposure to Cu, Ag, or Zn, the dietary metal assimilation efficiency (AE) and the uptake rate from the dissolved phase were quantified. The mussel's filtration rate, metallothionein (MT) concentration, and metal tissue burden as well as the metal subcellular partitioning were also determined to illustrate the potential mechanisms underlying the influences caused by one metal pre-exposure on the bioaccumulation of the other metals. The green mussels were pre-exposed to Cu, Ag, or Zn for different periods (1-5 weeks) and the bioaccumulation of Cd, Hg, Ag, and Zn were concurrently determined. Pre-exposure to the three metals did not result in any significant increase in MT concentration in the green mussels. Ag concentration in the insoluble fraction increased with increasing Ag exposure period and Ag ambient concentration. Our data indicated that Cd assimilation were not influenced by the mussel's pre-exposure to the three metals (Cu, Ag, and Zn), but its dissolved uptake was depressed by Ag and Zn exposure. Although Hg assimilation from food was not affected by the metal pre-exposure, its influx rate from solution was generally inhibited by the exposure to Cu, Ag, and Zn. Ag bioaccumulation was affected the most obviously, in which its AE increased with increasing Ag tissue concentration, and its dissolved uptake decreased with increasing tissue concentrations of Ag and Cu. As an essential metal, Zn bioaccumulation remained relatively stable following the metal pre-exposure, suggesting the regulatory ability of Zn uptake in the mussels. Zn AE was not affected by metal pre-exposure, but its dissolved uptake was depressed by Ag and Zn pre-exposure. All these results indicated that the influences of one metal pre-exposure on the bioaccumulation of other metals were metal-specific due to the differential binding and toxicity of metals to the mussels. Such factors should be considered in using metal concentrations in mussel's soft tissues to evaluate the metal pollution in coastal waters.     

Kinetics of 2,4-dichlorophenol and 4-Cl-m-cresol degradation by Pseudomonas sp. cultures in the presence of glucose

Comparison of the ability of Pseudomonas sp. to degrade 2,4-dichlorophenol and 4-Cl-m-cresol in separate cultures in the presence of glucose, as a conventional carbon source, is reported. The specific growth rates at 0.1 mM 2,4-dichlorophenol and 4-Cl-m-cresol were estimated to be 0.181 and 0.154 h(-1), respectively, showing that Pseudomonas sp. is mainly inhibited by 4-Cl-m-cresol. The percentage of consumption ranges between 65% and 11% for 2,4-dichlorophenol and between 37% and 8% for 4-Cl-m-cresol, respectively, depending on its initial concentration. The dechlorination of the two compounds was investigated in the growth media and it was found that chloride liberation in the case of 2,4-dichlorophenol took place during the exponential phase of growth, followed by pH decrease from 6.1 to 5.8 at 0.1 mM. In contrast, in the case of 4-Cl-m-cresol chloride ion release was observed to a lesser extent, indicating the different metabolic pathway of 4-Cl-m-cresol. 2,4-Dichlorophenol and 4-Cl-m-cresol degradation followed a first-order kinetics model, whereas glucose consumption fitted well a zero-order kinetics model.     

Bioaccumulation and physiological effects of mercury in Sesbania drummondii

The accumulation of mercury and its effect on growth, photosynthesis and antioxidative responses were studied in Sesbania drummondii seedlings. Mercury concentration in shoots as well as in the roots increased with increasing Hg concentrations in the growth solution. The accumulation of Hg was more in roots than shoots. At 100 mg l-1 Hg concentration, shoots accumulated 998 mg Hg kg -1 dry weight (dw) while roots accumulated 41,403 mg Hg kg-1 dw. Seedlings growth was not significantly affected at lower concentrations of Hg. A concentration of 100 mg l-1 Hg inhibited growth by 36.8%, with respect to control. Photosynthetic activity was assessed by measuring chlorophyll a fluorescence by determination of Fv/Fm and Fv/Fo values. Photosynthetic integrity was not affected up to 50 mg l-1 Hg concentration, however, concentrations higher than 50 mg l-1 affected photosynthetic integrity. Sesbania responded to Hg induced oxidative stress by modulating non-enzymatic antioxidants [glutathione (GSH) and non-protein thiols (NPSH)] and enzymatic antioxidants: superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR). Glutathione content and GSH/GSSG ratio increased up to a concentration of 50 mg l-1 while slight down at 100 mg l-1 Hg. The content of NPSH significantly increased with increasing Hg concentrations in the growth medium. The activities of antioxidative enzymes, SOD, APX and GR followed the same trends as antioxidants first increased up to a concentration of 50 mg l-1 Hg and then slight decreased. The results of present study suggest that Sesbania plants were able to accumulate and tolerate Hg induced stress using an effective antioxidative defense mechanisms.     

2,4-D Mineralization in soil profiles of a cultivated hummocky landscape in Manitoba, Canada

The objective of this study was to quantify 2,4-D (2,4-dichlorophenoxyacetic acid) mineralization in soil profiles characteristic of hummocky, calcareous-soil landscapes in western Canada. Twenty-five soil cores (8 cm inner diameter, 50 to 125 cm length) were collected along a 360 m transect running west to east in an agricultural field and then segmented by soil-landscape position (upper slopes, mid slopes, lower slopes and depressions) and soil horizon (A, B, and C horizons). In the A horizon, 2,4-D mineralization commenced instantaneously and the mineralization rate followed first-order kinetics. In both the B and C horizons, 2,4-D mineralization only commenced after a lag period of typically 5 to 7 days and the mineralization rate was biphasic. In the A horizon, 2,4-D mineralization parameters including the first-order mineralization rate constant (k(1)), the growth-linked mineralization rate constant (k(2)) and total 2,4-D mineralization at the end of the experiment at 56 days, were most strongly correlated to parameters describing 2,4-D sorption by soil, but were also adequately correlated to soil organic carbon content, soil pH, and carbonate content. In both B and C horizons, there was no significant correlation between 2,4-D mineralization and 2,4-D sorption parameters, and the correlation between soil properties and 2,4-D mineralization parameters was very poor. The k(1) significantly decreased in sequence of A horizon (0.113% day(-1)) > B horizon (0.024% day(-1)) = C horizon (0.026% day(-1)) and in each soil horizon was greater than k(2). Total 2,4-D mineralization at 56 days also significantly decreased in sequence of A horizon (42%) > B horizon (31%) = C horizon (27%). In the A horizon, slope position had little influence on k(1) or k(2), except that k(1) was significantly greater in upper slopes (0.170% day(-1)) than in lower slopes (0.080% day(-1)). Neither k(1) nor k(2) was significantly influenced by slope position in the B or C horizons. Total 2,4-D mineralization at 56 days was not influenced by slope positions in any horizon. Our results suggest that, when predicting 2,4-D transport at the field scale, pesticide fate models should consider the strong differences in 2,4-D mineralization between surface and subsurface horizons. This suggests that 2,4-D mineralization is best predicted using a model that has the ability to describe a range of non-linear mineralization curves. We also conclude that the horizontal variations in 2,4-D mineralization at the field scale will be difficult to consider in predictions of 2,4-D transport at the field scale because, within each horizon, 2,4-D mineralization was highly variable across the twenty-five soil cores, and this variability was poorly correlated to soil properties or soil-landscape position.     

Risks and benefits of compost-like materials prepared by the thermal treatment of raw scallop hepatopancreas for supplying cadmium and the growth of alfalfa (Medicago sativa L.)

Scallop hepatopancreas, fishery waste, contains relatively high levels of Cd and organic nitrogen compounds, the latter of which represent a fertilizer. In this study, raw scallop hepatopancreas tissue was thermally treated with sawdust and red loam in the presence of an iron catalyst to produce compost-like materials (CLMs). Two CLM samples were prepared by varying the content of raw scallop hepatopancreas tissue: 46 wt.% for CLM-1 and 18 wt.% for CLM-2. Mixtures of control soil (CTL) and CLMs (CLM content: 10 and 25 wt.%) were examined for the growth of alfalfa (Medicago sativa L.) to evaluate the risks and benefits of using this material for fertilization. The Cd content in shoots and roots of alfalfa, that were grown in the presence of CLMs, was significantly higher than those for the plants grown in the CTL, indicating that Cd had accumulated in the plants from CLMs. The accumulation of Cd in the alfalfa roots was quite high in the case of the 25% CLM-1 sample. However, alfalfa growth was significantly promoted in the presence of 10% CLM-1. This can be attributed to the higher levels of nitrogen and humic substances, which serve as fertilizer components. Although the fertilization effect in case of CLM-1showed a potential benefit, the accumulation of Cd in alfalfa was clearly increased in the presence of both CLMs. In conclusion, the use of CLMs produced from raw scallop hepatopancreas tissue can be considered to have a desirable benefit from standpoint of its use as fertilizer, but is accompanied by a risk of the accumulation of Cd in alfalfa plants.     

溶液中阴离子和腐殖酸对UV/H2O2降解2,4-二氯酚的影响

研究了UV/H2O2工艺对2,4-二氯酚(2,4-DCP)的去除效果和水中阴离子、腐殖酸对该工艺降解2,4-DCP的影响.结果表明:UV/H2O2工艺可以有效地去除水中2,4-DCP,光降解过程符合一级反应动力学模型;在H2O2投加量为8 mg/L、1个30 W低压汞灯照射下,2,4-DCP在蒸馏水和自来水中反应速率常数分别为0.023 2、0.016 2 min-1;NO-3、Cl-、HCO-3对2,4-DCP光降解有抑制作用,当3种阴离子摩尔浓度为0.5、10.0、20.0 mmol/L时,对2,4-DCP光降解的抑制程度为HCO-3＞NO-3＞Cl-;腐殖酸在低浓度时,促进光降解反应进行,在高浓度时,2,4-DCP的光降解受到抑制.自来水中的反应速率常数低于蒸馏水中的反应速率常数是由于水中多种阴离子和腐殖酸影响的结果.     

Vapour of the free acid of the herbicide 2,4-D is toxic to tomato and lettuce plants

Tomato and lettuce plants were exposed to vapour of the free acid of [14C-phenyl] 2,4-D at concentrations in the range 1-600 pg litre(-1) for periods of 6, 24 or 72 h. The rate of uptake of radiolabel by tomato was about twice that by lettuce at the same vapour concentration. Uptake rates were linearly related to external vapour concentration. The relationship between uptake and vapour concentration of 2,4-D for the two species was similar to published values for the butyl and iso-octyl esters. The distribution of herbicide residue in the plant immediately after exposure indicated that the apical leaves of lettuce are particularly active in assimilating vapour, whereas for tomato, leaf position had no influence. Forty days after exposure, both species showed symptoms of toxicity and reduction in shoot dry weight typical of similar doses of 2,4-D esters. It is concluded that the vapour of 2,4-D represents a potential hazard to susceptible plants, and that further work is needed to determine the conditions likely to lead to the production of vapour of the free acids of phenoxyalkanoic herbicides following spraying.