Constitutive expression of a high-affinity sulfate transporter in Indian mustard affects metal tolerance and accumulation

The Stylosanthes hamata SHST1 gene encodes a high-affinity sulfate transporter located in the plasma membrane. In this study the S. hamata SHST1 gene was constitutively expressed in Indian mustard [Brassica juncea (L.) Czern.] to investigate its importance for tolerance and accumulation of various oxyanions that may be transported by SHST1 and for cadmium, which is detoxified by sulfur-rich compounds. The transgenic SHST1 lines SHST1-12C and SHST1-4C were compared with wild-type Indian mustard for tolerance and accumulation of arsenate, chromate, tungstate, vanadate, and cadmium. As seedlings the SHST1 plants accumulated significantly more Cd and W, and somewhat more Cr and V. The SHST1 seedlings were less tolerant to Cd, Mo, and V compared to wild-type plants. Mature SHST1 plants were less tolerant than wild-type plants to Cd and Cr. SHST1 plants accumulated significantly more Cd, Cr, and W in their roots than wild-type plants. In their shoots they accumulated significantly more Cr and somewhat more V and W. Shoot Cd accumulation was significantly lower than in wild-type, and As levels were somewhat reduced. Compared to wild-type plants, sulfur accumulation was enhanced in roots of SHST1 plants but not in shoots. Together these results suggest that SHST1 can facilitate uptake of other oxyanions in addition to sulfate and that SHST1 mediates uptake in roots rather than root-to-shoot translocation. Since SHST1 overexpression led to enhanced accumulation of Cr, Cd, V, and W, this approach shows some potential for phytoremediation, especially if it could be combined with the expression of a gene that confers enhanced metal translocation or tolerance.     

Effects of organic amendments on the reduction and phytoavailability of chromate in mineral soil

In this study, seven organic amendments (biosolid compost, farm yard manure, fish manure, horse manure, spent mushroom, pig manure, and poultry manure) were investigated for their effects on the reduction of hexavalent chromium [chromate, Cr(VI)] in a mineral soil (Manawatu sandy soil) low in organic matter content. Addition of organic amendments enhanced the rate of reduction of Cr(VI) to Cr(III) in the soil. At the same level of total organic carbon addition, there was a significant difference in the extent of Cr(VI) reduction among the soils treated with organic amendments. There was, however, a significant positive linear relationship between the extent of Cr(VI) reduction and the amount of dissolved organic carbon in the soil. The effect of biosolid compost on the uptake of Cr(VI) from the soil, treated with various levels of Cr(VI) (0-1200 mg Cr kg(-1) soil), was examined with mustard (Brassica juncea L.) plants. Increasing addition of Cr(VI) increased Cr concentration in plants, resulting in decreased plant growth (i.e., phytotoxicity). Addition of the biosolid compost was effective in reducing the phytotoxicity of Cr(VI). The redistribution of Cr(VI) in various soil components was evaluated by a sequential fractionation scheme. In the unamended soil, the concentration of Cr was higher in the organic-bound, oxide-bound, and residual fractions than in the soluble and exchangeable fractions. Addition of organic amendments also decreased the concentration of the soluble and exchangeable fractions but especially increased the organic-bound fraction in soil.     

Overexpression of ATP sulfurylase in Indian mustard: effects on tolerance and accumulation of twelve metals

Indian mustard [Brassica juncea (L.) Czern.] transgenics overexpressing ATP sulfurylase (APS plants) were shown previously to have higher levels of total thiols, S, and Se. The present study explores the effect of ATP sulfurylase overexpression on tolerance and accumulation of other metals, both oxyanions and cations, reasoning that some anions may react directly with ATP sulfurylase, while other ions may be bound by its thiol end products. The APS transgenics were compared with wild-type plants with respect to tolerance and accumulation of As, Cd, Cr, Cu, Hg, Mn, Mo, Ni, Pb, V, W, and Zn, supplied individually in agar medium (seedlings) or in hydroponics (mature plants). At the seedling stage, APS transgenics were more tolerant than wild type to As(III), As(V), Cd, Cu, Hg, and Zn, but less tolerant to Mo and V. The APS seedlings had up to 2.5-fold higher shoot concentrations of As(III), As(V), Hg, Mo, Pb, and V, and somewhat lower Cr levels. Mature APS plants contained up to 2.5-fold higher shoot concentrations of Cd, Cr, Cu, Mo, V, and W than wild type. They also contained 1.5- to 2-fold higher levels of the essential elements Fe, Mo, and S in most of the treatments. Mature APS plants showed no differences in metal tolerance compared with the wild type. Overexpression of ATP sulfurylase may be a promising approach to create plants with enhanced phytoextraction capacity for mixtures of metals.     

Effects of plants on the removal of hexavalent chromium in wetland sediments

The effect of two wetland plants, Typha latifolia L. (cattail) and Phragmites australis (Cav.) Trin. ex Steud (common reed), on the fate of Cr(VI) in wetland sediments was investigated using greenhouse bench-scale microcosm experiments. The removal of Cr(VI) was monitored based on the vertical profiles of aqueous Cr(VI) in the sediments. The Cr(VI) removal rates were estimated taking into account plant transpiration, which was found to significantly concentrate dissolved species in the sediments. After correcting for evapotranspiration, the actual Cr(VI) removal rates were significantly higher than would be inferred from uncorrected profiles. On average, the Cr(VI) removal rates were 0.005 to 0.017 mg L(-1) d(-1), 0.0003 to 0.08 mg L(-1) d(-1), and 0.004 to 0.13 mg L(-1) d(-1) for the control, T. latifolia, and P. australis microcosms, respectively. The fate of the removed Cr(VI) was examined by determining the quantity and chemical speciation of the Cr in the sediment and plant materials. Chromium(III) was the dominant form of Cr in both the sediment and plants, and precipitation of Cr(III) in the sediment was the major pathway responsible for the disappearance of aqueous Cr(VI) from the pore water. Incubation results showed that abiotic reduction was the primary mechanism underlying Cr(VI) removal in the microcosm sediments. Organic compounds produced by plants, including root exudates and mineralization products of dead roots, are thought to be the factor that is either directly or indirectly responsible for the gap between Cr(VI) removal efficiencies in the sediments of the vegetated and unvegetated microcosms.     

Longevity of acid discharges from underground mines located above the regional water table

The duration of acid mine drainage flowing out of underground mines is important in the design of watershed restoration and abandoned mine land reclamation projects. Past studies have reported that acid water flows from underground mines for hundreds of years with little change, while others state that poor drainage quality may last only 20 to 40 years. More than 150 above-drainage (those not flooded after abandonment) underground mine discharges from Pittsburgh and Upper Freeport coal seams were located and sampled during 1968 in northern West Virginia, and we revisited 44 of those sites in 1999-2000 and measured water flow, pH, acidity, Fe, sulfate, and conductivity. We found no significant difference in flows between 1968 and 1999-2000. Therefore, we felt the water quality data could be compared and the data represented real changes in pollutant concentrations. There were significant water quality differences between year and coal seam, but no effect of disturbance. While pH was not significantly improved, average total acidity declined 79% between 1968 and 1999-2000 in Pittsburgh mines (from 66.8 to 14 mmol H+ L(-1)) and 56% in Upper Freeport mines (from 23.8 to 10.4 mmol H+ L(-1)). Iron decreased an average of about 80% across all sites (from an average of 400 to 72 mg L(-1)), while sulfate decreased between 50 and 75%. Pittsburgh seam discharge water was much worse in 1968 than Upper Freeport seam water. Twenty of our 44 sites had water quality information in 1980, which served as a midpoint to assess the slope of the decline in acidity and metal concentrations. Five of 20 sites (25%) showed an apparent exponential rate of decline in acidity and iron, while 10 of 20 sites (50%) showed a more linear decline. Drainage from five Upper Freeport sites increased in acidity and iron. While it is clear that surface mines and below-drainage underground mines improve in discharge quality relatively rapidly (20-40 years), above-drainage underground mines are not as easily predicted. In total, the drainage from 34 out of 44 (77%) above-drainage underground mines showed significant improvement in acidity over time, some exponentially and some linearly. Ten discharges showed no improvement and three of these got much worse.     

Particulate and dissolved phosphorus chemical separation and phosphorus release from treated dairy manure

In confined animal feeding operations, liquid manure systems present special handling and storage challenges because of the large volume of diluted wastes. Water treatment polymers and mineral phosphorus (P) immobilizing chemicals [AI2(SO4)3 x 18H2O, FeCl3-6H2O, and Class C fly ash] were used to determine particulate and dissolved reactive phosphorus (DRP) reduction mechanisms in high total suspended solid (TSS) dairy manure and the P release from treated manure and amended soils. Co-application exceeded the aggregation level achieved with individual manure amendments and resulted in 80 and 90% reduction in metal salt and polymer rates, respectively. At marginally effective polymer rates between 0.01 and 0.25 g L(-1), maximal aggregation was attained in combination with 1 and 10 g L(-1) of aluminum sulfate (3 and 30 mmol Al3+ L(-1)) and iron chloride (3.7 and 37 mmol Fe3+ L(-1)) in 30 g L(-1) (TSS30) and 100 g L(-1) TSS (TSS100) suspensions, respectively. Fly ash induced particulate destabilization at rates > or = 50 g L(-1) and reduced solution-phase DRP at all rates > or = 1 g L(-1) by 52 and 71% in TSS30 and TSS100 suspensions, respectively. Aluminum and Fe salts also lowered DRP at rates < or = 10 g L(-1) and higher concentrations redispersed particulates and increased DRP due to increased suspension acidity and electrical conductivity. The DRP release from treated manure solids and a Typic Paleudult amended with treated manure was reduced, although the amendments increased Mehlich 3-extractable P. Therefore, the synergism of flocculant types allowed input reduction in aggregation aid chemicals, enhancing particulate and dissolved P separation and immobilization in high TSS liquid manure.     

Natural alkalinity generation in neutral lakes affected by acid mine drainage

Lakes in surface mining areas are often subject to continuous loads of acid mine drainage. The knowledge of internal alkalinity generation in a lake is necessary to predict if the lake will stay circumneutral or may acidify. The most important processes of alkalinity production in lakes are sulfate reduction, denitrification, and the burial of N in the sediment. By summarizing data from the literature, we present probable rates of these different processes in circumneutral mining lakes. The critical acidity load that can probably be compensated for by internal processes, is 5.09 mmol(-) m(-2) d(-1) in productive lakes and 0.50 mmol(-) m(-2) d(-1) in less productive lakes. Under the assumption that methanogenesis is inhibited by high sulfate concentrations, the highest probable acidity loads in such lakes are 6.85 mmol(-) m(-2) d(-1) and 1.06 mmol(-) m(-2) d(-1), respectively. Denitrification, sulfate reduction, and N burial contributed significantly to total alkalinity production. Sulfate reduction had the largest potential. However, existing models cannot predict alkalinity generation from sulfate concentrations alone because the long-term stability of reduced S compounds in the sediment is crucial for a sustainable biological alkalinity generation. The larger acid-neutralizing potential of higher trophic lakes is caused both by higher rates of microbial activity and by a greater stability of reduced reaction products in the sediment. The largest uncertainties in our knowledge with respect to the total alkalinity budget are related to microbial processes in sulfate-rich freshwater lakes and the long-term stability of reduced reaction products in the sediment.     

Inoculation of plant growth promoting bacterium Achromobacter xylosoxidans strain Ax10 for the improvement of copper phytoextraction by Brassica juncea

In this study, a copper-resistant plant growth promoting bacterial (PGPB) strain Ax10 was isolated from a Cu mine soil to assess its plant growth promotion and copper uptake in Brassica juncea. The strain Ax10 tolerated concentrations up to 600 mg CuL(-1) on a Luria-Bertani (LB) agar medium and utilized 1-aminocyclopropane-1-carboxylic acid (ACC) as a sole N source in DF salts minimal medium. The strain Ax10 was characterized as Achromobacter xylosoxidans based on its 16S rDNA sequence homology (99%). The bacterium A. xylosoxidans Ax10 has also exhibited the capability of producing indole acetic acid (IAA) (6.4 microg mL(-1)), and solubilizing inorganic phosphate (89.6 microg mL(-1)) in specific culture media. In pot experiments, inoculation of A. xylosoxidans Ax10 significantly increased the root length, shoot length, fresh weight and dry weight of B. juncea plants compared to the control. This effect can be attributed to the utilization of ACC, production of IAA and solubilization of phosphate. Furthermore, A. xylosoxidans Ax10 inoculation significantly improved Cu uptake by B. juncea. Owing to its wide action spectrum, the Cu-resistant A. xylosoxidans Ax10 could serve as an effective metal sequestering and growth promoting bioinoculant for plants in Cu-stressed soil. The present study has provided a new insight into the phytoremediation of Cu-contaminated soil.     

Cadmium leaching from micro-lysimeters planted with the hyperaccumulator Thlaspi caerulescens: experimental findings and modeling

The use of heavy metal hyperaccumulating plants has the potential to become a promising new technique to remediate contaminated sites. We investigated the role of metal mobilization in the Cd hyperaccumulation of Thlaspi caerulescens (J. & C. Presl, 'Ganges'). In a micro-lysimeter experiment we investigated the dynamics of Cd concentration of leachate as well as Cd removal by plant uptake in four treatments: (i) Control (bare soil), (ii) T. caerulescens, (iii) nonhyperaccumulator Brassica juncea (L.) Czern. ('PI 426308'), and (iv) co-cropping of the hyperaccumulator and nonhyperaccumulator. The experimental findings were analyzed using one- and two-site rate-limited desorption models. Co-cropping of T. caerulescens and B. juncea did not enhance metal uptake by B. juncea. Although Cd uptake of T. caerulescens was 10 times higher than that of B. juncea, the Cd concentration of leachate of the T. caerulescens treatment did not decrease below that of the B. juncea treatment. The Cd depletion in leachate was well reproduced by the two-site rate-limited desorption model. The optimized desorption coefficient was three orders of magnitude higher in the rhizosphere than in the bulk soil. Our results indicate that T. caerulescens accelerates the resupply of Cd from soil pointing to an important role of kinetic desorption in the hyperaccumulation by T. caerulescens.     

Comparative effect of Al, Se, and Mo toxicity on NO3(-) assimilation in sunflower (Helianthus annuus L.) plants

Here, we study the effect caused by three trace elements--Al, Se, and Mo--applied at the same concentration (100 microM) and in their oxyanionic forms--NaAl(OH)(4), Na(2)SeO(4), and Na(2)MoO(4)--on NO(3)(-) assimilation (NO(3)(-), nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT) activities, and concentrations of amino acids and proteins) in sunflower (Helianthus annuus L. var. Kasol) plants. The most harmful element for sunflower plants proved to be selenate, followed by aluminate. On the contrary, the application of molybdate had no negative effect on the growth of this plant, suggesting the possibility of using sunflower for the phytoremediation of this metal, mainly in agricultural zones used for grazing where the excess of this element can provoke problems of molybdenosis in ruminants (particularly in cattle). In addition, we found that the alteration of NO(3)(-) assimilation by SeO(4)(2-) and Al(OH)(4)(-) directly influences the growth and development of plants, foliar inhibition of NR activity by SeO(4)(2-) being more harmful than the decrease in foliar availability of NO(3)(-) provoked by Al(OH)(4)(-).     

分光光度法测定测田废水中的COD_(Cr)

为了快速监测油田废水中的化学需氧量ＣＯＤＣｒ,因此采用ＴＬ－１（Ａ）型污水ＣＯＤＣｒ速测仪进行加热催化消解,然后再用分光光度比色法测定ＣＯＤＣｒ,实验中进行了方法的准确度、精确度及Ｃｌ－影响实验,并与标准的重铬酸钾法进行了对比实验,结果说明分光光度法简单快速、重现性较好、准确度较高,对同一产品的测定结果与重铬酸钾法非常一致。因此,本方法可用于油田废水中的ＣＯＤＣｒ监测。     

Low-temperature chromium(VI) biotransformation in soil with varying electron acceptors

Effective and low-cost strategies for remediating chromium (Cr)-contaminated soil are needed. Chromium(VI) leaching from contaminated soil into ground water and surface water threatens water supplies and the environment. This study tested indigenous Cr(VI) microbial transformation in batch systems at 10 degrees C in the presence of various electron acceptors. The effects of carbon addition, spiked Cr(VI), and mixing highly contaminated soil with less contaminated soil were investigated. The results indicated that Cr(VI) can be biotransformed in the presence of different electron acceptors including oxygen, nitrate, sulfate, and iron. Sugar addition had the greatest effect on enhancing Cr(VI) removal. Less dissolved organic carbon (DOC) was consumed per amount of Cr(VI) transformed under anaerobic conditions [0.8-93 mg DOC/mg Cr(VI)] compared with aerobic conditions [1.4-265 mg DOC/mg Cr(VI)]. Toxicity of high concentrations (< 160 mg/L) of spiked Cr(VI) were not evident. At Cr(VI) concentrations > 40 mg/L, aerobic conditions promoted faster Cr(VI) reduction than anaerobic conditions with nitrate or sulfate present. Biotransformation of Cr(VI) in highly contaminated soil (22,000 mg Cr/kg) was facilitated by mixing with less-contaminated soil. The study results provide a framework for evaluating indigenous Cr(VI) microbial transformation and enhance the ability to develop strategies for soil treatment.     

Chromate reduction by chromium-resistant bacteria isolated from soils contaminated with dichromate

Extensive use of hexavalent chromium [Cr(VI)] in various industrial applications has caused substantial environmental contamination. Chromium-resistant bacteria isolated from soils can be used to remove toxic Cr(VI) from contaminated environments. This study was conducted to isolate chromium-resistant bacteria from soils contaminated with dichromate and describes the effects of some environmental factors such as pH, temperature, and time on Cr(VI) reduction and resistance. We found that chromium-resistant bacteria can tolerate 2500 mg L(-1) Cr(VI), but most of the isolates tolerated and reduced Cr(VI) at concentrations lower than 1500 mg L(-1). Chromate reduction activity of whole cells was detected in five isolates. Most of these isolates belong to the genus Bacillus as identified by the 16S rRNA gene sequencing. Maximal Cr(VI) reduction was observed at the optimum pH (7.0-9.0) and temperature (30 degrees C) of growth. One bacterial isolate (Bacillus sp. ES 29) was able to aerobically reduce 90% of Cr(VI) in six hours. The Cr(VI) reduction activity of the whole cells of five isolates had a K(M) of 0.271 (2.61 mM) to 1.51 mg L(-1) (14.50 mM) and a V(max) of 88.4 (14.17 nmol min(-1)) to 489 mg L9-1) h(-1) (78.36 nmol min(-1)). Our consortia and monocultures of these isolates can be useful for Cr(VI) detoxification at low and high concentrations in Cr(VI)-contaminated environments and under a wide range of environmental conditions.     

Sulfate removal from waste chemicals by precipitation

Chemical oxidation using Fenton's reagent has proven to be a viable alternative to the oxidative destruction of organic pollutants in mixed waste chemicals, but the sulfate concentration in the treated liquor was still above the acceptable limits for effluent discharge. In this paper, the feasibility of sulfate removal from complex laboratory wastewaters using barium and calcium precipitation was investigated. The process was applied to different wastewater cases (two composite samples generated in different periods) in order to study the effect of the wastewater composition on the sulfate precipitation. The experiments were performed with raw and oxidized wastewater samples, and carried out according to the following steps: (1) evaluate the pH effect upon sulfate precipitation on raw wastewaters at pH range of 2-8; (2) conduct sulfate precipitation experiments on raw and oxidized wastewaters; and (3) characterize the precipitate yielded. At a concentration of 80 g L(-1), barium precipitation achieved a sulfate removal up to 61.4% while calcium precipitation provided over 99% sulfate removal in raw and oxidized wastewaters and for both samples. Calcium precipitation was chosen to be performed after Fenton's oxidation; hence this process configuration favors the production of higher quality precipitates. The results showed that, when dried at 105 degrees C, the precipitate is composed of hemidrate and anhydrous calcium sulfate ( approximately 99.8%) and trace metals ( approximately 0.2%: Fe, Cr, Mn, Co, Ag, Mg, K, Na), what makes it suitable for reuse in innumerous processes.     

In situ reduction of chromium(VI) in heavily contaminated soils through organic carbon amendment

Chromium has become an important soil contaminant at many sites, and facilitating in situ reduction of toxic Cr(VI) to nontoxic Cr(III) is becoming an attractive remediation strategy. Acceleration of Cr(VI) reduction in soils by addition of organic carbon was tested in columns pretreated with solutions containing 1000 and 10 000 mg L(-1) Cr(VI) to evaluate potential in situ remediation of highly contaminated soils. Solutions containing 0,800, or 4000 mg L(-1) organic carbon in the form of tryptic soy broth or lactate were diffused into the Cr(VI)-contaminated soils. Changes in Cr oxidation state were monitored through periodic micro-XANES analyses of soil columns. Effective first-order reduction rate constants ranged from 1.4 x 10(-8) to 1.5 x 10(-7) s(-1), with higher values obtained for lower levels of initial Cr(VI) and higher levels of organic carbon. Comparisons with sterile soils showed that microbially dependent processes were largely responsible for Cr(VI) reduction, except in the soils initially exposed to 10 000 mg L(-1) Cr(VI) solutions that receive little (800 mg L(-1)) or no organic carbon. However, the microbial populations (< or = 2.1 x 10(5) g(-1)) in the viable soils are probably too low for direct enzymatic Cr(VI) reduction to be important. Thus, synergistic effects sustained in whole soil systems may have accounted for most of the observed reduction. These results show that acceleration of in situ Cr(VI) reduction with addition of organic carbon is possible in even heavily contaminated soils and suggest that microbially dependent reduction pathways can be dominant.     

Uptake and release of cesium-137 by five plant species as influenced by soil amendments in field experiments

Phytoextraction field experiments were conducted on soil contaminated with 0.39 to 8.7 Bq/g of 137Cs to determine the capacity of five plant species to accumulate 137Cs and the effects of three soil treatments on uptake. The plants tested were redroot pigweed (Amaranthus retroflexus L. var. aureus); a mixture of redroot pigweed and spreading pigweed (A. graecizans L.); purple amaranth (A. cruteus L.) x Powell's amaranth (A. powellii S. Watson), referred to here as the amaranth hybrid; Indian mustard [Brassica juncea (L.) Czern.]; and cabbage (Brassica oleracea L. var. capitata). For control plants, the concentration ratios (CR) of 137Cs were greatest for redroot pigweed and the amaranth hybrid, with average CR values of 1.0 +/- 0.24 and 0.95 +/- 0.14, respectively. The lowest value was for Indian mustard at 0.36 +/- 0.10. The soil treatments included (i) application of NH4NO3 solution to the soil after plants had matured, (ii) addition of composted manure to increase organic matter content of the soil, (iii) combination of the manure and ammonium solution treatments, and (iv) controls. The ammonium solution gave little overall increase in accumulation of 137Cs. The use of composted manure also had little influence, but the combination of the composted manure with application of ammonium solutions had a distinctly negative effect on plant uptake of 137Cs. On average the fraction of 137Cs taken up from the soil was reduced by 57.4 +/- 1.2% compared with controls. This was the result of release of competing ions, primarily Ca, from the manure and was observed across all five plant species tested. The application of ammonium solution took place in the last two weeks before harvest. The reduction of plant 137Cs content, by addition of the ammonium solution, as it interacted with the manure, indicates that substantial quantities 137Cs can be released from the shoots of plants as a result of sudden changes in soil solution chemistry.     

Dissolution of trace element contaminants from two coastal plain soils as affected by pH

Trace element mobility in soils depends on contaminant concentration, chemical speciation, water movement, and soil matrix properties such as mineralogy, pH, and redox potential. Our objective was to characterize trace element dissolution in response to acidification of soil samples from two abandoned incinerators in the North Carolina Coastal Plain. Trace element concentrations in 11 soil samples from both sites ranged from 2 to 46 mg Cu kg(-1), 3 to 105 mg Pb kg(-1), 1 to 102 mg Zn kg(-1), 3 to 11 mg Cr kg(-1), < 0.1 to 10 mg As kg(-1), and < 0.01 to 0.9 mg Cd kg(-1). Acidified CaCl2 solutions were passed through soil columns to bring the effluent solution to approximately pH 4 during a 280-h flow period. Maximum concentrations of dissolved Cu, Pb, and Zn at the lowest pH of an experiment (pH 3.8-4.1) were 0.32 mg Cu L(-1), 0.11 mg Pb L(-1), and 1.3 mg Zn L(-1) for samples from the site with well-drained soils, and 0.25 mg Cu L(-1), 1.2 mg Pb L(-1), and 1.4 mg Zn L(-1) for samples from the site with more poorly drained soils. Dissolved Cu concentration at pH 4 increased linearly with increasing soil Cu concentration, but no such relationship was found for Zn. Dissolved concentrations of other trace elements were below our analytical detection limits. Synchrotron X-ray absorption near edge structure (XANES) spectroscopy showed that Cr and As were in their less mobile Cr(III) and As(V) oxidation states. XANES analysis of Cu and Zn on selected samples indicated an association of Cu(II) with soil organic matter and Zn(II) with Al- and Fe-oxides or franklinite.     

ESTIMATED BACKGROUND CONCENTRATIONS OF SULFATE IN DILUTE LAKES1

ABSTRACT: Lake water sulfate values were examined for two areas in western Norway and the western United States presently receiving low levels of sulfate in atmospheric deposition. Data from these areas were used to estimate background concentrations of sulfate in lakes found in areas currently receiving acidic deposition. The two areas contain dilute lakes with concentrations of sea-salt corrected Ca+ Mg less than 50 μeq/l or conductivity < 10μS cm^-1and receive precipitation with volume-weighted mean pH > 4.8. Based on observations from these areas, we conclude that background sulfate concentrations were probably no more than 10 to 15 μeq L^-1for areas of Norway and the U.S. containing lakes with low concentrations of base cations. For southern Norway and the northeastern U.S., present lakewater sulfate concentrations represent an increase of 7 to 10 fold above these estimated background values.     

Sulfur, chromium, and selenium accumulated in Chinese cabbage under direct covers

Currently, pollution of our agricultural soils and waters is increasing and is often associated with many human health ailments. Soils contaminated with low levels of heavy metals and other trace elements are frequently used for growing vegetable crops and in such a situation, these toxic contaminants often accumulate in the edible portions of these agricultural plants and thereby enter the human food chain. In 3 consecutive years of field experiments (1994-1996), two different crop-covering treatments--T (50 microm perforated polyethylene), and T2 (17 gm(-2) non-woven polypropylene)--were used to modify the environmental conditions for the growth of Chinese cabbage 'Nagaoka 50' [Brassica rapa L. (Pekinensis group)]. Open-air plots (T(0)) were used as controls. Analytical determinations of chromium (Cr), selenium (Se), two forms of sulfur (total-S and sulfate-S), and amino acids (Isoleucine, leucine, lysine, methionine, serine, threonine, and valine) were performed utilizing plant shoots for analysis. The T1 and T2 treated plants contained concentrations of lysine, methionine, serine, and threonine higher than in T(0). Under T1, the extent of Cr and Se removal in the field was more favorable. Direct covers could be used in contaminated agricultural zones for a variety of plant species, not just for use with those plants previously reported to be efficient at bio-accumulating toxic elements because the thermal effect created by the covers favors phytoextraction processes. However, it is clear that the accumulation of these toxic substances in the plants (Cr) would deem the plant material unsuitable for human consumption and use as animal fodder.     

Impact of soil amendments on reducing phosphorus losses from runoff in sod

Received for publication December 22, 2004. Research was initiated to study the interaction between soil amendments (lime, gypsum, and ferrous sulfate) and dissolved molybdate reactive phosphorus [RP(<0.45)] losses from manure applications from concentrated runoff flow through a sod surface. Four run-over boxes (2.2-m2 surface area) were prepared for each treatment with a bermudagrass [Cynodon dactylon (L.) Pers.] sod surface (using sod blocks) and composted dairy manure was surface-applied at rates of 0, 4.5, 9, or 13.5 Mg ha-1. The three soil amendments were then applied to the boxes. Two 30-min runoff events were conducted and runoff water was collected at 10-min intervals and analyzed for RP(<0.45). Results indicated that the addition of ferrous sulfate was very effective at reducing the level of RP(<0.45). in runoff water, reducing RP(<0.45) from 1.3 mg L(-1) for the highest compost rate with no amendment to 0.2 mg L(-1) for the ferrous sulfate in the first 10 min of runoff. Lime and gypsum showed a small impact on reducing RP(<0.45), with a reduction in the first 10 min to 0.9 and 0.8 mg L(-1), respectively. The ferrous sulfate reduced the RP(<0.45) in the tank at the end of the first runoff event by 66.3% compared with no amendment. In the second runoff event, the ferrous sulfate was very effective at reducing RP(<0.45) in runoff, with no significant differences in RP(<0.45) with application of 13.5 Mg ha(-1) compost compared with no manure application. The results indicate that the addition of ferrous sulfate may greatly reduce RP(<0.45) losses in runoff and has considerable potential to be used on pasture, turfgrass, and filter strips to reduce the initial RP(<0.45) losses from manure application to the environment.