However, further investigation will be necessary. We plan to utilize XAS to corroborate these results.Synthetic chelators such as EDTA and NTA can form stable, soluble complexes with heavy metals and were commonly used as cleaning agents during industrial processing at DoD sites. Metal–chelate complexes have entered the environment and may migrate freely in groundwater. When conditions necessitate immobilization of the contaminant, one approach for limiting the migration of the metal is to biodegrade the organic ligand. The resulting free metal ions are likely to adsorb to mineral surfaces or form oxide mineral precipitates that would transport poorly in groundwater. A number of EDTA- and NTA-degrading organisms have been identified. However, little is known about the enzymes that catalyze the degradation reactions and how these reactions proceed in the environment. In one study, microbial degradation of EDTA by the environmental isolate BNC1, was influenced by the complexed metal. Similar fundamental research focus-ing on the mechanisms of enzymatic degradation of synthetic chelators is expected to provide useful information for including these enzymes in engineered bio-remediation technologies. The current study focuses on the interaction of bacterial strains with copper chelates. We look at the effect of Cu bio-transformation in the presence of different copper chelates. Metal concentrations in growth media-biomass and pellets are analyzed using AA spectroscopy. The results of these studies of toxic metals and microorganism interaction will enable us to determine bio-remediation capabilities for copper and similar metals.Equimolar amounts of the ligands and of copper nitrate were mixed in enough water to make solutions ranging from 0.010 M to 3.0×10-3 M of the complexes and stirred for two hours. The pH of the solution was adjusted to 5.6.
The solution obtained was used to pre-pare the culture media. IR spectra in solution were obtained in a Nicolet Magna FTIR-750 spectropho-tometer in BaF2. A total of 64 scans were taken. UV-Visible spectra were taken on a Beckman 4B spectro photometer using 1.0 cm quartz cells. NMR spectra were taken using a Bruker 300 NMR spectrometer. Cultured cells from selected strains Streptococcus,big plastic pots Staphylococcus and Bacillus were inoculated into 100 mL of the liquid culture media spiked with each of the copper solutions to a final concentration of 20 ppm copper. They were placed in a shaker at 32°C at 200 rpm for 24 hrs. Every two hours 5 ml aliquots were removed and their absorbance measured at 520 nm. A control containing copper nitrate was prepared for comparison. After 24 hours of incubation, 10 mL of the liquid media were removed and centrifuged at 5000 rpm for 10 min. The cells were washed five times with 20 mL of buffer solution. The amount of copper remaining in the supernatant and in the washing was deter-mined by ICP. Experimental data: Figure 1 shows the growth curves for the bacillus studied in the presence of the com-plexes Cu, Cu, Cu, Cu and Cu. The curve for Cu is not shown because no growth was observed at 24 hours. Lower concentrations are currently being studied. Previous work in our lab has shown that the bacteria studied grow very slowly at concentrations higher than 0.35 mM of the complexes of the other ligands. From the curves, a similar pattern is observed for each complex, so no evidence for a dramatic effect was found. Nevertheless, the presence of copper in the concentration studied seems to increase the amount of cells growing at longer times . We summarize the results obtained in percent of copper for the different bacteria in different copper complexes.Tidal marsh plants form an expansive fringe around our coastal ecosystems, serving as a buffer against storms, a habitat for wildlife, an anchor for sediments and a phytoremediator of contaminated sediments. Their capacity to take up contaminants and possibly degrade them has had little attention in comparison to other plant systems.
To better understand the role of estuarine plants in reducing contamination in coastal sediments, three dominant estuarine plants from two sites of known contamination were chosen for bio-chemical adaptive responses. Juncus roemerianus and Spartina alterniflora are the most abundant plant species found in Mississippi tidal marshes and are major salt marsh species found in estuaries on the Gulf and southern Atlantic coasts. Both have extensive rhizome systems. Sagittaria lancifo-lia, called arrowhead or duck potato, also has stout, deeply buried rhizomes and is found abundantly in fresh to brackish marshes. These three species were chosen for study because of their abundance in the estuary and their tolerance to contaminants. The objective of the study was to compare the ability of the three marsh plants to adapt to elevated contaminant levels by examining glutathione and peroxidase responses. Glutathione acts as an antioxidant to protect labile macromolecules against attack by free radicals and hydrogen peroxide, which form as a result of oxidative stress. Peroxidase activity increases when plants are under toxic stress as the plant trans-forms or degrades the toxicant causing the stress. From previous studies, it appears that those plants with strong peroxidase systems can better cope when exposed to toxic chemicals. Three locations were chosen for study: the mouth of an estuarine small boat harbor located in Ocean Springs, Miss., a small inlet on East Beach in Ocean Springs which served as a control, and an inlet adjacent to Keesler Air Force Base on Back Bay in Biloxi, Miss. Analysis of sediments in the Ocean Springs Harbor indicated one area relatively high in silver and another high in cadmium and an extensive area of petroleum impacted sediments. The inlet adjacent to Keesler AFB had high levels of sediment petroleum hydrocarbons. This inland site was the only site colonized by all three plant species. Contaminated sediments pose a significant threat to environmental and human health. They are a sink for a wide range of pollutants.
Cleanup of contaminated sediments by physical means can threaten sensitive habitats. Phytoremediation offers an alternative method of sediment remediation. In naturally occur-ring ecosystems, a significant fraction of toxic organic compounds are sorbed either on the mineral solids or the organic matter in sediments. The resistance to contaminant desorption from the sediments affects bio-availability, toxicity and the efficiency of bio-remedation technology. Plants ooze materials from their roots called exudates. Little is known regarding what affects exudate concentrations and chemical composition or what role they play in possibly desorbing contaminants from sediment particles, making them more bio-available to microbes and plants. One objective of the exudate research is to quantify surfactant characteristics of exudates from estuarine plants with a new technique using a surfactant electrode developed by Orion. Another objective is to compare plant exudate patterns under different environmental conditions, and finally, to compare exudates when plants are exposed to polynuclear aromatic hydrocar-bons . Spartina alterniflora, commonly known as smooth cord grass, is an important salt marsh plant which generally occurs in extensive stands in saline areas along the Gulf as well as the Atlantic and Pacific coast-lines. Besides acting as a buffer against storm surges and as a habitat for young fish and wildlife, S. alterni-flora most certainly plays a role in phytoremediation. Though there are not yet supportive data regarding this plant’s ability to degrade sediment contaminants, a massive root system supplies large amounts of exudates to the sediment for microbial utilization. The authors postulate that these exudates also act as a surfactant,large plastic garden pots solubilizing soil-bound contaminants and thus allowing microbial degradation and possibly plant uptake and degradation/transformation. A study was initiated in summer 1999 to collect exudates from S. alterniflora and to measure surfactant characteristics. S. alterniflora seedlings were collected from a relatively clean estuary and carefully placed into jars with a 1% nutrient solution. Sterile filtering fiber was placed around the mouth of each jar to prevent evaporation and contamination. Identical systems were prepared for controls, except without plants. All jars were placed outside each day for 9 hours and brought inside overnight. Initial water levels were marked, and distilled water was added to the mark as needed to maintain the water level. Plants appeared healthy throughout the six-week experiment. Water containing plant exudates was removed from one set of microcosms weekly for analysis. Exudate solutions were placed in vials and flushed with nitrogen and refrigerated until analyzed using an Orion 960/940 Autochemistry Titration System. The instrument was calibrated using two industrial standard surfactants, sodium lauryl sulfate and hyamine or benzethonium chloride. Ionic and nonionic stan-dards were used to develop a technique for characterizing surfactants. The use of plants to remove/immobilize metals in soils is effective in many applications and non-destructive to natural environmental systems. We have examined the ability of coastal marsh plants to remove metals from contaminated sediments and the mechanisms of removal and storage in the plants.
Many terrestrial and aquatic plants produce metal-binding phytochelatins, synthesized from glutathione in response to heavy metals. Phytochelatins in wetland marsh plants have not previously been identified as a means these plants may employ in coping with elevated levels of heavy metals that are often found in coastal sediments. Phytochelatins are derived from glutathione, a tripeptide that serves as an antioxidant and has other important biochemical functions in plant and animal cells. Its structure is shown in Figure 1. In the presence of toxic heavy metals, many plants synthesize phytochelatins, which are chains with repeated links of two of the glutathione peptides, with each link containing a chelating S group and ending with a terminal glycine. Shorter chain phy-tochelatins are thought usually to result from low-level metal exposure with longer chains elicited as metal levels increase. Objectives of this study are to deter-mine whether marsh plants produce these compounds to sequester and store excessive heavy metals from their rhizosphere and determine if this particular defense mechanism continues to operate for plants that have been exposed to heavy metals long-term. In the first phase of this study we have tested three prominent marsh plants and associated sediments that were collected from sites with a documented history of heavy metal contamination.Phytoremediation may offer an improved solution to cleanup of contaminated soils. Plants can reach contaminants effectively and often can withstand high concentrations of toxic substances. They also serve as hosts to biode-grading microorganisms by providing suitable environments for their habitation in the soil rhizos-phere. Three species of marsh plants were chosen and metal-uptake capacity examined at a metal-contaminated site at Keesler Air Force Base in Biloxi, Miss. Metals associated with various components or phases of sediments show varying degrees of extractability, and presumably, bio-availability. There have been several analytical approaches used to estimate how various metals are partitioned among the sediment fractions. The metals removed by mild extractions are thought to represent that which is bio-available. In this study we chose a simultaneous extraction technique on separate sediment aliquots, preventing the cross contamination and loss problems inherent with other sequential extraction procedures. Results of plant tissue metal analysis are interpreted in terms of the distribution of metals in the bio-available sedimentary fractions.Results for sediment and tissue of S. lancifolia and J. roemerianus from Keesler AFB are shown in Figures 1 and 2. Sediment metals are shown as % of total in the sediments, and plant tissue values are bio-concentra-tion factors , ratios of tissue metal levels to the bio-available metals in sediments. Pb, Zn, Ni and Ag in sediments mostly occurred in Fe oxide fractions, which may not be readily available to plant uptake and account for low metal transfer from sediment to leaves. Similarly, most Cd in sediments of J. romerianus and S. alterniflora was bound to Fe oxides, with little Cd in tissues of these plants. However, Cd in S. lancifolia sediments was found mostly in the easily leachable Mn oxide fraction and was accompanied by a very high BF in leaves of this plant. This finding suggests that metals in Mn oxides may be of much greater importance in uptake ability than those bound to Fe oxides. Bio-available Cu and Cr in these sediments was mostly bound to organics. S. lancifolia showed greater facility in accumulating Cu, though neither it nor S. alterniflora showed any capacity to accumulate Cr. J. roemerianus leaves showed a BF that not only exceeds the BF in the roots, indicating translocation to leaves, but is much higher than for the other plants. We have found that J. roemerianus can move highly insoluble organic compounds from sediments through roots and into the leaves.