Biosurfactant technology for remediation of cadmium and lead contaminated soils

This research focuses on column experiments conducted to evaluate the potential of environmentally compatible rhamnolipid biosurfactant produced by Pseudomonas aeruginosa strain BS2 to remove heavy metals (Cd and Pb) from artificially contaminated soil. Results have shown that di-rhamnolipid removes not only the leachable or available fraction of Cd and Pb but also the bound metals as compared to tap water which removed the mobile fraction only. Washing of contaminated soil with tap water revealed that approximately 2.7% of Cd and 9.8% of Pb in contaminated soil was in freely available or weakly bound forms whereas washing with rhamnolipid removed 92% of Cd and 88% of Pb after 36 h of leaching. This indicated that di-rhamnolipid selectively favours mobilization of metals in the order of Cd>Pb. Biosurfactant specificity observed towards specific metal will help in preferential elution of specific contaminant using di-rhamnolipid. It was further observed that pH of the leachates collected from heavy metal contaminated soil column treated with di-rhamnolipid solution was low (6.60-6.78) as compared to that of leachates from heavy metal contaminated soil column treated with tap water (pH 6.90-7.25), which showed high dissolution of metal species from the contaminated soil and effective leaching of metals with treatment with biosurfactant. The microbial population of the contaminated soil was increased after removal of metals by biosurfactant indicating the decrease of toxicity of metals to soil microflora. This study shows that biosurfactant technology can be an effective and nondestructive method for bioremediation of cadmium and lead contaminated soil.     

Suborganismic and organismic effects of aldicarb and its metabolite aldicarb-sulfoxide to the zebrafish embryo (Danio rerio)

The new European chemical regulation (REACH) requires a short-term fish test for chemicals where the level of production exceeds 10tons per year. For ethical reasons (3R-concept), an alternative to the acute fish test should be introduced to decrease the number of animal testing with fish. The zebrafish embryo (Danio rerio) test became a valuable tool in ecotoxicology and already replaces the acute fish test for the evaluation of wastewater in Germany. Recent efforts are targeted to use this and other fish embryo tests for the effect assessment of chemicals. The toxic effects of the carbamate insecticide aldicarb and its metabolite aldicarb-sulfoxide to zebrafish embryos were analysed using two approaches with different endpoints. Organismic tests were conducted with zebrafish embryos exposed to the pesticides for 48h. In addition, suborganismic effects were examined analysing the enzyme inhibition of cholinesterases and carboxylesterases. On the organismic level, the only sublethal effect seen was the increase of heart rate at low and decrease at higher concentration with the use of aldicarb-sulfoxide but not with aldicarb (concentration range 0.2-300microM). In contrast, analysis of enzyme inhibitions showed high to very high effects caused by the two carbamates. The enzyme inhibition analysis of whole homogenates of exposed embryos may be advantageous for toxicant screening (biomarker of exposure) and might be used to bridge the gap of sensitivity of the (48h old) zebrafish embryos to adult fish when exposed to anti-cholinesterase substances (biomarker of prospective effect).     

Effect of chelating agents and solubility of cadmium complexes on uptake from soil by Brassica juncea

Brassica juncea, or Indian mustard, was grown in soil artificially contaminated with either a soluble salt, CdCl(2), at 186mg Cdkg(-1), or alternately an insoluble, basic salt, CdCO(3), at 90mg Cdkg(-1). These experiments study the range of Cd uptake by Indian mustard from conditions of very high Cd concentration in a soluble form to the other extreme with an insoluble Cd salt. After plants were established, four different chelating agents were applied. Chelating agents increased plant uptake of Cd from the CdCl(2) soil but did not significantly increase plant uptake of Cd from the CdCO(3) contaminated soil. Addition of ethylenediaminetetraacetic acid (EDTA) increased the plant concentration of Cd by almost 10-fold in soils contaminated with CdCl(2), with a concentration of 1283mg Cdkg(-1) in the dried EDTA-treated plants over a concentration of 131mg Cdkg(-1) in plants without added chelate. However, EDTA increased the aqueous solubility of Cd by 36 times over the soil matrix without added chelator, and thereby, increased the possibility of leaching. Other chelators used in both experiments were ethylenebis(oxyethylenenitrilo)tetraacetic acid, trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, and diethylenetriaminepentaacetic acid (DTPA) increasing Cd in plants to 1240, 962, and 437mg Cdkg(-1), respectively. The other chelating agents increased the solubility of Cd in the leachate but not to the extent of EDTA. Comparing all chelating agents studied, DTPA increased plant uptake in terms of Cd in dried plant concentration most relative to the solubility of complexed Cd in runoff water.     

Removal of dinitrotoluenes from water via reduction with iron and peroxidase-catalyzed oxidative polymerization: a comparison between Arthromyces ramosus peroxidase and soybean peroxidase

A two-step process for the removal of dinitrotoluene from water is presented: zero-valent iron reduction is coupled with peroxidase-catalyzed polymerization of the resulting diaminotoluenes (DAT). The effect of pH was examined in the reduction step: at pH 6 the reaction occurred much more rapidly than at pH 8. In the second step, optimal pH and substrate ratio, minimal enzyme concentration and effect of polyethylene glycol (PEG) as an additive for greater than 95% conversion of DAT, over a 3h reaction period were determined using high performance liquid chromatography. Two enzymes were investigated and compared: Arthromyces ramosus peroxidase (ARP) and soybean peroxidase (SBP). The optimal pH values were 5.4 and 5.2 for ARP and SBP, respectively, but SBP was more resistant to mild acid whereas ARP was more stable in neutral solutions. SBP was found to have a greater hydrogen peroxide demand (optimal peroxide/DAT molar ratio for SBP: 2.0 and 3.0 for 2,4-diaminotoluene (2,4-DAT) and 2,6-diaminotoluene (2,6-DAT), respectively; for ARP: 1.5 and 2.75 for 2,4-DAT and 2,6-DAT, respectively) but required significantly less enzyme (0.01 and 0.1 U ml(-1) for 2,4-DAT and 2,6-DAT, respectively) to convert the DAT than ARP (0.4 and 1.5 U ml(-1) for 2,4-DAT and 2,6-DAT, respectively). PEG was shown to have no effect upon the degree of substrate conversion for either enzyme.     

Fluorescence fingerprints and Cu2+-complexing ability of individual molecular size fractions in soil- and waste-borne DOM

Land spreading of organic materials introduces large amounts of dissolved organic matter (DOM) into the soil. DOM has the ability to form stable complexes with heavy metals and can facilitate their transport towards the groundwater. The effects on soil processes are difficult to assess, because different DOM components might react differently towards metal ions. The objective of this study was to investigate the fluorescence signature and the Cu2+-binding capacity of individual molecular size fractions of DOM from various sources. DOM extracted from leaf compost, chicken manure, sugar cane vinasse and a fulvic hypercalcaric cambisol was fractionated by the means of dialysis into four molecular size classes: MW<500, 50012000-14000 Da. Vinasse and leaf compost contained around 80% and 70%, respectively, of the total organic carbon in the fractions with low molecular weight (MW<3500 Da); in chicken manure and soil these fractions accounted for 40% and 50% only. Fluorescence was highest in the fraction MW>12000 Da for leaf compost, chicken manure and soil. The opposite result was obtained for vinasse, where the fractions with low molecular weight showed highest fluorescence intensities, distinguishing it from all other samples. Vinasse showed the greatest ability to bind Cu2+ with a resulting complex concentration of 6.31mgl(-1) while in contact with an excess of Cu2+. Leaf compost, soil and chicken manure followed with 2.69, 1.12, and 0.85mgl(-1), respectively. Within vinasse, the fraction MW<500 Da was able to form the most DOM-Cu complexes, indicating the importance of low molecular weight fractions in metal binding.     

Serum profiles of PCDDs and PCDFs, in individuals near the Escambia Wood Treating Company Superfund site in Pensacola, FL

The Escambia Wood Treating Company (ETC) Superfund site, Pensacola, FL, is contaminated with polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F), benzo(a)pyrene, lead and arsenic from pentachlorophenol (PCP), creosote, and other compounds used to treat utility poles and foundation pilings. Although ETC's operations ceased in 1982, soils in the areas surrounding the facility continue to exhibit elevated levels of contaminants attributable to ETC operations. In July 2000, individuals who may have been affected by contamination from the ETC site, including current and former residents and former workers and their household members were invited to participate in a study, which included a health and exposure history and routine blood analysis. We also conducted a toxicological health evaluation of a subset of these eligible workers/residents by analyzing serum levels of 17 PCDD/F congeners. Members of the ETC cohort exhibited elevated serum PCDD/F relative to the general population, and congener profiles in members of the cohort reflected patterns commonly observed in persons exposed to PCP. Hypertension prevalence in the cohort was found to correlate with PCDD/F levels, although no other significant relationships were identified with monitored health indices.     

Heterogeneous photocatalytic degradation of prometryn in aqueous solutions under UV-Vis irradiation

In this study, the heterogeneous photocatalytic degradation of prometryn using TiO(2) as photocatalyst was investigated. The main objectives of the study were: (I) to evaluate the kinetics of the pesticide disappearance, (II) to compare the photocatalytic efficiency of two different types of TiO(2), (III) to examine the influence of various parameters such as initial concentration of pesticide or catalyst and presence of oxidants (H(2)O(2) and K(2)S(2)O(8)), (IV) to evaluate the degree of mineralization and (V) to assess the detoxification efficiency of the studied processes. The experiments were carried out in a 500 ml pyrex UV reactor equipped with a 125 W high-pressure mercury lamp surrounded by a pyrex filter blocking wavelengths below 290 nm. Prometryn concentration was determined using HPLC. It was found that the degradation of the pesticide follows the first order kinetics according to the Langmuir-Hinshelwood model. Parameters like the type and concentration of the catalyst affect the degradation rate. A synergistic effect was observed when an oxidant was added in the TiO(2) suspensions increasing the reaction rate of photodegradation. In order to examine the extent of pesticide mineralization, DOC measurements were carried out. After 6h of illumination, mineralization was achieved up to almost 70%. The toxicity of the treated solution was evaluated using the Microtox test based on the luminescent bacteria Vibrio fisheri, in order to compare the acute toxicity of prometryn and its photoproducts. The detoxification efficiency was found to be dependent on the studied system and it did not follow the rate of pesticide disappearance.     

Seasonal variations of hydrophobic organic contaminant concentrations in the water-column of the Seine Estuary and their transfer to a planktonic species Eurytemora affinis (Calanoïda, copepoda). Part 1: PCBs and PAHs

Hydrophobic organic contaminants (HOC) (i.e. PAHs and PCBs) were measured in the water column and in Eurytemora affinis samples from the Seine Estuary collected from November 2002 to February 2005. Results showed seasonal variations of both total PCB and PAH levels in the suspended particulate matter (SPM) and in the copepods with maximum levels during winter times. PAH and PCB concentrations in the SPM ranged from 499 to 5819ngg(-1) and from 58 to 463ngg(-1), respectively. Phenanthrene, pyrene and benzo[b+j+k]fluoranthene (B[b+j+k]F) were the predominant PAH compounds in the water column, while CB 101, 118, 153 and 138 were the most abundant PCB congeners. PCBs and PAHs bioaccumulated by E. affinis (EA) varied between 383 and 1785ngg(-1) and 165-3866ngg(-1). CB101, 153, 138 and B[b+j+k] were, respectively, the major compounds of PCB and PAH fingerprints in EA. Thereby, the copepods could reach high accumulation factor (ACF) (91000 for PCBs and 17000 for PAHs). The principal component analyses of contaminant concentrations and environmental parameter datasets distinguished two groups of copepods. The winter time cluster, with high percentage of adult copepods, which bioaccumulated the highest PCB and PAH body-burdens, and the second cluster with juveniles showing the lowest HOC concentrations. Thus, PAH and PCB concentrations in EA exhibited significant correlations with the percentage of adults making up the samples.     

A comparative study on characterization of textile wastewaters (untreated and treated) toxicity by chemical and biological tests

Toxicity of textile wastewaters (untreated and treated) and their ingredient chemicals was quantified in terms of their chemical characteristics, fish (Gambusia affinis) mortality and end point growth responses of duckweed (Lemna aequinoctialis) in short-term bioassays. Other parameters of fish bioassay were erythrocyte morphology and its counts. Despite of a definite correlation between data of biological tests (LC/EC(50) values) with that of chemical tests, biological tests were found to be relatively more sensitive to both wastewaters and ingredient chemicals. Amongst all the examined parameters of test organisms, fish RBCs (morphology and counts) sensitivity to pollutants in the wastewaters was usually maximum and therefore, their study should be included in the routine fish bioassay. Other advantage of biological test such as on Lemna is even detection of eutrophic potential of wastewaters, as noted at their higher dilutions. The ingredient chemicals (major) contributing maximum toxicity to textile dye wastewater were, acids (HCl and H(2)SO(4)), alkali (Na(2)O SiO(2)), salt (NaNO(2)) and heavy metal (Cu), whereas dyes (4) were relatively less toxic.     

Modeling in-situ uranium(VI) bioreduction by sulfate-reducing bacteria

We present a travel-time based reactive transport model to simulate an in-situ bioremediation experiment for demonstrating enhanced bioreduction of uranium(VI). The model considers aquatic equilibrium chemistry of uranium and other groundwater constituents, uranium sorption and precipitation, and the microbial reduction of nitrate, sulfate and U(VI). Kinetic sorption/desorption of U(VI) is characterized by mass transfer between stagnant micro-pores and mobile flow zones. The model describes the succession of terminal electron accepting processes and the growth and decay of sulfate-reducing bacteria, concurrent with the enzymatic reduction of aqueous U(VI) species. The effective U(VI) reduction rate and sorption site distributions are determined by fitting the model simulation to an in-situ experiment at Oak Ridge, TN. Results show that (1) the presence of nitrate inhibits U(VI) reduction at the site; (2) the fitted effective rate of in-situ U(VI) reduction is much smaller than the values reported for laboratory experiments; (3) U(VI) sorption/desorption, which affects U(VI) bioavailability at the site, is strongly controlled by kinetics; (4) both pH and bicarbonate concentration significantly influence the sorption/desorption of U(VI), which therefore cannot be characterized by empirical isotherms; and (5) calcium-uranyl-carbonate complexes significantly influence the model performance of U(VI) reduction.