Breakdown products on metabolic pathway of degradation of benz[a]anthracene by a ligninolytic fungus

Cultures of the ligninolytic fungus Irpex lacteus incubated in a nutrient liquid medium degraded more than 70% of the initially applied benz[a]anthracene within 14 days. At the first step of metabolization, benz[a]anthracene was transformed via a typical pathway of ligninolytic fungi to benz[a]anthracene-7,12-dione (BaAQ). The product was further transformed by at least two ways, whereas one is complied with the anthracene metabolic pathway of I. lacteus. Benz[a]anthracene-7,12-dione was degraded to 1,2-naphthalenedicarboxylic acid and phthalic acid that was followed with production of 2-hydroxymethyl benzoic acid or monomethyl and dimethylesters of phthalic acid. Another degradation product of BaAQ was identified as 1-tetralone. Its transformation via 1,4-naphthalenedione, 1,4-naphthalenediol and 1,2,3,4-tetrahydro-1-hydroxynaphthalene resulted again in phthalic acid. None of the intermediates were identified as dead-end metabolites. Metabolites produced by ring cleavage of benz[a]anthracene using the ligninolytic fungus are firstly presented in this work.     

In situ and laboratory bioassays using Poecilia reticulata Peters, 1859 in the biomonitoring of an acidic lake at Camaçari, BA, Brazil

The suitability and viability of acute in situ bioassays were investigated in the biomonitoring program of an acidic lake contaminated with sulphur residues. Responses of organisms observed in laboratory and in situ bioassays were also assessed to determine whether or not they were similar and comparable, regarding accuracy and precision. Newborn Poecilia reticulata were employed as test organisms and exposed to the same water samples under in situ and laboratory conditions. Mortality/immobility was the endpoint assessed and dead/immobile organisms were counted at various time intervals during exposure. The mean calculated LT50 values and 95% confidence intervals were 1.61 (1.36-1.87) h in the laboratory bioassays and 0.72 (0.55-0.89) h in the in situ bioassays. Statistical comparison of these values revealed a significant difference (p<0.05). In situ bioassays were more accurate than those carried out in the laboratory, demonstrating higher sensitivity and better reproduction of what occurs in nature, while laboratory bioassays were more precise.     

Reductive dehalogenation of tetrabromobisphenol-A by sediment from a contaminated ephemeral streambed and an enrichment culture

This study was aimed at improving our understanding of the physiology of the microorganisms that reductively dehalogenate tetrabromobisphenol-A (TBBPA). Activity was followed in contaminated sediments from a polluted streambed as well as from fracture filling material underlying the stream. Reductive dehalogenation was observed in surface sediments but not in fracture filling samples from a depth of 3m. Likewise, anaerobic microbial activity, represented by sulphate reduction, was much higher in the surface sediment. In the culture enriched from the surface sediment, optimal microbial debromination of TBBPA took place at a salinity of 2% and 3% NaCl, temperature of 30 degrees Celsius, and pH of 7-8. Ethanol, pyruvate and the combination of hydrogen with acetate were the most suitable electron donors and carbon sources for this culture. Alternative electron acceptors like Fe(3+), SO(4)(2-), SO(3)(2-), NO(3)(-) and 2,4,6-tribromophenol inhibited TBBPA debromination. The debrominating bacteria were heat sensitive (80 degrees Celsius, for 10min) but were not inhibited by bromoethanesulphonate or molybdate. This study allowed optimisation of our culturing conditions, but was also important for understanding the factors which influence TBBPA debromination in situ.     

A review and numerical assessment of the random walk particle tracking method

We review the basic mathematical concepts of random walk particle tracking (RWPT) and its advantages and limitations. Three different numerical approaches to overcome the local mass conservation problem of the random walk methodology are examined: (i) the interpolation method, (ii) the reflection principle, and (iii) the generalized stochastic differential equations (GSDE). Analytical solutions of the spatial moments for a two-layer system are compared to model predictions using the different techniques and results demonstrate that the interpolation method reproduces correctly average velocity, but fails to reproduce macrodispersion at higher hydraulic conductivity contrasts between the two layers. On the contrary, the reflection principle and the GSDE approach underestimate average velocity, but reproduce macrodispersion better for high contrasts. The different behavior is based on an artificial shift of mass for increasing heterogeneities for the GSDE approach and the reflection principle, whereas the interpolation method suffers from the smoothing of the dispersion tensor. The behavior of these approaches was furthermore analyzed in two-dimensional heterogeneous hydraulic conductivity fields, which are characterized by different random function models. Solute transport was simulated correctly by all three approaches for the reference fields having Gaussian structures or non-Gaussian structures with an isotropic spatial correlation, even for a variance of the natural log of hydraulic conductivity of sigma(lnK)(2)=4. However, for the non-Gaussian model with a strong anisotropic spatial correlation and a variance of sigma(lnK)(2)=2 and higher, the interpolation method was the only technique modelling solute transport correctly. Furthermore, we discuss the general applicability of random walk particle tracking in comparison to the standard transport models and conclude that in advection-dominated problems using a high spatial discretization or requiring the performance of many model runs, RWPT represents a good alternative for modelling contaminant transport.     

GC and GC-MS characterization of crude oil transformation in sediments and microbial mat samples after the 1991 oil spill in the Saudi Arabian Gulf coast

The massive oil discharge in the Saudi Arabian coast at the end of the 1991 Gulf War is used here as a natural experiment to study the ability of microbial mats to transform oil residues after major spills. The degree of oil transformation has been evaluated from the analysis of the aliphatic and aromatic hydrocarbons by gas chromatography (GC) and GC coupled to mass spectrometry (GC-MS). The oil-polluted microbial mat samples from coastal environments exhibited an intermediate degree of transformation between that observed in superficial and deep sediments. Evaporation, photo-oxidation and water-washing seemed to lead to more effective and rapid elimination of hydrocarbons than cyanobacteria and its associated microorganisms. Furthermore, comparison of some compounds (e.g. regular isoprenoid hydrocarbons or alkylnaphthalenes) in the oil collected in the area after the spill or in the mixtures retained by cyanobacterial growth gave rise to an apparent effect of hydrocarbon preservation in the microbial mat ecosystems.     

Modelling the extra and intracellular uptake and discharge of heavy metals in Fontinalis antipyretica transplanted along a heavy metal and pH contamination gradient

Samples of the aquatic bryophyte Fontinalis antipyretica Hedw. were transplanted to different sites with the aim of characterizing the kinetics of the uptake and discharge of heavy metals in the extra and intracellular compartments. The accumulation of metals in extracellular compartments, characterized by an initial rapid accumulation, then a gradual slowing down over time, fitted perfectly to a Michaelis-Menten model. The discharge of metals from the same compartment followed an inverse linear model or an inverse Michaelis-Menten model, depending on the metal. In intracellular sites both uptake and discharge occurred more slowly and progressively, following a linear model. We also observed that the acidity of the environment greatly affected metal accumulation in extracellular sites, even when the metals were present at relatively high concentrations, whereas the uptake of metals within cells was much less affected by pH.     

Influence of hydrology on heavy metal speciation and mobility in a Pb-Zn mine tailing

Among the inorganic toxicants of greatest concern in mine tailings, Pb, Zn, Cu, Cd and As figure prominently due to their abundance and potential toxicity. Here we report on their biolability and solid-phase speciation in two sediment cores subject to variable hydrological regimes at an abandoned pyritic mine tailing. The oxic conditions of well-drained sediments induced pyrite oxidation and the subsequent liberation of H+, SO4(2-) and considerable quantities of Fe(III), which precipitated as goethite. Solubility of Pb, Zn, Cu and Cd was closely coupled to pH and goethite presence. Metal lability was particularly low in zones of neutralization, formed by the accumulation of calcite, first carried then deposited by percolating waters in both saturated and unsaturated cores. We conclude that differential hydrology induces variable heavy metal speciation and biolability in Pb-Zn mine tailings, and suggest that site-specific risk assessments must account for past and present hydrological regimes.     

Cosorption study of organic pollutants and dissolved organic matter in a soil

In this study we have evaluated the effects of dissolved organic matter (DOM) on sorption of imidacloprid, 3,4-dichloroaniline (3,4-DCA) and 4-bromoaniline (4-BA) on a typical calcareous soil (Luvic Xerosol) from south-eastern Spain. Two different types of DOM were used, that is to say, dissolved natural organic matter extracts from a commercial peat (DNOM) and a high-purity tannic acid (TA) solution. The experiments were carried out in a 0.01 M CaCl2 aqueous medium at 25 degrees C. The results indicated that the presence of both DNOM and TA, over a concentration range of 15-100 mg L(-1), produced an increase in the amount of 3,4-DCA and 4-BA sorbed and a decrease in the amount of imidacloprid retained on the soil studied. A modified distribution coefficient, K(doc), has been proposed as a safer parameter for soil sorption predictions of organic pollutants and it could be of help to model the fate of these in the environment.     

Geochemical and Pb isotopic evidence for sources and dispersal of metal contamination in stream sediments from the mining and smelting district of Príbram, Czech Republic

Stream sediments from the mining and smelting district of Príbram, Czech Republic, were studied to determine the degree, sources and dispersal of metal contamination using a combination of bulk metal and mineralogical determinations, sequential extractions and Pb isotopic analyses. The highest metal concentrations were found 3-4 km downstream from the main polymetallic mining site (9800 mg Pb kg(-1), 26 039 mg Zn kg(-1), 316.4 mg Cd kg(-1), 256.9 mg Cu kg(-1)). The calculated enrichment factors (EFs) confirmed the extreme degree of contamination by Pb, Zn and Cd (EF>40). Lead, Zn and Cd are bound mainly to Fe oxides and hydroxides. In the most contaminated samples Pb is also present as Pb carbonates and litharge (PbO). Lead isotopic analysis indicates that the predominant source of stream sediment contamination is historic Pb-Ag mining and primary Pb smelting (206Pb/207Pb=1.16), while the role of secondary smelting (car battery processing) is negligible.     

Aquatic risk assessment of the new rice herbicide profoxydim

A tiered protocol for assessing ecological risks has been applied to the rice pesticide profoxydim. The initial assessment (Tier I) was based on toxicity exposure ratio (TER) calculations based on laboratory data using a worst-case rice scenario. The first refinement (Tier II) was based on direct toxicity assessment (DTA) of water samples collected during a field-mesocosm study. Finally, a higher-tier assessment on the in situ assessment of paddy community responses (field-mesocosm-Tier III) was performed. A successive application of three pesticides, the herbicides azimsulfuron, propanil and the insecticide malathion, was used as reference controls. The refined assessments indicated a lower risk than that predicted from TER estimations. DTA-based Tier II showed toxicity effects only for concentrations above the recommended dose of profoxydim. Effects for reference controls were observed in DTA which were not expected from Tier I. The field-mesocosm study confirmed these effects but also showed that they were transient and of low relevance.