Relative proportions of polycyclic aromatic hydrocarbons differ between accumulation bioassays and chemical methods to predict bioavailability

Chemical methods to predict the bioavailable fraction of organic contaminants are usually validated in the literature by comparison with established bioassays. A soil spiked with polycyclic aromatic hydrocarbons (PAHs) was aged over six months and subjected to butanol, cyclodextrin and tenax extractions as well as an exhaustive extraction to determine total PAH concentrations at several time points. Earthworm (Eisenia fetida) and rye grass root (Lolium multiflorum) accumulation bioassays were conducted in parallel. Butanol extractions gave the best relationship with earthworm accumulation (r2 ≤ 0.54, p ≤ 0.01); cyclodextrin, butanol and acetone–hexane extractions all gave good predictions of accumulation in rye grass roots (r2 ≤ 0.86, p ≤ 0.01). However, the profile of the PAHs extracted by the different chemical methods was significantly different (p < 0.01) to that accumulated in the organisms. Biota accumulated a higher proportion of the heavier 4-ringed PAHs. It is concluded that bioaccumulation is a complex process that cannot be predicted by measuring the bioavailable fraction alone. The ability of chemical methods to predict PAH accumulation in Eisenia fetida and Lolium multiflorum was hindered by the varied metabolic fate of the different PAHs within the organisms.

Uptake Pathways of Polycyclic Aromatic Hydrocarbons in White Clover

An understanding of the primary pathways of plant uptake of organic pollutants is important to enable the risks from crops grown on contaminated soils to be assessed. A series of experiments were undertaken to quantify the importance of the pathways of contamination and the Subsequent transport within the plant using white clover plants grown in solution culture. Root uptake was primarily an absorption process, but a component of the contamination was a result of the transpiration flux to the shoot for higher Solubility compounds. The root contamination can be easily predicted using a simple relationship with K-OW, although if a composition model was used based on lipid content, a significant under prediction of the contamination was observed. Shoot uptake was driven by the transpiration stream flux which was related to the solubility of the individual PAH rather than the K-OW. However, the experiment was over a short duration, 6 days, and models based on K-OW may be better for crops grown in the field where the vegetation will approach equilibrium and transpiration cannot easily be measured, A significant fraction of the shoot contamination resulted from aerial deposition derived from volatilized PAH. This pathway was more significant for compounds approaching log K-OA > 9 and log K-AW < -3. The shoot uptake pathways need further investigation to enable them to be modeled separately, There was no evidence of significant systemic transport of the PAR so transfer outside the transpiration stream is likely to be limited.

Statistical inference of OH concentrations and air mass dilution rates from successive observations of non-methane hydrocarbons in single air masses

Bayesian inference has been used to determine rigorous estimates of hydroxyl radical concentrations () and air mass dilution rates (K) averaged following air masses between linked observations of nonmethane hydrocarbons (NMHCs) spanning the North Atlantic during the Intercontinental Transport and Chemical Transformation (ITCT)-Lagrangian-2K4 experiment. The Bayesian technique obtains a refined (posterior) distribution of a parameter given data related to the parameter through a model and prior beliefs about the parameter distribution. Here, the model describes hydrocarbon loss through OH reaction and mixing with a background concentration at rate K. The Lagrangian experiment provides direct observations of hydrocarbons at two time points, removing assumptions regarding composition or sources upstream of a single observation. The estimates are sharpened by using many hydrocarbons with different reactivities and accounting for their variability and measurement uncertainty. A novel technique is used to construct prior background distributions of many species, described by variation of a single parameter . This exploits the high correlation of species, related by the first principal component of many NMHC samples. The Bayesian method obtains posterior estimates of , K and following each air mass. Median values are typically between 0.5 and 2.0 × 106 molecules cm−3, but are elevated to between 2.5 and 3.5 × 106 molecules cm−3, in low-level pollution. A comparison of estimates from absolute NMHC concentrations and NMHC ratios assuming zero background (the “photochemical clock” method) shows similar distributions but reveals systematic high bias in the estimates from ratios. Estimates of K are ∼0.1 day−1 but show more sensitivity to the prior distribution assumed.

Remediation of soils contaminated with petrol and diesel with lime

Lime treatment of hydrocarbon-contaminated soils offers the potential to stabilize and solidify these materials, with a consequent reduction in the risks associated with the leachate emanating from them. This can aid the disposal of contaminated soils or enable their on-site treatment. In this study, the addition of hydrated lime and quicklime significantly reduced the leaching of total petroleum hydrocarbons (TPH) from soils polluted with a 50:50 petrol/diesel mixture. Treatment with quicklime was slightly more effective, but hydrated lime may be better in the field because of its ease of handling. It is proposed that this occurs as a consequence of pozzolanic reactions retaining the hydrocarbons within the soil matrix. There was some evidence that this may be a temporary effect, as leaching increased between seven and 21 days after treatment, but the TPH concentrations in the leachate of treated soils were still one order of magnitude below those of the control soil, offering significant protection to groundwater. The reduction in leaching following treatment was observed in both aliphatic and aromatic fractions, but the latter were more affected because of their higher solubilty. The results are discussed in the context of risk assessment, and recommendations for future research are made.

Bile metabolites of polycyclic aromatic hydrocarbons (PAHs) in European eels Anguilla anguilla from United Kingdom estuaries

A total of 94 European eels (Anguilla anguilla) were collected from five estuaries in the UK. The deconjugated metabolites of polycyclic aromatic hydrocarbons (PAHs) in the bile of the eels were separated using HPLC. Six PAH metabolites were identified: 1-hydroxy (1-OH) metabolites of phenanthrene, pyrene and chrysene; and the 1-OH, 3-OH and 7,8 dihydrodiol metabolites of benzo[a]pyrene (BaP). The mean concentration of the six metabolites was greatest in eels from the Tyne (49 muM) followed by the Wear (33 muM), Tees (19 muM), Thames (4 muM) and Severn (2 muM) estuaries. Although 1-OH pyrene was always the dominant compound, there were significant differences (P<0.05) between sites and between estuaries for some metabolites. Normalising the molar concentration of the bile metabolites to the bile biliverdin absorbance reduced sample variation. When the metabolites identified were-each expressed as a percentage of the total detected, the metabolite profile was characteristic for each estuary. (C) 2002 Elsevier Science B.V. All rights reserved.

GC/multiple collector-ICPMS method for chlorine stable isotope analysis of chlorinated aliphatic hydrocarbons

Stable isotopic characterization of chlorine in chlorinated aliphatic pollution is potentially very valuable for risk assessment and monitoring remediation or natural attenuation. The approach has been underused because of the complexity of analysis and the time it takes. We have developed a new method that eliminates sample preparation. Gas chromatography produces individually eluted sample peaks for analysis. The He carrier gas is mixed with Ar and introduced directly into the torch of a multicollector ICPMS. The MC-ICPMS is run at a high mass resolution of >= 10 000 to eliminate interference of mass 37 ArH with Cl. The standardization approach is similar to that for continuous flow stable isotope analysis in which sample and reference materials are measured successively. We have measured PCE relative to a laboratory TCE standard mixed with the sample. Solvent samples of 200 nmol to 1.3 mu mol ( 24- 165 mu g of Cl) were measured. The PCE gave the same value relative to the TCE as measured by the conventional method with a precision of 0.12% ( 2 x standard error) but poorer precision for the smaller samples.

Microbial relatives of the seed storage proteins of higher plants: conservation of structure and diversification of function during evolution of the cupin superfamily.

This review summarizes the recent discovery of the cupin superfamily (from the Latin term "cupa," a small barrel) of functionally diverse proteins that initially were limited to several higher plant proteins such as seed storage proteins, germin (an oxalate oxidase), germin-like proteins, and auxin-binding protein. Knowledge of the three-dimensional structure of two vicilins, seed proteins with a characteristic beta-barrel core, led to the identification of a small number of conserved residues and thence to the discovery of several microbial proteins which share these key amino acids. In particular, there is a highly conserved pattern of two histidine-containing motifs with a varied intermotif spacing. This cupin signature is found as a central component of many microbial proteins including certain types of phosphomannose isomerase, polyketide synthase, epimerase, and dioxygenase. In addition, the signature has been identified within the N-terminal effector domain in a subgroup of bacterial AraC transcription factors. As well as these single-domain cupins, this survey has identified other classes of two-domain bicupins including bacterial gentisate 1, 2-dioxygenases and 1-hydroxy-2-naphthoate dioxygenases, fungal oxalate decarboxylases, and legume sucrose-binding proteins. Cupin evolution is discussed from the perspective of the structure-function relationships, using data from the genomes of several prokaryotes, especially Bacillus subtilis. Many of these functions involve aspects of sugar metabolism and cell wall synthesis and are concerned with responses to abiotic stress such as heat, desiccation, or starvation. Particular emphasis is also given to the oxalate-degrading enzymes from microbes, their biological significance, and their value in a range of medical and other applications.

Increased apoptosis in first trimester extravillous trophoblasts from pregnancies at higher risk of developing preeclampsia

Preeclampsia complicates 5 to 10% of pregnancies and is a leading cause of maternal and fetal mortality and morbidity. Although the cause is unknown, inadequate invasion and remodeling of maternal uterine arteries by extravillous trophoblasts (EVTs) in the first trimester is a common feature. Uterine spiral artery resistance as detected by Doppler ultrasound is commonly used in the second trimester to identify pregnancies destined to develop preeclampsia. Correlation between high uterine resistance and the failure of trophoblast invasion has been reported as early as 12 weeks. However, the reason for this failure has not been established. Understanding the processes involved would significantly improve our diagnostic potential. In this study, we correlated increased first trimester uterine artery resistance with a biological abnormality in trophoblast function. EVTs derived from high-resistance pregnancies were more sensitive to apoptotic stimuli than those from normal-resistance pregnancies. Survival of EVTs from high-resistance pregnancies could be increased by nitric oxide, whereas inhibition of nitric oxide in cells from normal-resistance pregnancies increased apoptotic sensitivity. This predates the onset of symptoms by several weeks and provides evidence for a mechanism responsible for the incomplete uterine vessel remodeling and the differences in artery resistance between preeclamptic and normal pregnancies.

Incorporation of in situ and biomarker assays in higher-tier assessment of the aquatic toxicity of insecticides

This study was designed to test the feasibility of integrating in situ, single species exposures and biomarker analysis into microcosm studies. Experimental ponds were dosed with pirimiphos methyl (PM) and lindane. C. riparius fourth instar larvae were deployed for 48 h on nine separate occasions during the study period before and after treatment. Surviving larvae were analysed for acetylcholinesterase activity (AChE). Survival and biomarker data were compared to chironomid assemblage analysis by monitoring insects emerging from the microcosms. Survival of chironomids within the in situ systems commenced on day + 16 after treatment with 31.6% and 53.3% survival in the lindane and PM treated ponds, respectively. In contrast, the first emergence from the microcosms occurred on days + 27, in respect to lindane, and + 59 for the PM treated ponds. Thus the in situ bioassay was able to demonstrate gradual reduction in toxicity within the sediment before this was evident from macroinvertebrate monitoring. Significant ACNE inhibition was only detected on exposure to PM. Levels decreased from 75% on day + 16 to 26% by day +29. The biomarker analysis confirmed that, by the end of the study, the insecticide was no longer exerting an effect. We discuss how the use of in situ bioassays could also aid comparison of microcosm studies by adding a standardized dimension. (C) 2003 Elsevier Ltd. All rights reserved.

Higher oxides of chlorine: absorption cross-sections of Cl2O6 and Cl2O4, the decomposition of Cl2O6, and the reactions of OClO with O and O-3

The absorption cross-sections of Cl2O6 and Cl2O4 have been obtained using a fast flow reactor with a diode array spectrometer (DAS) detection system. The absorption cross-sections at the wavelengths of maximum absorption (lambda(max)) determined in this study are those of Cl2O6: (1.47 +/- 0.15) x 10(-17) cm(2) molecule(-1), at lambda(max) = 276 nm and T = 298 K; and Cl2O4: (9.0 +/- 2.0) x 10(-19) cm(2) molecule(-1), at lambda(max) = 234 nm and T = 298 K. Errors quoted are two standard deviations together with estimates of the systematic error. The shapes of the absorption spectra were obtained over the wavelength range 200-450 nm for Cl2O6 and 200-350 nm for Cl2O4, and were normalized to the absolute cross-sections obtained at lambda(max) for each oxide, and are presented at 1 nm intervals. These data are discussed in relation to previous measurements. The reaction of O with OCIO has been investigated with the objective of observing transient spectroscopic absorptions. A transient absorption was seen, and the possibility is explored of identifying the species with the elusive sym-ClO3 or ClO4, both of which have been characterized in matrices, but not in the gas-phase. The photolysis of OCIO was also re-examined, with emphasis being placed on the products of reaction. UV absorptions attributable to one of the isomers of the ClO dimer, chloryl chloride (ClClO2) were observed; some Cl2O4 was also found at long photolysis times, when much of the ClClO2 had itself been photolysed. We suggest that reports of Cl2O6 formation in previous studies could be a consequence of a mistaken identification. At low temperatures, the photolysis of OCIO leads to the formation of Cl2O3 as a result of the addition of the ClO primary product to OCIO. ClClO2 also appears to be one product of the reaction between O-3 and OCIO, especially when the reaction occurs under explosive conditions. We studied the kinetics of the non-explosive process using a stopped-flow technique, and suggest a value for the room-temperature rate coefficient of (4.6 +/- 0.9) x 10(-19) cm(3) molecule(-1) s(-1) (limit quoted is 2sigma random errors). The photochemical and thermal decomposition of Cl2O6 is described in this paper. For photolysis at k = 254 nm, the removal of Cl2O6 is not accompanied by the build up of any other strong absorber. The implications of the results are either that the photolysis of Cl2O6 produces Cl-2 directly, or that the initial photofragments are converted rapidly to Cl-2. In the thermal decomposition of Cl2O6, Cl2O4 was shown to be a product of reaction, although not necessarily the major one. The kinetics of decomposition were investigated using the stopped-flow technique. At relatively high [OCIO] present in the system, the decay kinetics obeyed a first-order law, with a limiting first-order rate coefficient of 0.002 s(-1). (C) 2004 Elsevier B.V. All rights reserved.

Simulating the formation of secondary organic aerosol from the photooxidation of aromatic hydrocarbons

The formation and composition of secondary organic aerosol (SOA) from the photooxidation of benzene, p-xylene, and 1,3,5-trimethylbenzene has been simulated using the Master Chemical Mechanism version 3.1 (MCM v3.1) coupled to a representation of the transfer of organic material from the gas to particle phase. The combined mechanism was tested against data obtained from a series of experiments conducted at the European Photoreactor (EUPHORE) outdoor smog chamber in Valencia, Spain. Simulated aerosol mass concentrations compared reasonably well with the measured SOA data only after absorptive partitioning coefficients were increased by a factor of between 5 and 30. The requirement of such scaling was interpreted in terms of the occurrence of unaccounted-for association reactions in the condensed organic phase leading to the production of relatively more nonvolatile species. Comparisons were made between the relative aerosol forming efficiencies of benzene, toluene, p-xylene, and 1,3,5-trimethylbenzene, and differences in the OH-initiated degradation mechanisms of these aromatic hydrocarbons. A strong, nonlinear relationship was observed between measured (reference) yields of SOA and (proportional) yields of unsaturated dicarbonyl aldehyde species resulting from ring-fragmenting pathways. This observation, and the results of the simulations, is strongly suggestive of the involvement of reactive aldehyde species in association reactions occurring in the aerosol phase, thus promoting SOA formation and growth. The effect of NO, concentrations on SOA formation efficiencies (and formation mechanisms) is discussed.