Photodecomposition of iodinated contrast media and subsequent formation of toxic iodinated moieties during final disinfection with chlorinated oxidants

Large amount of iodinated contrast media (ICM) are found in natural waters (up to µg.L-1 levels) due to their worldwide use in medical imaging and their poor removal by conventional wastewater treatment. Synthetic water samples containing different ICM and natural organic matter (NOM) extracts were subjected to UV254 irradiation followed by the addition of chlorine (HOCl) or chloramine (NH2Cl) to simulate final disinfection. In this study, two new quantum yields were determined for diatrizoic acid (0.071 mol.Einstein-1) and iotalamic acid (0.038 mol.Einstein-1) while values for iopromide (IOP) (0.039 mol.Einstein-1), iopamidol (0.034 mol.Einstein-1) and iohexol (0.041 mol.Einstein-1) were consistent with published data. The photodegradation of IOP led to an increasing release of iodide with increasing UV doses. Iodide is oxidized to hypoiodous acid (HOI) either by HOCl or NH2Cl. In presence of NOM, the addition of oxidant increased the formation of iodinated disinfection by-products (I-DBPs). On one hand, when the concentration of HOCl was increased, the formation of I-DBPs decreased since HOI was converted to iodate. On the other hand, when NH2Cl was used the formation of I-DBPs was constant for all concentration since HOI reacted only with NOM to form I-DBPs. Increasing the NOM concentration has two effects, it decreased the photodegradation of IOP by screening effect but it increased the number of reactive sites available for reaction with HOI.For experiments carried out with HOCl, increasing the NOM concentration led to a lower formation of I-DBPs since less IOP are photodegraded and iodate are formed. For NH2Cl the lower photodegradation of IOP is compensated by the higher amount of NOM reactive sites, therefore, I-DBPs concentrations were constant for all NOM concentrations. 7 different NOM extracts were tested and almost no differences in IOP degradation and I-DBPs formation was observed. Similar behaviour was observed for the 5 ICM tested. Both oxidant poorly degraded the ICM and a higher formation of I-DBPs was observed for the chloramination experiments compared to the chlorination experiment. Results from toxicity testing showed that the photodegradation products of IOP are toxic and confirmed that the formation of I-DBPs leads to higher toxicity. Therefore, for the experiment with HOCl where iodate are formed the toxicity was lower than for the experiments with NH2Cl where a high formation of I-DBPs was observed

Understanding bioavailability and toxicity of sediment-associated contaminants by combining passive sampling with in vitro bioassays in an urban river catchment

Bioavailable and bioaccessible fractions of sediment-associated contaminants are considered as better dose metrics for sediment-quality assessment than total concentrations. The authors applied exhaustive solvent extraction and nondepletive equilibrium sampling techniques to sediment samples collected along the Brisbane River in South East Queensland, Australia, which range from pristine environments to urban and industry-impacted areas. The wide range of chemicals expected prevents comprehensive chemical analysis, but a battery of cell-based bioassays sheds light on mixture effects of chemicals in relation to various modes of toxic action. Toxic effects were expressed as bioanalytical equivalent concentrations (BEQs) normalized to the organic carbon content of each sediment sample. Bioanalytical equivalent concentrations from exhaustive extraction agreed fairly well with values estimated from polydimethylsiloxane passive sampling extracts via the constant organic carbon to polydimethylsiloxane partition coefficient. Agreement was best for bioassays indicative of photosynthesis inhibition and oxidative stress response and discrepancy within a factor of 3 for the induction of the aryl hydrocarbon receptor. For nonspecific cytotoxicity, BEQ from exhaustive extraction were 1 order of magnitude higher than values from equilibrium sampling, possibly because of coextraction of bioactive natural organic matter that led to an overestimation of toxicity in the exhaustive extracts, which suggests that passive sampling is better suited in combination with bioanalytical assessment than exhaustive extraction

Effect-based approach for screening of chemical mixtures in whole blood of green turtles from the Great Barrier Reef

Organisms are exposed to mixtures of both known and unknown chemicals which are diverse and variable, and thus difficult and costly to characterise and monitor using traditional target analyses. The objective of this study was to validate and apply in vitro effect-based methods by which whole blood can be used to screen internal exposure to such complex chemical mixtures. For this study, we used whole blood of green sea turtles (Chelonia mydas). To ensure the chemical mixture in blood is transferred with minimal losses or bias, we tested a modified QuEChERS extraction method specifically developed for multi-and non-target instrument analysis. The extracts were dosed to a battery of in vitro bioassays (AhR-CAFLUX, AREc32, NF kappa B-bla, VM7Luc4E2, Microtox), each with a different mode of action (e.g., AhR receptor mediated xenobiotics, NrF2-mediated oxidative stress, NF kappa B-mediated response to inflammation, estrogen activity and baseline toxicity oxidative stress, respectively) in order to cover a wide spectrum of chemicals. Results confirmed the absence of interferences of the blood extract with the responses of the different assays, thus indicating the methods' compatibility with effect-based screening approaches. To apply this approach, whole blood samples were collected from green turtles foraging in agricultural, urban and remote areas of the Australian Great Barrier Reef. The effect-based screening revealed significant differences in exposure, with higher induction of AhR-CAFLUX, AREc32 and Microtox assays in turtles from the agricultural foraging ground. Overall, these results corroborated with concurrent health, target and non-target analyses in the same animals performed as part of a larger program. This study provides evidence that the proposed effect-based approach is suitable for screening and evaluating internal exposure of organisms to chemical mixtures. The approach could be valuable for advancing understanding on multiple levels ranging from identification of priority chemicals in effect-directed investigations to exploring relationships between exposure and disease, not only in sea turtles, but in any organism. (C) 2017 Elsevier B.V. All rights reserved

Pesticide occurrence and spatio-temporal variability in urban run-off across Australia

Stormwater is a major driving factor of aquatic ecosystem degradation as well as one of the largest untapped urban freshwater resources. We present results from a long-term, multi-catchment study of urban stormwater pesticides across Australia that addresses this dichotomous identity (threat and resource), as well as dominant spatial and temporal patterns in stormwater pesticide composition. Of the 27 pesticides monitored, only 19 were detected in Australian stormwater, five of which (diuron, MCPA, 2,4-D, simazine, and triclopyr) were found in >50% of samples. Overall, stormwater pesticide concentrations were lower than reported in other countries (including the United States, Canada and Europe), and exceedances of public health and aquatic ecosystem standards were rare (10% of samples). Spatio-temporal patterns were investigated with principal component analysis. Although stormwater pesticide composition was relatively stable across seasons and years, it varied significantly by catchment. Common pesticide associations appear to reflect 1) user application of common registered formulations containing characteristic suites of active ingredients, and 2) pesticide fate properties (e.g., environmental mobility and persistence). Importantly, catchment-specific occurrence patterns provide opportunities for focusing treatment approaches or stormwater harvesting strategies

Asymptotic analysis for a singularly perturbed Dirichlet problem

Let us consider the problem −∆u + λV (x)u = up in Ω, u = 0 on ∂ Ω, where Ω is a smooth bounded domain, p > 1, V is a positive potential and λ > 0. We are interested in the regime λ → +∞, which is equivalent to a singularly perturbed Dirichlet problem. It is known that solutions u must blow up as λ → +∞, and we address here the asymptotic description of such a blow up behavior. When the ”energy” is uniformly bounded, the behavior is well understood and the solutions can develop just a finite number of sharp peaks. When V is not constant, the blow up points must be c.p.’s of the potential V. The situation is more involved when V = 1, and the crucial role is played by the mutual distances between the blow-up points as well as the boundary distances. The construction of these blowing-up solutions has also been addressed. The first part in the thesis is devoted to strengthen such an analysis when just a Morse index information is available. A posteriori, we obtain an equivalence in the form of a double-side bound between Morse index and ”energy” with essentially optimal constants. This result can be seen as a sort of Rozenblyum-Lieb-Cwikel inequality, where the number of negative eigenvalues of a Schrodinger operator −∆ + V can be estimated in terms of a suitable Lebesgue norm of the negative part V− . Thanks to the specificity of our problem, we improve it by getting the correct Lebesgue exponent (in view of the double-side bound) as well as the sharp constants. We then turn to the question of concentration on manifolds of positive dimensions. The problem is well understood by a constructive approach but the asymptotic analysis is in general missing. Let us notice that on the annulus the radial ground state solution has Morse index and ”energy” which blow up as λ → +∞. Nonetheless, the radial Morse index is one which has allowed Esposito-Mancini-Santra-Srikanth to develop a fine asymptotic analysis to localize the limiting concentration radii. They are c.p.’s of a modified potential, whose role had been already clarified by the constructive results. The second part part of the thesis is devoted to develop an asymptotic analyis for solutions on the annulus which have partial symmetries. In particular, we consider the three-dimensional annulus and solutions which are invariant under rotations around the z-axis. Assuming an uniform bound on the reduced invariant Morse index, we obtain a localization of the limiting concentration circles in terms of a suitable modified potential. The main difficulty here is related to the presence of fixed points w.r.t. the group action (the z-axis) and the aim is to exhibit potentials V for which the concentration circles (for example, for the ground state solution) do not degenerate to points on the z-axis