Transformation of endocrine disrupting chemicals, pharmaceutical and personal care products during drinking water disinfection.

Pharmaceuticals and personal care products (PPCPs) and endocrine disrupting compounds (EDCs) are frequently detected in drinking water sources. This raises concerns about the formation of potentially more toxic transformation products (TPs) after drinking water disinfection. This study applied a combination of computational and experimental methods to investigate the biological activity of eight EDCs and PPCPs commonly detected in source waters (acetaminophen, bisphenol A, carbamazepine, estrone, 17α-ethinylestradiol, gemfibrozil, naproxen and triclosan) before and after disinfection. Using a Stepped Forced Molecular Dynamics (SFMD) method, we detected 911 unique TPs, 36% of which have been previously reported in the scientific literature. We calculated the likelihood that TPs would cause damage to biomolecules or DNA relative to the parent compound based on lipophilicity and the occurrence of structural alerts, and applied two Quantitative Structure-Activity Relationship (QSAR) tools to predict toxicity via receptor-mediated effects. In parallel, batch experiments were performed with three disinfectants, chlorine, chlorine dioxide and chloramine. After solid-phase extraction, the resulting TP mixtures were analyzed by chemical analysis and a battery of eleven in vitro bioassays covering a variety of endpoints. The laboratory results were in good agreement with the predictions. Overall, the combination of computational and experimental chemistry and toxicity methods used in this study suggest that disinfection of the studied EDCs and PPCPs will produce a large number of TPs, which are unlikely to increase specific toxicity (e.g., endocrine activity), but may result in increased reactive and non-specific toxicity.

A structural basis for the amphiphilic character of alginates - Implications for membrane fouling.

Ostensibly hydrophilic alginates are known to foul hydrophobic membranes, under various conditions. Here, controlled experiments have been conducted at high and low pH on the fouling of a polypropylene membrane by alginate and the results suggest that the observed fouling is due to an intrinsic property of the alginate. Thus quantum chemical calculations on the M and G monomers of alginate reveal that M adopts an equilibrium geometry that is hydrophilic on one face and hydrophobic on the other, i.e. is potentially amphiphilic. Molecular dynamics simulations on short alginate chains of different sequences interacting with a modelled polypropylene surface, show that this characteristic is carried over to the polymer and results in hydrophobic patches along the chain that facilitate attractive interactions with the polypropylene surface. This concept is buttressed by an analysis of the binding characteristics of a previously reported X-ray structure of the mannuronan C-5 epimerase AlgE4 enzyme.

The effect of electromagnetic fields, from two commercially available water treatment devices, on bacterial culturability.

Commercially available pulsed-electromagnetic field (PEMF) devices are currently being marketed and employed to ostensibly manage biofouling. The reliable application and industry acceptance of such technologies require thorough scientific validation - and this is currently lacking. We have initiated proof-of-principle research in an effort to investigate whether such commercially available PEMF devices can influence the viability (culturability) of planktonic bacteria in an aqueous environment. Thus two different commercial PEMF devices were investigated via a static (i.e. non-flowing) treatment system. 'Healthy' Escherichia coli cells, as well as cultures that were physiologically compromised by silver nano-particles, were exposed to the PEMFs from both devices under controlled conditions. Although relatively minor, the observed effects were nevertheless statistically significant and consistent with the hypothesis that PEMF exposure under controlled conditions may result in a decrease in cellular viability and culturability. It has also been observed that under certain conditions bacterial growth is actually stimulated.

The role of poly-M and poly-GM sequences in the metal-mediated assembly of alginate gels.

Whilst the involvement of poly-G sequences in the formation of metal-mediated alginate gels has been previously studied in some detail, investigations into the role of poly-M and poly-GM sequences has been relatively neglected. In this regard, the binding of sodium and calcium ions to poly-M and poly-GM decamers, and their influence on chain aggregation, has been modelled by conducting a series of molecular dynamics simulations. This work complements a previous analogous study carried out for the poly-G decamer, whereby up to three strands are systematically introduced into each simulation. As in the previous study, this method allows intrinsic binding modes and interchain structural motifs to be revealed, that are consistent with those observed in available AFM images of consolidated 3-D networks. It is apparent from these studies that different sequences have different structural implications for metal-mediated chain association.

Exploring the molecular basis for the metal-mediated assembly of alginate gels.

The binding of sodium and calcium ions to single and multiple poly-G decamer strands has been modelled by conducting a series of molecular dynamics simulations. Implications for metal mediated inter-strand interactions and gel assembly have been explored by systematically introducing up to three strands into each of these simulations. A particular emphasis has been placed on revealing intrinsic binding modes by an unbiased initial positioning of the metal ions. The results have revealed binding modes that provide a rationale for the observed gelling of alginate by calcium rather than sodium ions. A number of junction zones involving calcium ions have been identified that result in chain aggregation. This includes a distinctive perpendicular motif that appears to be ubiquitous in previously reported AFM images of open 3-D alginate networks. The coordination geometries of the metal ions have been characterised and the metal-mediated junctions between associated strands are described in detail.

Experimental and computational investigations of the interactions between model organic compounds and subsequent membrane fouling.

The formation of aggregates of sodium alginate and bovine serum albumin (BSA) (as representative biopolymers) with humic acid were detected by Liquid Chromatography (LC) UV254 response in the biopolymer region for mixture solutions. BSA interaction with humic acid showed that aggregation occurred both in the presence and absence of calcium, suggesting that multivalent ions did not play a part in the aggregation process. Similar analyses of the alginate interaction with humic acid also showed a positive interaction, but only in the presence of calcium ions. The fouling characteristics for the BSA-humic acid mixture appeared to be significantly greater than the fouling characteristics of the individual solutions, while for the sodium alginate-humic acid mixture, the fouling rate was similar to that of the sodium alginate alone. The effectiveness of hydraulic backwashing, 10-15% reversibility, was observed for the BSA-humic acid mixture, while the % reversibility was 20-40% for the sodium alginate-humic acid mixture. Increased humic acid and DOC rejection were observed for both BSA-humic acid and sodium alginate-humic acid solutions compared to the individual solutions, indicating that the biopolymer filter cakes were able to retain humic acids. When compared with BSA-humic acid mixture solution, greater removal of humic acid was observed for alginate-humic mixture, suggesting that sodium alginate may have a greater capacity for associations with humic acid when in the presence of calcium than BSA. Complementary molecular dynamics simulations were designed to provide insights into the specific mechanisms of interaction between BSA and humic acid, as well as between alginate and humic acid. For the BSA-humic acid system; electrostatic, hydrophobic and hydrogen bonding were the dominant types of interactions predicted, whilst divalent ion-mediated bonding was not identified in the simulations, which supported the LC-results. Similarly for the alginate-humic acid system, the interactions predicted were divalent ion-mediated interactions only and this was also supported the LC results. This work suggests that LC-UV254 might be used to identify aggregated biopolymers, and that combined with current characterisation techniques, be used to better explain performance variations between water sources.

Effect of IX dosing on polypropylene and PVDF membrane fouling control.

The performance of ion exchange (IX) resin for organics removal from wastewater was assessed using advanced characterisation techniques for varying doses of IX. Organic characterisation using liquid chromatography with a photodiode array (PDA) and fluorescence spectroscopy (Method A), and UV254, organic carbon and organic nitrogen detectors (Method B), was undertaken on wastewater before and after magnetic IX treatment. Results showed partial removal of the biopolymer fraction at high IX doses. With increasing concentration of IX, evidence for nitrogen-containing compounds such as proteins and amino acids disappeared from the LC-OND chromatogram, complementary to the fluorescence response. A greater fluorescence response of tryptophan-like proteins (278 nm/343 nm) for low IX concentrations was consistent with aggregation of tryptophan-like compounds into larger aggregates, either by self-aggregation or with polysaccharides. Recycling of IX resin through multiple adsorption steps without regeneration maintained the high level of humics removal but there was no continued removal of biopolymer. Subsequent membrane filtration of the IX treated waters resulted in complex fouling trends. Filtration tests with either polypropylene (PP) or polyvinylidene fluoride (PVDF) membranes showed higher rates of initial fouling following treatment with high IX doses (10 mL/L) compared to filtration of untreated water, while treatment with lower IX doses resulted in decreased fouling rates relative to the untreated water. However, at longer filtration times the rate of fouling of IX treated waters was lower than untreated water and the relative fouling rates corresponded to the amount of biopolymer material in the feed. It was proposed that the mode of fouling changed from pore constriction during the initial filtration period to filter cake build up at longer filtration times. The organic composition strongly influenced the rate of fouling during the initial filtration period due to competitive adsorption processes, while at longer filtration times the rate of fouling appeared to depend upon the amount of biopolymer material in the feed water.

Characterisation of organic matter in IX and PACl treated wastewater in relation to the fouling of a hydrophobic polypropylene membrane.

Extensive organic characterisation of a wastewater using liquid chromatography with a photodiode array and fluorescence spectroscopy (Method A), and UV(254) and organic carbon detector (Method B) was undertaken, as well as with fluorescence excitation emission spectroscopy (EEM). Characterisation was performed on the wastewater before and after ion exchange (IX) treatment and polyaluminium chlorohydrate (PACl) coagulation, and following microfiltration of the wastewater and pre-treated wastewaters. Characterisation by EEM was unable to detect biopolymers within the humic rich wastewaters and was not subsequently used to characterise the MF permeates. IX treatment preferentially removed low molecular weight (MW) organic acids and neutrals, and moderate amounts of biopolymers in contrast to a previous report of no biopolymer removal with IX. PACl preferentially removed moderate MW humic and fulvic acids, and large amounts of biopolymers. PACl showed a great preference for removal of proteins from the biopolymer component in comparison to IX. An increase in the fluorescence response of tryptophan-like compounds in the biopolymer fraction following IX treatment suggests that low MW neutrals may influence the structure and/or inhibit aggregation of organic compounds. Fouling rates for IX and PACl treated wastewaters had high initial fouling rates that reduced to lower fouling rates with time, while the untreated Eastern Treatment Plant (ETP) wastewater displayed a consistent, high rate of fouling. The results for the IX and PACl treated wastewaters were consistent with the long-term fouling rate being determined by cake filtration while both pore constriction and cake filtration contributed to the higher initial fouling rates. Higher rejection of biopolymers was observed for PACl and IX waters compared to the untreated ETP water, suggesting increased adhesion of biopolymers to the membrane or cake layer may lead to the higher rejection.

Gas phase supramolecular cluster ions of deoxyguanosine induced by binding to (2,2':6'2''-terpyridine)-platinum(II) and (diethylenetriamine)-platinum(II).

Electrospray ionization (ESI) of solutions containing deoxyguanosine (dG) and tridentate platinum chloride complexes yields clusters of general formula [Pt(II)(L)(dG)(n)](2+), where L = 2,2':6',2'' terpyridine (terpy), or diethyltriamine (dien). When these clusters were mass selected and subjected to collision induced dissociation (CID), the primary fragmentation channels arise from loss of dG and protonated dG to yield the fragment ions [Pt(II)(L)(dG)(n-x)](2+) and [Pt(II)(L)(dG)(n-x)-H](+) respectively. The relative abundances of the [Pt(II)(L)(dG)(n-x)](2+) fragments depend on the nature of the ligand, L. The most abundant peaks observed were: n-x = 5 for terpy and n-x = 4 for dien. In order to further understand these gas phase reactions, molecular dynamics calculations were carried out. These simulated collision calculations not only predict with fidelity the experimental profiles for the relative abundances for the [Pt(II)(L)(dG)(n-x)](2+) fragments, for both terpy and dien ligand systems, but they also provide structural insights into the complex interplay of hydrogen bonding and stacking interactions within these clusters.