Maria G. Antoniou

Intermediates and Reaction Pathways from the Degradation of Microcystin-LR with Sulfate Radicals

Degradation of the cyanotoxin microcystin-LR (m/z 995.5) using sulfate radical-based advanced oxidation technologies (AOTs) and identification of reaction intermediates formed during treatment were investigated in this study. To the best of our knowledge this is the first study on the degradation and identification of reaction intermediates for any cyanotoxin with SO(4)(•-). Tandem mass spectrometry designated the formation of nine (as m/z) reaction intermediates with four of them (m/z 1011.5, 1027.5, 1029.5, and 1045.5) having multiple peaks in the TIC chromatogram. New peaks that were not observed with hydroxyl radical formed during photocatalytic oxidation (PCO) have been detected such as m/z 1045.5. The initially formed intermediates involved the oxidation of the unsaturated bonds of MC-LR especially the diene bonds located on the chain of the Adda amino acid. Subsequent intermediates implicated the oxidative cleavage of small functional groups (i.e., -COOH), up to the complete removal of the Adda chain. The electrophilic character of SO(4)(•-) is proven by the multihydroxylation of the aromatic ring. Toward the end of treatment, simultaneous oxidation of the Adda chain and the cyclic structure occurred without the formation of linear products.

LC/MS/MS structure elucidation of reaction intermediates formed during the TiO2 photocatalysis of microcystin-LR

Microcystin-LR (MC-LR), a cyanotoxin and emerging drinking water contaminant, was treated with TiO(2) photocatalysts immobilized on stainless steel plates as an alternative to nanoparticles in slurry. The reaction intermediates of MC-LR were identified with mass spectrometry (MS) at pH of Milli-Q water (pH(sq)=5.7). Eleven new [M+H](+) were observed in the liquid chromatography mass spectrometry (LC/MS) chromatogram with some of them giving multiple peaks. Most of these reaction intermediates have not been reported from previous studies employing TiO(2) nanoparticles at acidic conditions (pH=4.0). Investigating the effects of pH (for 3.0<pH<7.0), toxin adsorption and initial toxin concentration on the degradation efficiency of the TiO(2) photocatalytic films showed that acidic conditions are preferable for the degradation. Combined with the limited surface area of the films and the absence of additional oxidants (i.e., H(2)O(2)) the degradation was slower and more intermediate steps were identified. Possible structures of the intermediates (formed at neutral pH) after analyzing the corresponding MS/MS spectra are reported. The collision-induced dissociation of the [M+H](+) of MC-LR and the intermediates 1011.5 and 1029.5 are discussed and possible fragmentation pathways and mechanisms are also proposed. Analysis of the MS/MS spectra indicates that the fragmentation of some amino acids is less favorable because of internal interaction with free groups of adjacent amino acids. The MS/MS spectra assisted in determining hydroxylation sites, by the formation or alteration of specific product ions such as m/z 599.

Required ozone doses for removing pharmaceuticals from wastewater effluents

The aim of the this study was to investigate the ozone dosage required to remove active pharmaceutical ingredients (APIs) from biologically treated wastewater of varying quality, originated from different raw wastewater and wastewater treatment processes. Secondary effluents from six Swedish wastewater treatment plants (WWTP) were spiked with 42 APIs (nominal concentration μg/L) and treated with different O₃ doses (0.5-12.0 mg/L ozone) in bench-scale experiments. In order to compare the sensitivity of APIs in each matrix, the specific dose of ozone required to achieve reduction by one decade of each investigated API (DDO₃) was determined for each effluent by fitting a first order equation to the remaining concentration of API at each applied ozone dose. Ozone dose requirements were found to vary significantly between effluents depending on their matrix characteristics. The specific ozone dose was then normalized to the dissolved organic carbon (DOC) of each effluent. The DDO₃/DOC ratios were comparable for each API between the effluents. 15 of the 42 investigated APIs could be classified as easily degradable (DDO₃/DOC ≤ 0.7), while 19 were moderately degradable (0.7 < DDO₃/DOC ≤ 1.4), and 8 were recalcitrant towards O₃-treatment (DDO₃/DOC >1.4). Furthermore, we predict that a reasonable estimate of the ozone dose required to remove any of the investigated APIs may be attained by multiplying the experimental average DDO₃/DOC obtained with the actual DOC of any effluent.

Can We Effectively Degrade Microcystins? - Implications on Human Health

Microcystins are cyclic heptapeptide toxins produced by a number of genera of cyanobacteria. They are ubiquitous in bodies of water worldwide and pose significant hazard to human, plant, and animal health. Microcystins are primarily hepatotoxins known to inhibit serine-threonine phosphatases leading to the disruption of cascade of events important in the regulation and control of cellular processes. Covalent binding of microcystins with phosphatases is thought to be responsible for the cytotoxic and genotoxic effects of microcystins. In addition, microcystins can trigger oxidative stress in cells resulting in necrosis or apoptosis. Their cyclic structure and novel amino acids enhance their stability and persistence in the environment. Humans are primarily exposed to microcystins via drinking water consumption and accidental ingestion of recreational water. Recreational exposure by skin contact or inhalation to microcystins is now recognized to cause a wide range of acute illnesses which can be life-threatening. Microcystins are primarily degraded by microorganisms in the environment, while sunlight can cause the isomerization of the double bonds and hydroxylation in the presence of pigments. Attempts to utilize these organisms in sand and membrane filters to treat water contaminated with microcystins showed complete removal and detoxification. Conventional water treatment processes may not fully eliminate microcystins when there are high levels of organic compounds especially during harmful bloom events. Combination of conventional and advanced oxidation technologies can potentially remove 100% of microcystins in water even in turbid conditions. This review covers selected treatment technologies to degrade microcystins in water.

Effect of pH on the formation of disinfection byproducts in swimming pool water – Is less THM better?

This study investigated the formation and predicted toxicity of different groups of disinfection byproducts (DBPs) from human exudates in relation to chlorination of pool water at different pH values. Specifically, the formation of the DBP groups trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs) and trichloramine (NCl(3)), resulting from the chlorination of body fluid analog, were investigated at 6.0 ≤ pH ≤ 8.0. Either the initial concentration of active chorine or free chlorine was kept constant in the tested pH range. THM formation was reduced by decreasing pH but HAN, and NCl(3) formation increased at decreasing pH whereas the formation of HAAs remained constant. Under our experimental conditions, the formation of NCl(3) (suspected asthma inducing compound) at pH = 6.0 was an order of magnitude higher than at pH = 7.5. Furthermore, the effect of the presence of bromide on DBP formation was investigated and found to follow the same pH dependency as without bromide present, with the overall DBP formation increasing, except for HAAs. Estimation of genotoxicity and cytotoxicity of the chlorinated human exudates showed that among the quantified DBP groups, HAN formation were responsible for the majority of the toxicity from the measured DBPs in both absence and presence of bromide.

Investigation of the photocatalytic degradation pathway of the urine metabolite, creatinine: The effect of pH

This study investigated the degradation pathway of creatinine (a urine metabolite) with immobilized titanium dioxide photocatalysts. The degradation of creatinine was studied at three different pH values (acidic, neutral and basic) in the absence of buffering solutions. The intermediates formed were identified by using electrospray ionization mass spectrometer (ESI-MS) in both negative and positive ion mode. Two distinct mechanistic pathways which govern the photocatalytic degradation of creatinine irrespective of the pH of the initial solution were identified. The initial solution pH affected only the selectivity between the two mechanisms. The primary oxidation steps of creatinine with hydroxyl radicals included demethylation, hydrogen abstraction, hydroxylation, oxidation, and ring opening. At acidic pH, additional transformation steps of the two mechanisms were identified. The intermediates detected in the positive ion mode, contained at least one atom of nitrogen in their structure, explaining the observed low nitrogen mineralization of creatinine with TiO(2) photocatalysis. The intermediates in the negative ion mode were low molecular weight organic acids that contained only carbon and hydrogen atoms.

Evaluation of pretreatments for inhibiting bromate formation during ozonation

This study compared several pretreatment methods for inhibiting BrO formation during ozonation of tap water, from the DTU (Technical University of Denmark) campus, including H2O2 addition (peroxone), pH depression, and NH and Cl2/NH addition. At the same time, the inhibition of atrazine and carbamazepine removal was evaluated for each pretreatment. The required delivered O3 dose to achieve 90% removal of atrazine in the tap water from the DTU campus was 3.5 mg/L, which produced 130–170 μg/L BrO . Peroxone did not reduce the required O3 dose for contaminant removal; however, it limited BrO formation to below the drinking water limit of 10 μ g/L. Depression of solution pH to 6.0, reduced BrO formation to half, but it was still well above the water limit. Pretreatment with NH also reduced BrO formation by approximately 50%, though it reduced atrazine degradation to 65%. Pretreatment with Cl2/NH reduced BrO formation close to the 10 μ g/L limit; however, atrazine removal did not exceed 75%. Carbamazepine was completely removed under all the tested experimental conditions with the 3.5 mg/L O3 dose.

Sources and Occurrence of Cyanotoxins Worldwide

The eutrophication of water resources, mainly attributed to antrophogenic activities such as sewage and agricultural runoffs, has led to a worldwide increase in the formation of cyanobacterial harmful algal blooms (Cyano-HABs). Cyano-HABs have the ability to produce and release toxic compounds, commonly known as cyanotoxins, which comprise a potent threat for human and animal health as well as negative economical impacts. This chapter presents an overview on the sources and occurrence of species of cyanobacteria and their association with the production of cyanotoxins throughout the world. The main bloom-forming cyanobacteria that have been detected include Microcystis, Cylindrospermopsis, Anabaena, Aphanizomenon, and Planktothrix. The main cyanotoxins related to these cyanobacteria are microcystins, cylindrospermopsin, anatoxin-a and saxitoxins.

A Collaborative Evaluation of LC-MS/MS Based Methods for BMAA Analysis: Soluble Bound BMAA Found to Be an Important Fraction

Exposure to β-N-methylamino-l-alanine (BMAA) might be linked to the incidence of amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease. Analytical chemistry plays a crucial role in determining human BMAA exposure and the associated health risk, but the performance of various analytical methods currently employed is rarely compared. A CYANOCOST initiated workshop was organized aimed at training scientists in BMAA analysis, creating mutual understanding and paving the way towards interlaboratory comparison exercises. During this workshop, we tested different methods (extraction followed by derivatization and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analysis, or directly followed by LC-MS/MS analysis) for trueness and intermediate precision. We adapted three workup methods for the underivatized analysis of animal, brain and cyanobacterial samples. Based on recovery of the internal standard D3BMAA, the underivatized methods were accurate (mean recovery 80%) and precise (mean relative standard deviation 10%), except for the cyanobacterium Leptolyngbya. However, total BMAA concentrations in the positive controls (cycad seeds) showed higher variation (relative standard deviation 21%–32%), implying that D3BMAA was not a good indicator for the release of BMAA from bound forms. Significant losses occurred during workup for the derivatized method, resulting in low recovery (<10%). Most BMAA was found in a trichloroacetic acid soluble, bound form and we recommend including this fraction during analysis.

Novel pre-treatments to control bromate formation during ozonation

Worldwide water shortage increase and water quality depletion from microbial and chemical compounds, pose significant challenges for todays water treatment industry. Both the development of new advanced oxidation technologies, but also the enhancement of existing conventional technologies is of high interest. This study tested improvements to conventional ozonation that reduce the formation of the oxidation-by-product bromate, while maintaining the effectiveness for removal emerging contaminants (atrazine). MnO4-, ClO2-, ClO2, ClO-, CH3COOO-, HSO5- or S2O8-2 with NH4+ were tested as pre-treatments to ozonation of ground water. Each oxidant and NH4+ were added in a single stage or separately prior to ozonation. To the best of our knowledge, this is the first study that has tested all the above-mentioned oxidants for the same water matrix. Based on our results, the most promising pre-treatments were MnO4--NH4+, ClO2--NH4+ and ClO2-NH4+. MnO4--NH4+ was the only pre-treatment that did not inhibit atrazine removal. When compared with the previously proposed Cl2/NH4+ pre-treatment, MnO4-+NH4+ was found as effective for preventing BrO3- formation, while atrazine removal was higher. In addition, MnO4-+NH4+ can be added in a single stage (compared to the 2 stage addition of Cl2/NH4+) without causing the formation of potentially harmful chlorination-by-products.